Dust control in blasting works on three levels, in this order: eliminate the source, enclose and extract it, then protect the person.
Most problem installations skip the first two and rely on the third.
The ventilation principle
In a blast room, contaminated air has to move from the operator’s breathing zone towards the extraction. Not the other way round.
The usual configuration: air enters at the top and is extracted at the bottom, through a downdraught distributed across the whole floor area.
Order of magnitude for the downdraught: about 0.4 m/s average, over the entire area.
An acceptable but less good alternative is cross-draught ventilation — air crosses the room laterally, at an average velocity of about 0.5 m/s across the vertical section.
Velocities at openings
At any opening in the enclosure, air has to flow inwards. That is what stops dust getting out.
Orders of magnitude used as design references:
| Equipment type | Indicative inward velocity |
|---|---|
| Blast cabinet | ~2.5 m/s |
| Rotary table | ~1.0–1.3 m/s |
| Blast room | ~1.5 m/s |
All openings need baffles, so that abrasive is not thrown out through them.
Extraction velocity: neither too high nor too low
Here is a trade-off many people miss.
Too high — you extract the good abrasive along with the dust. Abrasive cost climbs without you seeing why.
Too low — dust-laden air is not cleared in time after the cycle ends. The operator walks into an enclosure that is still full.
The usual reference at the enclosure outlet: up to about 2.5 m/s.
Ductwork
Extraction ductwork needs frequent inspection for blockages and leaks. Dust settling in the duct reduces the flow gradually, and the drop is invisible until it becomes serious.
Badly designed ductwork turns a good filtration system into one that does nothing.
Personal protection, in its place
Personal equipment is the last line.
Particulate filter masks are used for short or occasional exposures — cleaning, emptying collectors, transferring abrasive — and only with silica-free abrasives.
When the atmosphere is very dusty, the filter loads up quickly and breathing becomes difficult. At that point you move to supplied-air equipment; you do not persist with the filter.
Related reading
- Industrial dust filtration: self-cleaning solutions
- Blast Rooms and Painting Booths — Large-Scale Industrial Installations
- Blast Cabinet
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