DSEAR and the dust nobody classified

Most organisations that hold solvents know they are within DSEAR. Fewer connect the regulations to the dust extraction system, the flour silo, the sanding booth or the bags of metal powder. Dust is where a surprising share of serious industrial explosions start.

What DSEAR requires

The Dangerous Substances and Explosive Atmospheres Regulations 2002 require a risk assessment for dangerous substances, elimination or reduction of the risk so far as is reasonably practicable, arrangements for emergencies, and information and training. Then the part most often missing: classification of the places where explosive atmospheres may occur into zones, with the conclusions documented.

HSE is explicit that hazardous area classification for flammable dusts is done the same way as for gases and vapours. Only the numbering differs. Zones 20, 21 and 22 for dust atmospheres, against 0, 1 and 2 for gases and vapours. Equipment in those places has to suit the zone, which is where the ATEX equipment requirements bite.

The Approved Code of Practice, L138, sets out what compliance looks like in practice.

Why dust gets missed

Four reasons. They recur across sectors.

It does not look like a dangerous substance. Wood dust, flour, sugar, custard powder, starch, coal, aluminium, magnesium, titanium, some plastics and a great many pharmaceutical intermediates are all combustible in suspension. None of them arrives with a hazard placard on a road tanker, and the risk assessment tends to follow the placard.

The hazard is in the equipment, not the room. The explosive atmosphere is usually inside the extraction ductwork, the filter unit, the silo, the mill or the conveyor. Enclosed places, where the concentration can sit in the explosible range. A walk round the shop floor finds nothing, because the shop floor is not the zone.

Secondary explosion is the mechanism people have not heard of. A small primary event inside plant disturbs dust that has settled on beams, ledges and cable trays. That suspended layer ignites, and the second explosion is the one that takes the building apart. This is why housekeeping is a control measure under DSEAR and not a matter of tidiness, and why a walk that looks up tells you more than one that looks down.

The assessment was done once, for the process as designed. Then a new material came in, an extraction run was extended, a filter was swapped for a different unit, or production rates went up. The zones were never revisited, because nobody understood them to be a live document.

What good looks like

Start with a materials list. Everything on site that could form a combustible dust, with the data obtained and not assumed: particle size, minimum ignition energy, explosibility. Then classify the places where an explosive atmosphere may occur, inside plant as well as around it, and document the reasoning. Then check equipment against the zone it sits in, control ignition sources, and add explosion protection where it is needed. Then write housekeeping as a control with a defined standard, not as “keep the area tidy”.

Then set a trigger for revisiting all of it when the process changes, because it will.

The question worth asking this week

Not “are we DSEAR compliant”. That gets a yes from somebody thinking about the solvent store. Ask instead: which of our dusts have been assessed for explosibility, and where are our dust zones drawn? If the second half gets a blank look, the assessment covered the liquids.