Hazardous Areas Classification For North America

1 Hazardous Areas Classification and Protection For North America Electrical devices used in Hazardous Areas need to be certified for use according the requirements specified for the area . In North America , certification is provided by: Factory Mutual (FM) - An approval agency primarily concerned with insurance underwriting. Underwriters Laboratories (UL) - An independent, not-for-profit product safety testing and certification organization. Canadian Standards Association (CSA) - A not-for-profit membership-based association serving business, industry, government and consumers in Canada developing standards addressing public safety and health. The type of protection required depends on the risk involved in the area . In general, Hazardous locations in North America are separated by classes, divisions, and groups to define the level of safety required for equipment installed in these locations. Classes The classes defines the general nature of Hazardous material in the surrounding atmosphere.

2 Class Hazardous Material in Surrounding Atmosphere Class I Hazardous because flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class II Hazardous because combustible or conductive dusts are present. Class III Hazardous because ignitable fibers or flying's are present, but not likely to be in suspension in sufficient quantities to produce ignitable mixtures. (Group classifications are not applied to this class.) Divisions The division defines the probability of Hazardous material being present in an ignitable concentration in the surrounding atmosphere. Division Presence of Hazardous Material Division 1 The substance referred to by class is present during normal conditions. Division 2 The substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown. Groups The group defines the Hazardous material in the surrounding atmosphere. Group Hazardous Material in Surrounding Atmosphere Group A Acetylene Group B Hydrogen, fuel and combustible process gases containing more than 30% hydrogen by volume or gases of equivalent hazard such as butadiene, ethylene, oxide, propylene oxide and acrolein.

3 Group C Ethyl and ethylene or gases of equivalent hazard. Group D Gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol, hexane, methanol, methane, natural gas, naphtha, propane or gases of equivalent hazard. Group E Combustible metal dusts, including aluminum, magnesium and their commercial alloys or other combustible dusts whose particle size, abrasiveness and conductivity present similar hazards in connection with electrical equipment. Group F Carbonaceous dusts, coal black, charcoal, coal or coke dusts that have more than 8% total entrapped volatiles or dusts that have been sesitized by other material so they present an explosion hazard. Group G Flour dust, grain, wood, plastic and chemicals. The specific Hazardous materials within each group and their automatic ignition temperatures can be found in Article 500 of the National Electrical Code and in NFPA 497. Group A, B, C and D apply to class I locations. Group E, F and G apply to class II locations.

4 Temperature Code A mixture of Hazardous gases and air may ignite in contact with a hot surface. The condition for ignition depends on several factors as surface area , temperature and concentration of gas. Equipment approved receives a temperature code indicating the maximum surface temperature of the equipment. Maximum Surface Temperature Temperature Code oF oC T1 842 450 T2 572 300 T2A 536 280 T2B 500 260 T2C 446 230 T2D 419 215 T3 392 200 T3A 356 180 T3B 329 165 T3C 320 160 T4 275 135

5 T4A 248 120 T5 212 100 T6 185 85 Equipment that not exceed a maximum surface temperature of 212 oF (104 oF ambient temperature) is not required to be marked with a temperature code (NEC). Recommended reading for this topic: National Electrical Code, NFPA 70, Chapter 5, Article 500 29 CFR 1910 Subpart S, Electrical NFPA 497, " Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous Classified Locations" NFPA Handbook, "Electrical Installations in Hazardous Locations, " by P. J. Schram and M. W. Earley NFPA 70E, Chapter 5, " Hazardous (Classified) Locations" NFPA 325, "Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids" ANSI/UL 913, "Intrinsically Safe Apparatus" NFPA 496, "Purged and Pressurized Enclosure for Electrical Equipment in Hazardous Locations.

6 " Dust-ignition Proof, Explosion Proof, Instrinsically Safe, and Nonincendive Protection of Hazardous Areas Explosions of volatile liquids and gases resulting in severe fire conflagrations are real hazards, involving high economic costs and often, injury or loss of life. The types of protection required for electrical components in the Areas depends on the risks involved. In general, the types of protection can be summarized to: Dust-ignition Proof A dust ignition proof component prevents dust entering from outside. Arcs, sparks and heat generated inside of the enclosure will not be able to ignite the exterior surroundings near the component. Explosion Proof An explosion proof component is capable to keep an internal explosion of a specific flammable air-vapor mixture within the component enclosure without releasing burning or hot gases to the external environment which may be potential explosive. The explosion proof equipment must also operate below safe temperatures.

7 The potentially sparking parts are encapsulated in a special house which is designed to prevent explosions by preventing the entry of Hazardous material in potentially Hazardous concentrations encapsulate potential Hazardous materials in a encapsulation chamber capable to contain any explosion or fire, preventing to spread outside the chamber causing secondary explosions Intrinsically Safe An intrinsically safe component is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific Hazardous substance under normal or abnormal (fault) operating conditions. ( - Wiring Practices for Hazardous area Instrumentation) In simple terms, this means that intrinsically safe equipment and wiring will limit electrical and thermal energy to a level below what required to cause start an explosion. Intrinsically safe equipment operates on low power levels. Safety barriers are grounded so that they are effective under fault conditions, and intrinsic safety is provided through voltage and current limiters.

8 Zener diodes and resistors limiting the energy are usually mounted away from the Hazardous Areas . Failure to replace enclosure covers or bolts will not imperil protection. Intrinsically safe wiring must be separated from non-intrinsically safe wiring by at least 2 inches in order to prevent the transfer of unsafe levels of energy to the Hazardous area and it is vital that planning and installation of intrinsically systems are done with care and attention. Note! Intrinsically safety can be compromised after initial installation due to improper maintenance or repair. It is important to ensure that such works are carried out properly. Nonincendive Nonincendive components are non-sparking and incapable of releasing sufficient electrical or thermal energy to cause ignition of a Hazardous substances under normal operating conditions.