Phoenix Journal · LEV Testing
A single shift in a dusty kitchen rarely feels dangerous, and that is exactly the problem. The harm from flour and food dust is cumulative, adding up quietly over months and years until the damage is done.
Nobody develops occupational asthma from one dusty morning at the bench. They develop it from ten thousand of them.
That is the hard truth about dust exposure in a commercial kitchen or bakery - it does its damage slowly, by accumulation, in doses too small to notice on any given day. A puff of flour when a bag is tipped, a haze rising off the divider, the fine film that settles on shelves and light fittings overnight - none of it feels like a hazard in the moment. Your staff breathe it, cough once or twice, and get on with the order. The body, however, is keeping a running total.
Understanding dust as a cumulative exposure rather than a daily nuisance changes how you think about control. It means the goal is not simply to keep the air tolerable today, but to keep the lifetime dose as low as reasonably practicable - which is exactly the language the Health & Safety Executive uses. It also explains why a local exhaust ventilation (LEV) system that quietly loses performance over a year or two is so dangerous - the risk creeps up invisibly, one shift at a time, long before anyone notices a problem.
What the numbers mean
Flour dust carries a Workplace Exposure Limit set out in the HSE's EH40 guidance - 10 mg/m³ averaged over eight hours, and 30 mg/m³ averaged over any fifteen-minute period. Those are ceilings, not targets. The HSE is clear that with good control practice, exposure below 2 mg/m³ is usually achievable, and because flour is a respiratory sensitiser it carries a "SEN" notation - meaning exposure should be driven as far below the limit as you reasonably can, not merely nudged under it.
The reason for that caution sits in the third figure above. Bakers have among the highest rates of occupational asthma of any trade in the country, and flour and grain dust rank as the second most common cause of the condition after isocyanates. The eight-hour averaging in the WEL is itself a nod to accumulation - it recognises that a short burst of heavy dust and a long, low, steady haze can carry the same total load into the lungs by the end of a shift. What matters is the area under the curve, not the height of any single peak.
Why the dose adds up
The lungs have no reset button. Fine dust that reaches the deep airways is not simply exhaled at the end of the day - a portion stays, and the body's response to it compounds over time. With a sensitiser like flour, the mechanism is not gradual scarring but something more decisive. Repeated exposure primes the immune system until, at some unpredictable point, it crosses a threshold and becomes sensitised. From that moment the relationship with the substance changes completely.
Two features of that process make cumulative exposure so serious. The first is latency. Sensitisation can take anywhere from a few weeks to more than thirty years to develop, which means a worker can spend a long and apparently healthy career at the bench with the total dose quietly climbing beneath the surface. There is no early alarm that fires as you approach the tipping point. The second is that once someone is sensitised, there is no safe level of exposure at all. Concentrations far below any workplace limit - a trace of flour drifting from a nearby bench - can be enough to trigger a serious reaction. And the damage tends to be permanent - most people who develop occupational asthma live with breathing problems for the rest of their lives, whether or not they ever set foot in a kitchen again.
This is why treating dust as a daily comfort issue misses the point so badly. Air that feels "fine" today can still be adding to a total that will matter enormously in fifteen years. The only exposure a worker never has to recover from is the one they never breathed - so every shift where the dust is kept genuinely low is a permanent deposit in their favour, and every shift where control has quietly slipped is a withdrawal they cannot see.
Controlling the total, not just the day
If the harm is cumulative, then so is the protection - and the systems you rely on to keep dust down have to be treated as long-term commitments rather than one-off installations. Good housekeeping helps, and there are practical steps that pay off day to day, from switching to low-dust flour to careful handling at the tip point - our guide on how to reduce flour dust exposure in a bakery sets those out in detail. But the workhorse in most commercial kitchens and bakeries is local exhaust ventilation, capturing dust at the source before it ever reaches the air your staff breathe.
The catch is that an LEV system degrades exactly the way exposure accumulates - slowly and invisibly. Ductwork clogs, filters load up, fans wear, and dampers drift out of position. Suction falls off so gradually that nobody at the bench registers the change, yet the daily dose creeping into everyone's lungs rises in step. If you have noticed capture getting weaker, our explainer on why a dust extractor loses suction covers the usual culprits. This is precisely the failure mode that scheduled testing exists to catch - a system that looks fine but is quietly under-performing is far more common than one that has visibly stopped.
That is why the law does not leave LEV to chance. Under the Control of Substances Hazardous to Health Regulations, any LEV system must undergo a thorough examination and test by a competent person at least once every 14 months - and for many dusty processes, good practice is more often than that. The test confirms the system is still pulling the volumes it was designed for, that capture at each hood is adequate, and that nothing has drifted since the last check. Where flour is handled in volume, the Dangerous Substances & Explosive Atmospheres Regulations apply alongside COSHH, because accumulated dust is a fire and explosion risk as well as a health one - another reason not to let it build up in ducts and plant. In every case, the aim is the same - to keep the running total as low as it can reasonably go, year after year, so that the dose your team carries at the end of a career is one their lungs can live with.
Questions
Possibly, because the harm from dust is cumulative rather than immediate. Air can sit well within comfort while still carrying flour or food dust in concentrations that add to a lifetime dose over months and years. The only reliable way to know is to measure exposure and confirm your extraction is performing, rather than judging by how the room feels on the day.
Under COSHH, any local exhaust ventilation system must have a thorough examination and test by a competent person at least once every 14 months. For dustier processes, more frequent checks are often sensible good practice. The test verifies the system is still capturing dust at the source and hasn't quietly lost performance since the last inspection.
Generally no. Occupational asthma is usually permanent, and most people who develop it live with breathing problems for the rest of their lives, even after leaving the job. Once a worker is sensitised to flour, there is no safe level of exposure at all, which is why prevention through good control and regular LEV testing matters so much more than any later remedy.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.