COSHH Risk Assessments: Controlling Hazardous Substances
From cleaning products to welding fume, hazardous substances are part of daily work in most UK organisations. A COSHH risk assessment is how you control them. This guide explains what COSHH covers, how exposure happens, the hierarchy of control and how to use a safety data sheet.
What COSHH covers
COSHH stands for the Control of Substances Hazardous to Health Regulations 2002. The regulations require employers to prevent or adequately control employees' exposure to substances that can harm health. They sit alongside the general duty to assess risk under the Management of Health and Safety at Work Regulations 1999, but deal specifically with substances rather than the workplace as a whole.
"Hazardous substances" is broader than people often assume. It includes chemicals and products that contain them, fumes, dusts, vapours, mists, gases, and biological agents. Common examples are cleaning chemicals, paints and adhesives, wood and flour dust, solvents, and the fume produced by soldering or welding. COSHH does not cover lead, asbestos or radioactive substances — these have their own separate regulations.
If a substance carries a hazard pictogram on its label, or a job creates dust or fume, COSHH almost certainly applies. The test is whether it could harm health, not whether it looks dangerous.
How exposure happens
To control a substance you first have to understand how it gets into the body. There are four main routes of exposure:
- Inhalation — breathing in dust, fume, vapour or gas. This is the most common route in the workplace.
- Skin contact and absorption — substances landing on or soaking through the skin, sometimes causing dermatitis.
- Ingestion — swallowing, usually accidentally via contaminated hands, food or drink.
- Injection — substances entering through a cut or puncture, for example a contaminated needle or high-pressure equipment.
Your assessment should think about who is exposed, by which route, how often, and for how long. The general method is the same as any risk assessment — if you need a refresher, see our walkthrough of how to write a risk assessment and the five steps to risk assessment.
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The hierarchy of control
COSHH expects you to control exposure by working through measures in order of effectiveness, not by reaching straight for masks and gloves. The hierarchy runs roughly as follows:
- Eliminate — stop using the substance, or change the process so it is no longer needed.
- Substitute — swap it for a safer alternative or a less hazardous form, such as pellets instead of powder.
- Engineering controls — enclose the process or fit local exhaust ventilation to capture fume and dust at source.
- Organisational and procedural controls — limit how many people are exposed and for how long, with safe systems of work.
- Personal protective equipment (PPE) — respirators, gloves and eye protection, used as the last line of defence and never as the only one.
Where the regulations set a Workplace Exposure Limit (WEL) for a substance, exposure must be kept below that limit and reduced as far as is reasonably practicable. Controls also need to be maintained — for example, ventilation should be examined and tested regularly to confirm it still works.
Reading a safety data sheet
The safety data sheet (SDS) is your most useful source of information. Suppliers must provide one for hazardous products, and it follows a standard 16-section format. The sections most relevant to your COSHH assessment are: hazard identification (Section 2), composition (Section 3), first-aid measures (Section 4), handling and storage (Section 7), and exposure controls and personal protection (Section 8). Section 8 will tell you whether an exposure limit applies and what protective measures the supplier recommends.
Remember that the SDS describes the product in general — it is not your risk assessment. Your job is to take that information and apply it to how the substance is actually used in your workplace.
✓ Key takeaways
- COSHH 2002 requires employers to prevent or adequately control exposure to hazardous substances.
- It covers chemicals, dusts, fumes, vapours and biological agents, but not lead, asbestos or radioactive material.
- Exposure occurs by inhalation, skin contact, ingestion or injection.
- Apply the hierarchy of control: eliminate, substitute, engineering, procedural, then PPE.
- Use the supplier's safety data sheet — especially Sections 2 and 8 — to inform, but not replace, your assessment.
Keeping it current
A COSHH assessment, like any risk assessment, must be reviewed when something changes — a new product, a new process, or a change in how much is used. Train the people who work with substances so they understand the hazards and use the controls correctly, and keep records of any health surveillance where it is required. Controlled well, hazardous substances can be handled safely; controlled poorly, they cause the kind of long-term ill health that is hard to undo.