What is COSHH?

COSHH stands for the Control of Substances Hazardous to Health Regulations 2002 (as amended). It is a UK law that requires employers to control exposure to substances that can harm health.

What counts as a hazardous substance

COSHH covers a wide range of materials, not just obvious chemicals.

• Chemicals and chemical products, such as cleaning fluids, solvents, paints and adhesives
• Fumes, including welding fumes and exhaust fumes
• Dusts, including wood dust and silica dust, especially at high concentrations
• Vapours and gases released during work processes
• Mists, such as those from spray painting or coolant mist from machining
• Nanotechnology materials
• Biological agents, including bacteria and other micro-organisms, if a worker's normal work brings them into contact with these
• Germs that cause disease, found in materials such as sewage, blood and other bodily fluids or fluids from patients, and clinical waste

What COSHH does NOT cover

This is a classic trap in awareness tests, so learn it well.

• Asbestos, which has its own separate law: the Control of Asbestos Regulations 2012
• Lead, which is covered by the Control of Lead at Work Regulations 2002
• Substances that are hazardous purely because of radioactivity, explosive or flammable properties at extreme temperature or pressure, or purely because of their physical state, unless they are also hazardous to health

The eight-step approach employers must follow

HSE guidance sets out a simple structure for COSHH compliance.

• Assess the risks to health from hazardous substances used or created by the work
• Decide what precautions are needed
• Prevent or adequately control exposure
• Ensure control measures are used and maintained
• Monitor exposure where necessary
• Carry out health surveillance where appropriate
• Prepare plans and procedures to deal with accidents, incidents and emergencies
• Ensure employees are properly informed, trained and supervised

Common mistakes to avoid

• Assuming COSHH only means bottled chemicals. It also covers dust, fumes, vapours and biological agents
• Forgetting that asbestos and lead sit outside COSHH under their own regulations
• Thinking a substance is only hazardous if it is labelled with a hazard symbol. Some naturally occurring or generated substances, like wood dust, are still covered
• Believing COSHH assessments are a one-off task. They must be reviewed regularly and whenever the work changes

What COSHH covers

COSHH stands for the Control of Substances Hazardous to Health Regulations 2002 (as amended). It applies to any substance at work that can harm health - not just things labelled 'toxic'. This includes chemicals, dusts, fumes, vapours, gases, mists, nanotechnology, biological agents (bacteria and other microorganisms), and even naturally occurring substances like flour dust or wood dust.

Substances NOT covered by COSHH

• Asbestos - has its own law, the Control of Asbestos Regulations 2012.
• Lead - covered by the Control of Lead at Work Regulations 2002.
• Substances hazardous only because of radioactivity, high pressure, or extreme temperature - these fall under other regulations.
• Common mistake: candidates assume asbestos falls under COSHH. It does not - remember it has its own dedicated regulations.

The four routes of entry into the body

• Inhalation - breathing in dust, gas, vapour, fume or mist. This is the most common route and often the fastest way a substance reaches the bloodstream and lungs.
• Skin (dermal) absorption - substances passing through unbroken skin, or through cuts and abrasions. Some solvents pass through skin easily even without any injury present.
• Ingestion - swallowing a substance, often accidentally from contaminated hands, food, drink or cigarettes at the workbench.
• Injection (inoculation) - a substance entering through a puncture wound, cut, or needle-stick injury, forcing material directly into tissue or the bloodstream.

Why routes of entry matter

Knowing the route tells you which control measure actually works. Respiratory protective equipment (RPE) stops inhalation but does nothing for a skin hazard; gloves stop dermal contact but do nothing for inhalation. A common exam trap is picking one control (like gloves) and assuming it covers every route - always match the control to the specific route of entry.

Common mistakes to avoid

• Thinking a substance must be labelled with a hazard symbol to be covered by COSHH - it does not; harmful natural dusts and biological agents count too.
• Forgetting that ingestion can happen from poor hygiene (eating with contaminated hands), not just deliberately swallowing something.
• Overlooking injection as a route - needle-stick and puncture injuries in workshops and healthcare settings are a real and testable route of entry.
• Assuming skin absorption needs broken skin - many chemicals penetrate healthy, unbroken skin.

Why hazard symbols matter

Every hazardous substance you meet at work should carry standardised warnings so you know the risk before you open the container. In GB/EU workplaces this is the CLP system (Classification, Labelling and Packaging), which uses nine red-diamond pictograms called GHS hazard pictograms. These replaced the old orange square symbols years ago, so if you still see an orange square hazard sign, treat the info as out of date.

The nine GHS pictograms

• Flame - flammable substances
• Flame over circle - oxidising substances
• Gas cylinder - gases under pressure
• Corrosion - corrosive to metal or skin, causes burns
• Skull and crossbones - acute toxicity, can kill in small doses
• Exclamation mark - lower-level hazards e.g. irritant, harmful, drowsiness
• Health hazard (person with starburst chest) - carcinogen, respiratory sensitiser, reproductive toxin
• Environment - toxic to aquatic life
• Exploding bomb - explosives or self-reactive substances

Each pictogram is a red diamond on a white background - that shape and colour combination is what makes it instantly recognisable, so learn the shape as well as the picture inside it.

Signal words and statements

Labels also carry a signal word: 'Danger' for the more severe hazards, 'Warning' for less severe ones. Alongside this sit H-statements (Hazard statements, e.g. H314 'causes severe skin burns') and P-statements (Precautionary statements, e.g. P280 'wear protective gloves'). You do not need to memorise every code number, but you must know that H = hazard and P = precaution.

Safety Data Sheets (SDS)

A Safety Data Sheet must be supplied by the manufacturer or supplier for every hazardous substance and must follow a fixed 16-section format (this is a legal requirement under REACH/CLP, not optional guidance). Key sections to know:

• Section 2: Hazard identification
• Section 4: First aid measures
• Section 7: Handling and storage
• Section 8: Exposure controls / PPE
• Section 11: Toxicological information

The SDS is not the same as the product label - the label gives quick on-the-spot warnings, the SDS gives full technical detail for risk assessment and emergency response.

Common mistakes

• Confusing the exclamation mark (irritant) with the skull and crossbones (acute toxicity) - the exclamation mark is a lower hazard band
• Assuming an unlabelled container is safe - COSHH requires all hazardous substances to be correctly labelled and stored
• Thinking the SDS is optional paperwork - it is a legal requirement and must be accessible to anyone who could be exposed

What risk assessment means under COSHH

A COSHH risk assessment is a legal duty on the employer before any work with a hazardous substance starts. It must identify what substances are used, who could be exposed, how exposure happens (inhalation, skin contact, ingestion, injection), and how likely harm is. It must be 'suitable and sufficient' - not a generic tick-box copied from elsewhere.

The five key steps

• Identify the hazardous substances present and gather safety data sheets
• Identify who might be harmed - workers, cleaners, visitors, contractors, pregnant workers
• Evaluate the risks - how much, how often, how long, by what route
• Decide and record the controls needed, following the hierarchy
• Review regularly, and always after an incident, a process change, or a new substance

The hierarchy of control - the exam favourite

HSE ranks controls from most to least effective. Always try the higher options first:

• Elimination - stop using the substance altogether, the best control
• Substitution - swap for something less hazardous, or a safer form (paste instead of powder)
• Engineering controls - local exhaust ventilation (LEV), enclosure, containment
• Administrative controls - safe systems of work, training, reduced exposure time, signage
• Personal protective equipment (PPE) - always the last resort, never the first choice

Common mistakes to avoid

• Reaching for PPE first instead of working down the hierarchy
• Treating the assessment as a one-off - it must be reviewed periodically and after any significant change
• Forgetting vulnerable groups such as young workers, new or expectant mothers, and those with existing health conditions
• Assuming a data sheet alone is a risk assessment - it is only one input
• Not recording the assessment where five or more employees are involved, which is a specific legal requirement

Key legal hook

COSHH assessments sit under the Control of Substances Hazardous to Health Regulations. Employers must not carry out work that could expose employees to a hazardous substance unless a suitable and sufficient assessment has been made and the necessary control measures implemented.

Why PPE and RPE matter

Under COSHH, personal protective equipment (PPE) and respiratory protective equipment (RPE) are the LAST line of defence, not the first. The hierarchy of control always comes first: eliminate, substitute, engineering controls (like extraction), then safe systems of work. PPE/RPE is only used to control residual risk that cannot be removed any other way.

RPE selection basics

• RPE must be suitable for the hazard, the job, and the wearer.
• Every RPE user should have a face-fit test if using a tight-fitting mask (disposable FFP3 or half-mask). A poor fit means no protection, even with the right filter.
• Facial hair breaks the seal on tight-fitting masks, so a fit test with stubble is invalid.
• FFP3 masks filter at least 99% of airborne particles and are the usual minimum standard for fine dusts and fume in construction and industrial settings.
• RPE must have an assigned protection factor (APF) that is high enough for the measured or expected exposure. If exposure could exceed the APF, use a higher-protection option (for example powered respirators).

Workplace Exposure Limits (WELs)

• WELs are set by HSE and published in EH40/2005 (updated periodically).
• Two time periods are used: long-term exposure limit (8-hour time-weighted average, TWA) and short-term exposure limit (15-minute reference period).
• Substances with a 'Sen' notation can cause sensitisation (like asthma or dermatitis) even at low doses, so exposure must be reduced as low as reasonably practicable, not just kept under the WEL.
• Meeting the WEL is a legal minimum, not proof of safety. Exposure should always be reduced further where reasonably practicable.

PPE practical rules

• PPE must be suitable, properly fitted, stored correctly, maintained, and replaced when damaged.
• Employers must provide PPE free of charge and train workers on how to use, store, and check it.
• Gloves must match the chemical hazard. Different glove materials resist different substances, so the wrong glove can let a chemical straight through.
• Employers must monitor exposure and health where there is a risk to health, including health surveillance for certain substances (like isocyanates or asbestos-related work).

Common mistakes

• Treating PPE as the main control instead of the last resort.
• Assuming a dust mask (not a proper respirator) protects against fine or hazardous particulates.
• Skipping face-fit testing or reusing someone else's mask.
• Believing 'under the WEL' always means 'safe' for sensitisers.
• Poor storage (dirty, damaged, or contaminated PPE) reducing protection over time.

Storing hazardous substances safely

Substances covered by COSHH must be stored so they cannot leak, react with each other, or be accessed by unauthorised people. Always check the label and safety data sheet (SDS) for storage instructions before putting anything away.

• Keep substances in their original, correctly labelled container wherever possible.
• Never store incompatible substances together - for example, acids and alkalis, or oxidisers and flammables, must be kept apart to stop dangerous reactions.
• Flammable liquids need a dedicated flammables cabinet or store, away from ignition sources, and the store should be well ventilated.
• Store chemicals below head height and heavy containers on lower shelves to reduce manual handling and spill risk.
• Keep an up to date inventory of what is stored and where, so emergency services know what they are dealing with.

Dealing with spills

Every workplace using hazardous substances should have a written spill procedure, and staff should know where the spill kit is kept before they ever need it.

• Only deal with a spill yourself if it is small and you have been trained and have the right PPE - otherwise evacuate and call for help.
• Stop the source of the spill first if it is safe to do so, then contain it to stop it spreading, using absorbent granules, pads or booms.
• Ventilate the area and remove ignition sources for flammable spills.
• Dispose of contaminated absorbent material as hazardous waste, not general rubbish.
• A common mistake is using water to clean up a spill without checking the SDS - some chemicals react violently with water or spread further.

Emergency arrangements

COSHH assessments must include what to do if things go wrong, not just how to work safely day to day.

• Every site needs clear emergency procedures covering fire, spillage, and exposure (skin, eye, or inhalation), displayed and understood by all staff.
• Emergency eyewash stations and safety showers must be provided where there is a risk of splashes to eyes or skin, and kept unobstructed and regularly checked.
• Know the location of the nearest first aider and how to raise the alarm before an incident happens, not during one.
• If someone is exposed, follow the SDS first-aid section - eyewash usually needs at least 10-15 minutes of continuous irrigation.
• Report all spills and near misses, even small ones, so the assessment can be reviewed and repeat incidents prevented.

Common mistakes

People often decant chemicals into unlabelled containers, ignore incompatibility warnings, or assume a small spill is not worth reporting. All of these undermine the whole point of a COSHH assessment.