North America

In North America, hazardous areas are separated by Classes, Divisions and Groups to define the level of safety required for equipment installed in these locations.

Classes define the general form of the flammable materials in the atmosphere:

Class I Flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Class II Combustible or conductive dusts are present.
Class III Ignitable fibers or filings 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 define the probability of the presence of flammable materials:

Division I The substance referred to by class is present during normal conditions.
Division II The substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown.

Groups classify the exact flammable nature of the material:

Group A Acetylene
Group B Hydrogen (or gases of equivalent hazard)
Group C Ethylene (or gases of equivalent hazard)
Group D Gasoline (or gases of equivalent hazard)
Group E Metal Dust
Group F Coal Dust
Group G Grain Dust

Apparatus Temperature classification (T class)

Maximum surface temperature Temperature class
450°C (842 F) T1
300°C (572 F) T2
280°C (536 F) T2A
260°C (500 F) T2B
230°C (446 F) T2C
215°C (419 F) T2D
200°C (392 F) T3
180°C (356 F) T3A
165°C (329 F) T3B
160°C (320 F) T3C
135°C (275 F) T4
120°C (248 F) T4A
100°C (212 F) T5
85°C (185 F) T6

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