Stahl - Catalog - STAHL - #11

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0/5 0 Automation 17.04.2008 Basics of Explosion Protection Temperature Classes; Explosion Groups Temperature Classes Ignition temperature is the lowest temperature of a surface at which an explosive atmosphere ignites on it. Flammable vapours and gases can be classified into temperature classes according to their ignition temperature. The maximum surface temperature of a piece of equipment must always be lower than the ignition temperature of the gas-air mixture or vapour-air mixture in which it is placed. Temperature Classes to IEC Temperature class IEC / EN NEC 505-10 Maximum permissible surface temperature of the equipment [°C] Ignition temperatures of flammable substances [°C] Temperature class NEC 500-3 CEC 18-052 T1 450 > 450 T1 T2 300 280 260 230 215 > 300 ( 450 > 280 ( 300 > 260 ( 280 > 230 ( 260 > 215 ( 230 T2 T2A T2B T2C T2D T3 200 180 165 160 > 200 ( 300 > 180 ( 200 > 165 ( 180 > 160 ( 165 T3 T3A T3B T3C T4 135 120 > 135 ( 200 > 120 ( 135 T4 T4A T5 100 > 100 ( 135 T5 T6 85 > 85 ( 100 T6 Explosion Groups Explosion protected electrical equipment is divided into 2 groups: Electrical equipment of group II os further subdivided in groups IIA, IIB and IIC, depending on the danger level of the gas or vapour atmosphere in which they are operated. Equipment of group IIC is suitable for use in the most dangerous atmospheres. Group I Electrical equipment for mining Group II Electrical equipment for all other hazardous areas Examples of the Classification of Gases and Vapours into Explosion Groups and Temperature Classes T1 T2 T3 T4 T5 T6 I Methane IIA Acetone Ethane Ethyl acetate Ammonia Benzene (pure) Acetic acid Carbon monixide Methane Methanol Propane Toluene Ethyl alcohol i-amyl acetate n-butane n-butyl alcohol Gasoline Diesel fuel aviation fuel Heating oils n-hexane Acetaldehyde Ethyl ether IIB Town gas (coal gas) Ethylene IIC Hydrogen Acetylene Carbon disulphide There is no classification of dust material into temperature classes or explosion groups. This means that the respective values are to be taken into account. The minimum ignition energy Emin (of a gas-air mixture) is the energy of an electrical spark that is capable of igniting the most critical (highest ignition performance) mixture under defined test conditions. Ignition temperature Tign (of a gas-air mixture) is the lowest temperature of a hot wall surface at which the mixture is ignited after short-term contact. The glow temperature Tglow (of a dust layer) is the lowest temperature of a hot surface on which ignition occurs in a 5 mm thick layer of dust. The maximum surface temperature of the equipment must be compared with the ignition temperature and the glow temperature while also taking into account the safety factor: • temperature limiting regarding dust clouds: Tmax = 2/3 Tign • temperature limiting regarding dust layers: Tmax = Tglow - 75 K (5 mm dust layer) The lower of the two values represents the maximum permissible surface temperature of the equipment.