Intrinsically Safe

Classifications

Many international standards for intrinsic safety exist throughout the world, of which, the most influential is the European Committee for Electrotechnical Standardization (CENELEC) and is used throughout most of Western Europe. The US National Fire Protection Agency (NFPA) and Canadian Standards Association (CSA) have their own standards in force but are moving towards adopting (CENELEC) standardization.

The following chart compares common specifications of explosion protection for the European Union and North America.

	North America Classification by Classes, Divisions and Groups	European Classification by Zones
Type of Hazard	Explosive mixtures of air with: Class I: Gases or vapours Class II: Dusts Class III : Fibres or flyings	Explosive mixtures of air with flammable gases or vapours. Group I : Mines where methane may be present. Group II: Places with potentially explosive atmosphere other than mines susceptible to methane.
Degree of Hazard	Division 1 : An explosive concentration of the hazardous material be continuously, intermittently or periodically present under normal conditions.	Zone O : An explosive air/gas mixture is continuously present for long periods. Zone 1 : An explosive air/gas mixture is likely to exist under normal operating conditions for short periods.
	Division 2 : An explosive concentration of the hazardous material is present only under fault conditions and if such a condition occurs, it will exist only for a short period.	Zone 2 : An explosive air/gas mixture is not likely to occur under normal operating conditions and if such a condition occurs, it will exist only for a short period.
Ignition by Spark	Explosive atmospheres are grouped according to their ignition capabilities.	Explosive gasses are grouped according to their ignition capabilities.
	Representative atmospheres are: Group A : acetylene Group B : hydrogen Group C : ethylene Group D : propane Group E : metal dust Group F : carbon dust Group G : flour, starch, grain	Representative gases are: Group I : methane Group IIC : hydrogen, acetylene Group IIB : ethylene Group IIA : propane
Ignition by Hot Surface	Hazardous area apparatus is classified according to the maximum surface temperature produced under fault conditions at an ambient temperature of 40ºC (or as otherwise specified). T1: 450ºC T2: 300ºC T2A: 280ºC T2B: 260ºC T2C: 230ºC T2D: 215ºC T3: 200ºC T3A: 180ºC T3B: 165ºC T3C: 160ºC T4: 135ºC T4A: 120ºC T5: 100ºC T6: 85ºC North America only
Gas Characteristics	Information regarding gas grouping by ignition energy and gas ignition temperatures are contained in: NFPA 497M Manual for Classification of Gases, Vapours and Dusts for Electrical Equipment in Hazardous (Classified) Locations CSA No. C22-1 NEC Article 500 British Standard Code of Practice for Electrical Apparatus and Associated Equipment for use in Explosive Atmospheres (other than Mining Application), BS5345: Part 1 - Basic requirements for all parts of the code.

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