What Is COSHH? A Plain Guide for Site Workers and Employers

What is COSHH? It's the Control of Substances Hazardous to Health Regulations 2002, the law on harmful substances at work in England, Wales and Scotland. Your employer has to stop those substances getting into your lungs, onto your skin or into your body. Where that isn't reasonably practicable, they have to keep your exposure under adequate control. It covers far more than the tins in the store.

Most people meet COSHH as a folder of safety data sheets in the site office. On a building site, though, some of the most harmful exposures are ones you make yourself. Silica dust from a cut-off saw and wet cement on your forearms never come with a data sheet. What protects you is an assessment of the task, and a folder of data sheets isn't one.

What counts as a hazardous substance under COSHH

HSE's list takes in chemicals and products that contain them, fumes, dusts, vapours, mists, gases and biological agents, which are the germs that cause disease. Liquids, gels and powders that get on your skin or in your eyes count too. If the packaging carries a hazard symbol, HSE treats the product as hazardous. Regulation 2 goes further and brings in dust of any kind once it's in the air above set levels.

Substance	Where you meet it	What HSE says it can do
Wet cement, concrete and mortar	Mixing, laying, screeding, kneeling in a pour	Burns and ulcers if trapped against skin, and dermatitis
Silica dust	Cut-off saws on paving, blocks and kerbs, chasing, scabbling	Lung cancer, silicosis, COPD and asthma
Wood dust	Cutting and sanding with power tools	Asthma, four times more common in carpenters and joiners than in other UK workers
Solvents	Paints, paint strippers, thinners and glues	Headaches, nausea and dizziness, and dermatitis or liver, kidney and nerve disease after repeated exposure
Isocyanates	Polyurethane paints, foams, glues and flooring	Occupational asthma, dermatitis, and irritated eyes, nose and throat
Germs	Old water systems, rats, sewage, dirty cuts	Legionnaires' disease, Weil's disease, hepatitis A, tetanus

Examples from HSE's construction hazardous substances guidance, checked October 2026.

If your work appears in the middle column, the substance beside it belongs in your COSHH assessment.

Wet cement can cause a serious burn quickly if it's trapped against your skin, inside a glove or a boot. The chromium in it can cause allergic dermatitis. HSE says the additive that cuts that risk only works until the shelf date on the bag, so check the date.

Silica is the big one. HSE puts the workplace exposure limit at 0.1 mg/m3 averaged over eight hours. Dry cutting paving or kerbs with a cut-off saw can produce peaks of up to 70 mg/m3. HSE also says over 500 construction workers "are believed to die from exposure to silica dust every year". That's HSE's own estimate, so treat it as one.

Legionella, from old or badly kept water systems, is one of the germs COSHH covers. For the duties around water systems, see legionella awareness training.

What COSHH doesn't cover

Lead, asbestos and radioactive substances sit outside COSHH, because each has its own regulations. Regulation 5 names the Control of Lead at Work Regulations 2002 and the Control of Asbestos Regulations 2012. If you're stripping old paint that may contain lead, or you find something you think is asbestos, COSHH isn't the rulebook. For what the asbestos rules ask, see is asbestos awareness training a legal requirement.

Regulation 5 also leaves out a substance whose only danger is that it can burn or explode, or that it's very hot, very cold or under pressure. The word that matters is "only". A thinner that's flammable and harmful to breathe is still covered for the harm to your health.

The employer's duties under the COSHH regulations

The COSHH regulations put most of the duties on the employer. Each of HSE's steps maps onto a regulation.

Step	Regulation	What it looks like on site
Assess the risks	6	Look at each task, who does it, for how long and how the substance gets in. With 5 or more employees, record the significant findings
Prevent exposure, or control it	7	Swap first, such as water-based paint for solvent-based. Then control at source, such as water suppression or on-tool extraction. PPE comes last
Make sure controls are used	8	Supervise. Extraction nobody switches on controls nothing
Keep controls working	9	Local exhaust ventilation, meaning extraction at the source, is examined and tested at least every 14 months
Monitor exposure	10	Air sampling, where the assessment shows it's needed
Health surveillance	11	For example, regular skin checks for people working with cement
Plan for accidents and emergencies	13	Spill kits, first aid and eyewash ready before work starts
Inform, instruct and train	12	Tell people the risks and show them how the controls work

Steps from HSE's COSHH basics, regulation numbers checked on legislation.gov.uk, October 2026.

If you remember one row, make it regulation 7, which puts a safer substance or process ahead of every mask and glove.

Two points catch small firms out. If you're self-employed with no staff and you work on a construction site, regulation 3 applies COSHH to you as both employer and employee. Only the duties on monitoring and health surveillance drop away. And when contractors come onto your premises, HSE says you need to know what substances they're bringing, and they need to know your controls. COSHH training sits on top of the general duty to train, which health and safety training for employees explains.

A safety data sheet is not a COSHH assessment

	Safety data sheet	COSHH assessment
Who produces it	The supplier	The employer
What it's about	One product	One task, on your site
What it tells you	The product's hazards, handling, storage and emergency measures	Who's exposed, how much, for how long, and the controls to use
Dust and fume made by the work	Not covered, because nobody supplies them	Must be covered

Based on HSE's COSHH pages and regulation 6, October 2026.

Use the data sheet as the starting point for the assessment.

Regulation 6 says the assessment must weigh things a supplier can't know, such as how much is used, how long people are exposed, maintenance work and two substances used together. "A safety data sheet is not a risk assessment," HSE says. Its COSHH FAQs add that even a good data sheet doesn't replace one. For dust and fume the work makes, HSE says to treat a substance as hazardous in the form it takes during the job.

How to read the hazard symbols on a label

The symbols are on the hazard label on the product's packaging. HSE describes them as diamonds with a red border and a white background. A product can carry more than one, and HSE lists nine.

• Exploding bomb, for explosive.
• Flame, for flammable.
• Flame over a circle, for oxidising.
• Corrosion, for corrosive.
• Skull and crossbones, for acute toxicity.
• Environment, for hazardous to the environment.
• Exclamation mark, for a health hazard or harm to the ozone layer.
• Health hazard, for a serious health hazard.
• Gas cylinder, for gas under pressure.

The label also carries a signal word, "Danger" for more severe hazards and "Warning" for less severe ones, plus statements such as "causes serious eye damage" and "wear eye protection".

Older stock may still carry the old orange square symbols. HSE's brief guide to COSHH, last revised in 2012, still prints them and says new symbols have been replacing them gradually since 2009. Give an orange square the same respect.

What COSHH expects from workers

Regulation 8 puts a duty on you as well. You have to make full and proper use of the controls you're given, put equipment back where it's kept and report any defect straight away. A few habits from HSE's construction guidance matter more than they look.

• Wash cement off your skin as soon as you can, and wash exposed skin at breaks.
• Be clean-shaven if you wear a tight-fitting mask, and get it face-fit tested.
• Vacuum dust up instead of sweeping it.
• Never use solvent to get paint or glue off your skin.

If your employer asks you to attend health surveillance, regulation 11 says you go, in working hours and at their cost. Under regulation 12, they also have to tell you the significant findings of the assessment and give you access to the safety data sheets. If your employer has no procedures at all for the chemicals you work with, HSE says you can report it to HSE or your council's environmental health officer, anonymously if you want.

COSHH training under regulation 12

Regulation 12 is the training duty. If your employer's work is liable to expose you to a hazardous substance, they must give you information, instruction and training. It has to fit the level, type and length of your exposure.

HSE says handing someone a page of written information is poor practice. Anyone using a respirator needs face fitting and training, and anyone in gloves needs to know how to take them off without contaminating their skin.

We run a COSHH Awareness course online. It teaches you to spot hazardous substances, how they get into the body, how to work to a COSHH assessment, and how to use controls and PPE and respond to incidents. The job-specific part, such as next week's products and what the assessment says about them, has to come from your employer.

Assess the job, not the tin

COSHH exists to catch the harm that labels miss. If you run a team, build the assessment from the tasks, starting with anything that gets cut, mixed, sanded or sprayed. If you're on the tools, ask what the assessment says before the first cut. For the other health risks on site, see the full range of health and safety courses.

Frequently asked questions