What Is a COSHH Assessment and How Do You Do One?
Pro Site Docs · Guide
If your work involves dust, fumes, chemicals, or any substance that could harm health, you'll need a COSHH assessment. It's one of the most common documents asked for on site — and one of the most misunderstood.
Here's a clear guide to what COSHH is, when you need an assessment, and how to actually carry one out.
What is COSHH?
COSHH stands for the Control of Substances Hazardous to Health Regulations. In plain terms, it's the law that requires employers and contractors to control substances that can harm people's health at work.
In construction, hazardous substances are everywhere: silica dust from cutting concrete or stone, cement, solvents, adhesives, paints, wood dust, fumes from welding, and many more. COSHH exists because these substances cause real, serious harm — conditions like silicosis, occupational asthma and dermatitis — often years down the line.
When do you need a COSHH assessment?
You need one whenever work involves a substance hazardous to health. That covers a huge amount of construction work — if you're cutting, grinding, mixing, painting, gluing, or generating dust or fumes, COSHH almost certainly applies.
The assessment is what shows you've identified the hazardous substances, understood the risk, and put controls in place to protect people.
How to do a COSHH assessment
A proper COSHH assessment works through these steps:
1. Identify the hazardous substances. List everything on the job that could harm health — dusts, chemicals, fumes. Safety data sheets (from suppliers) tell you what's hazardous and how.
2. Assess who could be harmed and how. Consider your workers, other trades, and how exposure happens — breathing it in, skin contact, swallowing.
3. Evaluate the risk. How much exposure, how often, how harmful the substance is.
4. Decide on control measures. Work through the hierarchy: can you avoid the substance entirely? Use a less harmful alternative? Control it at source (e.g. water suppression or on-tool extraction for dust)? Only then rely on PPE like masks and respirators.
5. Record it and act on it. Write it down, put the controls in place, and make sure people actually follow them.
6. Review it. If the work, substances or conditions change, the assessment needs updating.
The silica dust point worth stressing
If there's one COSHH risk that gets overlooked far too often, it's respirable crystalline silica — the fine dust from cutting or grinding concrete, stone, brick and mortar. It's one of the biggest killers in construction, and controlling it (water suppression, extraction, proper RPE) should be front and centre of any relevant COSHH assessment. Reviewers know this, so a COSHH assessment that ignores dust control on a cutting job won't wash.
Common mistakes
- Generic assessments that don't reflect the actual substances on the job.
- Relying only on PPE instead of controlling the hazard at source first.
- Ignoring dust — treating it as less serious than chemicals.
- Never reviewing — using an old assessment that no longer matches the work.
The bottom line
A COSHH assessment isn't paperwork for its own sake — it's how you stop substances on site causing lasting harm. Identify what's hazardous, work out who's at risk, control it at source before reaching for a mask, write it down and keep it current. Do that and you're protecting your people and staying compliant.
Use our ready-made COSHH assessment templates covering cement, silica, diesel, solvents and more, or start with free templates.