Use in Hazardous Environments • 219Classification meeting CENELEC and IECWAGO-I/O-SYSTEM 750PROFINET IOHydrogen being commonly encountered in chemical plants, frequently theexplosion group IIC is requested for maximum safety.6.3.3 Unit categoriesMoreover, the areas of use (zones) and the conditions of use (explosiongroups) are subdivided into categories for the electrical operating means:UnitcategoriesExplosiongroupArea of useM1 I Fire-damp protectionM2 I Fire-damp protection1G II Zone 0 Explosive environment by gas, fumes or mist2G II Zone 1 Explosive environment by gas, fumes or mist3G II Zone 2 Explosive environment by gas, fumes or mist1D II Zone 20 Explosive environment by dust2D II Zone 21 Explosive environment by dust3D II Zone 22 Explosive environment by dust6.3.4 Temperature classesThe maximum surface temperature for electrical components of explosionprotection group I is 150 °C (danger due to coal dust deposits) or 450 °C (ifthere is no danger of coal dust deposit).In line with the maximum surface temperature for all ignition protection types,the electrical components are subdivided into temperature classes, as far aselectrical components of explosion protection group II are concerned. Here thetemperatures refer to a surrounding temperature of 40 °C for operation andtesting of the electrical components. The lowest ignition temperature of theexisting explosive atmosphere must be higher than the maximum surfacetemperature.Temperature classes Maximum surfacetemperatureIgnition temperatureof the combustible materialsT1 450 °C > 450 °CT2 300 °C > 300 °C to 450 °CT3 200 °C > 200 °C to 300 °CT4 135 °C > 135 °C to 200 °CT5 100 °C >100 °C to 135 °CT6 85°C > 85 °C to 100 °C
