Chem Hoods21st Century

transcript

Sponsored by:

Campus Consortium for Environmental Excellencehttp://www.c2e2.org

American Chemical Society,Division of Chemical Health & Safetyhttp://www.dchas.org

Ralph Stuart, CIHEnvironmental Safety Manager

University of Vermont

• Design History• Open windows • Laboratory furniture • Pre-installed building equipment• Integrated laboratory ventilation systems

• In the 1980’s, the rule of thumb was that face velocities between 100 and 150 fpm were the best indication of “safety”

• In the 1990’s, studies indicated that measuring face velocity was not enough, so tests using tracer gas were developed (ASHRAE 110 testing)

• 1980’s: “It’s the labs’ problem”• 1990’s: OSHA Lab Standard led to

Environmental Safety certification of face velocity

• Around this time, maintenance workers began to deal with hoods more systematically

• Upward exhaust• Managing combined exhausts

• In the 2000’s, ASHRAE tracer gas testing of containment “as installed” has become common

• From an energy point of view, hoods are the equivalent of a open window year round.• Energy considerations focus on the volume of air moved

(air changes per hour) rather than its speed.• Traditionally, facility managers have erred on the safety

side by over-ventilating laboratories• As the number of hoods has proliferated and fuel

costs have risen, energy concerns have made assessing “hood performance” more complicated • Many ways of reducing the air volume exhausted have

been proposed.• HVAC engineers now speak of “high performance” hoods

with regard to energy use, but (hopefully) without a change in safety performance

• Laboratory buildings represent 15-20% of campus floor space, but consume around 40% of the campus’ energy

• Studies have found that only about 20% of the installed hoods are used and someone is at used hoods only 20% of that time.

• These observations lead to questions:• Are chemical hoods and laboratory ventilation are the

best approach to laboratory safety?• Do our laboratories really need to be open 24-7

with full HVAC services?• Can we make assumptions about chemical risks

in the lab?

• Fume hoods were developed to control flammable chemicals to control fires • The chief reason for the popularity of fume hoods is that it is a

very adaptable design• The design has been re-purposed to serve as containment

devices to protect human health from unclear potential risks using the ALARA approach

• However, user behavior can trump design: • To achieve ALARA, it’s important that lab workers follow good

hood work practices• Proper use of a chemical hood requires a risk

assessment of the chemicals used so that the protection strategy is clear.

• ANSI Standard Z9.5-2003• Outlines a Laboratory Ventilation Management Program

with appointment of “responsible person” to oversee laboratory ventilation systems.

• The general approach of the standard follows the “management system” approach.

• This standard is referenced by many designers as well as in the Labs-21 proposed LEED criteria

• Process Analysis• Plan: Design• Do: Use• Check: Cost of operation• Act: System maintenance

• Stakeholders• Laboratory Designers• Laboratory Workers• Upper administration and

sustainability office• Facility Operations and

Maintenance

• Laboratory Designers: What hoods should we buy?

• Laboratory Workers: When should I use hoods?

• Upper Management and Sustainability Office: Do hoods have to cost so much?

• Campus Facility Managers: How much money do I need to operate and maintain hoods?

• External standards• Fire Protection: NFPA 45• Containment: ASHRAE 110• Energy Use: LEED and Labs-21

• Possible design criteria• Hoods must pass ASHRAE As Installed (0.1 ppm

leakage at 4 liters/minute); passing face velocity must be established at installation

• Energy conservation in design: basis of design documentmust describe design features (occupancy sensors, sash sensors etc.) and be translated to users

• 40% workforce turnover every 2 years• User signals and training:

1. Tell tales to determine if the hood is on2. Warning signs in first 6 inches of hood3. Safe Operating Height sticker4. Close the sash reminder poster

• GHG impact: one chemical hood is the energy equivalent of about 3 houses

• Each hood represents about $5000 to $10,000/year in energy costs

• Laboratory buildings represent at least 35% of a research campus’s energy use

• Hood maintenance needs:• Face velocity check• Calibration of alarms and controls • Preventive maintenance of fans and hood

components• Repairs• System adjustments during renovations

• Re-commissioning and retro-commissioning for proper hood performance, with regard to both safety and energy

Robin M. IzzoAssociate Director

Princeton UniversityEnvironmental Health and Safety

• Effective at lower face velocity

• Pass ASHRAE, EU tests• Problems – design and

use• Higher first costs• Larger footprint

• Close sash when no one is using the hood

• Princeton Step Pad Study: time in front of hood = 5%

• Technology has improved• Issues:

• Auto close vs. open• Timing• Proximity vs. motion

• Variable Air Volume is almost the standard• Set back when unoccupied

• Timers• Light switch• Sash position• Occupancy Sensors

• Higher first costs, quick payback• Higher maintenance than Continuous air

• Especially useful with VAV systems• Maximum number of hoods in use with sash

open at the same time• Significant first cost savings• Be realistic!!• Always design n+1

• Teaching lab solution• Three settings:

• On• Off• Set-up

• Lab instructor controls with key• Princeton: per week

• on 15 hours, off 153 hours

• Not really fume hoods• Limitations

• Filters• Flow• Code requirements

• Maintenance• Limited application• Gaining popularity• Emerging technologies

• Old School: minimum 10-12 ACH (air changes per hour) occupied

• New School: varies• Computational Flow Dynamics Modeling• Active Chemical Monitoring• Some have gone to 4-8 ACH occupied or

lower based on these

• Know the applications• Know the building• Maintenance is key• Still need a minimum airflow in the lab• Limiting factor - USERS

• Very few regulations specifically about fume hoods

• Many guidance documents• International Mechanical Code 510

• Adopted by many municipalities• 2006 version includes exemptions for labs• Your mileage may vary

• Defines Hazardous Exhaust• Precludes manifolding• Requires sprinklering within the duct• Requires detection within the duct• MOST LAB APPLICATIONS fit under the

laboratory exemption• Documentation is the key

• Work with your design team• Talk to the users• Understand the applications• Look beyond those applications• Try the options on for size

• Installation, visits, meetings• There is no panacea – just because it works

for Princeton…