Respiratory sensitisers vs irritants

Respiratory sensitisers

A respiratory sensitiser causes an allergic reaction in the airways. The first exposures may cause nothing at all, but once a person becomes sensitised the immune system treats that substance as an enemy for good. After that, even a trace in the air can trigger a full asthma attack - tightness, wheeze, breathlessness. This is the mechanism behind most cases of occupational asthma, and the change is usually permanent. In kitchens the usual suspects are flour and grain dust at the bakery bench, some enzyme-based and quaternary ammonium cleaning products, ethanolamines in heavy degreasers, and latex in older gloves.

On a label or safety data sheet, look for the CLP hazard statement H334: “May cause allergy or asthma symptoms or breathing difficulties if inhaled”, and for the ‘Sen’ notation against a substance in the HSE’s EH40/2005 Workplace Exposure Limits list.

Where you have some control

• They are named and traceable - H334 and the ‘Sen’ notation flag them clearly on the paperwork.
• Substitution often works: a lower-dust flour handling method or an enzyme-free sanitiser removes the hazard at source.
• Good LEV captures the dust or mist before it reaches the breathing zone, which is the single most effective engineering control.

Where they bite

• There is no safe dose once someone is sensitised - a level that passes a Workplace Exposure Limit can still trigger an attack.
• The damage is usually for life, so a sensitised worker may have to leave the trade altogether.
• Because sensitisers can slip past the numerical limit, the law expects exposure to be reduced As Low As Reasonably Practicable (ALARP), not merely below the WEL.

Respiratory irritants

An irritant works by chemical assault rather than allergy. Breathe in enough and it inflames the nose, throat and airways there and then - stinging eyes, coughing, a raw chest. Classic kitchen irritants are chlorine released when bleach meets an acid or ammonia cleaner, ammonia itself, and the sulphur dioxide (SO₂) and nitrogen oxides (including NO₂) that come off gas ranges and char-grills. Irritants generally follow a dose-response rule: the more there is in the air, the worse the effect, and the effect tends to ease once the person gets clean air.

That makes irritants more predictable than sensitisers - but do not mistake predictable for harmless. High single exposures can cause lasting damage, and repeated low-level irritation can leave an airway raw and reactive. Irritants will also set off anyone who already has asthma, occupational or not.

Where you have some control

• They usually warn you - the smell, the sting and the cough give an immediate signal that levels are too high.
• Effects are dose-related, so cutting the concentration with ventilation and dilution genuinely reduces harm.
• Many incidents are avoidable procedure failures, such as mixing bleach with an acidic descaler, that training and clear signage can stop.

Where they bite

• A single heavy exposure - a cloud of chlorine gas in a closed room - can cause severe, sometimes permanent injury.
• Repeated irritation may lead to irritant-induced asthma and worsen existing lung conditions.
• Because the effect fades with fresh air, people underestimate the risk and skip the extraction or the respirator.

What the rules actually require

Whichever hazard you are dealing with, COSHH puts the same duty on you: assess the risk, control it at source, and keep that control working. Local exhaust ventilation - canopy hoods, downdraught benches, spot extraction over a cleaning station - is the workhorse control for airborne kitchen contaminants. The HSE’s guidance document HSG258, “Controlling airborne contaminants at work”, sets out how a system should be designed, commissioned and checked across its whole life.

The legal backstop is Regulation 9 of COSHH. It requires that LEV is thoroughly examined and tested by a competent person at least once every 14 months - and for some high-risk processes, more often. Competent testers typically hold the BOHS P601 qualification, and a proper thorough examination measures capture performance, not just that a fan spins. For a sensitiser especially, that measured evidence matters, because ALARP means you have to show the air is as clean as it reasonably can be, not simply that it scrapes under a limit.

The practical takeaway is simple. Treat irritants as a concentration problem you manage with good ventilation, sensible procedures and quick response to spills or mixing errors. Treat sensitisers as a substance you keep out of the air altogether wherever you can, because once someone reacts there is no dialling it back. In both cases, the extraction is only a control if it is proven to work - and that proof is exactly what statutory LEV testing exists to give you. It also pairs naturally with the wider hygiene picture, so it is worth knowing your TR19 Grease and TR19 Air terms before you next commission a clean or a test.