COSHH Assessment | What It Is, the Law & Who Needs One

A COSHH assessment is the evaluation an employer must carry out to identify and control the risks from substances hazardous to health in the workplace, the chemicals, dusts, fumes, vapours, mists, gases, and biological agents that can cause harm if not properly managed. It is a legal requirement under the Control of Substances Hazardous to Health Regulations 2002, commonly known as COSHH, which apply to a far wider range of workplaces than many employers realise. Hazardous substances are not confined to laboratories and chemical plants: cleaning products, solvents, dusts, and many everyday workplace materials fall within COSHH, meaning the duty reaches offices, workshops, manufacturers, and businesses of almost every kind. Failure to assess and control these risks causes thousands of cases of occupational ill health each year and exposes employers to enforcement. This guide explains what a COSHH assessment is, the law behind it, what it covers, who can carry one out, and how to get it right, in the UK and internationally.

Why COSHH Assessment Matters

Substances hazardous to health cause a significant burden of occupational ill health, much of it preventable through proper assessment and control. The harm is often gradual and invisible at first, occupational asthma from inhaled substances, dermatitis from skin contact, and, in the most serious cases, occupational cancers from carcinogenic substances, developing over months or years of exposure that proper controls would have prevented.

The scale is significant. Work-related ill health from hazardous substances, including respiratory disease, skin disease, and certain cancers, accounts for a substantial part of the overall burden of occupational ill health in the UK each year. Unlike an acute injury, this harm often emerges long after the exposure, making it easy for employers to underestimate the risk until the consequences appear.

The law requires employers to prevent or adequately control this exposure, and the COSHH assessment is the mechanism for doing so. Enforcement is active, and in 2024/25 the HSE secured over £33 million in fines across its activity, with exposure to hazardous substances among the matters that attract penalties.

A COSHH assessment is the foundation of controlling these risks and meeting the legal duty. Health and Safety Consultants help employers identify the hazardous substances in their workplace and put genuine, adequate controls in place.

1. What COSHH and a COSHH Assessment Are

COSHH stands for the Control of Substances Hazardous to Health, both the name of the regulations and the shorthand for the duty to manage hazardous substances at work.

What COSHH covers: A COSHH assessment addresses substances hazardous to health, which include a wide range of materials:

Chemicals and products containing chemicals (cleaning products, solvents, adhesives, paints)
Dusts, fumes, mists, vapours, and gases
Biological agents (bacteria and other micro-organisms), including Legionella
Products that produce hazardous substances when used (for example, fumes from a process)

What a COSHH assessment is: A COSHH assessment is a systematic evaluation that identifies the hazardous substances present or produced in the workplace, assesses the risk they pose to health, and determines the measures needed to prevent or adequately control exposure. It is a specific form of risk assessment focused on substances hazardous to health.

What it produces: The assessment identifies the substances, how people could be exposed (inhalation, skin contact, ingestion), who is at risk, the level of risk, the controls needed, and the actions required, recorded so the employer can demonstrate it and act on it.

What COSHH does not cover: COSHH does not cover certain substances with their own specific regulations, asbestos, lead, and radioactive materials are covered by separate legislation, and explosive or flammable risks are addressed under other rules. But for the broad range of hazardous substances in everyday workplaces, COSHH is the governing duty, supported by Arinite's COSHH service.

2. The Legal Requirement for COSHH Assessment

COSHH assessment is a clear legal duty, set out in specific regulations under the overarching health and safety framework.

The Control of Substances Hazardous to Health Regulations 2002: The COSHH Regulations 2002 require employers to prevent or, where this is not reasonably practicable, adequately control employees' exposure to substances hazardous to health. The duty to assess the risk is central: an employer must not carry out work liable to expose employees to hazardous substances without first making a suitable and sufficient assessment of the risk and the steps needed to comply.

The core COSHH duties:

Assess the risks from hazardous substances
Prevent or adequately control exposure, following the hierarchy of control
Ensure control measures are used and maintained
Monitor exposure where necessary
Carry out health surveillance where appropriate
Provide information, instruction, and training to employees
Plan for emergencies involving hazardous substances

The wider framework: COSHH sits within the general duties of the Health and Safety at Work Act 1974 and the broader risk assessment duty of the Management of Health and Safety at Work Regulations 1999. The HSE provides detailed guidance on COSHH for employers.

The recording requirement: As with risk assessment generally, where five or more people are employed the significant findings of the COSHH assessment should be recorded, and in practice almost all employers should keep written records as evidence of compliance.

3. What Counts as a Substance Hazardous to Health

A common reason employers fail to carry out COSHH assessments is not realising how broadly hazardous substances are defined, well beyond obvious industrial chemicals.

The breadth of hazardous substances: Substances hazardous to health include far more than the chemicals found in a laboratory or factory:

Cleaning products: Bleaches, detergents, disinfectants, and other cleaning chemicals used in virtually every workplace
Solvents and adhesives: Used in many trades and processes
Paints, inks, and coatings
Dusts: Including wood dust, flour dust, and many others generated by processes
Fumes and vapours: From welding, soldering, processes, and substances
Biological agents: Bacteria and micro-organisms, including Legionella (addressed by Arinite's Legionella service) and risks in areas such as healthcare and waste handling
Products that generate hazardous substances: Where a process creates dust, fume, or vapour

How to identify hazardous substances: Many hazardous substances are identified by the hazard symbols and information on their labels and safety data sheets (SDS), which suppliers must provide. The safety data sheet sets out the hazards and is a key input to the COSHH assessment. But not all hazardous substances come with a label, dusts and fumes generated by processes, for example, require the employer to recognise the hazard.

Why even offices may be in scope: Because cleaning products and other everyday substances fall within COSHH, even office-based workplaces may have COSHH duties, typically modest, but real. The breadth of the definition is why COSHH applies to so many more workplaces than employers often assume.

4. The Steps of a COSHH Assessment

A COSHH assessment follows a structured process to identify and control the risks from hazardous substances.

Step 1: Identify the hazardous substances Identify all the substances hazardous to health present or produced in the workplace, those brought in (using labels and safety data sheets) and those generated by work activities (dusts, fumes, vapours).

Step 2: Identify how people could be exposed and who is at risk Determine the routes of exposure, inhalation, skin or eye contact, ingestion, and identify who could be exposed, including employees, contractors, and others, and any especially vulnerable people.

Step 3: Evaluate the risk Assess the risk to health, considering the hazardous properties of the substances, the amount used and the way it is used, the duration and frequency of exposure, and any workplace exposure limits (WELs) that apply.

Step 4: Decide on control measures Decide how to prevent or adequately control exposure, following the hierarchy of control: eliminate or substitute the substance where possible, then engineering controls (such as local exhaust ventilation), then ways of working that reduce exposure, with personal protective equipment (PPE) as the last resort, not the first.

Step 5: Record, implement, and act Record the significant findings, implement the control measures, and ensure they are used and maintained.

Step 6: Review Review the assessment regularly and whenever there is a significant change, a new substance, a changed process, or evidence the controls are not adequate.

This structured approach ensures the assessment is suitable and sufficient and genuinely controls the risk, rather than being a paperwork exercise.

5. The Hierarchy of Control for Hazardous Substances

A central principle of COSHH, and a frequent point of failure, is the hierarchy of control: the order in which control measures should be considered, with PPE as a last resort rather than the default.

The hierarchy, in order of preference:

Eliminate: Can the hazardous substance be removed from the process altogether? The most effective control is to not use the substance at all.

Substitute: If it cannot be eliminated, can a less hazardous substance, or a less hazardous form (for example, a paste instead of a powder that creates dust), be used instead?

Engineering controls: Where the substance must be used, engineering controls reduce exposure, local exhaust ventilation (LEV) to capture fumes or dust at source, enclosure of the process, or other technical measures.

Ways of working (administrative controls): Systems of work that reduce exposure, limiting the time of exposure, reducing the number of people exposed, and good hygiene practices.

Personal protective equipment (PPE): Respirators, gloves, eye protection, and protective clothing, as a last resort, used to control residual risk after the higher measures have been applied, not as the primary control.

Why the order matters: A common failure is to jump straight to PPE, handing out gloves and masks, without first considering whether the substance could be eliminated, substituted, or controlled at source. PPE relies on correct selection, fit, and consistent use, and protects only the wearer, making it the least reliable control. A proper COSHH assessment works through the hierarchy in order, using PPE only for the residual risk that higher controls cannot eliminate.

6. Who Can Carry Out a COSHH Assessment?

A COSHH assessment must be carried out by a competent person, and the competence required depends on the complexity of the substances and processes involved.

The competence requirement: The COSHH Regulations require the assessment to be carried out by someone competent, with the knowledge, skills, and experience to identify the hazardous substances, understand the routes and risks of exposure, interpret safety data sheets and workplace exposure limits, and specify adequate controls.

Simple vs complex situations: For simple situations, a small number of everyday substances such as cleaning products used in straightforward ways, a suitably informed person within the business may be able to carry out the assessment using HSE guidance and safety data sheets. For more complex situations, multiple substances, processes that generate dust or fume, substances with workplace exposure limits, or situations requiring exposure monitoring or health surveillance, genuine specialist competence is needed.

Why competence matters: Hazardous substances can cause serious, sometimes irreversible, harm, and the assessment requires understanding that goes beyond reading a label, interpreting exposure limits, recognising process-generated hazards, specifying effective engineering controls, and determining whether monitoring and health surveillance are needed. An inadequate assessment leaves workers exposed to substances that can cause asthma, dermatitis, or cancer.

The professional route: For many businesses, particularly those using a range of hazardous substances or processes that generate them, engaging competent Health and Safety Consultants to carry out or oversee COSHH assessments ensures they are genuinely adequate, connecting to the wider competent person duty. Arinite's COSHH service provides this specialist competence.

7. Workplace Exposure Limits, Monitoring, and Health Surveillance

Beyond the assessment and controls, COSHH creates further duties where exposure to certain substances is involved, which a proper assessment identifies.

Workplace Exposure Limits (WELs): Many hazardous substances have a Workplace Exposure Limit, the maximum concentration of the substance in the air, averaged over a period, to which workers may be exposed. WELs are published by the HSE. The COSHH assessment must take account of any applicable WEL, and control measures must ensure exposure is kept below it (and, for the most hazardous substances, as low as reasonably practicable).

Exposure monitoring: Where the assessment indicates it is necessary, for example, where there is a risk of exceeding a WEL, or where control measures could fail with serious consequences, the employer must monitor exposure, measuring the concentration of the substance workers are exposed to, to confirm controls are adequate.

Health surveillance: For certain substances and exposures, the assessment may identify the need for health surveillance, the ongoing monitoring of workers' health to detect early signs of work-related ill health, such as lung function testing for respiratory sensitisers or skin checks for substances causing dermatitis. Health surveillance is required where there is a reasonable likelihood of disease and valid techniques exist to detect it.

Why these matter: WELs, monitoring, and health surveillance are areas where specialist competence is particularly important, determining whether a WEL applies, whether monitoring is needed, and whether health surveillance is required goes beyond basic assessment and is exactly where professional support adds value, ensuring the employer meets these specific duties where they arise.

8. COSHH Across Different Sectors

COSHH applies across an enormous range of workplaces, but the nature and extent of the duty varies considerably by sector.

Manufacturing and industrial: The most COSHH-intensive sectors, using and producing a wide range of hazardous substances, dusts, fumes, solvents, and process chemicals, often requiring engineering controls such as LEV, exposure monitoring, and health surveillance. COSHH is a major part of health and safety management here.

Construction and trades: Exposure to dusts (including silica and wood dust), solvents, adhesives, and other substances, with significant respiratory and skin risks requiring careful assessment and control.

Healthcare: Hazardous substances including cleaning and disinfection chemicals, certain medicines, and biological agents, with specific control requirements.

Cleaning and facilities: Extensive use of cleaning chemicals, with skin and respiratory risks that are often underestimated.

Laboratories and science: A wide range of hazardous substances requiring rigorous assessment and control.

Offices and commercial: The lightest COSHH burden, typically limited to cleaning products and similar everyday substances, but still within scope, meaning even office-based employers usually have some, modest, COSHH duties.

Hospitality and food: Cleaning and sanitising chemicals, and substances such as flour dust (a recognised cause of occupational asthma) in bakeries.

A competent assessor brings the sector knowledge to identify the substances and risks that matter in each context, and the appropriate controls, see the breadth across Arinite's sectors.

9. How Often Should a COSHH Assessment Be Reviewed?

COSHH assessment is an ongoing duty, and keeping assessments current is essential to compliance and protection.

The review requirement: The COSHH Regulations require the assessment to be reviewed regularly and whenever there is reason to suspect it is no longer valid, or there has been a significant change. There is no fixed statutory interval, but the duty to keep it current is clear.

When review is needed:

New or changed substances: A new product, or a change in a substance used
Changed processes: A change in how work is done that affects exposure
New information: Updated safety data sheets, changed WELs, or new information about a substance's hazards
Evidence controls are inadequate: Monitoring results, ill-health cases, or other signs that controls are not working
After an incident: A spill, exposure incident, or near miss
Periodically: To confirm the assessment remains valid even absent specific change

The risk of the stale assessment: A COSHH assessment that no longer reflects the substances used, the processes, or current information about the hazards is no longer suitable and sufficient, and may leave workers exposed. Given that new products are introduced and processes change, regular review is essential.

Managing the cycle: Tracking COSHH assessments, the substances, the controls, the monitoring and health surveillance schedules, and review dates, across a business is a substantial task, particularly where many substances are used. Health and Safety Consultants and Software platforms manage this, holding the assessments, scheduling reviews, and tracking the recurring duties.

10. COSHH for International Organisations

For organisations operating across borders, the management of hazardous substances carries an international dimension, because chemical safety regimes vary by jurisdiction.

Chemical safety is regulated everywhere, differently: Every developed jurisdiction regulates hazardous substances at work, but the regimes, exposure limits, classification systems, and documentation requirements differ. A UK COSHH assessment satisfies UK requirements but not necessarily those of other countries.

Classification and labelling: Internationally, the classification and labelling of chemicals is increasingly aligned through the Globally Harmonised System (GHS), which underpins the hazard symbols and safety data sheets used in the UK, the EU (through CLP), and many other countries, providing some common ground. But the assessment and control duties, exposure limits, and surveillance requirements remain national.

The multinational challenge: An organisation using hazardous substances across multiple countries must ensure assessment and control meet each jurisdiction's requirements, while maintaining consistent group standards for protecting workers wherever they are.

Coordinated international support: International Health and Safety Consultants help multinational organisations manage hazardous substances across all their locations, meeting each country's requirements while maintaining consistent group standards, often within an ISO 45001 framework, with Health and Safety Consultants and Software providing consolidated visibility of chemical safety compliance across countries.

11. Common COSHH Failures

Understanding the common failures helps employers manage hazardous substances properly and avoid the pitfalls that lead to ill health and enforcement.

Not realising COSHH applies: The most basic failure, employers, particularly in less obviously industrial sectors, who do not realise that cleaning products and everyday substances bring them within COSHH, and have never carried out an assessment.

Generic assessments: Using a generic COSHH assessment that does not reflect the actual substances used, how they are used, and the actual processes, failing the suitable and sufficient standard.

Jumping to PPE: Skipping the hierarchy of control and relying on PPE as the primary measure, rather than first considering elimination, substitution, and engineering controls.

Ignoring process-generated substances: Assessing only the substances brought in and labelled, while ignoring the dusts, fumes, and vapours generated by processes, often the most significant risks.

No monitoring or health surveillance where needed: Failing to identify and carry out the exposure monitoring or health surveillance that the assessment should have flagged.

Controls not maintained: Installing engineering controls such as LEV but not maintaining and testing them, so they cease to be effective.

Not reviewing: Carrying out the assessment once and never reviewing it as substances, processes, and information change.

The solution: A competent, specific COSHH assessment that works through the hierarchy of control, identifies process-generated substances, flags monitoring and health surveillance where needed, ensures controls are maintained, and is reviewed, avoids all of these. This is what professional support delivers.

12. How Arinite Delivers COSHH Assessment

Arinite provides COSHH assessment and hazardous substance management as part of comprehensive health and safety support to over 1,500 businesses across the UK and 50+ countries, with a 95%+ client retention rate.

Arinite's COSHH service:

Competent, specific assessment: COSHH assessments carried out by competent professionals, identifying all the hazardous substances, including those generated by processes, genuinely specific to the substances, processes, and workplace, rather than generic.

Hierarchy of control: Controls determined by working through the hierarchy, eliminate, substitute, engineering controls, ways of working, and PPE as a last resort, rather than defaulting to PPE.

WELs, monitoring, and health surveillance: Identifying where workplace exposure limits apply, where exposure monitoring is needed, and where health surveillance is required, ensuring these specific duties are met.

Sector expertise: Knowledge across sectors, from manufacturing and construction to healthcare, cleaning, and offices, to identify the substances and risks that matter in each context, see the sectors page.

Review and ongoing management: Keeping assessments current as substances, processes, and information change, and tracking the recurring monitoring and surveillance duties.

Health and Safety Consultants and Software: A platform managing COSHH assessments, holding safety data sheets, scheduling reviews, and tracking the recurring duties and records.

Integrated with wider support: COSHH managed as part of a coherent approach alongside Legionella (a biological agent within COSHH), general risk assessment, policy, training, and independent Health and Safety Audits, overseen by a competent person.

International Health and Safety Consultants: Hazardous substance management across 50+ countries, meeting local requirements while maintaining consistent group standards.

Named clients including Bell Rock Capital, Figma, Akamai, SUSE, Nikon, Shutterstock, Hearst, IPG, and B&Q rely on Arinite for COSHH assessment and the wider management of their health and safety obligations.

Frequently Asked Questions

What is a COSHH assessment?

A COSHH assessment is the evaluation an employer must carry out to identify the substances hazardous to health in the workplace, assess the risk they pose, and determine the measures needed to prevent or adequately control exposure. It is a specific form of risk assessment focused on hazardous substances, required under the Control of Substances Hazardous to Health Regulations 2002.

Is a COSHH assessment a legal requirement?

Yes. The COSHH Regulations 2002 require employers not to carry out work liable to expose employees to substances hazardous to health without first making a suitable and sufficient assessment of the risk and the steps needed to comply. It sits within the wider duties of the Health and Safety at Work Act 1974.

What counts as a substance hazardous to health?

A wide range of materials: chemicals and products containing them (cleaning products, solvents, adhesives, paints), dusts, fumes, mists, vapours, gases, biological agents (including Legionella), and substances generated by processes. Many are identified by hazard symbols and safety data sheets, but process-generated dusts and fumes require the employer to recognise the hazard. Even offices, through cleaning products, may be in scope.

What is the hierarchy of control in COSHH?

The order in which control measures should be considered: eliminate the substance, then substitute a less hazardous one, then engineering controls (such as local exhaust ventilation), then ways of working that reduce exposure, with personal protective equipment (PPE) as a last resort. A common failure is jumping straight to PPE rather than first considering the more effective controls higher up the hierarchy.

Who can carry out a COSHH assessment?

A competent person with the knowledge, skills, and experience to identify hazardous substances, understand exposure routes and risks, interpret safety data sheets and workplace exposure limits, and specify adequate controls. For simple situations a suitably informed person may suffice, but complex situations, multiple substances, process-generated hazards, or monitoring and health surveillance needs, require specialist competence.

How often should a COSHH assessment be reviewed?

Regularly, and whenever there is reason to suspect it is no longer valid or there has been a significant change, a new or changed substance, a changed process, new hazard information, evidence that controls are inadequate, or after an incident. A stale assessment that no longer reflects the substances and processes used is no longer suitable and sufficient.

Taking the Next Step

A COSHH assessment is a legal requirement and a genuine protection against the often-invisible harm that hazardous substances cause, harm that reaches far more workplaces than the obvious industrial ones. Getting it right, with a competent, specific assessment that works through the hierarchy of control, identifies where monitoring and health surveillance are needed, and is kept current, protects workers from serious occupational ill health and meets a clear legal duty.

Assess your position: Take our Health and Safety Quiz to evaluate your compliance, including the management of hazardous substances.

Discuss your needs: Book a free Gap Analysis Call with an Arinite consultant to understand your COSHH and wider health and safety obligations.

Arrange a COSHH assessment: Contact Arinite to arrange a competent COSHH assessment for your workplace, anywhere in the UK and beyond.

Arinite provides COSHH assessment, Health and Safety Consultants, and Health and Safety Audits services to over 1,500 global businesses across the UK and 50+ countries. Key external resources: HSE guidance on COSHH | Control of Substances Hazardous to Health Regulations 2002 | Health and Safety at Work Act 1974 | HSE enforcement statistics | OSHCR consultant register

COSHH Assessment: What It Is, the Law, and Who Needs One