Phoenix Journal · LEV Testing
Flour dust is the second most common cause of occupational asthma in Great Britain, and older bakery premises make it far harder to control. Understanding the exposure limits, the ductwork problem and your LEV duties is the first step to protecting your team.
If you run a bakery in a building that has seen a few decades of service, you already know the flour gets everywhere. It settles on ledges, drifts up into roof voids and finds its way into every corner the mixer throws it. What is easy to miss is that the same fine dust is a recognised cause of long-term lung disease, and that older premises make it much harder to keep under control.
Flour dust is not a nuisance you can dust off and forget. It is a respiratory sensitiser, which means repeated exposure can leave a worker permanently reactive to it - a single lungful can then trigger an asthma attack for the rest of their working life. In a modern unit with purpose-built extraction, the risk is manageable. In a converted shop, a listed building or a bakery that has grown room by room over the years, the airflow rarely does what you need it to, and the dust lingers where people breathe.
The numbers behind the risk
Flour dust carries a Workplace Exposure Limit set by the Health and Safety Executive. The long-term limit is 10 mg/m³ averaged over an eight-hour shift, with a short-term limit of 30 mg/m³ averaged over any fifteen-minute period. Both figures matter, because bakery work comes in bursts - tipping a sack, dusting a bench or knocking back dough can spike the airborne concentration for a few minutes even when the shift average looks acceptable.
There is an important detail attached to that limit. Flour dust is flagged ‘Sen’ in the HSE list, marking it as a substance known to cause occupational asthma. Because it is a sensitiser, there is no truly safe level - the duty is to reduce exposure as far below the limit as is reasonably practicable, not simply to sit under 10 mg/m³. HSE takes the view that good control practice can usually get you below 2 mg/m³ over eight hours, and that is the figure inspectors expect a well-run bakery to be working towards.
Why older buildings are harder
The trouble with an older bakery is rarely the effort your staff put in. It is the fabric of the place working against them. Extraction that was fitted for an oven twenty years ago was never designed to capture flour dust at the point it is released, and ductwork that has been extended, rerouted or shared between processes loses the airflow it needs at each junction. The result is a system that hums away looking busy while the capture hood over the mixer barely pulls the dust off the bench.
Several features of older premises make this worse. Low ceilings and cramped rooms mean there is nowhere for dust to disperse, so it stays in the breathing zone. Roof voids and false ceilings act as reservoirs, holding decades of settled flour that shakes loose whenever the building vibrates. Original brickwork, timber and porous surfaces trap dust that a wipe-clean modern wall would shed. And where a bakery has grown organically, extraction often serves the room it was first installed in rather than the process that now sits there. You end up with strong suction over a cold store and none at all over the sieve.
Manual handling is the other pinch point. Tipping bags of flour, hand-dusting proving baskets and cleaning down with a brush all generate clouds of fine particles exactly where someone is standing. In a tight older room with weak airflow, that cloud has nowhere to go. If you want to get ahead of it, our guide on how to reduce flour dust exposure in a bakery walks through the practical changes - low-dust flour, gentler tipping, scoops instead of throwing, and vacuuming rather than sweeping - that make the biggest difference before any engineering work.
What the law asks of you
Where you rely on extraction to control flour dust, that equipment counts as Local Exhaust Ventilation under the Control of Substances Hazardous to Health Regulations. That brings a specific, non-negotiable duty: LEV must be thoroughly examined and tested at least once every fourteen months, and the results kept for at least five years. The examination is not a quick look - it checks that each hood is capturing dust at the source, that airflow through the ducting meets the design intent, and that the system as installed still does the job it was fitted to do. In an older bakery where ducts have been altered over time, this is often the moment the gaps come to light.
The duty does not stop at the machinery. Because flour dust is a sensitiser, health surveillance is required for anyone exposed to it - a structured programme, run by a competent occupational health provider, to catch the early signs of breathing trouble before they become permanent. The reason for all of this is stark: flour dust and the enzymes added to some flours are the second most common cause of occupational asthma in Great Britain, and bakers develop the condition at many times the rate of the general working population. If you want to understand the mechanism, we explain why flour dust is a respiratory sensitiser and what that means for the people on your benches.
HSE has been running targeted inspections of bakeries, and a system that is out of test date, or that has never been tested at all, is one of the first things an inspector looks for. Getting your extraction examined properly is not box-ticking - it is the evidence that the control you rely on actually works, and the single clearest way to show you are meeting your duty of care.
Questions
Flour dust has a long-term Workplace Exposure Limit of 10 mg/m³ averaged over an eight-hour shift, and a short-term limit of 30 mg/m³ over any fifteen-minute period. Because flour dust is a respiratory sensitiser, the legal duty is to keep exposure as far below these limits as is reasonably practicable rather than just under them. HSE considers that good control practice can usually achieve less than 2 mg/m³ over eight hours.
Where you rely on extraction to control flour dust, it counts as Local Exhaust Ventilation under COSHH and must be thoroughly examined and tested at least once every fourteen months. The test checks that each hood captures dust at source and that airflow through the ducting still meets the original design. You should keep the report for at least five years, as it is often the first thing an HSE inspector asks to see.
Older buildings tend to have extraction that was never designed for flour dust at the point it is released, along with altered or extended ductwork that has lost airflow at the junctions. Low ceilings, roof voids and porous original surfaces all trap and hold settled dust in the breathing zone. The result is that flour lingers exactly where staff are working, making the exposure limits much harder to meet without proper testing and improvement.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.