Dust Zones (20 / 21 / 22)

Combustible dusts — grain, flour, sugar, wood, coal, aluminium — explode too, and dust atmospheres get their own zone system: Zone 20 for places where a dust cloud is present continuously (inside silos and hoppers), Zone 21 where clouds appear in normal operation (around filling points), and Zone 22 where they occur only briefly in abnormal conditions (settled-dust areas that can be disturbed). Equipment marking mirrors the gas world with Da/Db/Dc protection levels and a maximum surface temperature in °C, checked against both the dust cloud’s ignition temperature and, for settled layers, the layer ignition temperature with its safety margins. Lighting for mills, feed plants and grain terminals therefore reads differently from gas-area lighting — look for the D-suffixed marking and a stated surface temperature, and match both to the site’s dust study rather than borrowing a gas-zone fixture and hoping.