The saw is not the problem. The sander, the ducting and the filter unit are.
Wood dust fine enough to hang in the air is a combustible dust, so a joinery or woodworking shop falls under DSEAR wherever it collects: the sander, the extraction ducting and the filter unit rather than the saw. The assessment classifies any of those areas where an explosive dust cloud can form into dust zones, checks ignition sources such as hot bearings and sparks in the extraction, and records the controls.
Wood dust behaves like every other combustible dust: the explosible atmosphere forms inside the plant, not in the room. A joinery shop that feels dusty is a housekeeping problem. A filter unit with no relief is a structural one.
Sawing makes chips. Sanding and machining MDF make the fine fraction that will actually explode. Follow the fine dust and you find the risk.
Fine dust settles in horizontal runs and in bends. A duct that has been building a layer for five years is a connected series of charges waiting for the first event.
The highest dust concentration on the site, in a confined volume. Explosion relief, its direction, and what is standing in front of it.
Same problem, larger volume, and usually outside where the relief direction matters to people walking past.
Roughly a millimetre on the beams is enough for a secondary explosion. This is why the primary event rarely does the damage.
Tramp metal in the feed, a hot bearing on the extraction fan, and a smouldering ember carried down the duct from a sander.
Joinery workshops on the Withybush and Pembroke Dock estates, farm-diversification workshops in converted buildings, and boatyard sheds doing GRP and timber work in the same space.
The converted-building cases are the interesting ones, because the extraction was usually retrofitted into a structure that was never designed for it.
Fine wood dust is a combustible dust and will explode given the right conditions: fine enough particles, enough of them suspended in air, oxygen, confinement and an ignition source. The primary event is usually small and inside the plant. The damage comes from the secondary explosion when it shakes settled dust off the beams.
As a rule of thumb, dust that passes a 500 micron sieve is the fraction that matters, and finer is worse. Sanding dust and MDF dust are far more dangerous than saw chippings, which is why the sander and the extraction system deserve more attention than the saw.
The filter unit and the bag or bin are where the fine dust concentrates, so that is where the explosible atmosphere is. Siting it outside is good practice for exactly that reason, and where it sits relative to doors, windows and escape routes matters.
Yes, and it is the reason wood dust explosions destroy buildings rather than machines. A layer of about one millimetre across a workshop is enough to sustain a secondary explosion. Housekeeping is a control measure here, not tidiness.
No. Blowing down with an airline takes settled dust that was doing no harm and puts it into suspension at exactly the concentration that will ignite. Vacuum with suitable equipment instead.
The five conditions and why the secondary explosion does the damage.
Most joinery shops finish as well as machine.
Zone 20, 21 and 22 and the categories that go with them.
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