A COSHH assessment examines hazardous substances used or generated at work and the controls needed to prevent or adequately control exposure. In Great Britain, regulation 6 of the Control of Substances Hazardous to Health Regulations 2002 sets the assessment duty. Northern Ireland has separate regulations. Asbestos, lead and ionising radiation have distinct regulatory frameworks.
This page covers what COSHH applies to, what it excludes, how the assessment works, and the specific obligations around exposure limits, ventilation and health surveillance that distinguish a competent COSHH assessment from a generic one.
What COSHH covers — and what it doesn’t
COSHH covers substances hazardous to health, including relevant chemicals, biological agents, dusts and process-generated contaminants. Exposure may occur through breathing, swallowing, skin or eye contact, absorption or injection. Examples include:
- Chemicals: cleaning products, solvents, paints, glues, inks, fuels, industrial chemicals.
- Dusts: silica dust from masonry, wood dust, flour dust, dust from cutting or grinding operations.
- Fumes and vapours: welding fume, solvent vapour, fumes from heated processes.
- Mists: spray paint, machine oil mist, agricultural sprays.
- Biological agents: bacteria, viruses, fungi, blood-borne pathogens, legionella (which has its own ACOP — L8 — but sits within the COSHH framework).
- Process-generated substances: anything created by the work itself, including dust from sanding, fume from welding, or by-products of chemical reactions.
What COSHH doesn’t cover, despite common confusion:
Asbestos is covered by the Control of Asbestos Regulations 2012, not COSHH. The duties are similar in shape but the asbestos regulations are stricter — licensed work, formal medical surveillance, specific notification requirements.
Lead is covered by the Control of Lead at Work Regulations 2002. These mirror COSHH in structure but include specific biological monitoring (blood lead testing) and removal-from-exposure thresholds.
Ionising radiation is covered by the Ionising Radiations Regulations 2017 and the Justification of Practices Involving Ionising Radiation Regulations 2004. Radiation work has its own framework with employer notification, dose assessment, classified persons and radiation protection advisers.
Substances hazardous solely because of explosive, flammable or oxidising properties sit primarily under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR), though there can be COSHH overlap if the same substance also causes health harm.
The practical effect of these exclusions is that a workplace handling asbestos, lead or radiation needs assessments specific to those regulations on top of any other COSHH assessments. A workplace cleaning agent that happens to be flammable still needs a COSHH assessment because the flammability isn’t the only hazard.
Identifying hazardous substances
The first step in a COSHH assessment is to identify the substances present. Three sources matter.
Labels and safety data sheets provide important hazard information. Suppliers must provide a 16-section SDS where the applicable chemicals legislation requires it; not every substance or product needs one. An SDS informs the assessment but is not itself a COSHH assessment. Classification and labelling rules identify hazards using pictograms, signal words and statements.
UK REACH applies in Great Britain; EU REACH continues to apply in Northern Ireland. These systems govern matters such as registration, authorisation and restrictions. Check the applicable supply and use requirements as well as workplace exposure controls.
Process-generated substances. Dust from cutting concrete. Welding fume. Vapour from heated solvent. These don’t have SDSs because they aren’t supplied — they’re created by the work. The assessor has to identify them by understanding the process. Silica dust from masonry cutting is the obvious example: it has no SDS but is one of the most damaging occupational health hazards in the UK construction industry.
The HSE publishes COSHH essentials — control guidance sheets for specific tasks across many industries — which are a useful supplement when working out what’s actually present in a process.
Routes of exposure
A COSHH assessment has to consider how workers could actually be exposed. Four routes matter.
Inhalation can expose workers to dust, fume, vapour, mist or gas. Some substances can damage the lungs or cause effects elsewhere in the body. Identify relevant routes for the actual process rather than assuming that every substance presents the same respiratory risk.
Skin and eye contact is the second route. Some substances damage the skin directly (corrosives, irritants); some are absorbed through intact skin (solvents, pesticides, some pharmaceuticals); some sensitise the immune system on repeated contact (epoxy resins, certain metals).
Ingestion is less common but happens — typically through hand-to-mouth transfer when workers eat, drink or smoke without washing first.
Injection is relevant for needlestick injuries in healthcare and high-pressure equipment incidents in industry.
The assessment should specify, for each substance and each task, the realistic exposure routes — not just list every theoretical possibility.
Workplace exposure limits
Many hazardous substances have a Workplace Exposure Limit (WEL) — a maximum concentration in the breathing zone of a worker, averaged over a reference period. The reference is usually an 8-hour time-weighted average for chronic effects, with a separate 15-minute short-term exposure limit for substances with acute effects.
WELs are published in EH40 — the HSE’s regularly updated list. The current edition should be consulted directly when carrying out an assessment because limits are periodically revised. An assessment that relies on an out-of-date WEL list isn’t suitable and sufficient.
COSHH requires prevention of exposure where reasonably practicable, or otherwise adequate control. WELs must not be exceeded, but staying below a limit is not the whole test. Apply good control practice and, for carcinogens, mutagens and respiratory sensitisers, reduce exposure as low as reasonably practicable.
The hierarchy of control under COSHH
COSHH regulation 7 sets out a control hierarchy similar to the general workplace hierarchy we cover on the five-steps page, but with COSHH-specific elements.
Elimination
Stop using the substance. Switch to a process that doesn’t generate it.
Substitution
Use a less hazardous substance instead — water-based instead of solvent-based, granules instead of dust, lower-toxicity alternatives.
Engineering controls
Total enclosure of the process, local exhaust ventilation (LEV) capturing the substance at source, segregation of workers from the contaminated area, automation that removes the worker from the exposure zone.
Procedural and administrative controls
Permit-to-work systems for high-risk tasks, job rotation to limit exposure time, restricted access, decontamination procedures.
Personal protective equipment
Respiratory protective equipment (RPE), gloves, coveralls, eye protection. PPE is the last resort because it depends on the user wearing it correctly throughout the exposure period and on it being suitable for the specific hazard.
Select RPE suitable for the substance, concentration, task and wearer. Tight-fitting facepieces need face-fit testing for the individual and an effective seal during use. Loose-fitting equipment may be appropriate in other circumstances. Provide training, maintenance and the checks required for the equipment.
Local exhaust ventilation and the 14-month rule
Most LEV systems require thorough examination and testing at least every 14 months. COSHH Schedule 4 specifies shorter maximum intervals for certain processes, and the assessment or equipment condition may justify more frequent checks. Routine maintenance remains necessary between examinations.
A competent person must carry out the examination and test using suitable methods for the system. Relevant training and experience matter; a particular named qualification is not universally prescribed. Keep the examination and test records for at least five years.
The 14-month rule exists because LEV systems silently degrade. Filters clog, ducts develop deposits, fan motors lose efficiency, hood positions drift as equipment moves. A system installed correctly and tested at the start can be substantially less effective two years later without anyone noticing.
Health surveillance
Health surveillance is required where the COSHH criteria are met, including relevant Schedule 6 work or exposure associated with an identifiable disease or adverse effect, a reasonable likelihood of occurrence and valid techniques for detecting it. It is not automatically required whenever any hazardous substance is present.
The appropriate programme depends on the hazard and exposure: it may include skin checks or respiratory surveillance. Obtain competent occupational-health advice. Noise audiometry and lead medical surveillance arise under separate regulations and should not be confused with the COSHH programme.
COSHH health records must be kept for at least 40 years from the last entry. These are the employer’s surveillance records, not unrestricted access to confidential clinical notes held by the health professional.
Records should support ongoing protection and appropriate follow-up. Keep personal medical information confidential and ensure that surveillance findings lead to action on exposure controls when necessary.
Information, instruction and training
Regulation 12 of COSHH is the often-overlooked third pillar. It requires the employer to provide workers with information, instruction and training on:
- The hazards of the substances they’re exposed to.
- The risks identified in the assessment.
- The control measures in place and the worker’s role in maintaining them.
- Any workplace exposure limits and the results of any monitoring.
- The collective and individual protection measures, including PPE and how to use it.
- Emergency procedures for spills, releases or exposure.
A COSHH assessment that records excellent controls but isn’t communicated to the workers actually doing the work doesn’t satisfy regulation 12. The training must be appropriate to the hazards and to the worker’s role — generic “COSHH awareness” e-learning rarely satisfies the regulation for high-hazard work.
Records and review
Where an employer has five or more employees, record the significant findings and steps taken to comply with COSHH. Include the substances, people affected, controls, monitoring, health surveillance and emergency arrangements relevant to the assessment.
Review is required when there is reason to suspect the assessment is no longer valid, when significant change has occurred, or when monitoring results suggest the controls aren’t working as expected. Significant change includes new substances, modified processes, new equipment, new workers in different roles, changes to workplace layout, or regulatory change such as a revised WEL in EH40.
Where the cluster connects
COSHH overlaps with several other vertical assessments. Legionella risk assessment sits within the COSHH framework as a biological-agent assessment. Pregnancy risk assessment requires specific consideration of chemical, biological and ionising-radiation hazards. Manual handling interacts with COSHH where the load being handled is itself hazardous. RAMS for construction typically includes COSHH content for specific high-hazard tasks.
For workplaces with significant hazardous-substance exposure, in-house competence pays for itself quickly. Formal Risk Assessment Training covers the general assessment method that underpins COSHH; specialised COSHH or occupational hygiene qualifications layer on top for industries where exposure is a material part of the work.
Frequently asked questions
What does COSHH stand for?
Control of Substances Hazardous to Health. The Control of Substances Hazardous to Health Regulations 2002 are the parent legislation, supported by ACOP L5 and a range of substance-specific HSE guidance.
Does COSHH cover asbestos?
No. Asbestos has its own regulations — the Control of Asbestos Regulations 2012 — with stricter duties around licensed work, medical surveillance and notification. Lead is similarly covered by the Control of Lead at Work Regulations 2002, and ionising radiation by the Ionising Radiations Regulations 2017. A workplace handling any of these needs assessments specific to those regulations.
How often does local exhaust ventilation need testing under COSHH?
For most LEV systems, at least every 14 months. Some processes have shorter statutory intervals, and risks or deterioration may require more frequent attention. A competent person must examine and test the system, with records kept for at least five years.
What is a workplace exposure limit?
A limit for airborne concentration averaged over a stated reference period, commonly eight hours or fifteen minutes. HSE publishes WELs in EH 40. Limits must not be exceeded, but compliance also requires adequate control and, for certain substances, exposure as low as reasonably practicable.
Who needs a COSHH assessment?
Employers must assess work liable to expose employees to substances hazardous to health under COSHH, with relevant duties also protecting others affected by the work. The assessment should reflect the actual substances, tasks and exposure, including contaminants generated by a process.
How long must health surveillance records be kept?
COSHH health records must be kept for at least 40 years from the last entry. Confidential medical records are handled separately by the health professional; employers should receive the information needed to manage health risks without unnecessary clinical detail.
Related guides
- How often should a risk assessment be reviewed?
- Who can carry out a risk assessment? The competence question explained
- Risk assessment examples: three worked examples for UK workplaces
Sources & references
- HSE — COSHH assessment
- HSE — COSHH Approved Code of Practice L 5
- HSE — Local exhaust ventilation guidance HSG 258
- HSE — COSHH health surveillance
- HSE — UK REACH
- HSE — Workplace exposure limits
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Mark writes about workplace health & safety, risk assessment and accredited online training for Risk Assessment Training, part of Online CPD Academy.