SEFA Laboratory Ventilation Design · PDF file9.5.3 Ventilation System Layout ... SEFA...

SEFA

Laboratory Ventilation

Design Guide

Exposure Control Technologies, Inc.

231-C East Johnson St.

Cary, NC 27513

919-319-4290

ExposureControlTechnologies.com

Table of Contents

1 Purpose and Introduction............................................................................ 1

2 Energy and Sustainability ............................................................................ 1

3 The Laboratory Design Process .................................................................... 2

4 Laboratory Demand for Ventilation ............................................................. 2

4.1 Types of Hazardous Procedures ............................................................................................... 2

4.2 Risk Assessment ....................................................................................................................... 3

4.2.1 Quantity of Materials Used and Generation Rates ................................................................ 3

4.2.2 Effluent Characteristics......................................................................................................... 4

4.2.3 Control Banding ................................................................................................................... 5

4.3 Lab Air Quality and Conditioning .............................................................................................. 6

4.4 Occupancy and System Utilization ............................................................................................ 6

5 Exposure Control Device Selection .............................................................. 6

5.1 Description of Exposure Control Device .................................................................................... 6

5.2 ECD Risk Matrix ........................................................................................................................ 6

5.3 Types of ECDs (need to harmonize descriptions with current RP from SEFA) ............................ 6

5.3.1 Laboratory Fume Hoods ....................................................................................................... 9

5.3.2 Constant Air Volume (CAV), Conventional Fume Hood ....................................................... 10

5.3.3 CAV, Bench-Type, Bypass Fume Hood ................................................................................. 10

5.3.4 Auxiliary Air Bypass Fume Hood ......................................................................................... 11

5.3.5 CAV – High Performance Fume Hoods (HP Fume Hoods) .................................................... 13

5.3.6 Variable Air Volume (VAV) Fume Hood Systems ................................................................. 13

5.3.7 Distillation Laboratory Fume Hoods .................................................................................... 14

5.3.8 Floor Mounted Laboratory Fume Hoods ............................................................................. 15

5.3.9 Perchloric Acid Laboratory Fume Hoods ............................................................................. 16

5.3.10 Radioisotope Fume Hoods .............................................................................................. 16

5.3.11 Pass Through Hood ......................................................................................................... 17

5.3.12 California Hood .............................................................................................................. 17

5.3.13 Teaching Lab Hood ......................................................................................................... 17

5.3.14 Ductless Fume Hood ....................................................................................................... 17

5.3.15 Laminar Flow Fume Hood ............................................................................................... 17

6 Exposure Control Device Operation ........................................................... 19

6.1 Laboratory Hood Operation ................................................................................................... 19

6.1.1 Escape of Contaminants ..................................................................................................... 19

6.1.2 Sash Opening Configurations .............................................................................................. 20

6.1.3 Airfoil Sills .......................................................................................................................... 22

6.1.4 Baffle Design and Configuration ......................................................................................... 22

6.1.5 Fume Hood Specifications .................................................................................................. 24

6.1.6 Distillation Laboratory Fume Hood Specifications ............................................................... 36

6.1.7 Walk-in Fume Hood Specifications...................................................................................... 36

6.1.8 Perchloric Acid Fume Hood Specifications .......................................................................... 36

6.1.9 Radioisotope Fume Hood Specifications ............................................................................. 37

6.1.10 Ductless Fume Hood Specifications ................................................................................. 37

6.1.11 Laminar Flow Fume Hood Specifications ......................................................................... 37

6.2 Ventilated Balance Enclosures (VBE) ...................................................................................... 37

6.2.1 Ventilated Balance Enclosure Specifications ....................................................................... 38

6.3 Canopy Exhaust Hoods ........................................................................................................... 38

6.3.1 Canopy Exhaust Hood Specifications .................................................................................. 39

6.4 Flexible Spot Exhausts (FSE) ................................................................................................... 39

6.4.1 Flexible Spot Exhaust Specifications ................................................................................... 40

6.5 Slot Hoods.............................................................................................................................. 40

6.5.1 Slot Hood Specifications ..................................................................................................... 41

6.6 Downdraft Necropsy Tables ................................................................................................... 41

6.6.1 Downdraft Necropsy Table Specifications ........................................................................... 42

6.7 Glove Boxes ........................................................................................................................... 42

6.7.1 Glove Box Specifications ..................................................................................................... 42

6.8 Biological Safety Cabinets ....................................................................................................... 43

6.8.1 Class I Biological Safety Cabinet .......................................................................................... 44

6.8.2 Class II, Type A Biological Safety Cabinet ............................................................................ 45

6.8.3 Class II, Type A2 Biological Safety Cabinet ........................................................................... 47

6.8.4 Class II, Type B1 Biological Safety Cabinet ........................................................................... 48

6.8.5 Class II, Type B2 (Total Exhaust) Biological Safety Cabinet ................................................... 49

6.8.6 Class III Biological Safety Cabinet ........................................................................................ 50

6.9 Ventilated Enclosure .............................................................................................................. 50

6.9.1 Ventilated Enclosure Specifications .................................................................................... 51

6.10 Canopy Hoods ........................................................................................................................ 51

6.10.1 Canopy Hood Specifications............................................................................................ 51

6.11 Gas Cabinets .......................................................................................................................... 51

6.11.1 Gas Cabinet Specifications .............................................................................................. 51

6.12 Flammable Liquid Storage Cabinets ........................................................................................ 52

6.12.1 Flammable Liquid Storage Cabinet Specifications ........................................................... 52

6.13 Special Purpose Hoods ........................................................................................................... 52

6.13.1 Special Purpose Hood Specifications ............................................................................... 52

7 Types of Laboratories ................................................................................ 52

7.1 Categorization and Risk Control Bands ................................................................................... 53

7.2 Bio-Safety Levels .................................................................................................................... 53

7.2.1 BSL 1 .................................................................................................................................. 53

7.2.2 BSL 2 .................................................................................................................................. 53

7.2.3 BSL 3 and Higher Labs......................................................................................................... 53

7.3 Teaching Laboratories ............................................................................................................ 53

7.4 Necropsy Laboratories ........................................................................................................... 53

7.5 Radiation Laboratories ........................................................................................................... 53

7.6 Gross Anatomy Laboratories .................................................................................................. 53

8 Laboratory Design and Layout Specifications ............................................ 53

8.1 Laboratory Systems and Operating Modes ............................................................................. 54

8.2 Hood Location ........................................................................................................................ 55

8.2.1 Air Distribution Effectiveness ............................................................................................. 56

8.2.2 Doors and Traffic Aisles ...................................................................................................... 57

8.2.3 Location and Type of Supply Diffusers ................................................................................ 57

8.2.4 Type of Air Supply Diffusers ................................................................................................ 60

8.3 Ventilation Effectiveness (Air Change Rates in Laboratories) .................................................. 62

8.4 Specification of Airflow Rates for Laboratories ....................................................................... 63

8.5 Calculating Air Change per Hour Rate (ACH) ........................................................................... 64

8.6 Laboratory Pressurization ...................................................................................................... 64

8.6.1 Lab Offset Volume .............................................................................................................. 65

8.7 Airflow Controls ..................................................................................................................... 66

8.7.1 CAV .................................................................................................................................... 66

8.7.2 VAV .................................................................................................................................... 66

8.7.3 Demand Control Ventilation (DCV) ..................................................................................... 66

8.7.4 Occupancy Based Control Schemes .................................................................................... 67

8.7.5 Purge Modes ...................................................................................................................... 67

8.8 Laboratory Temperature Control ............................................................................................ 67

9 Lab Ventilation .......................................................................................... 67

9.1 Laboratory Exhaust Ventilation .............................................................................................. 67

9.1.1 Materials of Construction ................................................................................................... 68

9.1.2 Manifolds and Duct Design ................................................................................................. 73

9.1.3 Dampers ............................................................................................................................ 74

9.1.4 Duct Pressures ................................................................................................................... 74

9.1.5 Duct Velocities ................................................................................................................... 74

9.1.6 Exhaust Fans ...................................................................................................................... 75

9.1.7 Exhaust Stack ..................................................................................................................... 77

9.1.8 General Exhaust ................................................................................................................. 77

9.1.9 Fire Dampers ...................................................................................................................... 77

9.2 Air Supply Systems ................................................................................................................. 77

9.2.1 100% OA vs. Recirculated (can you recirculated GEX and when) ......................................... 78

9.2.2 Outside Air Intakes ............................................................................................................. 78

9.2.3 Airflow Measurement ........................................................................................................ 78

9.2.4 Humidity Control ................................................................................................................ 78

9.2.5 Supply Air Temperature...................................................................................................... 78

9.2.6 Fire Dampers ...................................................................................................................... 78

9.2.7 Noise .................................................................................................................................. 78

9.2.8 Insulation ........................................................................................................................... 78

9.2.9 Filtration ............................................................................................................................ 78

9.3 Energy Recovery .................................................................................................................... 79

9.4 Smoke and Fire Control .......................................................................................................... 79

9.5 Noise ..................................................................................................................................... 79

9.5.1 Criteria ............................................................................................................................... 79

9.5.2 Equipment ......................................................................................................................... 80

9.5.3 Ventilation System Layout .................................................................................................. 82

9.5.4 Layout of Laboratory .......................................................................................................... 83

9.5.5 External Noise .................................................................................................................... 84

9.5.6 Vibration ............................................................................................................................ 85

9.5.7 Other Considerations ......................................................................................................... 85

9.6 Insulation ............................................................................................................................... 86

9.7 Filtration ................................................................................................................................ 86

9.8 Energy Recovery .................................................................................................................... 87

10 Laboratory Ventilation Construction, Renovation and Commissioning ...... 87

10.1 Lab Designer's Checklist ......................................................................................................... 87

10.2 TAB Plan................................................................................................................................. 87

10.3 Commissioning Plan (building and lab) ................................................................................... 87

10.4 ECD Commissioning................................................................................................................ 87

10.5 Laboratory Environment Tests (LETs) ..................................................................................... 87

10.6 System Mode Operating Tests (SOMTs) .................................................................................. 87

11 Laboratory Ventilation Management Program .......................................... 87

11.1 LVMP and the Design Process ................................................................................................ 88

11.2 Routine Testing ...................................................................................................................... 88

11.3 Management of Change ......................................................................................................... 88

11.4 BAS Trends and Reports ......................................................................................................... 88

12 References ................................................................................................ 89

SEFA Laboratory Ventilation Design Guide

1

1 Purpose and Introduction

The primary objective in laboratory design should be to provide a safe environment for laboratory

personnel to conduct their work. Secondary objectives include providing maximum flexibility for

research, efficiently operating systems and sustainability.

The Laboratory Ventilation Design Guide (Guide) was prepared to aid the design community with

planning and design issues related to laboratory and critical environment ventilation. The Guide is a

resource document for use by design professionals, management and staff during planning, design

and construction of new and renovated laboratory facilities.

The requirements in the Guide illustrate some of the basic health and safety ventilation design

features required for new and remodeled laboratories. These health and safety guidelines are to be

incorporated, as appropriate, in facility-specific construction documents by the architects and

engineers to ensure that health and safety protection is engineered into the design of any new or

renovated facility.

While many of the requirements for health and safety ventilation design and engineering are

incorporated in the Guide, it is impossible to cover all possible concerns and not all regulatory issues

or design situations are contained herein. The architects, engineers, designers and planners should

in all cases, consult with Environmental Health and Safety personnel for guidance on questions

regarding health, safety and the environment.

Safety is the inviolable constraint. No matter how well designed a laboratory is, improper usage of

its facilities will always overcome the engineered safety features.

2 Energy and Sustainability

Due to high ventilation needs of laboratories, the associated energy use required to operate labs far

exceeds the energy required to operate typical office buildings. Depletion of energy resources and

resultant increase in energy costs advocates efficient energy use should be a prominent criteria in

laboratory design. Even the most energy efficient laboratory design may increase energy use over

time due to:

changes in laboratory use and equipment

changes in laboratory physical configuration

HVAC equipment and controls performance degradation.

It is important to design sustainability in laboratories. Items influencing sustainability include:

life of HVAC components

preventative maintenance

physical location and ease of access to components and controls


2

BAS monitoring of performance trends

technical capability of facility maintenance personnel

management of change

3 The Laboratory Design Process

[content to be added]

Determine process

Select ECDs

Design Lab

Design Systems

4 Laboratory Demand for Ventilation

Researchers are potentially exposed to a wide variety of hazards. The hazards must be

characterized and evaluated to determine the demand for ventilation, ensure appropriate exposure

control devices (laboratory hoods) and establish appropriate operating specifications and

performance criteria. The demand for ventilation is defined by the airflow required to ensure a safe

and comfortable lab environment at varying levels of occupancy. The Ventilation Demand Risk

Assessment includes evaluation of:

1. Hazards

The types of hazards and procedures

Hazard generation characteristics (i.e. gases, vapors, mists, dusts, etc.)

Quantity of materials used or generated during lab procedures

2. Safety Requirements

Hood Types

Hood Exhaust Requirements

Laboratory Pressurization (Transfer Air)

Laboratory Airflow for dilution (ACH)

3. Comfort Requirements

Conditioning Loads

Temperature

Humidity

4. Occupancy

Operating Hours

Time Spent In Laboratory

Time Spent in Office

4.1 Types of Hazardous Procedures

The quantity, toxicity and characteristics of airborne hazardous materials generated during

laboratory procedures determines the level of ventilation control required to provide adequate

Comment [GG1]: potential content ideas


3

protection. Research safety staff should work with Principal Investigators (PIs) to characterize

hazardous procedures, estimate the volume of hazardous material used and determine potential

generation rates. The following categories can be helpful for characterizing hazardous procedures:

Storage: Emissions may occur from improperly sealed containers during storage. The rate

and quantity of generation may be small, but not negligible. Complaints of odors indicate

escape of small concentrations from inadequately sealed containers.

Closed Process: Materials are contained within an experimental apparatus, which may

include beakers, flasks, tubing, equipment, etc. The volume of material that could be

released during a catastrophic incident such as accidental over pressurization, damage to

the system, or leaks should be estimated. Closed processes are often found in chemical

dispensing and transferring procedures.

Normal Process: A normal process typically involves procedures that result in low volume

generation and where little energy is added to the process. Generation of materials is

typically through diffusion, evaporation, etc. Some procedures in a normal process involve

liquid transfers (pouring) and small quantity weighing. Pipetting is an example of a normal

process.

Complex Process: A complex process generally involves procedures that apply significant

energy and produce a larger volume of airborne contaminants. Such processes might

involve volatile reactions, stirring and mixing, heating and boiling, bulk material transfers

and weighing. The application of energy complicates the determination of contaminant

generation rates.

Leaks to Catastrophic Failure: Release of material from a physical defect (pinhole in weld,

worn gaskets, etc.) up to sudden and total release of entire contents (rupture, activation of

emergency release valve).

4.2 Risk Assessment

4.2.1 Quantity of Materials Used and Generation Rates

There are no standardized categories for the quantities of materials used or generated during

laboratory procedures. Research conducted by Exposure Control Technologies, Inc. (ECT, Inc.)

indicates the following common contaminant generation rates typically resulting from lab activities

or scenarios:

Table 1 Sample of Laboratory -Scale Generation Rates

Source Category Generation Rate

Fugitive emissions and leaky

seals on containment vessels Storage and Closed Process* <0.1 lpm

Evaporation and Spills Normal Process 0.1 - 1 lpm


4

Boiling/mixing/stirring Complex Process 1 - 14 lpm

Leaking or Failed

Compressed Gas Cylinders Leaks to Catastrophic Failure* <0.1 lpm to >1400 lpm

Note: * - Worst case release from catastrophic failure should be estimated.

Table 2 Quantity of Material Used or Generated During Hazardous Processes

Description/Quantity Volume Mass Generation Rate

Minute < 1 mL < 1 mg < 0.01 lpm

Small < 10 mL < 1 g < 0.1 lpm

Moderate < l L < 10 g < 1 lpm

Large < 10 L < 100 g ≥ 1 lpm

Extra Large ≥ 10 L ≥ 100 g ≥ 10 lpm

4.2.2 Effluent Characteristics

The design of the laboratory ventilation system is dependent on the quantity, generation rate and

characteristics of the contaminant (sometimes called effluent). In particular, determining effluent

characteristics is necessary to specify capture and transport velocities, select appropriate materials

of construction and establish the exhaust stack discharge criteria. The following categories can be

used to help characterize the hazardous effluent.

Gas – A substance that exists in the gaseous state and lacks inherent volume and shape at

normal atmospheric conditions. Examples: oxygen or helium.

Vapor - A substance in the gaseous state, exerting a partial pressure that can be condensed

into the liquid form. Examples: formaldehyde, xylene and acetone.

Fume - Condensed solid particles produced by physicochemical reactions such as

combustion, sublimation, or distillation. Examples: fumes from spectroscopy samples and

laser surgical procedures.

Mist - Airborne liquid droplets associated with the disruption of a liquid. Examples include

sonication, spraying, mixing, and violent chemical reactions.

Particulate - Solid particles (Silica gel, Aluminum oxide) or nanoparticle products that are

temporarily suspended in a volume of air. Deposition of suspended particulates is

dependent on particle size and turbulence.


5

To properly design ventilation systems, prevent staff exposure and deposition of materials within

the hood and duct system, effluent characteristics must be known. These topics are reviewed in

later sections of this chapter. In addition, selection of stack discharge criteria and exhaust filtration

requirements depend on the characteristics of the substance being controlled. For example, a HEPA

filter is commonly used on hoods and is extremely efficient at removing particles greater than 0.3

micrometers in diameter, but it is ineffective for removing most gases and vapors.

4.2.3 Control Banding

Renovating laboratory buildings to reduce energy consumption or upgrade the capabilities of the

mechanical systems requires understanding the functional requirements of the building occupants

and risks associated with the research activities. Work in research laboratories can vary and often

involves a diverse range of hazardous materials and procedures. Evaluating and minimizing risk by

ensuring proper protection of people, property and the environment can be a challenging task that

requires specialized skills, experience and expertise evaluating laboratories, hazards and exposure

control systems.

The control banding process involves meeting with stakeholders to define specific facility objectives,

interviews with principal investigators, surveys of the laboratories, inspection of the laboratory

hoods, review of the ventilation systems, evaluation of hazards and analysis of key metrics.

Information collected from the laboratories and exposure control devices is compiled, analyzed,

weighted and assigned to different control bands developed specifically to achieve the desired

objectives. The bands are developed to distinguish low risk from high risk for the purposes of

assigning air change rates (Air Changes Per Hour – ACH) and other relevant ventilation parameters

and specifications. Error! Reference source not found. below illustrates the control banding process

for laboratories.


6

Figure 1 Lab Ventilation Risk Assessment Process

4.3 Lab Air Quality and Conditioning


4.4 Occupancy and System Utilization


5 Exposure Control Device Selection

5.1 Description of Exposure Control Device


5.2 ECD Risk Matrix


5.3 Types of ECDs (need to harmonize descriptions with current RP from SEFA)

Start

YES

Or

Survey LabIdentify

ECDs

Haz. Op. Analysis

Evaluate Room Air Change

Effectiveness

Determine Theoretical

ACH

Preliminary ACH

Acceptable

Accept Preliminary ACH as Final

Increase ACH to Next High Category

Stop

NO

Apply Chem Generation

Emission Model

1.

Evaluate Hazardous

Processes in ECDs

Assign ECD Risk and Airflow

Specifications

Evaluate Hazardous

Processes outside ECD

ECD Risk Assessment

Physical or OtherHazard

Airborne Health Hazard

Implement Safety Measures

Lab Ventilation Risk Assessment

Is ECD Necessary

Remove or Hibernate ECD

Assign Lab Risk and Airflow

Specifications

Is ECD Appropriate

Install or Utilize

Appropriate ECD

Improve Room Air Change

EffectivenessPhysical or OtherHazard

Implement Safety Measures

YES

NO

YES

NO

2.

3.

4.

5.

6.

7.8.

9.

10.

Haz. Op. Analysis


7

ECDs must be constructed, manufactured, installed, and used according to specific requirements.

Mechanical Engineers, Principal Investigators, Laboratory Directors, Research Safety Officers, and

other experts, should be responsible for selecting devices and sizes that are appropriate for the

intended use. ECDs are often the primary means of protecting personnel and should be considered

an integral part of the overall building HVAC system. They should be part of the Test, Adjustment

and Balance (TAB) and Commissioning of mechanical systems prior to building acceptance, lab

occupancy and hood use. Any design process that involves selection and installation of ECDs should

consider:

Any user-specific needs from the Laboratory Demand Ventilation Assessment

The type of ECD needed to perform a specific operation

Specific containment and ECD size requirements

Satisfactory performance testing of potential ECD/control-system configurations

There are many different types of ECDs. Figure 2 shows different ECDs and potential applications.


8

Figure 2 Diagram of Different ECD Types and Potential Applications

Laboratory Fume Hoods

Bench-Top Bypass Hood

High Performance Fume Hood

VAV Fume Hood

Distillation Hood

Floor Mounted Hood

Perchloric Acid Hood

Radiation Hood

Auxiliary Air Hood

Hazard: Chemical

Toxicity: Low to IDLH

Generation Rate: Small to Large

Effluent Gases, Vapors, Mists, Fumes, etc.

Hazard: Radioisotopes, Chemical


Effluent Generation Rate: Small to Moderate

Effluent Type: Gases, Vapors, Mists, Fumes, etc.

Hazard: Chemical, Perchloric Acid




Hazard: Chemical

Toxicity: Low to High

Effluent Generation Rate: Small to Large


Biological Safety

Cabinets

Class II Type A1

Class II Type A2

Class II Type A2 Ducted

Class II Type B2

Class II Type B1

Class III Glove BoxGloveBox

Hazard: Biological

Toxicity: Low to Moderate

Effluent Generation Rate: Small

Effluent Type: Particulates

Hazard: Chemical, Biological



Effluent Type: Gases, Vapors, Particulates

Hazard: Chemical, Biological, Radionuclides




Other Lab Hoods Canopy Hood

Slot Hood

Snorkel

Downdraft Table

Class I

Ventilated Balance Enclosure

Ventilated Enclosure



Effluent Generation Rate: None



Toxicity: Low to High



Hazard: Chemical

Toxicity: Negligible to Low


Effluent Type: Gases, Vapors, Particulates, Heat

Ventilated Cylinder Cabinet


9

5.3.1 Laboratory Fume Hoods

Laboratory fume hoods are available in many different types, sizes and configurations to

accommodate laboratory procedures and processes. Unlike biological safety cabinets that have well

defined classes and types to identify different models, fume hoods are not categorized. They are

often identified by describing the size and key components of the design. For example, a common

fume hood is a 6-ft, bench-top, bypass fume hood. This fume hood can easily be confused with a 6-

ft, bench-top, radiation hood that differs only by the design and construction of the internal liner.

Furthermore, hoods can be further described by the type and configuration of the moveable sash

leading to a description such as a 6-ft, bench-top, vertical sash, bypass fume hood. The distinction

between fume hood types and sizes is cumbersome, but critical to ensure the hood is appropriate

for the intended procedures. Figure 3 shows the common components that comprise a fume hood

and could be used to differentiate hood types.

Figure 3 Typical Laboratory Fume Hood Components (from ASHRAE 110)

Hood size is generally the nominal size, determined by the width of the hood including the width of

the opening plus the width of the exterior enclosing panels. The size is not a measure of the sash

opening width. This oversight during design has caused many errors in flow specifications and

subsequent problems during TAB of the systems.

Other critical dimensions include the width, depth and height of the interior chamber. The hood

must be large enough to accommodate apparatus and equipment used in the hood during

hazardous procedures. Typical specifications for the depth and interior height of a bench-top fume

hood are a minimum of 24 inches and 48 inches, respectively; OSHA Lab Standard 1910.1450 has

requirements for a specific size of laboratory fume hood. According to the standard, fume hood

openings must provide at least 2.5 linear feet of space per person for every two people working with

hazardous chemicals in the laboratory. The interior dimensions together with the opening size and

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=10106


10

design of the hood components are used to determine the flow specifications and resulting ability to

provide containment performance.

5.3.2 Constant Air Volume (CAV), Conventional Fume Hood

Conventional fume hoods were intended to operate at a constant exhaust volume. They have all

the components of a typical fume hood with the exception of sufficient bypass area to maintain a

constant hood static pressure and prevent excessive face velocities when closing the sash. As such,

conventional fume hoods are not recommended as flows can vary depending on the sash

configuration and resulting hood static pressure. Figure 4 shows the airflow entering the hood

through the opening when the sash is open and through the bypass opening when the sash is

closed.

Figure 4 Diagram Showing Airflow Patterns When the Sash is Opened and Closed

5.3.3 CAV, Bench-Type, Bypass Fume Hood

A bench-top bypass fume hood is a generic type of chemical hood that has a bypass opening above

the sash through which room air can enter the hood chamber when the sash is lowered. Bench-top

bypass hoods can be used for a variety of chemical procedures and are appropriate for generation of

small to large quantities of low to highly toxic materials. Bypass fume hoods can have vertical,

horizontal or combination sash types and open or restricted bypass areas. Refer to Figure 5 for a

photo of a CAV, Horizontal Sash, Bench-top, Bypass Fume Hood.

Sash Full Open Reduced Sash Open Sash Closed

Vortex Region

Bypass Bypass Bypass


11

Figure 5 Hood Depicting Bypass Openings at the Top

The bypass is sized to meet the following conditions:

The total airflow volume is essentially the same at all sash positions. The hood static pressure should not vary more than 5-10% when opening or closing the sash.

The bypass must provide a barrier between the hood work space and the room when the sash is lowered. The bypass opening is dependent only on sash operation.

The bypass areas shall be sufficient to prevent velocities exceeding three times the design average face velocity at sash heights less than 10% open (Vbypass ≤ 3 x Vfavg).

5.3.4 Auxiliary Air Bypass Fume Hood

An auxiliary air hood is a bypass hood equipped with an air supply plenum mounted over the sash

opening. The auxiliary air supply is designed to provide either conditioned, or in some cases

unconditioned, air gathered from outside the building and directed to the plane of the hood sash.

The objective is to reduce the volume of conditioned laboratory make up air necessary for the hood

to operate by providing this alternate source of make-up air. In concept, the design provides energy

savings by supplying minimally conditioned or unconditioned outside air to the hood for exhaust

rather than all of the exhaust being expensive conditioned air from the laboratory. In addition, an

auxiliary air hood would function in a laboratory that had a shortage of air supply.

However, auxiliary fume hoods come with a variety of deficiencies including:

Supplying unconditioned auxiliary air may affect room temperature stability and the variations in air temperature may cause unwanted reactions to sensitive processes undertaken in the hood

Bypass Grilles


12

The balance between the auxiliary air flow and the exhaust flow is critical to ensure that auxiliary air is properly captured by the hood. Adjusting the flow to achieve the desired volumes can be complicated

Excessive auxiliary air discharge velocities can jeopardize hood containment due to excessive cross drafts produced by the auxiliary air supply discharge

Current recommendations discourage the use of auxiliary air-type hoods in new construction. Their

use may be justified under special circumstances, when renovations to the existing ventilation

system are inadequate and where expansion of system ventilation capacity may be mechanically

unfeasible or too costly. Auxiliary air must not be supplied behind the sash as this arrangement can

pressurize the work chamber and cause escape from the hood. Figure 6 shows the auxiliary air

entering above the sash when the sash is lowered and through the sash opening when the sash is

raised.

Figure 6 Auxiliary Air Supply System and Resulting Airflow Patterns at Different Sash

Configurations

Manufacturers of auxiliary air hoods specify that the auxiliary air volume should be as much as 70%

of the required exhaust air volume. ECT, Inc. has found that the resultant auxiliary air velocity is too

high for capture and the downward flow shears past the opening and can cause hood escape. ECT,

Inc. data suggests auxiliary air velocities should not exceed 1.5 to 2 times the average face velocity

(Vaux air ≤ 1.5~2.0 x Vfavg). The auxiliary air velocity is measured 6 inches below the outlet of the

plenum.

Due to the impact of auxiliary air at the opening, the auxiliary air must be turned off or redirected

during measurement of fume hood face velocities.


13

5.3.5 CAV – High Performance Fume Hoods (HP Fume Hoods)

A high performance (HP) fume hood is a bypass fume hood operated at face velocities 30% to 40%

less than traditional fume hoods. A traditional, bench-top, bypass fume hood generally requires an

average face velocity of approximately 100 fpm at the full open sash opening to provide

containment. High performance fume hoods incorporate enhanced aerodynamic design features,

particularly the airfoil sill, sash handle, side posts and baffles, that enable equivalent containment at

reduced face velocities (as low as 60 fpm). By providing equivalent performance, a HP hood can be

used for the same hazards and procedures appropriate for a traditional fume hood. The primary

benefit of a HP fume hood is the reduction in total exhaust flow at the design opening and potential

for reduced energy use. However, HP hoods may be more expensive than traditional hoods and the

savings from reduced flow would need to justify the additional expense. Despite the aerodynamic

modifications, HP hoods are still affected by cross drafts and other external factors the same as

traditional fume hoods. In addition, all HP fume hoods do not perform the same and validation

testing is recommended to evaluate performance prior to purchase.

5.3.6 Variable Air Volume (VAV) Fume Hood Systems

A VAV fume hood is the same design as a CAV, bypass fume hood but the bypass area is restricted to

accommodate reduced flow when the sash is closed. Therefore, the key differences between a CAV

bypass fume hood and a VAV bypass fume hood is the size of the bypass and the application of VAV

controls to modulate flow. There are multiple types of VAV control strategies applied to VAV fume

hoods. The simplest VAV control type is two state control that limits flow modulation to only two

flows (low and high or occupied and unoccupied). A full VAV control system modulates flow in

response to sash position and attempts to maintain a constant face velocity when operating

between the minimum and maximum flow set points. VAV controls can be based on sash position,

velocity, or occupancy.

The type of VAV system dictates the fume hood operating specifications and the applicable test

methods. When determining the type of VAV control and required operating specifications, all hood

operating modes need to be considered including:

sash open

sash closed

hood in use but unoccupied (materials being generated in the hood with no one standing at the opening or sash closed)

hood in use and occupied (materials being generated in the hood and a person is standing in front of the hood with the sash open


14

Depending on the type of controls, flow can be reduced through a VAV fume hood when the sash is

lowered or the hood or lab is unoccupied. However, the VAV controls become more complex when

accommodating multiple modes of operation, increasing the potential for problems that can affect

energy savings and, more importantly, hood containment. Special techniques and methods are

necessary to evaluate and maintain operation of VAV controls and ensure safe and efficient

operation.

Use of VAV fume hoods are not appropriate for all applications, such as processes involving

generation of acid mists or vapors greater than 1 liter per minute (> 1 lpm). When the sash is closed

or the hood is unoccupied (or not equipped with an occupancy sensor), the resultant exhaust air

volume may not be adequate to maintain sufficient dilution and resist condensation/accumulation

of hazardous materials within the hood and exhaust ducts. To address this, a minimum sash height

should be specified or the hood should be operated as CAV during the procedure.

5.3.7 Distillation Laboratory Fume Hoods

A distillation fume hood (Figure 7) is designed for use with tall apparatus and procedures that

involve small to medium quantities of low to high toxicity materials. A distillation hood has the

same components as a bench top hood with the exception that the design provides a greater

interior height for use of a larger apparatus. The distillation hood work surface should be between

12 and 18 inches above the floor.

Figure 7 Diagram of a Distillation Hood


15

Distillation hoods can have vertical rising sashes or horizontal sliding panels. Generally more than

one sash panel is used on a vertical rising sash. The vertical sash design generally enables a rather

large opening and care must be taken in determining the maximum allowable sash opening and

required exhaust flow.

5.3.8 Floor Mounted Laboratory Fume Hoods

A floor mounted hood (Figure 8) is used for large apparatus and storage of containers that pose

some hazard but will not fit into an approved storage cabinet. A floor mounted hood is suitable for

the same type of work conducted in bench-top hoods and distillation hoods and typically equipped

with horizontal sliding sashes, although some models may be equipped with multiple vertical sliding

sashes.

Floor mounted hoods can also be termed “walk-in” hoods. However, the name "walk-in hood"

implies that the hood can be entered and the name is a misnomer as the same safety precautions

should be applied to this hood as those required for a bench-top hood. The hood must never be

entered during generation of hazardous materials.

Floor mounted hoods are particularly susceptible to variations in face velocity across the opening

and room air disturbances due to the large opening area afforded by the hood design. For this

reason it is prudent not to use a floor mounted hood for work with highly toxic materials.

Figure 8 Photo of a Floor-Mounted Hood Equipped With Horizontal Sash Panels


16

5.3.9 Perchloric Acid Laboratory Fume Hoods

Perchloric Acid Laboratory Fume Hoods should be clearly labeled “For Use with Perchloric Acid”.

The hood should be constructed from materials that are non-reactive, acid-resistant, and relatively

impervious. Type 316 stainless steel with welded joints should be specified. Corners should be

rounded to facilitate cleaning. Work surfaces should be watertight, with an integral trough at the

rear of the hooded area, for collection of wash-down water.

A wash-down system (Figure 9) must be provided that has spray nozzles to adequately wash the

entire assembly including the stack, blower, all ductwork, and the interior of the hood, with an easily

accessible strainer to filter out particulates. The wash-down system should be activated

immediately after the hood has been used and the hood must be washed down following the use of

perchlorates. Waste stream must be disposed of in accordance with hazardous waste policies.

Figure 9 Diagram of Perchloric Acid Fume Hood with Duct Wash System

The ductwork should be constructed of stainless steel with smooth-welded seams. All welded

ductwork should be installed with a minimal amount of horizontal runs and no sharp turns.

Ductwork also must not be shared with any other hood or joined (manifold) with other non-

perchloric acid exhaust systems. Perchloric acid is highly reactive to organic materials; materials

used in the construction of the fume hood, including gaskets, caulking, etc., must be compatible

with this hazard.

5.3.10 Radioisotope Fume Hoods

Radioisotope fume hoods should meet all requirements for constant volume bypass-type or VAV

fume hoods. The primary exception is the interior liner material should be stainless steel with coved


17

corners to facilitate cleaning. Refer to the Radiation Chapter for more information about use of

radioactive materials and system requirements.

5.3.11 Pass Through Hood


5.3.12 California Hood


5.3.13 Teaching Lab Hood


5.3.14 Ductless Fume Hood


5.3.15 Laminar Flow Fume Hood



18

Table 3 Recommended Criteria and Specifications for ECDs

Functional and Performance Tests

CAV Fume Hood

CAV HP Fume Hood

VAV Fume Hood

Biosafety Cabinet

VBE FSE Canopy Slot Hood VE Down draft table

Filtered Ductless

Hood

Inspection Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass Pass

Flow Design Design Design

(1) Design Design Design Design Design Design Design Design

Hood Static Pressure Inches W.G.

<0.5 <0.5 <0.5 <1.0 <1.0 (2) Design Design Design Design Design N/A

Capture or Face Velocity (FV)

100 fpm 60 fpm 100 fpm 75 – 100

fpm 60-100

fpm Design 100 fpm Design 100 fpm

100 fpm (3)

100 fpm

Cross Draft Velocity <50% of

FV <50% of

FV <50% of

FV <50% of FV <50% of FV

<50% of FV

<50% of FV

<50% of FV

N/A <50% of

FV <50% of FV

VAV Response N/A N/A < 5 sec. N/A N/A N/A N/A N/A N/A N/A N/A

VAV Stability N/A N/A < 20% COV

N/A N/A N/A N/A N/A N/A N/A N/A

Smoke Test No

Escape No

Escape No

Escape No Escape

& Split No Escape

Good Capture

Good Capture

Good Capture

No Escape

Good Capture

No Escape

ASHRAE 110 Tracer Gas < 0.1

ppm (4) < 0.1

ppm (4) < 0.1

ppm (4)

< 0.1 ppm (4)

< 0.1 ppm

(4)

Alternative Tracer Gas Design < 0.1 ppm

(5)

< 0.1 ppm (6)

Filter Leak Tests None

detectable None

detectable

None detectable

Auxiliary Air < 1.5 x Vavg.

The flow at the design opening and the minimum flow shall be defined in advance. The minimum flow should be capable of providing 375 ACH.

The hood static pressure is measured downstream of the filter if equipped.

Down draft velocity measured 6 inches above table in downward direction.

Criterion for “as installed” tests.

VBEs can be tested with a particulate challenge. The criteria should be appropriate to the procedure

Downdraft tables should be challenged with an evaporative challenge such as IPA in a spill tray located on the work surface.


19

6 Exposure Control Device Operation

6.1 Laboratory Hood Operation

Airflow drawn through the opening of a fume hood creates an air barrier at the plane of the sash to

minimize escape of contaminants generated inside the hood chamber. A fume hood cannot be

counted on to provide 100% containment due to the sash opening or lack of complete physical

isolation. Only a glove box approaches 100% containment and should be considered whenever

working with materials that are immediately dangerous to life and health (IDLH). The effectiveness

of the air barrier is a function of the speed, direction, distribution and turbulence of the air entering

the hood through the plane of the sash opening. The plane of the sash opening is defined as the

imaginary vertical plane formed at the exterior surface of the outermost glass panel. Hazardous

materials generated within the hood should not escape outside the plane of the sash. The

aerodynamics of the hood entries and the baffles at the back of the hood help control the direction

and distribution of flow through the opening and the capture efficiency of the hood. See Figure 10

for a diagram of the hood showing the airflow through the plane of the sash and the location of the

imaginary air barrier formed at the sash plane.

Figure 10 Diagram Showing Side View of Fume Hood and Airflow Patterns

6.1.1 Escape of Contaminants

The direction, speed, turbulence and distribution of airflow through the opening are the primary

factors associated with hood containment. The direction of airflow into the hood through the sash

opening is generally perpendicular to the plane of the sash. The speed of the air measured at the

sash plane is referred to as the face velocity. The average face velocity is the average from a grid of

multiple air speed measurements across the opening. The distribution of airflow through the

opening as indicated by the variation of velocities across the opening is referred to as spatial


20

variation or sometimes referred to as uniformity of flow across the opening. Turbulence is

dependent on flow rate and hood design, resulting in differences in face velocity over time

(sometimes called temporal variation). Escape at any given average face velocity can be expected to

increase as spatial and temporal variations exceed 20%.

Escape from the hood can occur at any location across the opening. However, certain areas are

more prone to escape including the horizontal and vertical edges of the sash panels along the

vertical edge of the side posts above the horizontal top of the airfoil sill. Escape is exacerbated by

the presence of a person standing in the opening. The photo in Figure 11 shows escape below the

sash and above the airfoil using smoke to visualize airflow patterns and a mannequin located at the

hood opening simulating a hood operator. The aerodynamic design of the sash handle, airfoil sill

and side posts are primary factors affecting distribution, turbulence and escape at those locations.

Visualization of escape using a smoke source located in the hood is best done both with and without

a person standing at the opening.

Figure 11 Image of Hood Depicting Areas Prone to Escape

Additional factors that affect the spatial and temporal variations of face velocities include room air

currents (cross drafts) and temperature gradients in the lab near the hood opening. Cross drafts

from supply diffusers or people walking by the hood easily disrupt containment. Many times,

escape from hoods is caused by improper supply of air through diffusers located too close to fume

hoods. The discharge temperature of the air from the diffuser can also skew airflow through the

opening and create excessive turbulence. See section 6.2 for additional information regarding

appropriate diffuser types and locations.

6.1.2 Sash Opening Configurations

Fume hoods are equipped with moveable sash panels to vary the opening area. Depending on the

design of the hood, sashes can consist of single or multiple panels that sometimes slide vertically


21

(vertical sash) or slide horizontally (horizontal sash) to increase or decrease the access opening.

Sashes should be configured to provide the minimum area necessary to safely conduct the work

performed in the hood. ECT. Inc. studies indicate the potential for escape is proportional to the size

of the opening.

The design opening area is the area of the opening where the hood is intended or designed for use.

The design opening may be less than the maximum achievable opening (100% full open) and is

sometimes different than the preferred user opening. The Hazard Demand Ventilation Assessment

must identify the opening areas required for the user to access and safely conduct procedures in the

hood.

The design opening should be clearly indicated and a mechanical stop installed to remind the users

of the opening restrictions. Under the vertical sash configuration, the user can access the entire

width of the hood opening, but access to the top of the hood chamber is limited by the sash panels

(See Figure 12 below). In Figure 13, the hood user is operating the hood in the right, horizontal, sash

opening configuration. In a horizontal sash configuration, the user has access to the top of the hood

chamber, but has limited access from side to side. Hood containment can be equivalent at either

sash configuration, but hood performance improves at smaller openings.

Vertical design openings are typically limited to a height below the breathing zone of the user and

results of performance tests conducted by ECT, Inc. have demonstrated that the maximum width of

horizontal sash opening should not exceed 30 inches. Operating a fume hood at sash openings

larger than the design opening can result in escape from the hood due to insufficient face velocities

or increased spatial and temporal variations.

Figure 12 Fume Hood with Vertical Sash at Restricted Height Design Opening


22

Figure 13 Example of Fume Hood with Horizontal Sash Opening

6.1.3 Airfoil Sills

All bench-top fume hoods should be equipped with an airfoil sill (Figure 14). The airfoil sill

streamlines flow into the hood over the work surface and reduces turbulence and reverse flow

along the bottom of the opening. The airfoil sill minimizes vortex formation and reverse flow at the

bottom of the opening to improve hood containment.

A B

Figure 14 Diagram of Fume Hood Work Surface Showing Airflow Patterns with and without Airfoil

Sill

6.1.4 Baffle Design and Configuration


23

The design of the baffle and configuration of the capture slots affects the direction and uniformity

airflow through the opening and capture of airborne materials within the hood. Improper baffle and

slot configuration can result in escape from the hood regardless of the average face velocity.

Contrary to popular belief, the baffles should not be adjusted to accommodate the density of the

materials used in the fume hood. The baffles and slots are adjusted to achieve the flow patterns

that ensure satisfactory hood containment and contaminant removal from the hood.

The diagram in Figure 15 presents a side view of the hood showing the baffle and slots in the baffle.

Baffle panels and with adjustable slot widths can change the direction and distribution of flow

through the opening. The hood shown in the middle diagram has the top slot open creating an

upward flow of air through the opening. Conversely, the diagram of the hood on the right shows a

downward flow of air through the top of the opening and increased directional flow across the work

surface with the top slot nearly closed.

Top

Baffle

Top Slot Open

Middle

Bottom

Slots

Plenum

Velocity

Top Slot Closed

Qe Qe Qe

Figure 15 Design and Configuration of Baffle Panels and Capture Slots

Ensure baffle panels are properly installed and adjusted to achieve proper airflow distribution and

hood containment. The baffles should be adjusted by qualified personnel during hood

commissioning tests and evaluated following installation of equipment and apparatus in the hood.

Equipment and apparatus in the hood can disrupt airflow patterns and adjustments of the baffle

may be necessary to ensure containment.

Figure 9 shows a photo of smoke flow in a hood with the top slot of the baffle fully open. The

upwardly directed airflow combined with reduced flow across the work surface results in reverse

flow and escape over the airfoil sill downstream of the mannequin at the opening. The photo of the

hood on the right of Figure 16 shows airflow patterns when the top slot was nearly closed. The

closed top slot creates a slight downward flow through the opening at the top of the hood and

increased flow across the work surface that reduced reverse flow in front of the mannequin and

enabled satisfactory hood containment.


24

Figure 16 Fume Hood Showing Reverse Flow and Escape Near Airfoil Sill With Top Slot Fully Open

(Left). Fume Hood Showing Capture at Bottom Slot With Top Slot Closed (Right)

6.1.5 Fume Hood Specifications


6.1.5.1 Functional Requirements and Performance Criteria

A laboratory hood must meet the functional requirements and performance criteria defined by the

Hazard Ventilation Demand Assessment in section 3. In general, a laboratory fume hood system

should prevent overexposure of personnel to hazardous airborne materials generated in the hood

by capturing and exhausting contaminants from the lab environment. Meeting the performance

criteria are the expected result of operating the systems in accordance with the operating

specifications. Performance criteria can be specific such as “the laboratory hood system shall

minimize the concentration of contaminant x below permissible exposure limits or the criteria can

be more generic such as “escape shall not exceed a specified concentration of a tracer gas

generated during containment tests”. The operating specifications define how the systems operate

to provide the given level of performance. For example, meeting the performance criteria for

containment requires operating the fume hood at a specified exhaust flow to achieve the average

face velocity at the design sash opening. Performance criteria for each laboratory hood should be

appropriate for the intended function and specified prior to conducting functional tests.

Performance criteria for different laboratory hoods and performance tests are described in Table 4

below.


25

Table 4 Performance Criteria for Select Hoods and Tests

Laboratory Hood Performance Test Recommended Performance Criteria

Chemical Fume

Hood

General Safety Containment must prevent overexposure to materials

generated within the hood.

ASHRAE 110 Airflow

Visualization see note 1

Hood must completely contain smoke inside the plane

of the sash at the design opening.

ASHRAE 110 Tracer Gas

Containment Test

Hood must prevent escape below 0.1 ppm at a 4 lpm

generation rate at the design sash opening.

Class III Glovebox

General Safety Containment must prevent overexposure to materials

generated within the hood.

Tracer Gas

Containment Test

Glovebox must prevent escape of tracer gas to below

5x10-7 cc/sec see note 2.

Canopy Hoods General

Canopy hoods are not recommended for personnel

protection. Canopy hoods should remove heat and

prevent increase in lab temperatures to less than 1

degree.

Slot Hoods General Safety Capture must prevent overexposure to materials

generated within design capture area.

Snorkel Hoods General

Capture at contaminant source must prevent

overexposure and accumulation of concentrations to

unsafe levels within the lab.

Downdraft

Necropsy Tables

General Capture must prevent overexposure to materials

generated on the table.

Airflow Visualization

Test

Smoke must be captured by the table exhaust when

generated less than six inches above and within the

perimeter of the table.

Notes: (1) - The ANSI/ASHRAE 110 methods are described in more detail below.

(2) - Tracer Gas Test Performance Criteria per Protocol.


26

6.1.5.2 Laboratory Hood Operating Specifications and Test Criteria

Appropriate operating specifications must be established for every laboratory hood system.

Specifications for operating a laboratory hood system are based on satisfying the performance

criteria and can be unique to the laboratory hood system. Parameters included in specifications can

include:

Operating Modes

Opening Configuration

Range of Flow and Velocity

Differential Pressure and System Static Pressure

Maximum Cross Draft Velocities

VAV Speed of Response and Flow Stability

Monitor Accuracy

Qualitative and Quantitative Containment Requirements

Table 5 lists test requirements for various ECD. Table 6 presents recommended operating and

performance criteria.


27

Table 5 ECD Test Requirements

Functional and

Performance Tests

CAV Fume

Hood

VAV

Fume

Hood

Biosafety

Cabinet VBE FSE Canopy Slot Hood VE

Down

draft

table

Filtered

Ductless

Hood

Inspection X X X X X X X X X X

Flow X X X X X X X X X X

Hood Static Pressure X X X X X X X X X X

Capture or Face

Velocity X X X X X X X X X X

Cross Draft Velocity X X X X X X X X X X

VAV Response X

VAV Stability X

Smoke Test X X X X X X X X X X

ASHRAE 110 Tracer Gas X X X X

Alternative Tracer Gas X X X

Filter Leak Tests X X X

Auxiliary Air Test X(1)

Note: Auxiliary air test should be done on all fume hoods equipped with auxiliary air.


28

Table 6 Recommended Operating Specifications and Performance Criteria

Device Test /Parameter Industry Recommended Criteria/Specs

(Unless otherwise specified in the Design Documents) Notes

All Fume Hoods

Sash Design

Opening N/A

Affects Hoods equipped with Vertical Sash, Horizontal

Sashes or Combination Sash.

Cross Draft Test Vcd 50 fpm

At Design sash opening

From any direction using average over 30 seconds at each

test location

Tracer Gas

Containment

AI, AU = <0.1 ppm

Peak = 30 second rolling average < 0.5 ppm

Sash Closed – No detectable escape from hood,

Hood interior vortex concentration less than 3 times steady

state exhaust duct concentration

Traditional

Fume Hood

Face Velocity

100% Open Sash

Vfavg = 100 fpm

Vfmin 90 fpm

Vfmax 110 fpm

VAV hoods can have 100 fpm face velocity at 100% sash full

open

± 10% prevents significant exhaust variation and room

pressure issues.

Face Velocity

Design Sash

Opening

Vfavg = 100 fpm

Vfmin 90 fpm

Vfmax 110 fpm

Mechanical sash stop installed.

Monitor must indicate within 5% of actual face velocity

Unoccupied mode with sash open (occupancy sensor)

Variance Fume

Hoods N/A

The hoods covered by the variance shall operate with an

average face velocity of at least 80 fpm with a minimum of

61 fpm at any point and with a maximum sash height of 18”

High

Performance

Fume Hood

Face Velocity

100% Sash Opening Vfavg 60 fpm

Criteria applicable to high performance hood or equivalent

design.

High

Performance

Fume Hood

Face Velocity Design

Sash Opening Vfavg 60 fpm

Retro-Fit Fume

Hoods

Face Velocity

Maximum Sash

Opening

See Manufacturer Recommended

Operating Specifications


29



Face Velocity

Design Sash

Opening

See Manufacturer Recommended

Operating Specifications

Hood Flow, Face

Velocity or

Pressure

Monitor

6” opening to Full

Open Monitor must indicate within 5% or 5 fpm. Based on 10 second average velocity or flow reading

VAV Controls

VAV Response for

fume hoods.

Achieve 90% of the face velocity set-point within 5

seconds from the time the sash is opened.

Includes determination of steady state flow at minimum and

maximum to determine start and 90% of final flow.

Stability Test Coefficient of Variation

COV< 20% COV% = (3*Std.Dev.)/SSTAvg.flow

Fume Hood

Minimum Flow

or Min. ACH

Min. Flow at Sash

Closed via Pitot

Tube Exhaust

Ensure contaminants are properly diluted and

exhausted from the hood.

ANSI/AIHA Z9.5 suggests that 150 ACH to 375 ACHfh

may be appropriate.

Flow must be controllable within stability requirements and

subject to minimum duct velocities (see Note 1).

Lab

Offset Volume (i.e.

transfer air)

Difference between supply and exhaust flow for laboratory

to achieve directional flow and pressurization.

Differential Pressure (-) to adjacent non-lab spaces(1) If potential for generation of airborne hazardous material.

Differential Pressure (+) to adjacent non-lab spaces (2) If no potential for generation of hazardous airborne

materials

Recirculation of Lab

Air 100% outside air w/no recirculation

Air can be recirculated within a lab unit for local

conditioning.

Air may be recirculated when monitored for airborne

concentrations.

Air may be recirculated when no hazardous materials are

present.


30



Lab:

Tissue Culture,

Cleanroom

Differential Pressure

(+) to vestibule (anteroom)

and/or

(-) to adjacent non-lab spaces

If potential for generation of hazardous airborne materials,

but requires isolation or no infiltration to main lab

Exhaust Duct

Velocities

Vapors, Gases,

Smoke and Sub

Micron Particles

ACGIH – Industrial Ventilation Manual

1,000-2,000 fpm or any desired velocity

See Note 1 below

Criteria for duct velocity or hood ACH may be affected by

exhaust duct size.

Fumes: i.e. Zinc and

Aluminum Oxide

Fumes

2,000-2,500 fpm

Very Light Dust: i.e.

Cotton Lint, Wood

Flour, Litho-Powder

2,500-3000 fpm

Dry Dust and

Powders Cotton

Dust

3,000 -3,500 fpm

Average Industrial

Dust Shavings

Sawdust, Grinding

Dust

3,500-4,000 fpm

Heavy Dusts: i.e.

Metal Turnings,

Lead

4,000-4,500 fpm

Heavy Moist Dust:

i.e. Buffing Lint

(Sticky), Lead Dust

with Small Chips

> 4,500 fpm


31



Lab Hood

Exhaust

Stack Discharge

Velocity or Criteria

3,000 fpm + 10 ft above roof, or

< 100 µg/m³ per g/s or 10,000:1 dilution factor.

Criteria for stack design should be based on preventing

exposure and re-entrainment rather than discharge velocity.

Notes:

1. Minimum duct velocities must be capable of transporting effluent out of system and preventing accumulation of materials within the duct system. The

minimum flow must also be sufficient to permit accurate and precise measurement and control within acceptable tolerances. The minimum flow through VAV

fume hoods can be a function of the fume hood internal ACH and the resulting capture and duct transport velocity.


32

6.1.5.3 Operating Mode

Depending on the design of the ventilation system, a laboratory hood can have multiple modes of

operation to meet changing demands for ventilation. Operating modes should be well defined and

assigned appropriate performance criteria and operating specifications. The operating modes for a

laboratory fume hood can be simple or complex depending on the capability of the controls. Simple

CAV systems have only one mode of operation where the hood operates continuously at full flow

regardless of use. More complex VAV control systems enable multiple modes of operation that

might vary flow depending on the position of the sash or whether someone is standing at the

opening.

Operating modes for a VAV fume hood equipped with sash sensors and an occupancy detector could

include:

Sash Open;

Sash Closed;

Sash Open – Occupied (person at hood opening); and

Sash Open – Unoccupied (person not at the hood opening).

For other hood types the operating modes may vary depending on the function. For example, the

operating modes for a FSE might include only two operating modes such as operating and not

operating.

6.1.5.4 Flow and Velocity Specifications

The design opening area for each hood type and the required face velocity or capture velocity must

be known to determine the exhaust flow. Flow (Q) is the product of opening area (A) multiplied by

the average velocity (V) where Q = V x A. The design face velocity is typically 100 fpm for traditional

fume hoods and 60 fpm for high performance fume hoods.

Exhaust flow for a VAV fume hood can range from a minimum with the sash closed to a maximum

with the sash full open (100%). The flow at a given sash configuration is equal to the design face

velocity multiplied by the opening area. However, the exhaust flow can be reduced when the sash

opening is reduced without sacrificing containment. See Figure 17 for the difference between flow

with the sash open and sash closed.


33

Figure 17 Laboratory Hood Flow Specifications at Sash Open and Sash Closed

Establishing the minimum flow for a VAV fume hood is more complicated than the simple Q = V x A

calculation, as the minimum exhaust must ensure containment with the sash closed and prevent

accumulation of unsafe concentrations within the fume hood.

The 2012 ANSI/AIHA Z9.5 American National Standard for Laboratory Ventilation requires the

minimum exhaust volume ensures that contaminants are properly diluted and exhausted from a

hood. From the standard:

"The following considerations shall be taken into account (as applicable) when setting the

minimum hood flow rate for each hood:

Control of ignition sources within the hood,

Design of the hood, the materials used in the hood and the anticipated maximum generation rates,

Potential for increased hood interior corrosion,

Effect on exhaust stack discharge velocity,

Fume hood density,

Need to affect directional airflows, and the

Operating range of the hood exhaust equipment and the associated control system."


34

The standard also uses the internal volume of the hood and air changes per hour (ACH) to help

specify the minimum flow. See Figure 18 for a diagram of the critical measurements to calculate the

internal ACH.

The standard suggests that 150 ACH to 375 ACH is typically adequate but does not define a specific

acceptable minimum ACH. The minimum exhaust flow in cfm can be calculated by multiplying the

appropriate ACH by the internal hood volume and dividing by 60 minutes per hour (Q = ACHhood x

Vol.hood/60). Selecting the appropriate internal ACH depends on:

Understanding the Hazards and Processes

The lower explosion limit (LEL) and the safety factor (most facilities use 10-25% of the LEL)

Hood design, internal airflow patterns and the mixing factor

Capability of the VAV controls to ensure stable flow at reduced rates

Conducting dilution tests to determine the minimal flow acceptable for the hood

Maintaining appropriate duct transport velocity

Figure 18 Diagram of Hood Showing Dimensions for Calculating the Hood Air Change Rate

Table 7 contains specifications and criteria for dilution tests.


35

Table 7 Specifications and Criteria for Dilution Tests

Test Criteria Notes

Pitot traverse and calculated flow based on sash height opening

Sash heights to minimal spec. calculate and confirm minimum exhaust set point for protocol.

Measure to confirm minimum flow to provide minimum of 150 ACH

Exhaust Flow Exhaust flow should be within 5% of BAS reported

flow.

Calculation of flow using average face velocity increases error for flow.

Measurement by Pitot tube is preferred with sufficient length of straight duct.

Dynamic Response and Stability Test

VAV Response Test:

Time required for VAV to modulate flow with sash closed to 90% of steady state flow with sash at design opening must be less than or equal to 5 seconds.

The response time includes the time required to raise the sash.

Sash is raised at approximately 1.5 ft/sec

VAV Stability Test:

The variation determined by the coefficient of variation shall be less than 10% of the steady state flow with the sash closed or with the sash at the design sash opening.

The coefficient of variation is calculated as: %COV = 100 × (3 × standard deviation) / average steady state flow

Tracer Gas Containment Tests (static mannequin and Sash Movement Effect Test (VAV Tracer Gas

Containment Tests)

The maximum 5-minute average BZ concentration

must be 0.05 ppm.

The maximum 30-second rolling average shall be less than 0.1 ppm. Rolling average is the average of any consecutive 30-second period.

The peak concentration shall not exceed 0.5 ppm.

The maximum 5-minute average concentration applies to any test configuration or mannequin position.

30-second rolling averages shall be calculated during opening scan and sash movement tests. The 30-second rolling average negates instrument detection methods and replaces peak escape.

Tracer Gas Dilution Tests The internal concentration shall not exceed 25% of

the Lower Explosion Limit (LEL) for the worst flammable material used in the hood.

The dilution tests determine the hood dilution factor that is used to calculate potential concentrations inside the hood knowing the exhaust flow and contaminant generation rate.

Definitions: Vcd – Cross-draft velocity, Vfavg – Average face velocity, Vfmin – Minimum face velocity, Vfmax – Maximum face velocity, COV – Coefficient of variation.


36

6.1.5.5 Laboratory Hood Monitors

ANSI/AIHA Z9.5 requires that all hoods be equipped with a hood monitor (Figure 19) that indicates

flow, pressure or face velocity and provides both audible and visual alarms to provide the hood user

with information about the operation of the fume hood system. The audible and visual alarms alert

users to improper exhaust flow or low face velocity.

The hood monitor should be capable of indicating the airflow is in the desired range and capable of

indicating improper flow or face velocity is high or low by 10%.

Fume hood monitors should be calibrated annually and/or whenever hood airflow is modified,

within a tolerance of + -5%.

Figure 19 Example of Through-the-Wall Velocity Sensor

6.1.6 Distillation Laboratory Fume Hood Specifications


6.1.7 Walk-in Fume Hood Specifications


6.1.8 Perchloric Acid Fume Hood Specifications

Heated perchloric acid should only be used in a laboratory hood specifically designed for its use and

identified as “For Perchloric Acid Operations”.

Perchloric acid fume hoods and exhaust duct work shall be constructed of materials that are acid

resistant, noreactive, and impervious to perchloric acid.


37

Ductwork for perchloric acid hoods and exhaust systems shall take the shortest and straightest path

to the outside of the building and not be manifolded with other exhaust systems. A water wash

down system shall be provided for washing down the hood interior behind the baffle and the entire

exhaust system.

Hood work surface shall be watertight with a minimum depression of 13 mm at the front and sides

with an integral trough at the rear of the hood to collect wash down water.

Exhaust fans supporting perchloric hoods should be acid and spark resistant. The exhaust fan motor

should not be located within the ductwork.

Hood surfaces should have all welded construction and have accessible round corners for ease of

cleaning.

6.1.9 Radioisotope Fume Hood Specifications

Hoods designated for use with radioactive materials shall be identified with the radiation hazard

symbol.

Hoods intended for use with radioactive isotopes must be constructed of stainless steel or other

materials that will not be corroded by the chemicals used in the hoods.

The hood interiors must have coved corners to facilitate decontamination.

Radioisotope hoods equipped with HEPA or Charcoal/HEPA filters require a bag-out plenum for

mounting such filters and fan capacity for proper operation of the hood with the filter installed.

Cabinets that may be supporting radioisotope hoods shall be adequate to support shielding for the

radioactive materials to be used in the fume hood.

6.1.10 Ductless Fume Hood Specifications


6.1.11 Laminar Flow Fume Hood Specifications


6.2 Ventilated Balance Enclosures (VBE)

Weighing of hazardous materials should be conducted in a low volume exhaust hood designed to

enclose sensitive analytical balances. VBE (Figure 20, also called Weighing Enclosure) includes many

of the same components of a typical chemical lab hood. However, weighing enclosures generally do


38

not include double wall construction (interior liner and exterior hood enclosure panels) or sliding

sashes. They are operated at lower face velocities than chemical lab hoods to reduce turbulence

that disturbs the balance and increases unwanted loss of material (approximately 60 fpm or less).

The design of a balance enclosure and exhaust flow (face velocity) must be sufficient to prevent

unacceptable escape into the lab space. Exhaust from balance or weighing enclosures should be

appropriately discharged from the lab space or filtered prior to recirculation.

Figure 20 Typical VBE (Weighing Enclosure) Station

6.2.1 Ventilated Balance Enclosure Specifications

A balance enclosure is a ventilated enclosure designed to specifically house a laboratory balance.

Typically made of transparent materials, balance enclosures are designed to protect users and the

laboratory environment by directing airflow away from the breathing zone of the user.

Testing protocol and criteria should be provided by the manufacturer, including testing filter

integrity if a filter is a component of the system.

6.3 Canopy Exhaust Hoods

Canopy exhaust hoods (Figure 21) are receiving hoods provided for the removal of heat and

negligible hazards from specific laboratory apparatus such as furnaces, ovens, and sterilizers.

Canopy hoods should not be relied upon for personnel protection where processes could be

enclosed and containment better assured.


39

Figure 21 Photo of Canopy Hood

Canopy hoods can be enclosed to improve capture and minimize flow requirements. Use of canopy

hoods should be carefully scrutinized as occupant safety is limited and airflow requirements result in

high operating costs. Figure 22 shows a large canopy hood in an improper configuration, used to

capture hazardous emissions generated outside the enclosure.

Figure 22 Improperly Configured Canopy Hood Located Over Apparatus

6.3.1 Canopy Exhaust Hood Specifications


6.4 Flexible Spot Exhausts (FSE)

Flexible Spot Exhausts (Figure 23, also called snorkel hoods) are point source extraction hoods used

to remove chemical fumes or heat from laboratory instrumentation or processes that are not readily

conducted in a fume hood or other ventilated enclosure. Some examples include high-performance

liquid chromatography (HPLC), gas chromatography/mass spectroscopy (GC/MS), and atomic


40

absorption (AA) equipment. The flow through a FSE is often limited by the duct size and the system

static pressure; capture effectiveness is a function of the proximity to the contaminant source and

the design of the hood inlet. Generally, flanged inlets will provide better capture than un-flanged

openings.

Figure 23 Flexible Snorkel Exhausts

FSE are most commonly employed in fixed positions over equipment or applied to partial enclosures

associated with sonicators and balances, microscopes, tissue photography or surgical laser plumes.

Successful FSE bench applications are highly specific to the mass of the contaminant and the velocity

and angle of emission. These factors require a high level of user knowledge and often require re-

adjustment of the FSE during use to ensure efficient capture. Investigate the intended use of the

FSE and evaluate the design and location of the exhaust inlet to ensure satisfactory capture of

hazardous materials.

6.4.1 Flexible Spot Exhaust Specifications


6.5 Slot Hoods

Slot hoods have limited application in research laboratories and are designed to capture emissions

generated with marginal velocities near the slot openings. Slot hoods provide a limited range of

capture. The capture is a function of the hood dimensions, slot aspect ratio, exhaust flow (capture

velocity) and contaminant emission characteristics. In addition, the orientation of the user with

respect to the opening can also influence capture. Locate a slotted hood so that the direction or

airflow is not around the operator; see Figure 24 for a diagram of airflow patterns and orientation of

the user. In laboratory programs, slot hoods are most commonly used to control vapors from tray

photo processing. Historically, slot hoods have also been used to control formaldehyde during


41

preserved tissue sorting. The American College of Governmental Industrial Hygienists (ACGIH)

Ventilation Manual should be used as a guide to the design of slot hoods1.

Figure 24 Front and Side View of Slot Hood

6.5.1 Slot Hood Specifications


6.6 Downdraft Necropsy Tables

This special vent application (Figure 25) allows unobstructed top access while limiting release of

preservative chemicals and odors into the room air. It must be carefully cleaned to prevent

blockage of vents. It is intended only for necropsy or similar animal studies should not be used

where other vent hoods would be more appropriate.

1 ACGIH

®: Industrial Ventilation: A Manual of Recommended Practice for Design, 27

th Edition. Cincinnati, Ohio:

American Conference of Governmental Industrial Hygienists, 2010.


42

Figure 25 Downdraft Necropsy Table

6.6.1 Downdraft Necropsy Table Specifications


6.7 Glove Boxes

Glove boxes (Figure 26) are tightly sealed, fully enclosed systems often required to ensure total

containment of chemical and biological contaminants. Such enclosures permit manual

manipulations within the box by means of armholes provided with thick gloves, which are sealed to

the box at the armholes. Depending on the application, the glove material may be susceptible to

cracking and wear (especially where they are joined to the box) and must be carefully inspected.

Figure 26 Glove Box

6.7.1 Glove Box Specifications


43


6.8 Biological Safety Cabinets

Laminar-flow biological safety cabinets shall meet minimum standards for cabinet classifications in

NSF 49 for personnel, environmental, and product safety and shall be listed and identified by a

distinctive NSF seal. Field re-certification, performed by an NSF 49-listed, competent technician and

conducted according to the procedures outlined in NSF 49, will be required once the cabinet(s) is

installed. Cabinet classification shall be determined in consultation with the laboratory managers.

These types of cabinets have special design requirements depending on their intended use:

Protecting personnel from harmful agents inside the cabinet

Protecting the work product, experiment, or procedure from contamination by the laboratory environment, leading to invalidated test results

Protecting the laboratory environment from contaminants inside the cabinet.

There are three different types of cabinets, categorized as Class I, II or III. Each type of cabinet

operates differently with a limited range of application and include:

Class I cabinets provide environmental protection, limited personnel protection, and no product protection. Class I cabinets may be appropriate for use with low to moderate risk biological agents.

Class II cabinets are designed to provide environmental protection, product protection and varying degrees of personnel protection. Class II cabinets are subcategorized according the types A, B and 100% Total Exhaust. Class II Type A cabinets are typically exhausted to the room and use of volatile chemicals is restricted. Type B and Total Exhaust cabinets are ducted to the outside and enable limited use of volatile materials.

Class III cabinets, sometimes called glove boxes, provide the highest level of protection for product, personnel and the environment.

For more information, U.S. Department of Health and Human Resources, Primary Containment

for Biohazards: Selection, Installation and Use of Biological Safety Cabinets. Table 8 below

provides information about different biological safety cabinets.

Table 8 Biological Safety Cabinets

Type % Cabinet Air

Recirculated

% of

Exhaust

Minimum

Face

Velocity

Exhaust

Connection

Suitable for use

with toxic

chemicals and

radionuclides?


44

Class I 0% 100% 75 fpm Hard Duct No

Class II

Type A1 70% 30% 75 fpm

None or

Thimble No

Class II

Type B1 30-50% 50-70% 100 fpm Hard Duct

Minute

Quantities

Class II

Type B2

Total Exhaust

0% 100% 100 fpm Hard Duct Minute

Quantities

Class II

Type A2 70% 30% 100 fpm

Thimble or

Hard Duct

Minute

Quantities

Class III 0% 100% N/A Hard Duct

Minute

quantities,

No volatile chemicals

6.8.1 Class I Biological Safety Cabinet


45

Figure 27 Diagram of Class I Biological Safety Cabinet

The Class I biological safety cabinet is applicable for low to moderate risk agents and where product

protection is not required. The cabinet protects the user in similar fashion to a fume hood with the

exception that exhaust air may be filtered prior to being exhausted (see Figure 27 above). Some

Class I cabinets are exhausted through a HEPA filter to the lab. However, cabinets should be hard

ducted to exhaust air outdoors. It is not recommended to return exhaust air to the room.

6.8.1.1 Class I BSC Specifications


6.8.2 Class II, Type A Biological Safety Cabinet


46

Figure 28 Class II, Type A1 Biological Safety Cabinet

The Class II, Type A1 biological safety cabinet is applicable for low to moderate risk agents and

where there is no use of volatile, toxic chemicals or volatile radionuclides. A Class II, Type A1

cabinet provides personal protection, product protection and environmental protection.

Class II, Type A cabinets re-circulate approximately 70% of the cabinet air after it passes through a

HEPA filter. The remaining 30% of the cabinet air is HEPA filtered and exhausted to the laboratory

room or to the outdoors. Refer to the Figure 28 for Class II, Type A biological safety cabinet for

airflow patterns.

Airflow through the face into the front grille provides personnel protection. Class II, Type A1

cabinets are designed for a 75 fpm-100 fpm inflow velocity. HEPA filtered down-flow (vertical

laminar flow) provides product protection with 50% of the air exhausted through the front grille and

50% of the air exhausted through the rear exhaust grille. Volatile chemical should not be used in a

Type A cabinet due to the volume of re-circulation and potential for accumulation of concentrations

in the work area.

6.8.2.1 Class II, Type A BSC Specifications



47

6.8.3 Class II, Type A2 Biological Safety Cabinet

Figure 29 Class II, Type A2 Biological Safety Cabinet

The Class II, Type A2 cabinet has nearly identical flow patterns as a Type A cabinet (see Figure 29

above). However, there are three main differences between the Type A2 and Type A cabinet:

A Type A2 cabinet requires 100 fpm inflow velocity while a Type A cabinet requires only 75 fpm

Contaminated areas within a Type A2 cabinet are maintained under negative pressure with respect to the cabinet exterior or are surrounded by a negative pressure area. In comparison, a Type A cabinet can have contaminated positive pressure areas adjacent to the hood exterior

Type A2 cabinets are exhausted to the outdoors. Type A cabinets can be exhausted to the laboratory given the right conditions of use


48

Type A2 cabinets can be used for low to moderate risk agents involving minute quantities of toxic

chemicals and trace radionuclides. The cabinet protects the user by maintaining a continuous flow

of room air into the front exhaust grille at a minimum of 100 fpm inflow velocity. The work opening

is generally limited to a height of 8 inches and the sash is not moveable. The biological substance is

protected from airborne impurities by a continuous down flow of HEPA filtered air. As in a Class II,

Type A cabinet, approximately 70% of the cabinet air is re-circulated after it passes through the

HEPA filter. The remaining cabinet air, 30%, is passed through another HEPA filter prior to exhaust

to the outside.

6.8.3.1 Class II, Type A2 BSC Specifications


6.8.4 Class II, Type B1 Biological Safety Cabinet

Figure 30 Class II, Type B1 Biological Safety Cabinet

The Class II, Type B1 biological safety cabinet is applicable for low to moderate risk agents and

minute quantities of toxic chemicals and trace radionuclides that will not affect interior cabinet

components. The cabinet provides protection for the user by providing a continuous flow of air into

the cabinet at a minimum velocity of 100 fpm through an 8 inch opening height. Approximately 30%


49

of the cabinet air is re-circulated after passing through a HEPA filter (see Figure 30 above). The

majority of cabinet air (70%) passes through another HEPA filter prior to exhaust to the outdoors.

The biological agents are protected from airborne impurities by a descending vertical laminar air

from a HEPA filter mounted above the work surface. The laminar supply flow splits above the work

surface with approximately 70% flowing toward the rear exhaust grille and 30% flowing into the

front exhaust grille. All exhaust air captured by the rear exhaust grille flows through a HEPA filter

for discharge to the outdoors. All potentially contaminated plenums and ducts are under negative

pressure with respect to the laboratory.

6.8.4.1 Class II, Type B1 BSC Specifications


6.8.5 Class II, Type B2 (Total Exhaust) Biological Safety Cabinet

Figure 31 Class II, Type B2 (Total Exhaust) Biological Safety Cabinet

The Class II, Type B2 biological safety cabinet is applicable for use with higher risk agents, toxic

chemicals and radionuclides where product protection is of concern. Product protection from

airborne impurities is provided by a continuous down flow of HEPA filtered air. Protection of the

user is provided by a continuous flow of air into the cabinet at a velocity of 100 fpm through a

typical 8 inch opening.


50

Supply air to the cabinet for product protection passes through a HEPA filter to provide a

descending vertical laminar flow over the work surface. Inflow and supply down-flow are exhausted

to the outdoors with no re-circulation (see Figure 31 above). All internal plenums and ducts are

under negative static pressure with respect to the cabinet exterior. The work opening is typically

limited to a height of 8 inches.

6.8.5.1 Class II, Type B2 BSC Specifications


6.8.6 Class III Biological Safety Cabinet

The Class III biological safety cabinet is a gas tight enclosure that is sometimes referred to as a glove

box. Reference section 6.7 Glove Boxes for more information. Caution is advised when using

volatile chemicals due to the low exhaust flow and risk of accumulating potentially explosive

concentrations.

6.8.6.1 Class III BSC Specifications


6.9 Ventilated Enclosure

A ventilated enclosure (Figure 32) is suitable for operations that are largely unattended but will emit

small volumes of potentially hazardous materials or excessive heat. The enclosure should be

constructed to contain the process and designed to provide effective dilution and removal of

materials and heat generated within the enclosure. Ventilation Enclosures are appropriate for a

variety of applications such as:

Robotic Sampling Equipment

Test Instrumentation such as laser diffractometers

Rotary Evaporators

Drying Ovens

Closed process equipment


51

Figure 32 Example of a Ventilated Enclosure Containing a Laboratory Oven

6.9.1 Ventilated Enclosure Specifications


6.10 Canopy Hoods

A canopy hood is a ventilated enclosure used to collect and disperse heat and non-hazardous

effluent. Canopy hoods are receiving hoods and as such, shall be used when there is a force, such as

heat, to deliver the contaminant to the receiving hood. Often custom-sized and constructed for use

in specific applications, canopy hoods are not typically efficient and should be installed for use only

under specific conditions, when other more efficient options are not available.

6.10.1 Canopy Hood Specifications


6.11 Gas Cabinets

Gas cabinets or special exhaust cabinets could be required to house individual toxic/pyrophoric gas

cylinders. Leak detectors and low-exhaust flow alarms, as well as a gas purge system, should be

required to provide for safe exchange of cylinders.

6.11.1 Gas Cabinet Specifications


52


6.12 Flammable Liquid Storage Cabinets

Venting of storage cabinets is not required for fire protection purposes, but venting may be required

to comply with local codes or authorities having jurisdiction. Non-vented cabinets should be sealed

with the bungs supplied with the cabinet or with bungs specified by the manufacturer of the

cabinet. If cabinet venting is required, the cabinet should be mechanically vented to the outside

and:

Both metal bungs must be removed and replaced with flash arrestor screens (normally provided with cabinets). The top opening serves as the fresh air inlet.

The bottom opening must be connected to an exhaust fan by a length of rigid steel tubing that has an inside diameter no smaller than the vent opening.

The fan should have a non-sparking fan blade and non-sparking shroud.

The cabinet should exhaust directly to the outside (the cabinet should not be vented through the fume hood).

The total run of exhaust duct should not exceed 25 feet.

The design velocity of the duct should not be less than 2,000 fpm.

The cabinets should be conspicuously marked, “Flammable - Keep Fire Away.”

6.12.1 Flammable Liquid Storage Cabinet Specifications


6.13 Special Purpose Hoods

Special purpose hoods are defined as any hood that does not conform to the specific types

described above. Special hoods may be used for operations for which other types are not suitable

(e.g., robot sampling equipment, liquid nitrogen dewars, ETO sterilizers). Other applications might

present opportunities for achieving contamination control with less bench space or less exhaust

volume (e.g., using the hoods as special mixing stations, evaporation racks, heat sources, or

ventilated worktables).

6.13.1 Special Purpose Hood Specifications


7 Types of Laboratories


53


7.1 Categorization and Risk Control Bands


7.2 Bio-Safety Levels


7.2.1 BSL 1


7.2.2 BSL 2


7.2.3 BSL 3 and Higher Labs


7.3 Teaching Laboratories


7.4 Necropsy Laboratories


7.5 Radiation Laboratories


7.6 Gross Anatomy Laboratories


8 Laboratory Design and Layout Specifications

Given the high costs of conditioning air in laboratories, it is prudent to minimize the supply air

quantity into the space whenever possible while complying with the primary objectives of providing

safe and productive laboratories. The design goals should be to maximize the utility of the exhaust

and air supply systems such that they:

Satisfy the exhaust flow requirements of exposure control devices under all modes of operation


54

Provide a healthy environment without negatively impacting performance of laboratory hoods

Provide comfortable and productive work environments for occupants

If performance conflict arises, the occupant and general public safety requirements take priority.

The performance aspect of secondary laboratory containment must also be evaluated as a

component of the cascading principle of risk, where primary containment occurs in the laboratory

hood and the lab space provides secondary containment.

The primary components are the exhaust air devices and the supply air devices. Exhaust side

components include the laboratory hoods, general exhaust, ductwork and controls. On the supply

side are air supply diffusers, ductwork, controls, thermostat, reheat valves and coils. The

components of a typical laboratory and associated ventilation systems are shown in Figure 33.

Figure 33 Diagram of a Laboratory Depicting Supply and Exhaust Flow Components

8.1 Laboratory Systems and Operating Modes

The type of system influences the design decisions about type and location of supply diffusers,

location of hoods and resultant airflow patterns under different modes of operation. Modulating air

supply volume and discharge air temperatures can influence airflow patterns by affecting throw

patterns, terminal velocities and temperature gradients within the lab.


55

With the advent of Variable Air Volume (VAV) systems, Usage Based Controls (UBC), Occupied/Un-

Occupied modes, and Energy Recovery Units (ERU), the control of air distribution becomes very

complex due to the inter-dependency of the system components and variable operating conditions.

The harmonious integration of the air distribution components with laboratory hoods becomes a

challenge to the laboratory designer. The performance of many laboratory hoods especially

chemical fume hoods, are dependent on the lab environment and the air supply conditions near the

opening face of a laboratory hood.

8.2 Hood Location

Proper placement of fume hoods in a laboratory is critical to their safe and efficient operation. Poor

location with respect to sources of cross drafts can cause turbulence at the plane of the sash and

increase the possibility of contaminant escape. Undesirable airflow patterns affecting the

uniformity of flow into the hood sash opening can be produced when hoods are located too close to

one another.

Adherence to the following guidelines for properly locating chemical fume hoods will minimize the

adverse effects caused by excessive supply air velocities and proximity to personnel traffic. The

lettered points below are graphically represented in Figure 34.

A. Locate hoods at the back of labs or in alcoves.

B. There should be a minimum clearance of 4 ft. between a fume hood and the nearest door.

C. A minimum clearance of 8 ft. is required between a fume hood and door opposite the fume

hood.

D. Hoods should not be located within 3 ft. of obstructions that cause undesirable airflow

patterns at the plane of the sash. Obstructions include walls, partitions, and large

equipment such as freezers.

E. Hoods should be located at least 4 ft. from a main traffic aisle.

F. Hoods should be located at least 4 inches from adjacent walls unless the design of the hood

prevents spatial variations in face velocity from wall effects.

G. Hoods should not face each other within distances of less than 5 ft. from sash plane to sash

plane or the distance equal to the nominal length of the largest hood, whichever is greatest.

H. There is no recommendation for distances between laboratory hoods adjacent to one

another unless the location causes face spatial velocity variances greater than 20%. The

spatial variation is a measure of the uniformity of airflow through the opening and

distribution of velocities across the opening.


56

I. The distance from the hood to a diffuser depends on the type of diffuser, throw pattern and

terminal velocities resulting over the range of temperature and supply volume. See section

3.2.3 for additional information regarding effective diffuser location.

Figure 34 Diagram of Laboratory Showing Location of Laboratory Hoods

8.2.1 Air Distribution Effectiveness

Distribution effectiveness can be affected by people, movement within the room, location of

obstructions and equipment, heat sources, and differences in HVAC system operating modes. The

design of the air distribution systems must take into account all of these factors for maximum

effectiveness. Selection of diffusers for VAV laboratories is particularly challenging due to the

changing supply volume and discharge temperatures. The air supply from supply diffusers in labs

must not affect the operation of the fume hoods when the sashes are open regardless of the

discharge temperature and must provide adequate room air mixing at low volumes when the sashes

are closed. As such, the air distribution systems must properly condition the space, compliment

hood performance at all operating modes and minimize installation and operating costs.

Min.

Min.8'

4'

X = HW (Min)

Min.

X = HwMin.

A

A A

B, D

C

D

F

GG

H

Supply Diffuser

Traffic Aisle Way

4' Min.

E

I

4"

HW

Freezer

HW

3'(Min)

Hw


57

The effectiveness of the air distribution system can be judged by several factors including:

Utilizing the maximum percentage of air to condition the space and minimizing or eliminating “short circuiting” with little or no utility

Causing minimal or no effect on the operation of the laboratory hood

Maintaining Indoor Air Quality (IAQ)

Providing minimal “First Cost” and subsequent operational costs

Maintaining differential pressure relationship to adjoining spaces

8.2.2 Doors and Traffic Aisles

Doors and traffic aisles provide the means of access and egress for both equipment and laboratory

personnel. Both the location and size of the doors and traffic aisles in the laboratory influence

airflow patterns and must be accounted for when investigating overall air balances and occurrence

of undesirable airflow patterns. The swing of a door or traffic past a hood can produce considerable

cross drafts in excess of 200 fpm and must be located to minimize impact on hood performance. It

is recommended to locate laboratory hoods at least 4 ft. from doors or traffic aisles.

Doors located between laboratories and adjoining spaces shall be equipped with automatic door

closers to optimize secondary containment and design pressurization. Self-closing doors are to be

able to be opened with a minimum of effort as to allow access and egress for physically challenged

individuals.

8.2.3 Location and Type of Supply Diffusers

Conditioned air is introduced to laboratories through supply diffusers. Supply diffusers come in

many sizes and types and can be mounted in the ceiling, walls or floor. The type of diffuser and

volume of air supplied at a given temperature generally determines the throw pattern and terminal

velocity. The terminal velocity is the resultant velocity at a given distance from the diffuser under a

specific set of conditions. Improper sizing, selection and location of diffusers when combined with

location of the hoods and laboratory furniture can dramatically affect room airflow patterns and

ability to satisfy the design objectives.

The hood density or number of fume hoods that can be placed within a laboratory space is

constrained by several factors including:

Distance between fume hoods and air diffusers

Physical size of the fume hoods

Available ceiling space for the installation of supply diffusers


58

Type of air diffuser and discharge characteristics

These factors result in a complex interaction of numerous variables that affect performance of

laboratory fume hoods and must be considered to minimize potential problems. Locating properly

sized diffusers at least 5 ft. from laboratory fume hoods reduces hood turbulence due to cross drafts

and variations in air supply temperature. The distance of 5 ft. from the front and sides of the fume

hood defines a zone (No Diffuser Zone, NDZ). Placement of any diffuser within the NDZ should be

avoided unless the diffuser is required for room air circulation and air supply from the diffuser does

not impact fume hood performance. High velocity diffusers should be avoided near laboratory fume

hoods.

When the placement of diffusers is close to this zone, certain locations may be preferred as shown

in Figure 35 below.

Figure 35 Good, Better, and Best Locations for Supply Diffusers

Three zones are identified surrounding the NDZ. Diffuser Zone 3 is a good location for locating a

supply diffuser, Diffuser Zone 2 is a better location and Diffuser Zone 1 is the best location. Lab

designers should use caution when locating diffusers in Zone 3 in front of a hood opening. Air

directed perpendicular to the plane of the sash can be more detrimental to hood performance than

cross drafts of similar velocity directed parallel to the opening.

6 FT

DiffuserZone 1

DiffuserZone 1

DiffuserZone 2

DiffuserZone 2

DiffuserZone 3

5' 0"

45°


59

As the NDZ extends five feet from the front and sides of the hood, the size or area of the NDZ is a

function of the size of the fume hood as shown below in Figure 36.

6 FT8 FT

6 Foot Fume Hood

NDZ = ~79 Ft2

8 Foot Fume Hood

NDZ = ~84 Ft2

4 Foot Fume Hood

NDZ = ~64 Ft2

10 Foot Fume Hood

NDZ = ~89 Ft2

4 FT 10 FT

Figure 36 Diagram Showing No Diffuser Zone (NDZ) as a Function of Hood Size

To minimize restrictions caused by the size of the NDZ, fume hoods may be placed such that the

NDZs overlap (Figure 37) or extend outside the laboratory envelope. This recommendation is

compliant with the guidelines for placement of adjacent fume hoods established previously.

6 FT 8 FT

6 Foot Fume Hood

NDZ

= ~79 Ft2

8 Foot Fume Hood

NDZ

= ~84 Ft2

+

Total NDZ

Non

Overlapping

= 163 Ft2

Total NDZ

Overlapping

= 124 Ft2

As Depicted

6 FT

=

8 FT

Figure 37 Diagram of Laboratory Hoods Showing Adjacent and Overlapping NDZs

As the fume hood density in a lab space increases, the effective area of the combined NDZ(s) also

increases. As such, the amount of ceiling space available for the installation of diffusers, lighting

fixtures, or other furnishings decreases accordingly.


60

Once the fume hoods have been selected, the air flow requirements must be specified and the lab

designer must select air diffusers that have performance characteristics capable of delivering the

required air volume, provide adequate mixing for space conditioning and minimize effects on fume

hood performance. Ideally cross drafts at the plane of the sash should be limited to a maximum of

50% of the design face velocity.

Air diffusers create airflow patterns with velocities that are directly proportional to the volume of air

being delivered. As the air is distributed into the space, the supply velocities will degrade due to

expansion of the discharge plume. The degradation of the velocity is expressed by the term,

Terminal Velocity (TV). TV is usually set at 50 fpm for ceiling diffusers and 100 fpm for slots.

The terminal throw is the distance from the diffuser at which the air velocity meets the TV.

Matching the diffuser TV and terminal throw to the hood face places constraints on the placement

of diffusers. The discharge characteristics are particularly important when diffusers are not

mounted flush to the ceiling or are free standing in labs with high ceilings. Diffusers that are flush

mounted in ceiling grids depend on the ceiling surface to produce the mixing characteristics for the

diffuser. Air diffusers should be selected and placed that can deliver the maximum volume of air

while minimizing the distance from the diffuser for achievement of the maximum TV.

In addition to locating diffusers at least 5 feet from laboratory hoods, the outlet area of the diffuser

should be sufficient (approximately 2 times the area of the fume hood design openings). The 2:1

ratio can help determine the number of diffusers required to provide adequate make-up air to the

lab. The number and size of the diffusers together with the area of the NDZ indicates the limit of

fume hood density (# of hoods/lab).

8.2.4 Type of Air Supply Diffusers

Terminal ceiling diffusers or booted-plenum slot diffusers should be specifically designed for VAV air

distribution, where applicable. Booted plenum slots should not exceed 4 ft. in length, unless more

than one source of supply is provided. “Dumping” action at reduced air volume and sound power

levels at maximum delivery should be minimized. For VAV systems, the diffuser spacing selection

should not be based on the maximum or design air volumes, but rather on the air volume range that

the system is expected to operate within the majority of the time. The designer should consider the

expected variation in the range of the outlet air volume to ensure that the Air Diffusion Performance

Index (ADPI) values remain above the specified minimum for the project. This is achieved by

minimizing temperature variation, ensuring effective air mixing between supply and return air

streams, and preventing objectionable drafts in the occupied space.

The construction, sizing and positioning of the supply air diffusers is one of the most important tasks

of transmission and distribution of air in the laboratory. Numerous factors must be considered to

maximize the utility of the air supply to provide a safe and comfortable lab environment at


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minimum airflow. A mismatched sizing of ductwork connections (round, rectangular, or elliptical)

ending with placing improperly selected diffusers may cause the entire system to produce

undesirable airflow patterns. The following guidelines are to assist with the proper selection,

specification, placement and operation of supply diffusers:

The supply duct should be designed to provide satisfactory flow at the inlet of the diffuser

and follow the diffuser manufacturer’s requirements for inlet design. The ducts to each

diffuser must include a quality damper to ensure proper air balance and distribution of flow

between supply diffusers in a lab.

Terminal velocities from supply diffusers should not exceed 50% of the face velocity or

capture velocity of the laboratory hood at the plane of the sash regardless of supply volume

or discharge temperature resulting at different operating modes. For fume hoods operating

at an average face velocity of 100 fpm, the terminal throw velocity at the plane of the sash

should not exceed 50 fpm.

Perforated laminar flow diffusers or radial face diffusers are preferred over linear slot or

rectangular high velocity, high aspirating diffusers.

The diffusers should be selected and located to minimize areas of flow stagnation in the lab

and promote purging of flow and flow from areas of low hazard to high hazard.

Slot Diffuser - These diffusers are routinely used to provide an air curtain which will provide a

thermal barrier adjacent to windowed exterior walls. Horizontal throw of this type of diffuser

will range from 16-28 ft. to achieve a terminal velocity of 50 FPM with air volumes ranging from

300-500 cfm.

Perforated Diffuser with Modular Core – This type of diffuser is routinely used in laboratory and

office spaces. The modular core can be specified to deliver air in 1, 2, 3, or 4 directions.

Directional flow characteristics allow placement of diffusers near walls and corners of the space.

Horizontal throw of this type of diffuser will range from 9-13 ft. to achieve a terminal velocity of

50 fpm with air volumes ranging from 300-500 cfm.

Swirl Pattern Diffuser – This type of diffuser is specified for applications requiring reduced

horizontal throws. Horizontal throw of this type of diffuser will range from 5-13 ft. to achieve a

terminal velocity of 50 fpm with air volumes ranging from 300-500 cfm.

Radial Diffuser or Hemispherical Diffuser – Designed for critical space applications and

laboratories where turbulence due to air jets must be minimized. Horizontal throw of this type

of diffuser will range from 4-8 ft. and vertical throws of 6-7 ft. to achieve a terminal velocity of

50 fpm with air volumes ranging from 300-500 cfm. Radial and Hemispherical diffusers are most

appropriate for laboratories with fume hoods.


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Louvered Diffuser – These diffusers are generally high velocity diffusers routinely used in office

or commercial buildings where larger volumes of air and terminal velocities are a not a primary

concern. Horizontal throw from this type of diffuser will range from 16-28 ft. to achieve a

terminal velocity of 50 fpm with air volumes ranging from 300-500 cfm. Louvered diffusers are

not normally appropriate for use in laboratory environments.

8.3 Ventilation Effectiveness (Air Change Rates in Laboratories)

The preponderance of information indicates that reliance on a single airflow rate or specification of

a minimum Air Change per Hour (ACH) standard for laboratory safety is imprudent and can lead to a

false sense of safety. In reality, laboratory scale procedures with even modest emissions within the

laboratory (not captured by an exhaust device) can result in odorous or hazardous concentrations

that can exceed acceptable limits of concern (LOC) at any reasonable or recommended ACH. Table 9

below is a list of generally recommended ACHs from other guides and organizations, illustrating the

wide variety of opinions and recommendations for appropriate minimum ACH.

Table 9 List of Generally Recommended Ventilation Rates for Labs

Agency Ventilation Rate

OSHA 29 CFR Part 1910.1450 4-12 ACH

ASHRAE Lab Guides 4-12 ACH

Universal Building Codes – 1997 (UBC) 1 cfm/ft2

International Building Code – 2003 (IBC) 1 cfm /ft2

International Mechanical Code – 2003

(IMC) 1 cfm/ft2

United States Environmental Protection

Agency ( U.S. EPA)

4 ACH Unoccupied Lab

8 ACH Occupied Lab

American Institute of Architects (AIA) 4-12 ACH

National Fire Protection Association 45-

2004 (NFPA)

4 ACH Unoccupied Lab

8 ACH Occupied Lab

Nuclear Regulatory Commission Prudent

Practices 4-12 ACH

ANSI/AIHA Z9.5

Standard states that ACH is not an appropriate concept

for designing containment control systems. The specific

room ventilation rate should be established by the

owner.

ACGIH 24th Edition, 2001

The required ventilation depends on the generation

rate and toxicity of the contaminant and not the size of

the room in which it occurs.


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Effective airflow distribution in laboratories is important to laboratory occupants as it helps ensure a

healthy, productive and energy efficient environment for research and development. The process of

designing, specifying, and testing air distribution systems and components for laboratories is a

critical function of the architects, engineers, test and balance firms, and facility commissioning

agents. Lab air distribution systems need to minimize energy consumption, distribute sufficient

quantities of air to meet indoor air quality (IAQ) standards, provide occupants with a comfortable

work environment, and most importantly, effectively distribute air that will support the operation of

laboratory hoods. Furthermore, proper airflow distribution improves energy efficiency by ensuring

effective mixing, distribution and maximum utility of expensive conditioned air.

8.4 Specification of Airflow Rates for Laboratories

The minimum ACH specification for laboratories shall be derived rather than randomly selected and

specified based on historical standards. In place of a required minimum, the following guidelines

are recommended to derive the minimum required airflow rates in laboratories2:

An exposure control device (ECD) and laboratory risk assessment shall be conducted.

Potential sources of contaminant emissions shall be identified and ECDs including laboratory

exhaust hoods should be specified as appropriate to control emissions at the source. All

potential emission sources and assumptions should be clearly defined at the time of design.

Laboratory airflow rates should be based by definition on total exhaust flow for negatively

pressurized laboratories and total supply flow for positively pressurized laboratories. All lab

areas having potential for release of hazardous airborne contaminants should operate under

negative pressure with respect to adjacent non-laboratory spaces. The required pressure

differential between the spaces should be defined by the design team, or as specified on the

design documentation approved and released for construction.

The required exhaust flow should be sufficient to satisfy the exhaust demands of all

laboratory hoods and ECDs (within the lab) operating under all modes of operation;

including occupied and unoccupied operation modes (chemical fume hood sashes open or

closed), full heating and cooling modes, and emergency modes of operation. Emergency

modes of operation may include fire, smoke or “shelter in place” scenarios.

The volume of air supply to the laboratory should be sufficient to meet indoor air quality

(IAQ) requirements as specified by ASHRAE and other applicable codes and standards

2 Smith, T.C. and Yancey-Smith, S.L: “Specifying Airflow Rates for Laboratories.”, Journal of

Chemical Health and Safety 16(5): September/October 2009.


64

including the International Mechanical Code (IMC) and applicable State or local Indoor Air

Quality Code. The laboratory should operate with 100% outside air for the supply flow.

The quality, quantity and conditioning of the air supply should maintain the lab

environment’s comfort, temperature, and humidity specifications accounting for seasonal

fluctuations.

The accuracy and precision of the airflow control systems should be sufficient to maintain

the required specifications for exhaust, air supply and transfer air volumes (difference

between supply and exhaust). The airflow requirements of the exposure control devices

should never be compromised regardless of operating mode.

The transfer air should be mechanically supplied, of equal quality to lab supply air, and free of hazardous

contaminants. The control of transfer air quantities should prevent the spread of contamination

between laboratories in the event of spill or other emergency conditions.

8.5 Calculating Air Change per Hour Rate (ACH)

Following the above guidelines, the required exhaust and supply airflow should be established to

calculate and report the resultant ACH rate for each mode of operation. In the following formulas,

ACH has units of Cubic Feet per Minute (CFM) and Room Volume is in Cubic Feet (FT3). The value 60

has units of Minutes per Hour and is used for conversion.

ACH rate for a negatively pressurized lab:

ACH = ( of Exhaust Volumes / Room Volume ) x 60

ACH rate for a positively pressurized lab:

ACH = ( of Supply Volumes / Room Volume ) x 60

When combined with adherence to good work practices, establishment of minimum airflow rates in

accordance with the above guidelines will provide safe and comfortable lab environments.

However, the airflow rates or use of recommended ACH will not guarantee adequate dilution of

chemicals to safe levels that may be produced during:

Accidental spills in the lab

Serious breach in hood containment

Failure of gas cylinders

Contaminates generated outside an approved exposure control device

8.6 Laboratory Pressurization


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Research laboratories should be under "negative" pressure with respect to surrounding spaces to

ensure secondary control of hazardous emissions. A laboratory under negative pressure will reduce

the potential for materials to escape from the laboratory into surrounding areas.

For R&D facilities where product contamination or cross-contamination is of major concern, the

laboratory space is may be maintained under a positive pressure relative to external barometer or

static pressure in the facility. This approach will reduce the likelihood of particulate infiltrating the

space and potentially contaminating the research products. However, a positively pressurized lab

will not serve to provide secondary containment and hazardous airborne contaminants that escape

capture within the space can escape to adjacent areas. To mitigate this hazard, an anteroom or

airlock may be required to provide a negative pressure zone.

The magnitude of the “negative” and “positive” pressure is a function of the difference between

supply and exhaust volume and the room tightness. As room tightness can vary and is difficult to

specify, specifications to achieve positive or negative pressurization must include either room offset

volume or the desired room pressurization. When specifying pressure, it is recommended that the

differential pressure be 0.005 to 0.05 inches of water gage (W.G.). As a reference, 1.0” W.G.

pressure differential equals approx. 5.2 lbs. of force on the architectural components (walls,

fenestration, etc.). In Figure 38, the lab is under negative pressure to adjacent spaces when the

exhaust is greater than supply. Conversely, a positively pressurized room results from supply

exceeding exhaust.

Figure 38 Laboratory Pressurization and Direction of Airflow Resulting From Differences In Air

Supply and Exhaust Volumes

8.6.1 Lab Offset Volume


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The specifications for offset volume is dependent on the available transfer area, but is typically 100

cfm per door. The offset volume must be sufficient to achieve the desired pressurization. The

equation of air leakage from or to the laboratory is:

Ql = A · 776 · CD ( 2 · Δp / δa ) 0.5, where

Ql = Outflow or Inflow, from or to the space in ft3/min

A = Gap Area, ft2

Δp = Pressure Differential, inch W.G.

δa = Actual Air Density, lb/ft3

CD = Coefficient of Discharge (Dimensionless, usually between 0.6 to 0.8)

The offset volume should be at least two times the maximum error of the supply and exhaust

controls or approximately 10% of the maximum exhaust flow.

8.7 Airflow Controls

Many factors associated with the design of the laboratory can affect the ability of hoods to contain

hazardous chemicals. The location of the hoods in the laboratory, location and type of air supply

diffusers and terminal velocity of supply air can affect hood performance. The following sections

provide general guidelines for ensuring proper design of laboratories and reduction of factors

affecting hood performance. The type of system, constant air volume (CAV) or variable air volume

(VAV), influences the design decisions about type and location of supply diffusers, location of hoods

and resultant airflow patterns under different modes of operation.

8.7.1 CAV


8.7.2 VAV


8.7.2.1 Direct Pressure


8.7.2.2 Airflow Tracking


8.7.3 Demand Control Ventilation (DCV)


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8.7.4 Occupancy Based Control Schemes


8.7.5 Purge Modes


8.8 Laboratory Temperature Control

Maintaining proper environmental conditions expressed in both dry-bulb (DB) temperature and

relative humidity (RH) are goals of the air supply system. Diffuser selection and location along with

the air supply temperature, thermostat and reheat controls can affect the ability to properly control

lab conditions. Temperature control systems in a laboratory can affect hood containment3.

Maintaining constant lab temperatures often requires modulating the temperature and volume of

air supply to the lab. The change in discharge temperature and volume of air from a diffuser can

affect the throw patterns and room air currents near hood openings. The effects are particularly

problematic when diffusers are located near hoods (<6 ft.) and discharge temperatures vary more

than 5°F to 10°F in less than 5 minutes. The change in temperature or the temperature gradient can

cause excessive turbulence at the plane of the hood opening and potential for escape. Temperature

stratification within the space should be limited through proper selection of diffusers and limiting

the change in discharge temperatures to less than 5°F over a five minute period when diffusers are

located less than 6 ft. from a laboratory hood.

9 Lab Ventilation


9.1 Laboratory Exhaust Ventilation

This section includes guidelines for evaluating the design of the laboratory ventilation systems to

ensure compliance with standards and guidelines, and information to evaluate different system

configurations and operation of the flow control systems. Ensuring proper functioning of a

laboratory hood requires proper design and operation of all system components. The ability to

increase or decrease flow through the hoods and the laboratories requires the ability to modulate

flow through the exhaust and air supply systems. The increase and decrease in flow must be

3 Smith, T.C.: “The Unintended Practice of Using Employee Health as an Indicator of Proper Hood

Performance”, Journal of Chemical Health and Safety, January/February, 2004.


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synchronized for both the exhaust and supply systems to avoid air balance and space pressurization

issues.

Figure 39 illustrates the exhaust fans and air handlers connected to plenums and ductwork for

exhausting air from the laboratory hoods and supplying make-up air to the laboratory.

Figure 39 Diagram of a Laboratory Ventilation System

9.1.1 Materials of Construction

This section covers the ductwork installation and materials used in combined laboratory exhaust

systems, including duct and duct accessories (plenums, manifolds, connectors, louvers and dampers,

access doors, dampers, wall and roof penetrations, and cleaning). Ensuring proper materials of

construction prevents premature degradation of the ducts and system components.

The construction of the exhaust system and selection of materials are based on:

Nature of the hood effluents,

Ambient conditions (dry-bulb and wet-bulb temperatures, barometric pressure),

Potential for particulate loading,

Lengths and arrangement of duct runs,


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Exhaust fan drive and operational controls,

Flame and smoke spread rating, and

Resulting air velocities and pressure drops.

When selecting materials and designing ducts, the designer should take into consideration effluents

that are known or may be generated in the future. The laboratory fume hood effluents may vary in

temperature and general hazard classification including organic and inorganic chemical gases,

vapors, fumes, or smokes, and qualitatively as acids, alkalis, and solvents. Exhaust system ducts,

accessories, and coatings are subject to attack from such effluents by corrosion, which is the

destruction of metal by chemical, or electrochemical action; by dissolution (especially for coatings

and plastics), and melting which can occur with certain plastics and coatings at elevated operating

temperatures.

Ambient temperature of the space where ducts and fans operate may affect the vapor condensation

in the exhaust system and thus the metal corrosion with or without the presence of chemical agents

or hazardous gases. The ductwork and duct accessories are subject to a lesser attack when the

lengths of duct runs are relatively short and the air velocities are relatively high (but not excessively

high so that the velocity pressures would also be unreasonably high and cause failure or degradation

due to pressure on the components). The designer should also consider issues of engineering

economics such as the impact of cross sectional duct areas and duct pressures on first cost and

subsequent operating costs.

Horizontal duct runs create more surfaces for contaminant accumulation and moisture deposition

than vertical duct installations. Where the potential for condensation exists, the ducts should be

sloped and condensate drains should be utilized (the recommended slope of the horizontal runs is 1

inch per 10 ft. of duct length). Duct condensate may contain hazardous materials and acids in

solutions. As such, the design and construction of the duct manifold should prevent air and liquid

leaks.

If the hoods will be used for acid digestion or used with concentrated acids that are highly corrosive

to stainless steel, the hood, duct, and fan must be made of fiberglass reinforced plastic or material

with similar acid resistance. However, the Architect/Engineer must confirm design acceptability

with both the Fire Engineer and the local fire authority having jurisdiction prior to the Design

Development Phase.

Under all circumstances, the contaminated air stream should be diluted to prevent concentrations

exceeding 25% of a lower explosion limit (LEL). This provides an adequate safety factor.

The ductwork material selection depends on several factors, including:

Laboratory exhaust mode,

The size of the system (number of labs, hoods, etc.),


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The amount and concentrations of the fumes, gases and particulates,

Exhaust stream heat recovery,

Projected length of facility life cycle, and

Allowable cost.

Stainless steel (S.S.) is one of the most common laboratory exhaust materials. High corrosion

resistance, durability and appearance make it a preferred duct material. S.S. is environmentally

friendly and can be purchased with high recycled content.

Drawbacks to the use of stainless steel duct is its high cost and possible degradation resulting from

high concentrations and/or heating of hydrochloric acid or other mineral acids. A summary of

applications, advantages, limitations, and compatibility of various duct materials are shown in Table

10 below.

Table 10 Duct Materials and Compatibility

Materials Applications Advantages Limitations

Galvanized Steel

Widely used for most

non-lab air handling

systems. Not

recommended for

corrosive product

handling, or

temperatures above

400°F (200°C)

Relatively low cost, high

strength, rigidity,

durability, rust resistance

in ordinary conditions,

availability, non-porous,

workability.

Limited corrosion

resistance, inability

to be welded

(requiring

mechanical joining

of sections) or

painted.

Stainless Steel

Duct systems for kitchen

exhaust, moisture-laden

air, fume exhaust.

High resistance to many

common forms of

corrosion (but care is

definitely required in alloy

selection).

High material cost,

workability,

availability.

Fiberglass

Reinforced Plastic

(FRP)

Chemical exhaust,

scrubbers, underground

duct systems.

Corrosion resistant, ease

of modification.

Cost, weight, range

of chemical and

physical properties,

brittleness,

fabrication, code

acceptance.

Polyvinyl Chloride

(PVC)

Exhaust systems for

chemical fumes and

hospitals, underground

duct systems.

Corrosion resistance,

weight, weldability, ease

of modification.

Cost, fabrication,

code acceptance,

thermal shock,

weight.


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Carbon Steel (Black

Iron)

Breechings, Flues, stacks,

hoods, other high

temperature duct

systems, kitchen exhaust

systems, ducts requiring

paint or special coating.

High strength, rigidity,

durability, availability,

paintability, weldability,

non-porous.

Corrosion

resistance, weight.

Aluminum

Duct systems for

moisture-laden air,

louvers, special exhaust

systems, ornamental duct

systems. Often

substituted for galvanized

steel in HVAC duct

systems.

Weight, resistance to

some forms of corrosion,

availability.

Low strength,

material cost,

weldability, thermal

expansion.

Copper

Duct systems for

exposure to outside

elements and moisture-

laden air.

Accepts solder readily,

durable, resists corrosion,

non-magnetic.

Cost, electrolytic

action of in contact

with galvanized

steel, thermal

expansion, stains.

Polyvinyl Steel

(PVS)

Underground duct

systems, moisture-laden

air and corrosive air

systems.

Corrosion resistance,

weight, workability,

fabrication, rigidity.

Susceptible to

coating damage,

temperature

limitations (250°F or

120°C max.),

weldability, code

acceptance.

Concrete Underground ducts, air

shafts.

Compressive strength,

corrosion resistance

(although steel

reinforcement in concrete

must be properly treated).

Cost, weight,

porous, fabrication

(requires forming

processes).

Rigid Fibrous Glass Interior HVAC low-

pressure duct systems.

Weight, thermal insulation

and vapor barrier,

acoustical qualities, ease

of modification,

inexpensive tooling for

fabrication.

Cost, susceptible to

damage, system

pressure, code

acceptance,

questionable

cleanability.


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Gypsum Board Ceiling plenums, corridor

ducts, airshafts. Cost, availability.

Weight, code

acceptance, leakage,

deterioration when

damp.

Laboratory ventilation system ductwork shall not be internally insulated. Sound baffles or external

acoustical insulation at the source should be used for noise control.

Air exhausted from laboratory work areas shall not pass un-ducted through other areas.


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9.1.2 Manifolds and Duct Design

Laboratory hoods and the general exhaust from laboratories can be combined into an integrated

common manifold exhaust system. Two major considerations must be taken into account when

considering an integrated exhaust system:

hazardous materials generated in the laboratory hoods could be toxic, flammable, pyrophoric, or highly corrosive

ductwork and duct accessory material must be compatible

The materials used in laboratories may have a profound influence on the design and operation of

integrated exhaust systems including, but not limited to, control of hazardous energy (lock-out/tag-

out), hazard communication, maintenance provisions, filter loading, international building codes and

fire code implications such as NFPA 45 and 50A. The design should include a Ventilation Risk

Assessment that provides a mechanism for identifying risks and evaluating their magnitude. Issues

to address during design or renovations may include:

Type and quantity of hazards

Need for fire detection and suppression

Ventilation system arrangement and construction

Ventilation sensors and controls

Emergency safeguards and procedures

Manifolded fume hoods should meet the requirements of NFPA 45

Ducts used on systems involving flammable or explosive mixtures require analysis and meet

applicable NFPA 45 standards

The duct joint used to connect the hood to the exhaust ductwork must be flanged and sized

to mate with the fume hood exhaust collar and flange

Duct construction should be sufficient to prevent duct leakage of more than 1%

The manifold must be maintained under negative pressure at all times during hood use

A manifold designed to operate as a plenum must have a relatively constant pressure

throughout the plenum

Effluent streams from multiple hoods must be compatible and non-reactive

Unless the use of all hoods on the system can be safely and completely stopped, the static

pressure in the plenum must be maintained throughout the duration of use

Use of redundant fans and bypass dampers are highly recommended for use as backups and

meeting above conditions


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9.1.3 Dampers

The damper must have an external indicator showing the position of the damper blade. Electronic

dampers should provide feedback of damper position. The damper position and flow characteristics

must be known. Operation of the damper should exhibit a linear response for flow versus position

across the acceptable range of flow required for proper functioning of the hood. Damper housing

and shaft openings must be sealed to prevent leakage of materials from the duct interior.

Fire dampers are not allowed on fume hood exhaust systems and dampers must be resistant to

attack by hood effluents.

9.1.4 Duct Pressures

Ducts located within the building envelope should be under negative pressure and leak tight as

subject to duct leak testing and Sheet Metal and Air Conditioning Contractor’s National Association

(SMACNA) standards. The degree of leak tightness must be appropriate to hazards identified as part

of a ventilation risk assessment. Positively pressurized ducts on the downstream side of the exhaust

fan must be leak tight and located within properly ventilated areas (penthouses) or located exterior

to the building.

9.1.5 Duct Velocities

Duct transport velocities should be sufficient to prevent accumulation of materials within the ducts

that could potentially affect duct integrity or react with other effluents. Ranges of exhaust duct

velocities (ft./min.) depend on the nature of the contaminants and are summarized in Table 11.

Table 11 Ranges of Recommended Exhaust Duct Velocities

Nature of Contaminants Examples Velocity Range

(fpm)

Vapors, gases, smoke, and

sub-micron size particles All forms 500(see note 1) – 2,000

Fumes Zinc and aluminum Oxide fumes 1,000 – 2,000

Very fine light dust Cotton lint, wood flour Litho-

powder 2,000 – 2,500

Dry dust and powders Cotton dust 2,500 – 3,000

Average industrial dust Shavings Sawdust, grinding dust 3,500 – 4,000

Heavy dusts Metal turnings, lead 4,000 – 4,500

Heavy moist dust Buffing lint (sticky) Lead dust w/

small chips 4,500 or more

From "Industrial Ventilation: A Manual of Recommended Practice for Design", ACGIH


75

Note 1: Where sufficiently dilute, materials will be transported by the exhaust air. A lower limit of 500 fpm

provides the ability to accurately measure flow in the duct using commonly applied techniques including Pitot

tube traverse.

9.1.6 Exhaust Fans

Proper design, operation and maintenance of the exhaust fan is critical to safe use of laboratory

ventilation equipment. The following guidelines summarize important concepts:

Exhaust fans should be backward curved blade centrifugal or venturi-type fans.

Fan wheels and housings should be constructed of materials compatible with chemicals

being transported in the air through the fan. Fans should be spark-resistant construction in

accordance with the Air Moving and Control Association (AMCA) Standard 401. The fan

should be constructed so a shift of the wheel or shaft will not permit ferrous parts to rub or

strike. Bearings must not be placed in the air stream.

Fans must be direct drive or belt driven using fixed pitched sheaves. Variable pitch sheaves

are not recommended.

Fans used to exhaust flammable or explosive mixtures (i.e. perchloric acid) require special

analysis to determine the construction required, pressure relief, grounding etc. The fans’

construction should be as recommended by AMCA's Classification for Spark Resistant

Construction.

A one-inch NPT drain should be provided in the bottom of the fan scroll.

The fans should be placed to prevent positively pressurized ductwork inside the occupied

building interior.

The direction of fan rotation must be clearly marked and proper rotation direction

confirmed.

The fan speed must be within manufacturer's specifications for optimum performance

characteristics.

At least eight duct diameters of straight duct must precede the inlet to the fan.

Inlet duct diameter must not vary more than one inch from the fan inlet diameter.

9.1.6.1 VAV System Fans

VAV systems should be designed with control devices that sense ductwork static air pressure and

velocity air pressure. The measurements collected by these sensors should be used to control fan

airflow and static pressure output by modulating any combination of the following:

Variable inlet vanes


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Inlet/discharge dampers

Scroll dampers

Bypass dampers

Variable pitch blades

Variable frequency electric drive controls.

The control systems should have a minimum of one static pressure sensor mounted in ductwork

downstream of the fan and one static pressure controller to vary fan output through either the inlet

vane, the damper, the belt modulator, or the speed control. The VAV control systems should be

capable of maintaining the minimum outdoor air ventilation requirements set forth in ASHRAE 62.1

and other applicable standards under all modes of operation.

The VAV exhaust and supply fans should be capable of operating at the following three design

conditions, without significant noise or vibration and without overloading:

Normal peak load (including diversity)

Maximum cooling load (no diversity and with terminal box dampers open), and

Minimum cooling load (with terminal boxes at the minimum flow condition).

The minimum supply volume setting of the VAV terminal boxes should equal the largest of the

following:

30% of the peak supply volume

0.4 cfm/ft2 of conditioned zone area

The minimum outdoor airflow to satisfy ASHRAE Standard 62.1 ventilation requirements.

9.1.6.2 VAV Diversity

Diversity should be based on the unique characteristics and needs of the individual facility. Diversity

less than 80% must be supported by an assessment of researcher practice and consider the

effectiveness of both administrative and engineering controls.

9.1.6.3 VAV Sensitivity

VAV Sensitivity is a measure of the ability of the ventilation systems to detect, resolve and modulate

flow equivalently or in proportion to modulation of flow through individual terminal units. A system

with a VAV Sensitivity of 100% has perfectly linear response where a change of 1 cfm at a fume hood


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exhaust terminal is matched at the exhaust fan or air handling unit. Large systems tend to be less

sensitive where flow modulation at an individual terminal is less than 5% of total system flow.

9.1.7 Exhaust Stack

Unless otherwise specified, fume hood exhaust stacks must be in the vertical-up direction at a

minimum of 10 ft. above the adjacent room line. The height of the stack must be sufficient to

ensure contaminated exhaust air does not re-enter the building.

The effluent must be discharged in a manner and location to avoid reentry into the building at

concentrations greater than the allowable breathing zone concentrations under any wind or

atmospheric conditions. Air intakes should be located at least 30 ft. from the exhaust discharge. Per

ANSI/AIHA Z9.5, the "stack discharge velocity shall be at least 3000 fpm unless it can be

demonstrated that a specific design meets the dilution criteria necessary to reduce the

concentration of hazardous materials in the exhaust to safe levels at all potential receptors". A wind

wake model can be used verify dilution at velocities less than 3000 fpm.

Aesthetic considerations concerning external appearance should not overcome the requirements

set forth above. If applicable, a masking structure must not reduce the effectiveness of the exhaust

stack.

9.1.8 General Exhaust

This can be used for temperature control on VAV systems. General exhaust may be used to

augment laboratory exhaust where air supply rates significantly exceed the hood exhaust air

volumes and room differential pressure requirements cannot be met. The air exhausted from the

laboratory through the general exhaust must not be re-circulated unless the air is adequately

filtered and meets the requirements set forth in ANSI Z9.5 for re-circulation of laboratory exhaust

air.

9.1.9 Fire Dampers

Fire dampers should be provided in accordance with NFPA guidelines and local codes, except in the

exhaust systems from laboratory areas.

9.2 Air Supply Systems

Proper design and operation of the air supply system is critical to achieving acceptable indoor air

quality and important for achieving proper functioning of fume hoods. The laboratory air supply

system must be in compliance with ANSI/ASHRAE 62, American National Standard for Ventilation for


78

Acceptable Indoor Air Quality. In addition the system must be capable of providing sufficient air to

the laboratory to meet climatic requirements (i.e. temperature, humidity, etc.) and ensure proper

room air balance and space pressurization under all operating modes.

ANSI/AIHA Z9.5 does not allow air exhausted from laboratory spaces to be recirculated to other

areas unless certain criteria are met as defined in section 5.4.7.1.

9.2.1 100% OA vs. Recirculated (can you recirculated GEX and when)


9.2.2 Outside Air Intakes


9.2.3 Airflow Measurement


9.2.4 Humidity Control


9.2.5 Supply Air Temperature


9.2.6 Fire Dampers


9.2.7 Noise


9.2.8 Insulation


9.2.9 Filtration


From VHA doc

Filters should be sized for a maximum face velocity of 500 fpm. Filter media should be

fabricated such that fibrous shedding does not exceed levels specified in ASHRAE 52.2. The filter


79

housing and all air-handling components downstream should not be internally lined with fibrous

insulation. Double-wall construction or an externally insulated sheet metal housing is

acceptable. The filter change-out pressure drop, not the initial clean filter rating, must be used

in determining fan pressure requirements. Pressure gauges and sensors should be placed across

each filter bank to allow rapid and accurate assessment of filter dust loading, as reflected by air

pressure drop across the filter. All such sensors should be connected to, and feed real-time

readings to, the BAS. Additional considerations include:

Contaminated air at concentrations higher than the allowable breathing zone concentrations should be treated to the extent necessary to ensure compliance with applicable federal, state or local regulations with respect to air emissions.

All filters should have a monitor capable of indicating filter effectiveness. A pressure gauge must be installed across filters to ensure proper pressure drop.

The range of operating pressures across the filter must be known.

Air supply should be filtered to meet the cleanliness requirements for the laboratory. Filtration includes use of 85% efficient filters to HEPA filters. Unless otherwise specified, air supply systems must be equipped with 85%-95% efficient filters.

Where required in fume hood exhaust systems, absolute filters will have an efficiency of 99.97 percent, as determined by the dioctyl phthalate aerosol test for absolute filters and should satisfy ASHRAE 52.2. (Note – An “absolute” filter is one capable of removing as near as possible to 100 percent by weight of solid particles greater than a stated micron size).

9.3 Energy Recovery


9.4 Smoke and Fire Control


9.5 Noise

9.5.1 Criteria

There are two important criteria requirements for laboratories; background noise, and speech

intelligibility.

Background noise is quantified in several ways. The most commonly used form is the noise criteria

(NC) method defined by ASHRAE. Other methods available and also described by ASHRAE include

the RC, dBA, NCB, and RC Mark II methods. Each of these has different advantages. The guidelines

listed below are applicable to the NC, NCB, RC and RC Mark II (when applicable to the criteria used,


80

the guidelines recommend a neutral spectrum). Some interpretation of noise data is required to

understand the impacts, and this is best addressed by an acoustical consultant.

Laboratory background noise levels are dependent on the intended use of the space. Background

noise requirements presented in the ASHRAE Handbook HVAC Applications lists common laboratory

types, each of which has different background noise requirements.

It is not enough to only look at background noise within a laboratory. Sound absorptive surfaces are

required for good speech communication is an integral part of noise control within a laboratory

space.

For smaller teaching laboratories (<750 sq.ft.) it is recommended that the ceiling be finished with an

acoustical lay-in tile ceiling (NRC ≥ 0.8) or equivalent wall/ceiling treatment.

For larger teaching laboratories (> 750 sq.ft.), a combination of ceiling and wall treatment is

recommended to improve speech intelligibility. The total area of treatment should be equal to or

greater than the plan area of the space, but should be evenly distributed on the ceiling and two

walls. If there is a predominant lecturing position, the surface behind the lecturer should remain

untreated, but the opposite wall should be treated acoustically (approximately 20% coverage with

NRC ≥ 0.8 material).

For non-teaching laboratories, it is recommended that some acoustically absorptive materials are

included in the finish schedule to control reverberation; this will improve background noise levels

and speech intelligibility. As a minimum, it is recommended that mineral lay-in tile ceilings (NRC ≥

0.5) or an equivalent wall/ceiling treatment be used.

9.5.2 Equipment

Laboratories place high demands on the mechanical systems that serve them and often require

large, noisy equipment. Table 12 below lists typical equipment associated with laboratory

ventilation systems and recommendations for equipment selection.

Table 12 Recommendations for Selection of Equipment

Equipment Recommendations

Fans

Choose quiet fans (slow and large diameter are better for noise)

Airfoil and forward curved designs are typically 10 dB quieter than straight blade radial or vane-axial fans (10 dB is perceived to be a 50% noise reduction).

Plug-type fans are typically quieter than enclosed centrifugal fans

Multiple fan, wall-type systems are generally quieter than


81

single large fan systems.

Silencers

Reserve at least 5 feet of straight duct space for silencers on intake and outlet for all fans.

Elbow silencers provide improved attenuation at low frequencies.

For a laboratory setting, exposed fibrous liners are rarely acceptable, particularly in exhaust silencers susceptible to entrapment of chemicals, particulates or bacteria.

Hospital-type silencers are available with protective plastic films that protect the fibrous materials from the air flow.

No-media (packless) silencers are also available, but provide less attenuation than typical media-type silencers, therefore additional silencer length may be required.

Ducts (general)

Good transitions are essential to avoid rumble in duct systems. This typically requires straight sections of a minimum 3 duct diameters in length between transitions.

Duct velocities are discussed further in the section below, but in general larger ducts with lower flow rates are best for avoiding flow induced noise and rumble.

Large pressure drops across various duct components typically create turbulence and noise. Lower pressure drops are desirable from a noise perspective.

Acoustical duct linings protected by a plastic film and a perforated metal cover can be considered for reducing noise transmission in some systems. This must be evaluated on a case-by-case basis.

Valves

Valves are a major source of sound in HVAC systems.

Valve noise is difficult to attenuate because of the close proximity to the room inlet/outlet.

Sound characteristics are highly dependent on flow volume and pressure drop.

Where possible choose quieter valves. Aerodynamic (venturi) valves are preferred over opposed blade dampers.

Over-sizing valves (running them at low flow ratings) or running multiple valves can be an effective means of reducing valve noise.

Pressure drops below 1 inch are preferred.

Integral valve silencers provide benefit to attenuating valve noise, but are not always adequate to meet desired background noise levels.

Duct space should be made available for a minimum of a 3-foot silencer on the room side of valves.

Flex Duct

Reduces noise significantly when installed properly.

Best placed above ceilings with good acoustic transmission loss (noise breaks out and is absorbed in ceiling plenum).

Avoid tight bends that create noise through turbulence.


82

Terminals (diffusers and

grilles)

Can be the most significant source of background noise.

Difficult to attenuate.

Square or round diffusers are quieter than strip diffusers due to slower velocities.

Sock diffusers are quietest because of a low throw/low speed supply.

Should be selected at 10 NC points below the target background noise level.

Equipment in the laboratory

(not necessarily ventilation

equipment)

Choose quiet lab equipment whenever possible (centrifuge, refrigerators, autoclave (blower fan), bio-safety cabinet, etc.)

Consider pressure drops of selected equipment (hoods, bio-safety cabinets)

9.5.3 Ventilation System Layout

For any noise source it is beneficial to separate the source from the receptor by distance, or by

blocking (attenuating) the sound through some form of barrier. This is true for duct layouts as well.

Longer duct runs provide greater separation between noisy equipment and the spaces that they

service. However, even with longer duct runs, silencers are often required to attenuate the sound.

Mechanical rooms should be separated from noise sensitive spaces, ideally with buffering spaces

(e.g., storage space, restrooms) between the mechanical room and noise sensitive spaces. Where

this is not possible, anticipate cavity wall construction, floating floors and/or resiliently suspended

sound barrier ceiling systems.

It is important to leave space for silencers in the ductwork, preferably immediately outside

mechanical rooms. If the silencers must go inside a mechanical room, they require a high sound

transmission loss (TL) casing, or must be enclosed with a drywall enclosure to prevent the ‘quiet

side’ from being impact by mechanical room noise. All ‘quiet side’ ducts in the mechanical room

must also be enclosed.

Silencer lengths will increase where shorter duct runs are present. Options exist for both straight

and elbow type silencers. Leave 3 duct diameters of straight duct between silencer and fans or

transitions (e.g., elbows).

Main ducts should be placed over spaces that are less sensitive to noise (e.g., corridors, storage,

restrooms). Where this is not possible, duct flow velocities should be limited and duct enclosures

may be required. The ASHRAE Handbook HVAC Applications contains recommendations for

maximum airflow velocities.


83

Branch and final run-out ducts flow velocities must also be limited. The ASHRAE Handbook HVAC

Applications contains recommendations for maximum air speeds for different conditions and noise

criteria.

VAV terminals should be placed outside spaces requiring NC 35 or less. If they must be placed in a

space requiring NC 35 or less, they must be equipped with a silencer, and may require an enclosure.

VAV terminals should be as far from the outlet/inlet as possible with silencers located between the

terminal and outlet/inlet to control noise.

Where possible, it is recommended that insulated flex duct be used for the final elbow connecting

the duct to the terminal unit (e.g., diffuser, grille, etc.). The flex duct should be above an acoustical

ceiling and should be well aligned with a smooth corner to avoid creating turbulence (noise) in the

airflow. The flex duct must be well aligned with the terminal unit to avoid excessive noise at the

connection.

Terminal units should be selected to be 10 NC points below the target background noise level for

the design flow volume, and should be located away from areas of communication (i.e., away from

lecturing position and away from student seating area). Placing terminal units around the perimeter

of the room is best with students seated centrally for lectures.

9.5.4 Layout of Laboratory

Laboratories are best set up with all noise producing equipment located around the perimeter

rather than above students or teachers. This allows for better communication for teaching purposes

within a central area. Noise producing equipment includes exhausts and intakes, fume hoods, and

any other lab equipment (e.g., refrigerators, centrifuge, autoclave (blower fan), bio-safety cabinet,

etc.).

For teaching purposes, fume hoods are best located around the perimeter rather than as a central

cluster where they become obstructions for teaching and students cannot sit away from the fume

hoods. This also provides the benefit of clear visual sightlines, which can improve safety through

improved supervision, ability to provide visual cues or non-verbal communication, and for

emergency egress.

Alcoves for fume hoods typically create a quieter space by separating the fume hoods from teaching

areas, but also create barriers that impair supervision and communication while in use.

Smaller labs put students and teachers closer together which is a benefit for speech intelligibility

(i.e., less strain on teachers and better attention and comprehension from students). Larger

laboratories can provide a similar benefit by placing the lecturing position at the center of one of the

longer walls (in rectangular plans), which reduces the student to teacher distance.


84

Higher ceilings are undesirable due to an increase in the volume of the space and an increase in

unwanted reverberation.

Acoustically absorptive finishes for the ceiling and walls are recommended as described in the

criteria section above. While such finishes help to improve communication by reducing

reverberation and background noise, they can collect chemicals, particulate, and bacteria.

Additional costs should be anticipated for available washable finishes, where required.

9.5.5 External Noise

Most laboratory buildings have significantly more ventilation equipment than buildings supporting

offices and teaching space only. The higher volume of air required demands larger fans and

heating/cooling equipment. Larger equipment typically produces more noise, which not only

impacts the indoor environment, but can also impact the outdoor environment.

Noisy intakes and exhausts can impact labs and nearby buildings, especially where equipment or

intakes/exhausts are in close proximity to windows. Allow for space in mechanical rooms and in

duct runs for silencers on exhausts and intakes. Other means of mitigating external noise emissions

may include use of plenums, acoustic louvers and noise barriers. Windows are usually the limiting

factor for indoor/outdoor noise transmission. Upgrading to better acoustical performance windows

is a means of mitigation. As with duct systems within the building, separation through distance,

duct length, or by creating noise barriers/attenuators is necessary to reduce noise levels. It is

important to note that barriers can conflict with exhaust re-entrainment requirements and should

be reviewed with a re-entrainment consultant..

Impacts on nearby buildings and outdoor pedestrian areas are important considerations. It is

important to check local legislation, codes, regulations, and/or ordinances to determine the site

requirements. City regulations provide a “do not exceed” limit for daytime and night-time noise

that varies with property use (see Seattle Municipal Code, Chapter 25.08 - Noise Control,

Subchapter III - Environmental Sound Levels for requirements in Seattle and King County).

It is often prudent to establish more stringent guidelines that target limiting impacts on neighbors

by setting criteria that minimize the change in background noise levels at nearby receptors. While

not required, it is a good strategy for maintaining relations with the surrounding community. A

noise impact study requires a baseline noise survey to determine pre-construction noise levels,

which can be compared to the future condition to determine change/impacts.

External noise modeling should be done early in the design of the building using proper modeling

techniques to determine impacts on surroundings and the building on itself. Models such as


85

Cadna/A, SoundPlan, ENM, etc. can be used. Noise model studies are often required in building

construction permitting.

9.5.6 Vibration

Vibration isolation of all mechanical and electrical equipment (including ducting, piping and conduit)

is an important part of controlling noise and vibration within a building. The primary purpose of

vibration isolation systems is to limit the transmission of vibration into the structure, which is

carried through the structure as structure-borne noise and re-radiated acoustically in spaces that

can be distantly separated from the source. Structure-borne noise is very difficult to attenuate by

means other than vibration isolators.

Proper selection and installation of vibration isolation systems (which may include but is not limited

to spring isolators, rubber/neoprene isolators, inertia bases, and hangers with spring or neoprene

elements) is an essential part of a complete noise control system.

9.5.7 Other Considerations

For teaching labs, there are other means of improving the function of the space without requiring

more stringent background noise limits. Noise can also be limited by operational controls such as:

Keeping sashes closed when not in use, and particularly while teaching,

Providing areas for pre-lab lectures away from fume hoods or in separate rooms,

Providing audio/video alternatives such as; screens to show demos, cameras to monitor students, or by pre-recording laboratory demonstrations and having students view them before labs (pre-lab quizzes provide confirmation of viewing).

In a cutting edge research environment where critical funding is highly dependent on maintaining a

competitive edge, privacy is often of significant concern. Where privacy is required, it must be

considered that communication within a loud space requires increased vocal effort that may be

heard clearly in quieter adjacent spaces such as corridors or offices. Limiting background noise

within the laboratory is an important part of maintaining privacy, but partition construction

(including doors, windows, penetrations, and duct layouts to control “cross-talk”) should also be

considered in this type of environment to maintain privacy and/or security.

Noise from laboratories can impact more sensitive adjacent spaces such as offices, conference

rooms, or classrooms. Transfer of noise should be controlled through proper partition design and

construction. Penetrations through walls, floors, and ceilings should be sleeved and sealed as

appropriate. Direct duct runs between spaces should be avoided. It is preferred to have central

supply and return ducts with individual duct runs into each room to avoid “cross-talk” issues.


86

While many of the topics covered within this document could be addressed by the architect or the

mechanical system designer, without due consideration of the interaction of the individual

components, there is potential for a detrimental combination of factors to be overlooked. An

acoustical consultant is required to review the ventilation system and room design and their

interaction with the building in a holistic way. This input is required early in a project, while it is still

possible to allocate space for necessary silencers, and to keep noise and vibration sources

sufficiently separated from sensitive receptors.

Systems should satisfy the noise criteria recommended for various types of spaces and the vibration

criteria listed in the ASHRAE Handbook Fundamentals. The combined noise level generated by

mechanical and electrical building equipment should not exceed 70 decibels (dBa) in mechanical

rooms. Where air handling equipment and air distribution systems cannot meet these

requirements, sound- and vibration-attenuation devices should be installed.

The noise exposure at the working position in front of the hood should not exceed 70 dBa with the

system operating and the sash open, nor should it exceed 55 dBA at bench-top level elsewhere in

the laboratory room. Total room performance with respect to noise levels must meet permissible

occupational limits specified in 29 CFR 1910.95.

9.6 Insulation

Laboratory ventilation ductwork should not be internally insulated. Fiberglass duct liners can

deteriorate with age and shed into the space resulting in Indoor Air Quality (IAQ) complaints,

adverse health effects, maintenance problems and significant economic impact.

9.7 Filtration

Filters should be sized for a maximum face velocity of 500 fpm. Filter media should be fabricated

such that fibrous shedding does not exceed levels specified in ASHRAE 52.2. The filter housing and

all air-handling components downstream should not be internally lined with fibrous insulation.

Double-wall construction or an externally insulated sheet metal housing is acceptable. The filter

change-out pressure drop, not the initial clean filter rating, must be used in determining fan

pressure requirements. Pressure gauges and sensors should be placed across each filter bank to

allow rapid and accurate assessment of filter dust loading, as reflected by air pressure drop across

the filter. All such sensors should be connected to, and feed real-time readings to, the BAS.

Additional considerations include:

Contaminated air at concentrations higher than the allowable breathing zone

concentrations should be treated to the extent necessary to ensure compliance with

applicable federal, state or local regulations with respect to air emissions.


87

All filters should have a monitor capable of indicating filter effectiveness. A pressure gauge

must be installed across filters to ensure proper pressure drop.

The range of operating pressures across the filter must be known.

Air supply should be filtered to meet the cleanliness requirements for the laboratory.

Filtration includes use of 85% efficient filters to HEPA filters. Unless otherwise specified, air

supply systems must be equipped with 85%-95% efficient filters.

Where required in fume hood exhaust systems, absolute filters will have an efficiency of

99.97%, as determined by the dioctyl phthalate aerosol test for absolute filters and should

satisfy ASHRAE 52.2. (Note – An “absolute” filter is one capable of removing as near as

possible to 100 percent by weight of solid particles greater than a stated micron size).

9.8 Energy Recovery


10 Laboratory Ventilation Construction, Renovation and Commissioning


10.1 Lab Designer's Checklist


10.2 TAB Plan


10.3 Commissioning Plan (building and lab)


10.4 ECD Commissioning


10.5 Laboratory Environment Tests (LETs)


10.6 System Mode Operating Tests (SOMTs)


11 Laboratory Ventilation Management Program


88


11.1 LVMP and the Design Process


11.2 Routine Testing


11.3 Management of Change


11.4 BAS Trends and Reports



89

12 References

1. ANSI/AIHA Z9.5, American National Standard for Laboratory Ventilation

2. NFPA 45, Fire Protection for Laboratories Using Chemicals

3. SEFA, Laboratory Fume Hoods, Recommended Practices

4. ACGIH, Industrial Ventilation Manual, 21st Edition

5. ASHRAE 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings

6. ASHRAE 62, Ventilation for Acceptable Indoor Air Quality

7. ACGIH®: Industrial Ventilation: A Manual of Recommended Practice for Design, 27th Edition.

Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 2010.

8. ACGIH®: Threshold Limit Values (TLV®) for Chemical Substances and Physical Agents. Cincinnati,

Ohio: American Conference of Governmental Industrial Hygienists, 2002.

9. AGS-1998-001: Guideline for Gloveboxes, 2nd Edition. Santa Rosa, Calif: American Glovebox

Society, 1998.

10. ANSI/ASHRAE 41.2-1987 (RA 92): Standard Methods for Laboratory Air Flow Measurement.

Atlanta, Ga.: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1992.

11. ANSI/ASHRAE 41.3-1989: Standard Method for Pressure Measurement. Atlanta, Ga.: American

Society of Heating, Refrigerating and Air Conditioning Engineers, 1989.

12. ANSI/ASHRAE 41.7-1984 (RA 00): Method of Test Measurement of Flow of Gas. Atlanta, Ga.:

American Society of Heating, Refrigerating and Air Conditioning Engineers, 2000.

13. ANSI/ASHRAE 110-1995: Method of Testing Performance of Laboratory Fume Hoods. Atlanta,

Ga.: American Society of Heating, Refrigerating and Air Conditioning Engineers, 1995.

14. SMACNA: HVAC Duct Construction Standards: Metal and Flexible, Merrifield, Va.: Sheet Metal

and Air Conditioning Contractors’ National Association, 1995.

15. Smith, T.C. and Yancey-Smith, S.L: “Specifying Airflow Rates for Laboratories.”, Journal of

Chemical Health and Safety 16(5): September/October 2009.

16. Smith, T.C., and Crooks, S.M.: “Implementing a Laboratory Ventilation Management Program.”

Journal of Chemical Health and Safety 3(2):12–16 (1996).

17. Smith, T.C.: “The Unintended Practice of Using Employee Health as an Indicator of Proper Hood

Performance”, Journal of Chemical Health and Safety, January/February, 2004.

18. Laboratories for the 21st Century, Best Practice Guide Optimizing Laboratory Ventilation Rates,

Draft, September 2008, Pg 1.

19. Heinsohn, Robert J., Industrial Ventilation Engineering Principles, University Park, PA 1991;

20. Diberardinis, Louis J., Guidelines for Laboratory Design, 2nd ed, 1993; pg 100.

21. Exposure Controls Technology Inc. data obtained from various ventilation studies.

22. American Conference of Governmental Industrial Hygienists (ACGIH). 2010. Industrial

Ventilation: A Manual of Recommended Practice for Design, 27th Edition. Cincinnati, Ohio.

23. ASHRAE Handbook Fundamentals

24. ASHRAE Handbook HVAC Applications.

25. Exposure Control Technologies, Inc. and Rowan William Davies & Irwin, Inc. : "Ventilation Noise

Issues".

Table 1 Document Section Status

Section Topic Status

1 Purpose and Introduction Complete

2 Energy and Sustainability Complete

3 The Laboratory Design Process Incomplete

4 Laboratory Demand for Ventilation Complete

4.1 Types of Hazardous Procedures Complete

4.2 Risk Assessment Incomplete

4.2.1 Quantity of Materials Used and Generation Rates Complete

4.2.2 Effluent Characteristics Complete

4.2.3 Control Banding Complete

4.3 Lab Air Quality and Conditioning Incomplete

4.4 Occupancy and System Utilization Incomplete

5 Exposure Control Device Selection Incomplete

5.1 Description of Exposure Control Device Incomplete

5.2 ECD Risk Matrix Incomplete

5.3 Types of ECDs (need to harmonize names/descriptions with current SEFA standard)

Incomplete

5.3.1 Laboratory Fume Hoods Complete

5.3.2 Constant Air Volume (CAV), Conventional Fume Hood Complete

5.3.3 CAV, Bench‐Type, Bypass Fume Hood Complete

5.3.4 Auxiliary Air Bypass Fume Hood Complete

5.3.5 CAV – High Performance Fume Hoods (HP Fume Hoods) Complete

5.3.6 Variable Air Volume (VAV) Fume Hood Systems Complete

5.3.7 Distillation Laboratory Fume Hoods Complete

5.3.8 Floor Mounted Laboratory Fume Hoods Complete

5.3.9 Perchloric Acid Laboratory Fume Hoods Complete

5.3.10 Radioisotope Fume Hoods Complete

5.3.11 Pass Through Hood Incomplete

5.3.12 California Hood Incomplete

5.3.13 Teaching Lab Hood Incomplete

5.3.14 Ductless Fume Hood Incomplete

5.3.15 Laminar Flow Fume Hood Incomplete

6 Exposure Control Device Operation Incomplete

6.1 Laboratory Hood Operation Complete

6.1.1 Escape of Contaminants Complete

6.1.2 Sash Opening Configurations Complete

6.1.3 Airfoil Sills Complete

6.1.4 Baffle Design and Configuration Complete

6.1.5 Fume Hood Specifications Incomplete

6.1.5.2 Laboratory Hood Operating Specifications and Test Criteria Complete

6.1.5.3 Operating Mode Complete

6.1.5.4 Flow and Velocity Specifications Complete

6.1.5.5 Laboratory Hood Monitors Complete

6.1.6 Distillation Laboratory Fume Hood Specifications Incomplete

6.1.7 Walk‐in Fume Hood Specifications Incomplete

6.1.8 Perchloric Acid Fume Hood Specifications Complete

6.1.9 Radioisotope Fume Hood Specifications Complete

6.1.10 Ductless Fume Hood Specifications Incomplete

6.1.11 Laminar Flow Fume Hood Specifications Incomplete

6.2 Ventilated Balance Enclosures (VBE) Complete

6.2.1 Ventilated Balance Enclosure Specifications Complete

6.3 Canopy Exhaust Hoods Complete

6.3.1 Canopy Exhaust Hood Specifications Incomplete

6.4 Flexible Spot Exhausts (FSE) Complete

6.4.1 Flexible Spot Exhaust Specifications Incomplete

6.5 Slot Hoods Complete

6.5.1 Slot Hood Specifications Incomplete

6.6 Downdraft Necropsy Tables Complete

6.6.1 Downdraft Necropsy Table Specifications Incomplete

6.7 Glove Boxes Complete

6.7.1 Glove Box Specifications Incomplete

6.8 Biological Safety Cabinets Complete

6.8.1 Class I Biological Safety Cabinet Complete

6.8.1.1 Class I BSC Specificiations Incomplete

6.8.2 Class II, Type A Biological Safety Cabinet Complete

6.8.2.1 Class II, Taype A BSC Specifications Incomplete

6.8.3 Class II, Type A2 Biological Safety Cabinet Complete

6.8.3.1 Class II, Type A2 BSC Specifications Incomplete

6.8.4 Class II, Type B1 Biological Safety Cabinet Complete

6.8.4.1 Class II, Type B1 BSC Specifications Incomplete

6.8.5 Class II, Type B2 (Total Exhaust) Biological Safety Cabinet Complete

6.8.5.1 Class II, Type B2 BSC Specifications Incomplete

6.8.6 Class III Biological Safety Cabinet Complete

6.8.6.1 Class III BSC Specifications Incomplete

6.9 Ventilated Enclosure Complete

6.9.1 Ventilated Enclosure Specifications Incomplete

6.10 Canopy Hoods Complete

6.10.1 Canopy Hood Specifications Incomplete

6.11 Gas Cabinets Complete

6.11.1 Gas Cabinet Specifications Incomplete

6.12 Flammable Liquid Storage Cabinets Complete

6.12.1 Flammable Liquid Storage Cabinet Specifications Incomplete

6.13 Special Purpose Hoods Complete

6.13.1 Special Purpose Hood Specifications Incomplete

7 Types of Laboratories Incomplete

7.1 Categorization and Risk Control Bands Incomplete 7.2 Bio‐Safety Levels Incomplete 7.2.1 BSL 1 Incomplete 7.2.2 BSL 2 Incomplete 7.2.3 BSL 3 and Higher Labs Incomplete 7.3 Teaching Laboratories Incomplete 7.4 Necropsy Laboratories Incomplete 7.5 Radiation Laboratories Incomplete 7.6 Gross Anatomy Laboratories Incomplete 8 Laboratory Design and Layout Specifications Incomplete

8.1 Laboratory Systems and Operating Modes Complete

8.2 Hood Location Complete

8.2.1 Air Distribution Effectiveness Complete

8.2.2 Doors and Traffic Aisles Complete

8.2.3 Location and Type of Supply Diffusers Complete

8.2.4 Type of Air Supply Diffusers Complete

8.3 Ventilation Effectiveness (Air Change Rates in Laboratories) Complete

8.4 Specification of Airflow Rates for Laboratories Complete

8.5 Calculating Air Change per Hour Rate (ACH) Complete

8.6 Laboratory Pressurization Complete

8.6.1 Lab Offset Volume Complete

8.7 Airflow Controls Complete

8.7.1 CAV Incomplete

8.7.2 VAV Incomplete

8.7.3 Demand Control Ventilation (DCV) Incomplete 8.7.4 Occupancy Based Control Schemes Incomplete 8.7.5 Purge Modes Incomplete 8.8 Laboratory Temperature Control Complete

9 Lab Ventilation Incomplete

9.1 Laboratory Exhaust Ventilation Complete

9.1.1 Materials of Construction Complete

9.1.2 Manifolds and Duct Design Complete

9.1.3 Dampers Complete

9.1.4 Duct Pressures Complete

9.1.5 Duct Velocities Complete

9.1.6 Exhaust Fans Complete

9.1.6.1 VAV System Fan Complete

9.6.1.2 VAV Diversity Complete

9.6.1.3 VAV Sensitivity Complete

9.1.7 Exhaust Stack Complete

9.1.8 General Exhaust Complete

9.1.9 Fire Dampers Complete

9.2 Air Supply Systems Complete

9.2.1 100% OA vs. Recirculated (can you recirculated GEX and when) Incomplete

9.2.2 Outside Air Intakes Incomplete 9.2.3 Airflow Measurement Incomplete 9.2.4 Humidity Control Incomplete 9.2.5 Supply Air Temperature Incomplete 9.2.6 Fire Dampers Incomplete 9.2.7 Noise Incomplete 9.2.8 Insulation Incomplete 9.2.9 Filtration Incomplete 9.3 Energy Recovery Incomplete 9.4 Smoke and Fire Control Incomplete 9.5 Noise Incomplete

9.5.1 Criteria Complete

9.5.2 Equipment Complete

9.5.3 Ventilation System Layout Complete

9.5.4 Layout of Laboratory Complete

9.5.5 External Noise Complete

9.5.6 Vibration Complete

9.5.7 Other Considerations Complete

9.6 Insulation Complete

9.7 Filtration Complete

9.8 Energy Recovery Incomplete

10 Laboratory Ventilation Construction, Renovation and Commissioning Incomplete 10.1 Lab Designer's Checklist Incomplete 10.2 TAB Plan Incomplete 10.3 Commissioning Plan (building and lab) Incomplete 10.4 ECD Commissioning Incomplete 10.5 Laboratory Environment Tests (LETs) Incomplete 10.6 System Mode Operating Tests (SOMTs) Incomplete 11 Laboratory Ventilation Management Program Incomplete 11.1 LVMP and the Design Process Incomplete 11.2 Routine Testing Incomplete

11.3 Management of Change Incomplete 11.4 BAS Trends and Reports Incomplete 12 References Incomplete

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