Guidelines on Hazardous Area Classification (1)

FICHTNER Consulting Doc No. WI-CI-GL-425

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GUIDELINES ON HAZARDOUS AREA CLASSIFICATION

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R0 ISSUED FOR USE 02.01.2014PLS/KV SG SG

Rev. No DESCRIPTION DATEPREP

BY CHK BY APPR BY

FICHTNER IndiaGUIDELINES ON HAZARDOUS AREA CLASSIFICATION

I N D E X

CLAUSE DESCRIPTION PAGE

NO. NO.

1.0 INTRODUCTION....................................................................................3

2.0 AREA CLASSIFICATION.........................................................................3

3.0 PROTECTION METHODS........................................................................5

4.0 ABBREVIATION....................................................................................7

5.0 REFERENCE AND STANDARDS...................................................................................8

DOC. NO.:WI-CI-GL-425 REV. NO. R0 PAGE 2 OF 9

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1.0 INTRODUCTION

The intent of this document is to provide a broad overview of hazardous area classifications and the types of protection techniques involved.

2.0 AREA CLASSIFICATION

When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapors, flammable liquids, combustible dusts, ignitable fibers or flyings, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area. Currently there are two systems used to classify these hazardous areas; the Class/Division system and the Zone system. The Class/Division system is used predominately in the United States and Canada, whereas the rest of the world generally uses the Zone system.

The area classification is done based on API RP 505 for North America and IEC 600079-10 for rest of the world. The definition for Class/Division/Group system for North America is provided by NFPA 70 – NEC Article 500 – 503, CEC Article 18 or Annex J and for Zone system is provided by IEC 60079, CENELEC EN 50014 for rest of the world.

2.1.0 Class/Division/Group System (NFPA 70 – NEC Article 500, CEC Section 18 or Annex J)

Hazardous locations per the Class/Division system are classified according to the Class, Division, and Group.

2.1.1 Class: The Class defines the general nature (or properties) of the hazardous material in the surrounding atmosphere which may or may not be in sufficient quantities.

a. Class I: Locations in which flammable gases or vapors may or may not be in sufficient quantities to produce explosive or ignitable mixtures.

b. Class II: Locations in which combustible dusts (either in suspension, intermittently, or periodically) may or may not be in sufficient quantities to produce explosive or ignitable mixtures.

c. Class III: Locations in which ignitable fibers may or may not be in sufficient quantities to produce explosive or ignitable mixtures.

2.1.2 Division: The Division defines the probability of the hazardous material being able to produce an explosive or ignitable mixture based upon its presence

a. Division 1: Indicates that the hazardous material has a high probability of producing an explosive or ignitable mixture due to it being present continuously, intermittently, or periodically or from the equipment itself under normal operating conditions.

b. Division 2: Indicates that the hazardous material has a low probability of producing an explosive or ignitable mixture and is present only during abnormal conditions for a short period of time.

2.1.3 Group: The Group defines the type of hazardous material in the surrounding atmosphere. Groups A, B, C, and D are for gases (Class I only) while groups E, F, and G are for dusts and flyings (Class II or III).

a. Group A: Atmosphere containing acetylene.


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b. Group B: Atmosphere containing a flammable gas, flammable liquid-produced vapor, or combustible liquid-produced vapor whose MESG is less than 0.45 mm or MIC ratio is less than 0.40. Typical gases include hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein.

c. Group C: Atmosphere containing a flammable gas, flammable liquid-produced vapor, or combustible liquid-produced vapor whose MESG is greater than 0.45 mm but less than 0.75 mm or MIC ratio is greater than 0.40 but less than 0.80. Typical gases include ethyl, ethylene, acetaldehyde, and cyclopropane.

d. Group D: Atmosphere containing a flammable gas, flammable liquid-produced vapor, or combustible liquid-produced vapor whose MESE is greater than 0.75 mm or MIC ration is greater than 0.80. Typical gases include acetone, ammonia, benzene, butane, ethanol, gasoline, methane, natural gas, naphtha, and propane.

e. Group E: Atmosphere containing combustible metal dusts such as aluminum, magnesium, and their commercial alloys.

f. Group F: Atmosphere containing combustible carbonaceous dusts with 8% or more trapped volatiles such as carbon black, coal, or coke dust.

g. Group G: Atmosphere containing combustible dusts not included in Group E or Group F. Typical dusts include flour, starch, grain, wood, plastic, and chemicals.

MESG (Maximum Experimental Safe Gap): The maximum clearance between two parallel metal surfaces that 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.

MIC (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.

2.2.0 Zone System (IEC 60079, CENELEC EN 50014 & NFPA 70 – NEC Article 505)

Hazardous locations per the Zone system are classified according to its Zone which can be gas or dust. For gas atmospheres electrical equipment is further divided into Groups and Subgroups. The Zone defines the probability of the hazardous material, gas or dust, being present in sufficient quantities to produce explosive or ignitable mixtures.

2.2.1 Gas

a. Zone 0: Ignitable concentrations of flammable gases or vapors which are present continuously or for long periods of time (i.e. > 1000 hours in a year)

b. Zone 1: Ignitable concentrations of flammable gases or vapors which are likely to occur under normal operating conditions (i.e. 10 - 1000 hours in a year)

c. Zone 2: Ignitable concentrations of flammable gases or vapors which are not likely to occur under normal operating conditions and do so only for a short period of time ((i.e. < 10 hours in a year))

Further, Electrical equipment are divided into three groups.

a. Group I: Equipment used in mines with atmospheres containing methane or gases and vapors of equivalent hazard.

b. Group II: Equipment used in places with an explosive gas atmosphere other than mines

susceptible to firedamp. It is further subdivided into three subgroups


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Group IIA: Atmospheres containing propane, or gases and vapors of equivalent hazard.

Group IIB: Atmospheres containing ethylene, or gases and vapors of equivalent hazard.

Group IIC: Atmospheres containing acetylene or hydrogen, or gases and vapors of equivalent hazard.

c. Group III: Equipment used in places with an explosive dust atmosphere other than mines susceptible to firedamp. It is further subdivided into three subgroups

Group IIIA: Atmospheres containing combustible flyings

Group IIIB: Atmospheres containing non-conductive dust

Group IIIC: Atmospheres containing conductive dust

2.2.2 Dust

a. Zone 20: An area where combustible dusts or ignitable fibers and flyings are present continuously or for long periods of time.

b. Zone 21: An area where combustible dusts or ignitable fibers and flyings are likely to occur under normal operating conditions.

c. Zone 22: An area where combustible dusts or ignitable fibers and flyings are not likely to occur under normal operating conditions.

3.0 PROTECTION METHODS

Various protection techniques and methods have been developed and employed, thus reducing or minimizing the potential risks of explosion or fire from electrical equipment located in hazardous locations. The following are the widely employed methods for various classifications as listed below

3.1.0 Class/Division system

Explosion-proof: A type of protection that utilizes an enclosure that is capable of withstanding an explosive gas or vapor within it and or preventing the ignition of an explosive gas or vapor that may surround it and that operates at such an external temperature that a surrounding explosive gas or vapor will not be ignited thereby. This protection technique shall be permitted for equipment in Class I, Division 1 or 2 locations. This type of protection is referred to as “d”.

Dust Ignition-proof: A type of protection that excludes ignitable amounts of dust or amounts that might affect performance or rating and that, when installed and protected in accordance with the original design intent, will not allow arcs, sparks or heat otherwise generated or liberated inside the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust. This protection technique shall be permitted for equipment in Class II, Division 1 or 2 locations.

Dust tight: Enclosures constructed so that dust will not enter under specified test conditions. This protection technique shall be permitted for equipment in Class II, Division 2 or Class III, Division 1 or 2 locations.

Purged and Pressurized. The process of supplying an enclosure with a protective gas at a sufficient flow and positive pressure to reduce the concentration of any flammable gas or vapor initially present to an acceptable level. This protection technique shall be permitted for equipment in any hazardous (classified) location for which it is identified. This type of protection is referred to as “p”.


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Intrinsically Safe: A type of protection in which the electrical equipment under normal or abnormal conditions is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentration. This protection technique shall be permitted for equipment in Class I, Division 1 or 2; or Class II, Division 1 or 2; or Class III, Division 1 or 2 locations. This type of protection is referred to as “i”.

Non-incendive: A type of protection in which the equipment is incapable, under normal conditions, of causing ignition of a specified flammable gas or vapor-in-air mixture due to arcing or thermal effect. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations. This type of protection is referred to as “n”.

Oil Immersion: Electrical equipment immersed in a protective liquid in such a way that an explosive atmosphere that may be above the liquid or outside the enclosure cannot be ignited. This protection technique shall be permitted for current-interrupting contacts in Class I, Division 2 locations. This type of protection is referred to as “o”.

Hermetically Sealed: Equipment sealed against the entrance of an external atmosphere where the seal is made by fusion, for example, soldering, brazing, welding, or the fusion of glass to metal. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.

3.2.0 Zone system

Flame-proof: A type of protection in which an enclosure can withstand the pressure developed during an internal explosion of an explosive mixture and that prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure and that operates at such an external temperature that a surrounding explosive gas or vapor will not be ignited there. This protection technique shall be permitted for equipment in Zone 1 & 2.This type of protection is referred to as “Ex d”. Example: DC Motors , Field Instruments , JB etc

Intrinsically Safe: A type of protection in which the electrical equipment under normal or abnormal conditions is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentrations. This protection technique shall be permitted for equipment in Zone 0,1 & 2. This type of protection is referred to as “Ex i”. Example: Field Instruments

Increase Safety: A type of protection in which various measures are applied to reduce the probability of excessive temperatures and the occurrence of arcs or sparks in the interior and on the external parts of electrical apparatus that do not produce them in normal service. Increased safety may be used with flame-proof type of protection. This protection technique shall be permitted for equipment in Zone 1 & 2.This type of protection is referred to as “Ex e”. Example: Induction Motors.

Non Sparking: A type of protection applied to electrical equipment such that in normal operation it is not capable of igniting a surrounding explosive atmosphere. This type of protection is referred to as “Ex n”. This protection technique shall be permitted for equipment in Zone 2.

Encapsulation: A type of protection in which the parts that can ignite an explosive atmosphere are enclosed in a resin. The resin must be sufficiently resistant to environmental influences so that the explosive atmosphere cannot be ignited by either sparking or heating, which may occur within the device. This is typically used with electronic devices. This protection technique shall be permitted for equipment in Zone 1 & 2. This type of protection is referred to as “Ex m”.

Oil Immersion: A type of protection where electrical equipment is immersed in a protective liquid in such a way that an explosive atmosphere that may be above the liquid or outside the enclosure cannot be ignited. This protection technique shall be permitted for equipment in Zone 2.This type of protection is referred to as “Ex o”. Example: transformers.


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Purged and Pressurized: This type of protection prevents the surrounding atmosphere from entering an enclosure by maintaining a positive pressure within the unit. Clean air or inert gas is used to maintain a higher pressure than the surrounding atmosphere. In purging, the electrical equipment is interlocked with a system which cycles clean air within the unit to remove explosive gases before start up. This protection technique shall be permitted for equipment in Zone 1 & 2.This type of protection is referred to as “Ex p”. Example: Analyzers

Powder Filling: Type of protection where electrical parts capable of igniting an explosive atmosphere are fixed in position and completely surrounded by filling material (glass or quartz powder) to prevent the ignition of an external explosive atmosphere. This protection technique shall be permitted for equipment in Zone 2.This type of protection is referred to as “Ex q”. Example: Weighing machines.

3.3.0 Temperature Code

A mixture of hazardous gases and air may be ignited by coming into contact with a hot surface. The conditions under which a hot surface will ignite a gas depend on surface area, temperature, and the concentration of the gas. The same can be said about combustible dusts. The T code of a product denotes the maximum surface temperature that a given product will not exceed under a specified ambient temperature. For example, a product with a T code of T3 means that its maximum surface temperature will not exceed 200_C provided it is operated in a ambient temperature defined by the manufacturer.

4.0 ABBREVIATION

API RP : American Petroleum Institute-Recommended Practice

CEC : Canadian Electrical Code

CENELEC : European Committee for Electro-technical Standardization


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IEC : International Electrotechnical Commission

MESG : Maximum Experimental Safe Gap

MIC : Minimum Igniting Current

NEC : National Electrical Code

NFPA : National Fire Protection Association

5.0 REFERENCE AND STANDARDS

5.1.0 Reference – Vendor (Provided separately)

ATEX wallchart-MTL

Flam Facts –MTL

FM_EXDust_HazardPoster

FM_EXGas_HazardPoster

Hazardous area classification-P&F

NEC & IEC_Cooper

P&F Products

5.2.0 Reference – Project (Provided separately)

Hazardous Area Classification -General Layout drawing

Field Instrument

Control Valve

Junction Box

Gas Chromatograph

5.3.0 Standards(Provided separately)

ANSI_API RP 505-1998

NFPA 70 (Article 500 to 505 - Pages No: 339 to 380)

IEC 60079


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Comparison of Protection Standards


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Guidelines on Hazardous Area Classification (1)

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