Phoenix Journal · LEV Testing
Flour dust is one of the UK's leading causes of occupational asthma, and once it has sensitised someone the change is permanent. Here is why it happens and how proper extraction and LEV testing keep your team safe.
Flour dust & occupational asthma
Flour looks harmless, but the fine fraction that hangs in the air long after the visible cloud has settled is one of the most significant causes of occupational asthma in the UK - and once it has sensitised someone, there is no undoing it.
A respiratory sensitiser is a substance that, once it has been breathed in enough times, trains the immune system to over-react to it. The first exposures often cause nothing you would notice. Then, at some unpredictable point, the body starts producing an immune response to the proteins and enzymes in the dust. After that, even a tiny amount - a puff from a bag of flour, a dusting on a bench - can trigger streaming eyes, a blocked nose, wheezing and a tight chest. This is not an irritation that fades once the air clears. It is a fixed change in how that person reacts, and it usually stays with them for life.
Flour dust earns this reputation because it is a mixture of biologically active material. The wheat proteins themselves are sensitisers, and so are the enzyme additives - amylase in particular - used to improve dough. HSE lists flour dust and these enzyme additives together as the second most common cause of occupational asthma in Britain, and the rate of new cases among bakers is now the highest of any occupation in any industry. Baker's asthma is not a rare event at the far edge of the risk curve. It is a routine, well documented outcome of poorly controlled dust.
The reason it slips past people is the particle size. Flour that feels soft and settles quickly to the eye still contains a fine, respirable fraction small enough to stay airborne for many minutes and to travel deep into the lungs. Tipping, sieving, dusting, scaling and cleaning down with a brush all throw this fraction into the breathing zone, where you cannot see it and do not feel it going in.
Flour dust has a Workplace Exposure Limit (WEL) under COSHH: a long-term limit of 10 mg/m₂ averaged over eight hours, and a short-term limit of 30 mg/m₂ averaged over 15 minutes. It is tempting to treat those figures as a pass mark - stay under them and you are fine. That reading is wrong, and it is exactly where a lot of bakeries and food producers get caught out.
Because flour dust is a sensitiser, the law does not simply ask you to stay below the WEL. It asks you to reduce exposure as far below the limit as is reasonably practicable. HSE's own good-practice position is that with well designed control, less than 2 mg/m₂ over eight hours is usually achievable - a fifth of the legal ceiling. And there is a harder truth underneath that: ill-health effects have been reported in some cases at exposures below 0.5 mg/m₂. In other words, meeting the WEL on paper does not guarantee your people are protected. The only safe direction of travel is downward.
This is why airborne monitoring and extraction performance matter more than housekeeping alone. You cannot judge a 2 mg/m₂ exposure by eye, and a bench that looks clean can sit in air that is quietly loading someone's lungs. Numbers, measured properly, are the only way to know where you stand.
For the person affected, the cost is a permanent condition. Baker's asthma and, less commonly, hypersensitivity pneumonitis (sometimes called baker's lung) do not clear up with a course of tablets. Once someone is sensitised, continued exposure makes them worse, and many are eventually unable to keep working around flour at all. That is a skilled team member you lose - not to a competitor, but to a hazard you were meant to control.
For the business, the consequences stack up quickly. Confirmed occupational asthma is reportable to HSE under RIDDOR 2013, which puts your workplace on the regulator's radar. From there you are exposed to enforcement action, civil claims and the disruption of an investigation, all of it turning on whether you can show you took reasonable steps to control a known, well publicised risk. With flour dust, ignorance is not a defence anyone will accept - the guidance has been clear for years.
Flour is not the only sensitising dust that behaves this way. Wood dust follows the same pattern of quiet, cumulative harm, and the parallels are worth understanding if you run any kind of mixed food or production site - our note on wood dust, the workshop hazard that is easy to underestimate, walks through the same sensitiser logic in a different setting. In both cases the substance is legal, familiar and easy to shrug off, and in both cases the damage is done long before anyone feels ill.
There is one more risk that sits alongside health. At sufficient concentration, airborne flour becomes a combustible dust with genuine explosion potential. The same fine fraction that reaches deep into the lungs is the fraction that will hang in the air and ignite. Good dust control is therefore doing two jobs at once - protecting breathing and reducing a fire and explosion hazard - which is another reason not to treat it as optional housekeeping.
Control follows a clear order, and personal protective equipment sits at the bottom of it, not the top. Start by cutting the dust at source: buy in liquid or low-dust ingredients where you can, keep tipping heights low, and stop dry brushing or blowing down with airlines - both of which put a settled hazard straight back into the air. Vacuum with a suitable filtered unit instead.
Where dust is generated - tipping bays, scaling stations, sieves, mixers and flour silos - the workhorse control is Local Exhaust Ventilation (LEV): extraction designed to capture dust at the point it is released, before it reaches anyone's breathing zone. An LEV system only earns its keep if it is designed for the task, used correctly, and kept in good order. Hoods drift out of position, ducting clogs with the very flour it is meant to remove, and fans lose performance - all invisibly, all while the system appears to run.
That is why the law requires LEV to be thoroughly examined and tested by a competent person at least once every 14 months under COSHH Regulation 9, in line with HSE guidance HSG258. A thorough examination and test is not a quick look - it measures capture and containment, checks the system against its original design intent, and gives you documented evidence that your controls are actually working. For a sensitiser like flour dust, that evidence is the difference between managing a known risk and hoping for the best. If you also want practical, day-to-day measures for the shop floor, our guide on how to reduce flour dust exposure in a bakery sets them out step by step.
Put together, these are not separate tasks - they are one system. Reduce the dust, capture what remains, measure that you have done so, and repeat on a schedule. Do that, and you protect skilled people from a life-changing condition while keeping the regulator, and your insurer, satisfied that you took the risk seriously.
Questions
Yes - the fraction that matters most is the fine, respirable dust you cannot see, which stays airborne long after any visible cloud settles and travels deep into the lungs. Flour dust is the second most common cause of occupational asthma in Britain, and effects have been reported at exposures below 0.5 mg/m₂. A clean-looking bench is no guarantee the air around it is safe, which is why airborne levels and extraction performance need to be measured rather than judged by eye.
Local Exhaust Ventilation used to control flour dust must be thoroughly examined and tested by a competent person at least once every 14 months under COSHH Regulation 9, following HSE guidance HSG258. The test checks that the system still captures dust at source and matches its original design, and it gives you documented proof your controls work. Because flour dust is a sensitiser, that evidence is central to showing you have reduced exposure as far as is reasonably practicable.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.