Phoenix Journal · LEV & Air Quality
Occupational asthma is one of the most common and most under-recognised work-related lung diseases in Britain. What makes it dangerous is not that the causes are exotic, but that they are ordinary: the flour in a bakery, the fume off a soldering iron, the mist from a paint gun. The trigger is usually sitting in plain sight.
Occupational asthma is an allergic response to something breathed in at work. Certain substances, called respiratory sensitisers or asthmagens, can cause a permanent change in the airways so that the lungs become hypersensitive. Not everyone exposed becomes sensitised, but once a person is, further exposure, even at very low levels, can trigger an attack. The HSE is clear that there is very little information on how much exposure is needed to induce that sensitised state, which is exactly why controlling exposure matters so much: you cannot know in advance who will react, or to how little.
The cruel feature of the disease is timing. Symptoms often appear hours after exposure, sometimes in the evening or at night, long after the person has left the workshop. That delay breaks the obvious link between cause and effect, so the cough, wheeze or breathlessness gets blamed on a cold, on getting older, on anything but the job. By the time the pattern is recognised, the damage may already be permanent, and for some people it ends the career they trained for.
The scale is easy to miss precisely because the disease is scattered across trades rather than concentrated in one place. Chest physicians report bakers as having one of the highest incidence rates of occupational asthma of any occupation, with flour and grain dust the second most commonly reported cause after isocyanates. A simple habit helps catch the risk before it catches a worker: check the safety data sheet, because a material that can cause asthma if inhaled carries the standardised hazard statement H334, and older labels used the risk phrase R42, may cause sensitisation by inhalation.
The usual suspects
The HSE's own casework points to a short list of repeat offenders. Isocyanates, found in two-pack spray paints and some foams and glues, are the most commonly cited cause and carry one of the lowest exposure limits of any substance. Flour and grain dust make baking one of the highest-risk trades. Wood dust, especially from hardwoods and MDF, sits behind a large share of woodworking cases. Then come rosin-based solder flux fume (colophony), latex, laboratory animals, cleaning products and enzymes, aldehydes such as glutaraldehyde, and welding fume, particularly from stainless steel.
What ties them together is how mundane they are. None of these look like poison. They are the raw materials of ordinary trades, which is precisely why the risk is so easy to walk past. The reassuring part is that the national trend has fallen as exposures were brought under control, which is the clearest evidence there is that managing the substance manages the disease.
High-risk groups read like a directory of skilled trades: bakers and food manufacturing, vehicle paint sprayers, woodworkers, welders, healthcare and cleaning staff, electronics repairers and anyone working with metalworking fluids. If your workshop touches any of these, occupational asthma is not a remote possibility. It is a named, foreseeable risk you are expected to manage.
Where control starts
Because sensitisation can happen at very low doses, the goal is not to keep exposure under a limit but to keep it as low as reasonably practicable. That means working down the hierarchy of control rather than reaching straight for a dust mask. Can the sensitiser be eliminated or swapped for a safer material? Can the process be enclosed or automated? Where exposure remains, local exhaust ventilation should capture the contaminant at source before it reaches anyone's breathing zone, with respiratory protection as the last line rather than the first. Opening a roller door and running a pedestal fan is not control; it just moves the problem around the room.
The one that gets overlooked
Sensitisers are not only powders. Welding, soldering and spraying all throw respirable fume and mist that carry asthmagens deep into the lungs, and the finest of it is invisible in normal light. Managing that means treating extraction as a health control, not a comfort feature: capturing the plume at the arc or the tip, and checking it actually works. It is worth reading how to manage welding fume beyond just buying extraction, because a unit that is switched off, badly positioned or never tested protects nobody. Add health surveillance for exposed staff so early symptoms are caught while modifying exposure can still make a difference, and the disease stops being something you only discover once it is too late. Metalworking fluid mist belongs on the same list, since it can sensitise the airways yet is easily dismissed as mere oily haze.
Questions
Occupational asthma is caused by becoming sensitised to a specific substance at work, so that later exposure triggers attacks. Work-aggravated asthma is pre-existing asthma that irritants at work, such as dust or cold air, make worse. Both matter, but occupational asthma is the one that can be prevented by controlling the sensitiser.
It varies. Sensitisation can take months or years of exposure, and there is no reliable way to predict who will react or at what dose. Once someone is sensitised, symptoms can be triggered by very low levels, which is why the aim is to keep exposure as low as reasonably practicable rather than simply under a limit.
Where the assessment shows a reasonable likelihood of disease, for example exposure to isocyanates or flour, health surveillance is a legal requirement under COSHH, not an optional extra. Catching early symptoms lets you modify a worker's exposure before the damage becomes permanent.
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