Combustible flour dust, safely under control.

A five-floor grain mill needed to keep dust off the floors and out of the working environment across the whole building, continuously. Flour is a combustible dust: left to accumulate, it is both a hygiene problem and an explosion risk.

Under UK DSEAR, an area where combustible dust can occasionally form an explosive atmosphere is classified as Zone 22 — and the vacuum working in it has to be built for that zone, not simply industrial-strength.

Depureco specified an ATEX-certified PUMA 15 central unit with an 11 kW side-channel blower, marked 1/3D — certified for a combustible-dust Zone 22 area, with Zone 20 certification for the inside of the collection chamber. Waste discharges into an AISI 304 stainless-steel container.

Two parallel pipelines carry an inlet to each of the five floors, so operators can clean down at the point where dust is generated. The whole system is built around explosion protection: a flameless vent to contain flame and over-pressure in the event of an ignition, an explosion-isolation flap to stop a flame front travelling back into the pipework, and antistatic filters and accessories throughout to remove ignition sources — with an automatic filter-cleaning system to keep suction consistent.

Collecting dust straight into the unit, at every floor, reduces the explosion risk that comes with accumulated flour, keeps pests out, protects product quality and improves air quality for the people working there — all from equipment built and certified for the zone it operates in.