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The Control of Substances Hazardous to Health Regulations 2002, known as COSHH, require employers to prevent or adequately control exposure to hazardous substances. Regulation 6 says you cannot carry out work that could expose people to them until you have assessed the risks. If you are new to COSHH, start with our guide what is COSHH?
What counts as a hazardous substance?
- Chemicals classified as hazardous, which carry hazard symbols
- Substances with a workplace exposure limit
- Dusts in substantial concentrations, such as silica and wood dust
- Fumes and gases produced by work, such as welding fume and diesel exhaust
- Biological agents, such as legionella or leptospira
Asbestos, lead and radioactive substances have their own regulations.
The steps
- List the substances and processes. Include those you buy and those your work creates, such as dust and fume.
- Find the hazards. Use the label and section 2 and 8 of the safety data sheet.
- Decide who could be exposed and how. Inhalation, skin contact, ingestion or injection, including cleaners, maintenance staff and visitors.
- Estimate the exposure. How much, how often and for how long, compared with any exposure limit.
- Decide the controls. Work through the hierarchy: eliminate, substitute, enclose, extract, then PPE.
- Record the findings. Required if you employ five or more people, and good practice anyway.
- Put it into practice. Train people, maintain controls, and arrange monitoring and health surveillance where needed.
- Review it. When things change, and regularly.
The principles of good practice
Schedule 2A of COSHH sets out eight principles for control. In short: design processes to minimise emission; consider all routes of exposure; make controls proportionate to the risk; choose the most effective and reliable options; use PPE only in combination with other controls; check and review controls regularly; inform and train everyone; and make sure the controls do not increase overall risk.
Worked example: cutting concrete kerbs
| Step | Findings |
|---|---|
| Substance | Respirable crystalline silica (RCS) dust created when cutting concrete with a petrol cut-off saw. |
| Hazard | RCS can cause silicosis, lung cancer and COPD. It has a workplace exposure limit of 0.1 mg/m³ as an 8 hour average. |
| Who | The saw operator, the labourer nearby, and other trades or the public downwind. |
| Exposure | Dry cutting can produce very high dust levels in seconds, well above the limit. |
| Controls | Order kerbs to size where possible to avoid cutting. Where cutting is needed, use water suppression on the saw, keep the water supply topped up, and use FFP3 or equivalent RPE that has been face fit tested. Keep others out of the dust cloud. |
| Other | Clean up wet slurry rather than dry sweeping. Health surveillance for regular cutters. Toolbox talk before work starts. |
Our guide to protecting stone workers from silica dust and our face fit testing guide cover these controls in more depth.
Monitoring and health surveillance
Regulation 10 requires exposure monitoring in some situations, such as where you need to check that exposure stays below a limit. Local exhaust ventilation must be thoroughly examined and tested at least every 14 months. Regulation 11 requires health surveillance where there is a known disease linked to the substance and a reasonable chance it could occur.
Training that helps
Our COSHH awareness training, COSHH spill kit training and COSHH eLearning cover the essentials for staff. For people who write assessments, the NEBOSH National General Certificate and NEBOSH Managing Risks cover chemical risk assessment and control in depth.
Frequently asked questions
Is a COSHH assessment a legal requirement?
Yes. Regulation 6 of COSHH requires a suitable and sufficient assessment before work that could expose people to hazardous substances.
Who should carry out a COSHH assessment?
A competent person who understands the work, the substances and the regulations. In practice this is often a manager or supervisor with support from a health and safety advisor.
Is a safety data sheet the same as a COSHH assessment?
No. The safety data sheet describes the substance. The COSHH assessment looks at how it is used in your workplace and what controls are needed.
How often should COSHH assessments be reviewed?
Whenever there is reason to think they are no longer valid, such as a new process, a change in substances or a health surveillance result, and regularly as good practice.
Read the source
The Control of Substances Hazardous to Health Regulations 2002, regulations 6 to 13 and Schedule 2A; HSE L5, the COSHH Approved Code of Practice; HSE EH40/2005 Workplace exposure limits; and HSE guidance on silica in construction. Facts checked on 6 October 2026.
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