Phoenix Journal · LEV Testing
Occupational asthma is asthma caused by something you breathe in at work, and it can develop in someone who has never had a breathing problem in their life. Here is how the exposure turns into lasting disease - and how proper extraction control stops it.
Occupational health · respiratory risk
Occupational asthma is asthma caused by something you breathe in at work, and unlike ordinary asthma it can start in an adult who has never wheezed a day in their life.
It is one of the most common work-related lung diseases in the country, and the frustrating part is that it is almost entirely preventable. Estimates put the share of adult asthma linked to workplace exposure at somewhere between 9 and 15 per cent - a large slice of a very common condition. The people most at risk are not doing anything reckless. They are bakers, spray painters, welders, woodworkers, cleaners, hairdressers, healthcare staff and kitchen workers who simply turn up and do their job in air that has not been properly controlled.
Understanding how the exposure turns into disease matters, because the mechanism explains why the usual defences - opening a window, wearing a paper mask, feeling fine for months - so often fail. The damage builds quietly, and by the time symptoms are obvious the sensitisation may already be permanent. Here is how it actually happens, step by step.
The mechanism above carries a hard lesson: personal toughness is irrelevant. You cannot feel yourself becoming sensitised, you cannot train your lungs to cope, and a dust mask pulled on halfway through a shift does little once fine particles are already in the air. The only reliable defence is stopping the sensitiser reaching the breathing zone in the first place, and under the Control of Substances Hazardous to Health Regulations that duty sits squarely with the employer.
For sensitisers the law goes further than a simple limit. Because these substances can cause harm at very low doses, exposure must be reduced to as low as is reasonably practicable, even where a published workplace exposure limit exists and even where air sampling shows you are under it. Some of those limits are strikingly tight - the limit for isocyanates, the single most common cause of occupational asthma in the UK, is just 0.02 mg/m³ averaged over eight hours. Flour dust carries a limit of 10 mg/m³ over eight hours, yet ill health has been reported well below that, which is why controlling to the lowest practicable level - not merely to the number - is the standard the regulator expects.
In practice, that control almost always means local exhaust ventilation - LEV, or extraction - capturing the dust, fume or mist at the point it is generated, before it drifts into the room. A hood over a mixing bowl, a downdraught bench in a spray booth, an on-tool extractor on a sander, a soldering-fume arm: each is designed to pull the hazard away from the worker's face. The catch is that LEV degrades. Ducts clog, filters load up, fans lose pull and dampers seize, all without any visible sign that the system is no longer doing its job. A very common finding in inspections of bakeries, woodworking shops and paint facilities is extraction that exists on paper but has quietly stopped protecting anyone.
That is why the same regulations require every LEV system to undergo a thorough examination and test at least every 14 months, and more often for higher-risk processes. The test confirms the system still captures what it is meant to capture, to the airflow the designer intended - the objective evidence that your control measure works, rather than a hopeful assumption that it does. Mandatory health surveillance for exposed workers sits alongside it, so that early sensitisation is picked up through questionnaires and lung-function checks before it becomes irreversible.
Kitchens and food production are far from immune. Flour dust in a busy bakery kitchen, cleaning-chemical mists in a wash-up area, and the general question of what people are breathing indoors all belong to the same conversation - one we explore further in our look at the occupational asthma causes hiding in plain sight and in our guide to sick building syndrome causes and practical fixes. The thread running through all of them is the same: air you cannot see is still air someone has to breathe.
Occupational asthma is preventable, but only where employers treat exposure control as an active, tested discipline rather than a one-off installation. The figures below capture why the margins are so tight and why regular verification matters.
If any of your processes generate dust, fume, mist or vapour that people breathe, the safest assumption is that control is only as good as its last test. Prove it, record it, and act on what the test tells you.
Questions
Yes, and this catches many people out. Sensitisation - the point at which your immune system starts reacting to a substance - can take weeks, months or even years to develop, so long service offers no protection. A worker who has handled flour or paint safely for a decade can still become sensitised and then react to tiny amounts of it.
Not necessarily. For respiratory sensitisers the law requires exposure to be reduced to as low as is reasonably practicable, even where you are below the published limit, because harm can occur at very low doses. Staying under the number is a floor, not a finish line, and control at source through effective extraction is expected alongside it.
Local exhaust ventilation must undergo a thorough examination and test at least every 14 months under COSHH, and more frequently for higher-risk processes. Because ducts clog, filters load and fans lose pull without any visible sign, testing is the only objective proof the system still captures the hazard. Employers also have a duty to carry out health surveillance for exposed workers.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.