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Where and when do explosion risks occur?

Potentially explosive atmospheres (explosive zones) are characterised by a mixture of air and combustible gases, vapours, mists or dusts and can in principle occur wherever combustible liquids, gases or dusts are manufactured, filled into containers, transported or stored.

Where is there an explosion hazard?

Potentially explosive mixtures with gases, mists or vapours Potentially explosive mixtures with dusts Ignition sources
Chemical factories Chemical factories Hot surfaces
Tank storage depots Power plants Flames
Refineries Paint factories Hot gases
Sewage treatment plants Grain mills Mechanically generated sparks
Airports Cement factories Electrical equipment (sparks)
Power plants Port installations Electrical equalising currents
Paint factories Feedstuff factories Electrostatic discharges
Paint spraying shops Wood-processing companies Shock waves in flowing gases
Port installations Metal-processing companie Chemical reactions
Plastic granules processing companies Ionising radiation
Lightning strike

Classification of equipment

Equipment is divided into two different classes: Group I comprises equipment for mining, whilst all the other sectors, including the chemical industry, are listed together in Group II. Group II is also subdivided by the letters A, B and C, but these are only used for certain types of ignition protection.

The most hazardous gases are defined in Group IIC. The gases are subdivided into temperature classes (T-classes) in order to take their various ignition temperatures into account. In order to prevent ignition of a gas, the maximum surface temperature of a device must be lower than the ignition temperature of the combustible material. The table below indicates the ignition temperatures of some gases frequently encountered.

Explosion groups Temperature class
T1 T2 T3 T4 T5 T6
Min. ignition temperature or max. surface temperature 450 °C 300 °C 200 °C 135 °C 100 °C 85 °C
I (Mining) Methane
II A Acetone i-Amylacetate Benzines Acetal-
Ammonia n-Butane Diesel
Benzene n-Butane
Fuel oils
Acetic acid n-Hexane
II B Town gas Ethylene Hydrogen
Ethyl ether
Ethylene oxid
II C Hydrogen Carbon disulphide