Emerson Fisher 4200, Fisher 546, Fisher 646, Fisher 846, Fisher 3582 Data Sheet

Hazardous Area Classifications	Product Bulletin
	9.2:001
D103222X012	June 2012

Hazardous Area Classifications and

Protections

The intent of this document is to provide a broad overview of hazardous area classifications and the types of protection techniques involved. The information provided in this bulletin is for educational purposes and should not be used in place of any other source or governing documents.

Not all approvals are covered in this bulletin. Contact your Emerson Process Management sales office for information on approvals not covered in this bulletin.

Contact your Emerson Process Management sales office for product specific hazardous area approval information or visit our website at www.Fisher.com.

Hazardous Area

Classifications

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.

Class/Division System

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

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.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.

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—Atmospheres containing acetylene.

b.Group B—Atmospheres 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.

www.Fisher.com

Product Bulletin	Hazardous Area Classifications
9.2:001
June 2012	D103222X012

Typical gases include hydrogen, butadiene, ethylene oxide, propylene oxide, and acrolein.

c.Group C—Atmospheres 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 either, ethylene, acetaldehyde, and cyclopropane.

d.Group D—Atmospheres 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—Atmospheres containing combustible metal dusts such as aluminum, magnesium, and their commercial alloys.

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

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

Zone System

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.

Zone—The Zone defines the probability of the hazardous material, gas or dust, being present in sufficient quantities to produce explosive or ignitable mixtures.

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.

Group—Electrical equipment used in gas atmospheres is divided into two groups.

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

ν Group II—All other equipment; which is further subdivided into three subgroups.

-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.

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 and do so only for a short period of time.

1.Gas

a.Zone 0—Ignitable concentrations of flammable gases or vapors which are present continuously or for long periods of time.

b.Zone 1—Ignitable concentrations of flammable gases or vapors which are likely to occur under normal operating conditions.

Protection Techniques and

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. Not all methods are listed.

2

Hazardous Area Classifications	Product Bulletin
	9.2:001
D103222X012	June 2012

Class/Division system

ν 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.

ν 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.

ν 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.

ν 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.

Zone system

ν 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 type of protection is referred to as “Ex d”.

ν 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 type of protection is referred to as “Ex i”.

ν 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 type of protection is referred to as “Ex e”.

ν Type n—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”.

Temperature Code

(T 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 depends 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.

3