COSHH Assessments: A Step-by-Step for Site Managers

COSHH, the Control of Substances Hazardous to Health Regulations 2002, covers anything on site that could harm someone through breathing it in, skin contact, swallowing, or absorption, from obvious chemicals like solvents and adhesives through to things people don't always think of as hazardous, such as cement dust, wood dust, or diesel exhaust fumes. If your site uses, stores, or generates any of these, you need a COSHH assessment covering it. Here's how to actually do one.

Step 1: Identify every hazardous substance on site

Start with a proper list, not a guess. Walk the site and check what's actually being used: cleaning products, paints and coatings, adhesives, fuels, and anything generating dust or fumes as a by-product of the work itself, like cutting, grinding, or welding. Don't forget substances that arrive as part of the work rather than being brought in deliberately, silica dust from cutting concrete or block is a common one that gets missed because nobody "brought it" to site, it's generated by the task.

Step 2: Get the safety data sheet for each one

Every hazardous substance you buy should come with a Safety Data Sheet (SDS) from the manufacturer or supplier, and if you don't have one, request it before the substance goes anywhere near the assessment. The SDS tells you the hazard classification, the exposure limits, and the manufacturer's recommended controls, which is the foundation the rest of the assessment is built on. Working from memory or a generic assumption about a product instead of its actual SDS is one of the most common ways COSHH assessments go wrong.

Step 3: Assess how exposure could actually happen

For each substance, work out realistically how someone could be exposed: inhalation of dust, vapour, or fumes, skin contact during handling, or ingestion (more common than people assume, from contaminated hands during breaks). Consider who's exposed, not just the person directly using the substance, but anyone working nearby, and how long and how often the exposure happens. A short, infrequent exposure to a substance is a different risk to prolonged daily exposure to the same thing.

Step 4: Apply the hierarchy of control

As with any risk assessment, PPE is the last line of defence, not the first. Work through, in order: can the substance be eliminated or substituted for something less hazardous, can the process be enclosed or substituted (wet cutting instead of dry, for instance, to suppress dust), can extraction or ventilation reduce airborne exposure, and only then does PPE come in as an additional control, not a replacement for the steps above it.

Step 5: Set out control measures and monitoring

Record the specific controls for each substance: engineering controls like local exhaust ventilation, safe systems of work like handling and storage procedures, and PPE where it's genuinely needed, matched to the substance (the right respirator rating for the actual hazard, not a generic dust mask). Where COSHH requires health surveillance for certain substances (isocyanates and some forms of silica exposure are common examples in construction), this needs to be built into the assessment and actually arranged, not just noted as a requirement.

Step 6: Cover storage, spills, and emergencies

A complete COSHH assessment includes how substances are stored (segregation of incompatible chemicals, secondary containment for liquids), what happens if there's a spill, and what first aid or emergency response is needed for each substance if something goes wrong. This is often the section left thinnest, and it's exactly the section that matters most if an incident happens.

Step 7: Review it, don't file it

COSHH assessments go out of date the moment the substances on site change, whether that's a new product, a new supplier with a different formulation, or a new task generating a hazard that wasn't there before. Building a review point into the job, rather than writing the assessment once at the start and never touching it again, is what keeps it actually reflecting what's happening on site.

COSHH assessments sit alongside the rest of your site's RAMS, and get reviewed the same way, as part of a document that reflects the actual job rather than a generic template. If your site's paperwork needs bringing together properly, that's the kind of document I write for UK construction sites. You can see the RAMS writing service here.