A COSHH assessment is the employer's written answer to one question: what is this substance going to do to the people using it, and what are we doing about it. The Control of Substances Hazardous to Health Regulations 2002 put the duty on the employer in regulation 6, and regulation 7 requires exposure to be prevented or, where that is not reasonably practicable, adequately controlled. On site, "the employer" is the subcontractor whose people are using the product, which is why a main contractor asks each trade for its own assessments.
What it is not
A COSHH assessment is not the safety data sheet. The safety data sheet is the manufacturer's description of the product. The assessment is your description of how your people use it, on this job, and what that exposure looks like. A folder of data sheets with no assessment behind them is the most common thing handed over, and it answers nothing.
It is also not a one-off. Regulation 6 requires the assessment to be reviewed when there is reason to suspect it is no longer valid or the work has changed. A silica assessment written for cutting blocks outdoors does not cover chasing walls in a closed room.
The substances that matter most on site
The ones that cause the long-term harm are dusts and fumes, not the products with the loudest labels:
- Respirable crystalline silica from cutting, grinding and chasing concrete, block and stone. The workplace exposure limit is low and the harm is silicosis and lung cancer.
- Wood dust from machining and sanding, particularly hardwood.
- Cement and wet concrete — burns and dermatitis, not just irritation.
- Isocyanates in two-pack paints and some foams, the leading cause of occupational asthma.
- Welding fume, now treated by HSE as a carcinogen whatever the metal.
- Diesel exhaust in enclosed areas.
What the assessment has to say
An assessment that a main contractor will accept, and that would stand up to an inspector, sets out:
- The substance and where it is met — which task, how often, for how long.
- The harm — what it does, by which route: breathed in, on the skin, swallowed.
- Who is exposed — including people nearby who are not doing the task.
- The controls, in the order the law prefers — eliminate or substitute first, then engineering controls such as on-tool extraction and water suppression, then ways of working, and RPE last. A dust mask is not a control strategy; it is what remains after the controls.
- The exposure limit — from EH40, looked up at the time of the assessment, because they change.
- Health surveillance and monitoring where the substance calls for it.
- Emergency action — spill, splash, inhalation.
- Who assessed it, when, and who has been briefed.
The briefing is the part that closes the loop. Regulation 12 requires people using the substance to be told what the assessment found.
What a template does not do
The assessment gives the structure, the prompts and the current exposure limit to check. It does not know which products your people carry or how they use them, and no document makes anyone compliant. A competent person in your business completes and signs it. Why we will never call a document "compliant".
Documents for this work
- COSHH Assessment — Silica Dust — the one most sites need first
- All eighteen COSHH assessments — one guided assessment per substance a site meets
- COSHH Register and Assessment Checklist — the site's register of what is on site and which assessment covers it
- Toolbox Talk — COSHH Basics — read the tin, then the sheet