Marine Chemist Association Annual Seminar August … · Marine Chemist Association Annual Seminar...

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Marine Chemist AssociationAnnual Seminar

August 2016Savannah GA

Hazardous Locations and Electrical Equipment

Hazardous Locationsand

Electrical Equipment

William G. Lawrence, P.E.

•30+ years with FM Approvals in Hazardous Locations•Principal Engineer, Hazardous Locations•Vice Chairman – UL STP 60079 – US National Standards - Hazardous Locations•Chairman – UL TG79.00 (General Requirements, 60079-0)•Principle Member – NFPA NEC Committee CMP14 (Articles 500-516)•Principle Member – NFPA EECA Committee (Area and Material Classification)•Chairman – US Technical Advisory Group to IEC TC31 (Explosive Atmospheres)•International Convenor – IEC TC31/WG22 (IEC 60079-0, -5, -6) GenReq, “q” “o” •International Convenor – IEC TC31/MT60079-7 (IEC 60079-7) “e”

Hazardous (Classified) Locations and the National Electrical Code®

Overview:

• Explanation of Classes, Groups, & Divisions

•Explanation of Gas Groups (MESG & MIC Ratio)

• Explosionproof Equipment

•Intrinsically Safe Equipment

What is a Hazardous (Classified) Location?

¾ A location where fire or explosive hazards may exist due to:

Flammable gases or vapors

Flammable liquids

Combustible dusts

Easily ignitable fibers and flyings

Articles 500 - 516

¾ Article 500 – includes, for example, definitions; area classification for classes, divisions and material groups; protection techniques; equipment marking.

¾ Article 501 – contains installation requirements for equipment located in gaseous atmospheres including explosionproof apparatus.

¾ Article 502 – contains installation requirements for equipment located in combustible dust atmospheres including dust-ignition-proof apparatus.

Articles (continued)

¾ Article 503 – contains installation requirements for equipment located in atmospheres with fibers and flyings

¾ Article 504 – contains installation requirements for Intrinsically Safe Apparatus

¾ Article 505 – includes Zones 0, 1 & 2 classifications, protection techniques & installation requirements

¾ Article 506 – includes Zones 20, 21 & 22 classifications, protection techniques, & installation requirements

Articles (continued)

¾ Article 510 to 516 – cover specific occupancies such as garages, filling stations, aircraft hangars, finishing operations.

A Hazardous Location is Defined by 5 Elements

¾ Class

¾ Division

¾ Group

¾ Temperature Class

¾ Ambient Temperature Range (if other than “Standard”)

Classes

¾ Class I - Gases and Vapors

¾ Class II - Combustible Dusts

¾ Class III – Fibers and Flyings

Divisions

¾ Division 1 –

Ignitable concentrations of gasses, vapor-in-air mixtures, combustible dusts and flying fibers can exist duringnormal conditions

¾ Division 2 –

Ignitable concentrations of gasses, vapor-in-air mixtures,combustible dusts and flying fibers exist duringabnormal conditions

Class I, Division 1 Examples

¾ All locations where ignitable concentrations of flammable gases or vapors are likely to occur normally

¾ Where volatile flammable liquids are transferred from one container to another

¾ Interiors of spray booths¾ Locations containing open tank or vats of volatile

flammable liquids¾ Drying rooms for the evaporation of solvents

Class I, Division 2 Examples

¾ Accidental rupture or breakdown of closed containers or closed systems

¾ Where failure of positive mechanical ventilation used to prevent ignitible concentrations of gases or vapors can occur

¾ Adjacent to, and surrounding, a Class I, Division 1 location¾ “Transition Division”

Inappropriate Activity in a Class I, Division 1 Location

Hand Drill in C3H8 Atmosphere

Hand Drill in H2 Atmosphere

Gas Groups

¾ Group A – Includes only Acetylene (C2H2)

¾ Group B – Typical gas is Hydrogen (H2)

¾ Group C – Typical gas is Ethylene (C2H4)

¾ Group D - Typical gas is Propane (C3H8)

Class I Gas Groups

¾ Class I groups (other than Group A) are differentiated based on their:

MESG; or

MIC ratio.

¾ This allows quantification of the gas properties to permit the proper selection of equipment.

Maximum Experimental Safe Gap

The maximum clearance between two parallel metal surfaces which has been found, under specified test conditions, to prevent an explosion in a test chamber from being propagated to a secondary chamber containing the same gas or vapor at the same concentration.

MESG Test Apparatus

Adjustable Gap

25 mmLength

Test Chamber

Secondary Chamber

Determining MESG

¾ The MESG is determined experimentally in a special test apparatus in accordance with IEC 60079-20-1.

¾ Many MESG values are published in ANSI/NFPA 497 and IEC 60079-20-1.

MESG Apparatus

MESG Apparatus(Below MESG)

MESG Apparatus(Above MESG)

MESG Examples

MESG of some common gases & vapors:

¾ Acetylene 0.25 mm¾ Hydrogen 0.28 mm¾ Ethylene 0.65 mm¾ Ethyl Alcohol 0.89 mm¾ Propane 0.97 mm¾ Methane 1.14 mm

MIC Ratio

Minimum Igniting Current Ratio

The ratio of the minimum current required from an inductive spark discharge to ignite the most easily ignitable mixture of a gas or vapor divided by the minimum current required from an inductive spark discharge to ignite methane under the same test conditions.

Intrinsic Safety Spark-Test Apparatus

CadmiumDisk

Wheel with fourTungsten wires

EnclosureContaining Most easily Ignitible gasin air mixture

Rotating Wheel & Whiskers(Note Sparks)

Flammable Mixture Introduced(Current below igniting current)

Flammable Mixture Introduced(Current above igniting current)

Determining MIC Ratio

¾ The MIC Ratio is determined experimentally in the IEC Spark Test Apparatus in accordance with IEC 60079-11.

¾ Many MIC Ratio values are published in ANSI/NFPA 497 and IEC 60079-20-1

MIC Ratio Examples

MIC Ratio of some gases/vapors:

¾ Acetylene 0.28¾ Hydrogen 0.25¾ Ethylene 0.53¾ Ethyl Alcohol 0.82¾ Propane 0.88¾ Methane 1.00

Classification of NEC Gas Groups

• Group A - Acetylene (C2H2) only

• Group B - MESG < 0.45 mm, orMIC Ratio < 0.4

• Group C - 0.45 mm < MESG < 0.75 mm, or0.4 < MIC Ratio < 0.8

• Group D - MESG > 0.75 mm, orMIC Ratio > 0.8

Temperature Class

¾ Surfaces, such as an explosionproof enclosure, or components* in intrinsically safe apparatus, must not exceed the autoignition temperature of the gas or vapor present

*There are exemptions for small components, typically used for intrinsic safety

¾ The maximum surface temperature is determined during the equipment certification process and a maximum surface temperature or temperature class is assigned

¾ Usually this is expressed by a temperature class (T Code)

Temperature Class

Degrees C Degrees F T-Code 450 842 T1 300 572 T2 280 536 T2A 260 500 T2B 230 446 T2C 215 419 T2D 200 392 T3 180 356 T3A 165 329 T3B 160 320 T3C 135 275 T4 120 248 T4A 100 212 T5 85 185 T6

Temperature Class (continued)

Due to the danger of explosion, equipment marked with a specific maximum surface temperature or temperature class must not be installed in a gas atmosphere with a lower autoignition temperature. For example, equipment marked as T3 (200°C) may not be located in a gas atmosphere with an autoignition temperature less than 200°C

What is Autoignition Temperature?

¾ The minimum temperature required to initiate or cause self- sustained combustion of a solid, liquid, or gasindependently of the heating or heated element.

Ambient Temperature Rangeand Other Normal Atmospheric Conditions

¾ The requirements in the standards are based upon the ignition of flammable or combustible materials under the following atmospheric conditions:

• ambient temperature -25˚C to +40˚

• an oxygen concentration no greater than 21%

• barometric pressure 0.8 to 1.1 atmosphere

Equipment intended for use in conditions other than the above may be subject to special investigation

Hazardous (Classified) Locations in the NEC1920 – First Recognition of “Extra Hazardous Locations”

Designated as “Section 32”

1928 - Introduction of “Classes” to differentiate materials (gas / dust / fiber)

1937 - Introduction of “Groups” to quantify material characteristicsRe-designated as “Article 500”

1947 - Introduction of “2 Division” System to differentiate risk of release

1971 - First Proposal to Include “3 Zone” System based on IEC standards

1996 - Introduction of “3 Zone” System as an Alternative Area Classification Scheme for gases

Hazardous (Classified) Locations in the NEC

1920 - Recognition of “Extra Hazardous Locations”

Hazardous (Classified) Locations in the NEC

Area Protection Technique

Division 1

Explosionproof

Intrinsic Safety

Purged/Pressurized (Type X or Y)

Listed as “Special Protection”

Division 2

Non-Incendive Equipment and other Division 2 Apparatus (Hermetically sealed, non-sparking, etc.)

Purged/Pressurized (Type Z)

Any Division 1 Protection Technique

Protection TechniquesClass I, Division 1 and Division 2

Explosion Protection Techniques and FM Approvals Standards for Division Apparatus

Techniques Approval Standard Suitable for use in

General Requirements Class 3600

Intrinsic Safety Class 3610 Class I,II & III, Div.1 & 2

Explosionproof Class 3615 Class I, Div. 1 & 2

Purged/Pressurized Class 3620 Class I & II, Div. 1 & 2

Non-incendive Class 3611 Class I, Div. 2; Class II, Div. 2Class III, Div. 1 & 2

Dust-ignition Proof Class 3616 Class II & III, Div. 1 & 2

Explosionproof Protection Technique

Explosionproof Equipment(Class I, Division 1)

Equipment enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.

Explosionproof Enclosures

¾ Must be strong enough to withstand the pressure of an internal explosion.

¾ Must have joints tight enough to prevent transmission of an explosion to an external explosive mixture.

¾ Must have surface temperatures below the Autoignition Temperature of the area of installation

Explosionproof Enclosure Joints(flamepaths)

The minimum length of a joint flamepath and maximum allowed clearance (gap) between surfaces is dependent upon the gas group and enclosure volume

• D >> C >> B >> A requires longer length / smaller gap

• Larger volume requires longer length / smaller gap

Flanged Joint Example

Threaded Joint Example

Testing of Explosionproof Equipment

¾ Explosion Pressure Tests

¾ Overpressure Test

¾ Flameproof Tests

¾ Surface Temperature Tests

Factors Affecting Explosion Pressures

¾ Geometry of the Enclosure¾ Locations of Ignition Source¾ Energy of Ignition Source¾ Ambient Pressure (pre-explosion)¾ Initial Temperature¾ Turbulence

Determination of Explosion Pressure

¾ Non conduit-connected compartments• Locate spark plug and transducer(s) to

maximize effects of pressure piling• More than one configuration often required

¾ Conduit-connected compartments• If seal required – test with short length of

conduit – normally 18 in. unless label specifies a shorter length

• If seal not required – test with 5/10/15 foot lengths of conduit

Non Conduit-Connected Compartment

Sample – Compliments of Endress + Hauser

Spark Plug

Transducer

Pressure Piling

Sample – Compliments of Limitorque, a unit of Flowserve Corporation

Conduit-Connected Compartment - 18 In.(Seal Required)

Spark Plug

Transducer

Conduit-Connected Compartment – 5 Ft

Conduit-Connected Compartment - 5 Ft

Spark Plug

Transducer

Spark Plug

Transducer

Spark Plug

Transducer

Explosion Pressure Example

Overpressure Tests

¾ Explosionproof - Divisions

• Type Test – 400% maximum explosion pressure

• Routine Test – Depends on Pressure Rise Time• 200% maximum explosion pressure for Rise Time > 5 mSec• 300% maximum explosion pressure for Rise Time ≤ 5 mSec

Pressure Rise Time

Over-Pressure Test Example

PressureSensing

PressureSupply

Over-Pressure Test Failure

Flameproof Tests

¾ Explosionproof

¾ Increases gap of “plain” joints to 150% of design maximum or uses more sensitive gas mixture with 80-100% gaps

¾No decrease in engaged length of threaded joints that meet standard requirements

Flameproof Test Example

Surface Temperature Tests

¾ Rated Voltage ± 10%

¾ “Worst Case” operation¾Locked Rotor for Motor¾Blocked Plunger for Solenoid¾Maximum rated load

¾ Temperature controls defeated, temperature based on limiting devices

Equipment Marking

9 Manufacturer’s name9 Type designation9 Serial number or date code9 Electrical ratings9 Hazardous Location ratings9 Ambient temperature ratings9 Enclosure ratings (optional)9 Caution warnings9 Certification mark

Marking Example

There is no Temperature Class (T Code) marking as the maximum surface temperature was less than 100°C.

¾ type of protection based on the restriction of electrical energy within apparatus and of interconnecting wiringexposed to the explosive gas atmosphere to a level below that which can cause ignition by either sparking or heating effects

The concept is based upon electrical sparks and thermal effects under BOTH normal and abnormal circuit conditions

Intrinsic Safety for Explosive Gas AtmospheresClass I, Division 1

Intrinsically Safe Circuit

¾ Spark or thermal effect produced normally or in faultconditions will not cause ignition of a flammable or combustible material in air.

Such circuits may be part, or all, of the circuits contained within Intrinsically Safe and Intrinsically Safe Associated Apparatus, or may be the interconnecting wiring between such apparatus.

Intrinsically Safe Apparatus

¾ Electrical apparatus in which all the circuits comply with the intrinsic safety requirements.

Examples: 4-20mA Transmitters (Pressure, Temperature, etc.), portable battery operated equipment such as 2-way radios.

Intrinsically Safe Apparatus

Intrinsically Safe Associated Apparatus

¾ Electrical apparatus that contains both intrinsically safe circuits and non-intrinsically safe circuits and is constructed such that non-intrinsically safe circuits will not adversely impact the intrinsically safe circuits. This type of apparatus provides intrinsically safe power to the intrinsically safe field apparatus.

Examples: 4-20mA Input/Output Modules, Barriers

Intrinsically Safe terminals

Intrinsically Safe Associated Apparatus

Simple Apparatus(Certification Not Required)

¾ Passive Components¾ Junction Boxes, Terminals, Dry Contacts, LED

¾ Sources of Stored Energy with only a single Capacitor or Inductor used in a simple circuit¾ RC Network

¾ Any additional sources of capacitance and inductance must be considered during the Entity parameter review of the system to be installed

¾ Sources of Generated Energy Which do not Generate More Than 1.5 volts, 100 mA, and 25 mW¾ Thermocouple, Photocell

FM Approvals Standards Applicable to Intrinsic Safety

¾ FM Approvals Standard Class 3600:2011Electrical Equipment for Use in Hazardous (Classified) Locations – General Requirements

¾ FM Approvals Standard Class 3610:2015Intrinsically Safe and Associated Intrinsically Safe Apparatus for use in Class I, II, III, Divisions 1 & 2, and Class I, Zones 0 & 1, Hazardous (Classified) Locations.

What Type of Electrical Apparatus is Covered by the Intrinsic Safety Concept?

¾ Fixed field apparatus, such as pressure, temperature or flow transmitters. Such equipment would be classed as “Intrinsically Safe Apparatus.”

¾ Apparatus typically installed in an unclassified locationand which provides intrinsically safe power to the “Intrinsically Safe Apparatus.” This apparatus is classed as “Intrinsically Safe Associated Apparatus.”

¾ Battery operated portable apparatus, such as flashlights, radios, and combustible gas detectors. Such equipment would be classed as “Intrinsically Safe Apparatus.”

How is Energy Limitation Achieved?

¾ Energy limitation is achieved, for example, through the use of:

• Associated Apparatus• Resistors to limit current• Diodes to clamp voltageIn conjunction with

• Apparatus• Limited energy storage components

(capacitors / inductors)

Faults¾ The maximum voltage and current are determined during normal,

one and two fault circuit conditions.

¾ The opening, shorting or grounding of the intrinsically safe field wiring is not counted as a fault. This is considered to be a normal occurrence.

Typical Faults

¾ Shorting of circuit component, e.g., semiconductor devices

¾ Opening of circuit components, e.g., resistors, diodes

¾ Shorting of inadequate spacing, e.g., creepage and clearance distances on PCB assemblies (both etch & components)

¾ Opening of fallible wiring

Protective Components

¾ Protective Components - are relied on for energy limitation and when properly rated and in compliance with the spacing distance requirements; are unlikely to become defective in a manner that will increase the energy in the circuit

¾ Components such as resistors, transformers, diodes (zener & signal), opto-couplers, and active components can be qualified as protective components.

Spark ignition can come from:

¾ Discharge of a capacitive circuit

¾ Interruption of an inductive circuit

¾ Connection and interruption of a resistive circuit

Thermal ignition can come from:

¾ Small Gauge Wire Strands

¾ Filaments

¾ Component Surface Temperatures

Design Considerations for Intrinsically Safe Apparatus

¾ Use protective components to limit capacitive and inductive arcing

¾ Design for highest possible Ui (Vmax) and Ii (Imax)

¾ Size components to limit surface temperatures to safe levels

¾ Separation distances must be met

Design Consideration for Intrinsically Safe Associated Apparatus

¾ Voltage and current limitation are needed to limit the energy available to the field wiring to intrinsically safe levels under normal, one or two fault conditions.

¾ Voltage and current limiting components must be rated at 1.5 times fault conditions, e.g., 2/3rds fault power.

¾ Separation distances must be met based on fault voltage.

Evaluation of Intrinsic Safety

¾ May be accomplished by testing the circuit in the Intrinsic Safety Spark-Test Apparatus.

¾ May be accomplished by determining circuit parameters and comparison to the Ignition Curves

Ignition Curves

¾ When using the comparison method for your equipment design, use the following figures in ANSI/ISA 60079-11 or, alternatively Tables A.1 & A.2 in Appendix A.

• Resistive curve – go to Figure A.1 for linear circuits

• Capacitive curve – go to Figure A.3

• Inductive curve – go to Figure A.4 or A.6

Equivalent Safety Circuit for a Linear Supply

The resistive, inductive and capacitiveIgnition curves may be used for thisType circuit when conducting the Comparison method.

Resistive Ignition Curve

To determine if a 24V, 100mA, circuit for use in Groups A & B is permitted, a 1.5X safety factor is imposed on the current which then allows for values not exceeding 30V.

Group C Curve

Group D Curve

Group A&B Curve

100 mA X 1.5 = 150 mA

Inductive Ignition Curve

The inductanceallowed in a 24 V, 100 mA circuit for use in Group A & B cannot exceed 4mH because ofthe 1.5X safety factor imposed on the current

Group A&B Curve

Group C Curve

Group D Curve

Capacitive Ignition Curve

The capacitance allowed in a 30 volt circuit for use in Groups A & B cannot exceed 0.067uF because of the 1.5X safety factor imposed on the voltage.

Group A&BCurve

Group CCurve

Group DCurve

0.067 uF

Example Control Drawing for Intrinsically Safe Apparatus

Model P1224RT

Ui = 30 VIi = 150mACi = 0.01µFLi = 0Pi = 1W

Class I, Division 1, Groups A,B,C&D,Class II, Division 1, Groups E,F&G,Class I, Zone 0, Group IIC

Company NameDrawing No.Revision Level

Notes, e.g.,1) Install in accordance with Articles

501 and 502 of the NEC and ISA RP12.06.01

2) Connect to terminals A&B3) etc.

Unclassified Location

AssociatedIntrinsicallySafeApparatus

Example of Control Drawing for Associated Intrinsically Safe Apparatus

Io = 90mACo = 0.1µFLo = 1mHPo = 0.65W

Uo = 29 V

Company NameDrawing No. & Revision Level

Model B123Class I, II & III, Division 1, Groups A-GClass I, Zone 0, Group IIC

Notes e.g.,1) Install in accordance with Articles 501 –

505 of the NEC and ISA RP12.06.012) etc.

Example of Control Drawing for Intrinsically Safe System Under Entity Concept

Ui = 30Vdc is > Vo = 29VdcIi = 150mA is > Io = 90mACi = 0.01µF + Cable C < Co = 0.1µFLi = 0 + Cable L < Lo = 1mHPi =1W > Po = 0.65W

Model P1224RT Model B123

Class I, II & III, Division 1, Groups A-GClass I, Zone 0, Group IIC

Company NameDrawing No. & Revision Level

Marking ExampleIntrinsically Safe Associated Apparatus

Control Drawing

Marking ExampleIntrinsically Safe Apparatus

ControlDrawing

HazLocRatings

Marking ExampleIntrinsically Safe Apparatus

ControlDrawing

HazLocRatings

Questions?

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