ATEX Lighting for the Food Industry (Dust Zones)

ATEX Lighting for the Food Industry

ATEX lighting for the food industry is about dust, not gas. Flour, sugar, starch, cocoa, milk powder and feed dust all form explosive atmospheres, and the zone is set by where the dust settles and where it is released: inside a silo or a mill it is Zone 20, within a metre of a filling point it is Zone 21, and the rest of the hall is normally Zone 22. The fixture then has to satisfy a second master, the hygiene plan, which means IP6X, smooth surfaces, no crevices that hold product and a lens that survives caustic wash-down. Linear fixtures over the line and floodlights on the silo top cover most plants we quote.

Dust zones, not gas zones

Zone 20 is inside the equipment, Zone 21 is where dust is released in normal operation, Zone 22 is where it can form a cloud only in a fault. A fixture marked only for gas cannot be used in any of them.

The layer, not the cloud

Dust settled on a hot luminaire insulates it and ignites at a lower temperature than the cloud in the air. The marking has to be read against the layer ignition temperature at 5 mm, which for organic dusts is often 200 to 300 degrees, not against the cloud figure.

Hygiene and wash-down

A fixture that fails the hygiene plan is a non-conformity even if it is certified. Smooth surfaces, no exposed screw heads holding product, a lens that resists caustic foam and a gasket that stays flexible after a thousand cycles.

Where the zones fall in a food plant

The dust study is usually done by the plant's own safety engineer, and it follows the same logic as a gas study: release sources, ventilation and the geometry of the building. The table below is the mapping we see most often, and it is the one we quote from when a plant has no drawing yet.

Area	Zone	Dust group and class	Fixture
Inside silo, mill or mixer	Zone 20	IIIC, T4	AELL linear 20–40 W
Filling and bagging point	Zone 21	IIIC, T4	AEL 50–100 W
Production hall, general	Zone 22	IIIC, T4	AELL linear 40–80 W
Packaging and palletising	Zone 22 or unclassified	Depends on the study	Tri-proof IP65
Cold store	Unclassified	Not applicable	Tri-proof, rated to −25 °C

A dust certificate read against the cloud temperature instead of the layer temperature is the most common specification error we see in food plants.

Light for inspection, not just for walking

Two numbers decide the light on a food line: the illuminance on the inspection point and the colour rendering. Inspection tables and quality gates want 300 to 500 lux at 80 CRI or better, while circulation aisles are fine at 100 to 150 lux. A 4000 K linear fixture over the line reads as neutral white, which is what a quality team wants when it judges colour, and it keeps the plant out of the warm-white look that makes a clean room feel like a warehouse.

What a HACCP audit asks about the lights

A food safety audit asks three questions about lighting: is it shatterproof over exposed product, can it be cleaned, and is it certified for the zone. The answer to all three has to be in the file, with the certificate for the exact model and a cleaning instruction the plant can actually follow at the interval it runs.

Dust zone map of a silo in cross section

A silo in cross section: Zone 20 inside, Zone 21 at the filling point, Zone 22 in the hall.

Is a gas-certified fixture valid in a dust zone?+

No. Gas and dust are separate markings: a fixture marked IIB T4 covers gas, while dust needs a IIIC group and a dust temperature class. A datasheet that shows only a G marking cannot be used in a dust zone, even when the enclosure looks identical.

Does the fixture have to be stainless steel?+

Not always. Die-cast aluminium with a food-grade polyester coating is accepted in most dry areas; stainless becomes necessary in wet rooms with caustic foam and where the fixture sits over open product. What matters more than the metal is the absence of crevices where product can sit.

Can the same fixture go into the cold store?+

Only if it is rated for the temperature: standard drivers are specified to minus 20 degrees and a cold store runs colder at the evaporator. A cold-store fixture also needs a gasket that stays flexible, or the IP rating is lost in the first year.