Equipment categories depending on gases, vapours or dust.

Depending on the type of hazardous atmosphere — whether gas, vapour or dust — equipment is classified into specific groups that determine its suitability for use. Each group corresponds to a separate class of explosive substances and implies increasingly stringent protection requirements. The classification is as follows:

For gas environments:

IIA: suitable for less hazardous environments in series II; equipment marked IIA, IIB or IIC can be used.

IIB: requires a higher level of protection than IIA; equipment marked IIB or IIC is compatible.

IIC: intended for the most hazardous environments in Series II, such as hydrogen or acetylene; in this case, only devices specifically classified as IIC should be used.

For dusty environments:

IIIA: allows devices of categories IIIA, IIIB or IIIC.

IIIB: compatible with equipment marked IIIB or IIIC.

IIIC: requires only Group IIIC equipment.