The Control of Substances Hazardous to Health (COSHH) Regulations are one of the most significant pieces of health and safety legislation. They place a legal duty on employers to protect employees and others from the risks posed by hazardous substances. These regulations apply across almost every industry, from manufacturing and laboratories, to schools, offices, catering, and construction.
The aim of COSHH is to prevent illness, injury, and long-term occupational disease caused by hazardous substances. This includes both acute effects (e.g., dizziness, burns, respiratory distress) and chronic conditions (e.g. asthma, dermatitis, silicosis, certain cancers).
What is a Hazardous Substance?
Under COSHH, a hazardous substance can be any material, solid, liquid, gas, vapour, mist, dust, fume, fibre, or biological agent, that could harm health. This includes:
- Supplied chemicals, such as cleaning agents, paints, adhesives, and solvents.
- By-products of work, such as welding fumes, wood dust, exhaust gases.
- Naturally occurring hazards, such as silica in stone or mould spores in damp areas.
Many hazardous substances are classified under the Classification, Labelling and Packaging (CLP) Regulation, which assigns hazard pictograms, signal words, and hazard statements. Others may have Workplace Exposure Limits (WELs) published in HSE’s EH40/2005 Workplace Exposure Limits, which specify legal limits for airborne exposure. Even without classification or a WEL, a substance must still be assessed if it poses a health risk.
Workplace Exposure Limits (WELs) and Air Monitoring
Workplace Exposure Limits (WELs), published in EH40/2005, are legally enforceable maximum concentrations of hazardous substances in workplace air. They are expressed as:
- Long-term limit: An 8-hour time-weighted average (TWA) for full-shift exposure.
- Short-term limit: A 15-minute TWA to prevent acute health effects.
Examples include 0.1 mg/m³ for respirable crystalline silica (long-term) and limits for chlorine gas (both long and short-term).
Where a WEL applies, employers must confirm compliance through air monitoring. This typically involves:
- Personal sampling: a device worn in the breathing zone, giving the most accurate measure of individual exposure.
- Static sampling: fixed-point monitoring, useful for background levels but less representative of personal exposure.
Sampling must:
- Be carried out by competent persons using calibrated equipment.
- Match the relevant averaging period (8 hours or 15 minutes).
- Be compared to the WEL in EH40 and the SDS (Section 8).
- Be documented, with records retained for the required period (longer where chronic health effects are possible).
Monitoring results should always be reviewed alongside health surveillance findings. WEL compliance does not guarantee absolute safety for all individuals, so results must feed back into risk assessments and control measures. Where results approach or exceed a WEL, immediate action is required, reviewing controls, engineering measures, and work practices.
Employer Responsibilities Under COSHH
Employers must.
- Prevent exposure where reasonably practicable.
- Reduce exposure to as low as reasonably practicable (ALARP), and always ensure levels remain below applicable WELs.
- Carry out COSHH assessments tailored to their workplace and processes.
- Implement and maintain controls, engineering, procedural, and PPE-based.
- Provide training and information in practical, understandable terms.
- Arrange monitoring and health surveillance where required.
- Prepare for emergencies such as spills or accidental releases.
- Follow training and safe procedures.
- Use controls and PPE correctly.
- Report defects, unsafe conditions, or signs of ill health.
- Cooperate with monitoring and health surveillance programmes as required by law.
How to Carry Out a COSHH Assessment
A COSHH assessment is more than a tick-box exercise. It is a structured process for identifying hazardous substances, understanding the risks, and deciding how to control them. It must be specific to your workplace and actual working practices, generic templates that ignore real-world conditions are a common cause of HSE enforcement action.
Whenever possible, the assessment should be based on direct observation of the task or process. Watching the activity in real time often reveals differences between written procedures and actual practice, such as chemicals being poured at shoulder height (increasing splash risk) or PPE being removed too early.
Step 1: Identify the Hazardous Substances
Compile a complete list of all hazardous substances used, stored, or generated. This includes both supplied products (with hazard labels) and by-products created during work. To identify these hazards:
- Check product labels for hazard pictograms, signal words, and precautionary statements.
- Obtain and review the latest SDS for each product.
- Section 1 confirms the product identity and supplier contact details (essential for sourcing updated information and emergency advice).
- Section 2 outlines hazard classifications, hazard statements (H-codes), and precautionary statements (P-codes) that indicate the type of harm the substance can cause.
- Section 3 lists hazardous ingredients and their concentrations, useful for checking if they have their own WELs or if they’re carcinogens, sensitisers, or mutagens.
This step sets the foundation for the entire assessment. Without accurate identification, later control measures may be ineffective.
Step 2: Understand How the Substance is Used
For each substance, you need to understand:
- The physical form (liquid, powder, gas, fume, vapour).
- The work process it’s used in (pouring, spraying, heating, sanding, mixing, etc.).
- The quantities handled and frequency of use.
- Whether the process is enclosed or open.
- Any environmental factors that could influence exposure (e.g., ventilation, temperature).
Observing the process is particularly important. What is written in the SOP may differ from how the task is done in practice.
How the SDS supports this step:
- Section 9 lists the physical and chemical properties, which help determine whether the substance is likely to become airborne (e.g., high vapour pressure means more vapour release).
- Section 10 covers stability and reactivity, highlighting incompatible materials, conditions to avoid, and the potential for hazardous decomposition products.
Step 3: Determine Who Might Be Harmed and How
When identifying who could be harmed, think well beyond the person directly handling the hazardous substance. Exposure can affect anyone who comes into contact with it, intentionally or accidentally, including maintenance teams, cleaning staff, contractors, delivery drivers, visitors, and, in some cases, members of the public if there is a risk of release beyond the work area.
It is important to consider how each group might be exposed, as the circumstances and risk level may differ. For example, maintenance staff may be exposed during plant repairs when normal controls are removed, while cleaners may encounter residue on surfaces or discarded containers.
You must assess all possible routes of exposure:
- Inhalation: breathing in dusts, vapours, fumes, or mists.
- Skin contact: direct touch, splashes, or handling contaminated tools or surfaces.
- Ingestion: often accidental, from hand-to-mouth transfer due to poor hygiene or eating/drinking in work areas.
- Eye contact: from splashes, airborne particles, or rubbing eyes with contaminated hands or gloves.
Direct observation of the task or process is essential at this stage. By watching how the work is actually done, you may identify unexpected exposure opportunities, for example, PPE being removed prematurely, controls being bypassed, or storage areas being accessed by non-operational staff.
How the SDS supports this step:
- Section 11 (Toxicological Information) describes the acute (short-term) and chronic (long-term) health effects for each exposure route, enabling you to link the way people are exposed with the specific harm it could cause.
- Section 2 (Hazards Identification) lists hazard statements that summarise key health risks, such as H334 “May cause allergy or asthma symptoms or breathing difficulties if inhaled” or H314 “Causes severe skin burns and eye damage.”
By combining direct observations with the health effects listed in the SDS, you can judge the potential severity of harm for each person or group identified. This makes it easier to prioritise controls, for example, recognising that contractors working briefly in a high-risk zone without PPE may face greater harm than permanent staff whose exposure is well controlled.
Step 4: Assess the Risks
This stage involves combining likelihood and severity to determine the overall level of risk for each hazardous substance and task. The goal is to decide how urgently action is needed and what level of control is appropriate. A good starting point is to use a risk rating matrix (low, medium, high) based on:
- Likelihood: how often and for how long workers are exposed, whether controls are in place and used correctly, and how likely those controls are to fail.
- Severity: the potential health effects, such as mild irritation versus irreversible disease or fatality.
Information sources for judging likelihood and severity:
- Observation of the task: Seeing how the substance is actually handled, not just how it’s described in procedures.
- SDS Section 11: Toxicological information, which describes the potential health effects and whether they are acute (immediate) or chronic (long-term).
- SDS Section 2: Hazard statements that summarise the key risks (e.g., H334 “May cause allergy or asthma symptoms or breathing difficulties if inhaled”).
- SDS Section 8: Exposure limits and control recommendations.
- Previous incidents or near misses which may reveal hazards not covered in the SDS.
Where a Workplace Exposure Limit applies, refer to the WELs and Air Monitoring section for detailed guidance on sampling methods and compliance checks.
COSHH assessments may be qualitative (judgement-based, relying on observation and SDS data and incident history) or quantitative (data-based, relying on monitoring). The choice depends on whether the risk can be clearly shown to be controlled. Where a WEL applies or where serious health effects are possible, quantitative assessment is normally required.
The outcome of this step directly determines the urgency and scope of control measures. For example, frequent inhalation exposure to a carcinogen with a low WEL will require immediate and robust engineering controls, while rare, low-level exposure to a mild irritant may require only procedural and PPE-based controls.
Step 5: Decide on the Control Measures
Once you understand the risks, you must decide how to reduce or remove them. This should always follow the hierarchy of control, applying the most effective measures first and using Personal Protective Equipment (PPE) only as a last resort.
- Eliminate: Remove the hazardous substance or process entirely if it is not essential. For example, can the job be done without using the chemical at all? Elimination removes the risk completely.
- Substitute: Replace the substance with a less hazardous alternative. For instance, swap a solvent-based paint for a water-based version, or use pre-cut materials to avoid dust generation.
- Enclose the process: Prevent the hazardous substance from escaping into the work environment, such as by using sealed mixing systems, glove boxes, or automated filling lines.
- Engineering controls: Use physical measures to capture or remove contaminants before they reach the worker, such as local exhaust ventilation (LEV), fume cupboards, or extraction arms.
- Administrative controls: Change the way work is organised to reduce exposure, such as limiting the number of people in the area, rotating tasks to reduce exposure time, or clearly marking hazardous zones.
- PPE (Personal Protective Equipment): Provide suitable protective gear, such as gloves, respirators, or protective clothing, but only when other controls cannot fully remove the risk. PPE should be specific to the hazard, fit-tested where required, and maintained in good condition.
How the SDS supports this step:
- Section 7 (Handling and Storage) sets out the conditions needed to minimise the risk of exposure during use and storage, including temperature control, segregation of incompatible substances, and spill prevention measures.
- Section 8 (Exposure Controls/Personal Protection) recommends engineering controls and specifies the types of PPE suitable for the hazard. However, you must adapt these recommendations to your specific workplace, for example, naming the exact type of glove material, the respirator filter class, and when each item must be worn. You should also include instructions for inspection, cleaning, and replacement.
Observation at this stage is essential to check whether the proposed controls will work in practice. If you see that equipment is awkward to use or PPE is uncomfortable, workers may be less likely to use them properly. This is also the time to confirm that any engineering controls are maintained, tested, and effective, and that administrative controls are realistic given the workload and staffing levels.
Step 6: Record the Assessment
Once you have gathered all the information and decided on control measures, you must document the COSHH assessment in a way that is clear, accessible, and specific. The written record should provide enough detail that someone unfamiliar with the process could still understand the hazards, how they are controlled, and what to do in an emergency. Your assessment should include:
- Substance details: name, manufacturer/supplier, product code, and date of SDS.
- Hazards: classification, hazard statements, and any specific warnings from the SDS.
- Exposure routes: inhalation, skin, ingestion, eye contact, and when/how these may occur.
- Include relevant WEL values and the agreed monitoring arrangements. Refer to the WELs and Air Monitoring section for full guidance.
- Control measures: existing controls and any improvements planned, with enough detail for them to be implemented consistently.
- Health surveillance requirements: type, frequency, and provider details if applicable.
- Emergency arrangements - what to do in case of exposure, spillage, or fire.
How the SDS supports this step:
- Section 4 (First Aid Measures) - provides essential details on immediate treatment for each route of exposure; use this to inform emergency response plans and staff training.
- Section 13 (Disposal Considerations)- ensures that disposal methods protect both human health and the environment and comply with legal requirements.
- Section 15 (Regulatory Information) - summarises the key legislation, restrictions, or special requirements that apply to the substance. This can help check that your assessment is aligned with current legal obligations.
When writing the assessment, avoid generic phrases such as “wear suitable gloves”, instead, state the exact glove material and standard (e.g., nitrile gloves conforming to EN 374, changed every 2 hours or immediately if damaged). The same applies to respirators, ventilation systems, and procedural controls.
Finally, store the COSHH assessment where it is easily accessible to those who need it, whether in a physical file or on an internal safety system. Workers must be able to refer to it quickly, especially in an emergency. Make sure the assessment is dated, signed by the assessor, and reviewed regularly.
Step 7: Implement, Monitor, and Review
Once the COSHH assessment is complete, the agreed control measures must be implemented promptly and in full. This means ensuring that:
- All required equipment, PPE, and engineering controls are in place.
- Workers are trained in their correct use.
- Supervisors are monitoring compliance as part of routine operations.
Implementation is not the end of the process, ongoing monitoring is essential to ensure that controls remain effective over time. This may involve:
- Visual inspections of control measures such as local exhaust ventilation (LEV), PPE, or process enclosures to check for damage, wear, or incorrect use.
- Performance checks such as LEV airflow testing, PPE fit testing, or filter change records.
- Reviewing incident reports, near misses, or worker health complaints to identify patterns that suggest controls are failing or new hazards are emerging.
Ongoing air monitoring must confirm compliance with applicable WELs. Refer to the WELs and Air Monitoring section for detailed requirements on sampling methods, frequency, competence and record retention.
Where the assessment identifies a potential for occupational disease that can be detected early, health surveillance must be introduced. This may include:
- Skin inspections for dermatitis risks.
- Lung function testing for airborne sensitisers such as flour dust or isocyanates.
- Biological monitoring for certain substances like lead.
The COSHH assessment should be a living document, reviewed and updated:
- At least annually to ensure continued accuracy.
- Whenever there is a process change, introduction of a new substance, or change in the form or concentration of an existing substance.
- Immediately after any incident, health surveillance finding, or monitoring result that indicates increased risk or control failure.
Any update should include a review of the SDS for each substance, ensuring that the most recent version is on file. Changes in SDS hazard classification, recommended controls, or WEL values must be cross-referenced against your current control measures to confirm they remain adequate.
Health Surveillance
Health surveillance detects early signs of work-related illness so that action can be taken promptly. Under COSHH, it is required where there is a link between the hazard and an identifiable disease or health effect, where the condition can be detected early, and where there is a reasonable likelihood of it occurring in the workplace.
Common examples include lung function tests for flour dust or isocyanate exposure, skin checks for epoxy resin users, and blood tests for lead. Surveillance should be overseen by qualified occupational health professionals, with findings stored securely for the legally required retention period, often 40 years for chronic hazards. The results may trigger a reassessment of controls and working methods.
Using Safety Data Sheets Effectively
SDS documents provide essential technical information for hazard identification and control planning. Sections 1-3 help identify the product and its hazards; Sections 4, 7, and 8 give practical handling, storage, and control measures; Sections 9-11 describe its properties, reactivity, and toxicology; Sections 13 and 15 address disposal and legal compliance. Always adapt SDS advice to the realities of your workplace rather than copying it directly.
Emergency Preparedness
Even with robust controls, incidents can occur. Employers must prepare for such events by ensuring spill kits, eyewash stations, and safety showers are available where needed, and that staff are trained to respond quickly and effectively. First aid arrangements should reflect the hazards identified in the COSHH assessment. Incident reporting and investigation should be used to prevent recurrence and strengthen controls.
Enforcement and Penalties
The HSE and local authorities can enforce COSHH through inspections and investigations. Non-compliance can lead to improvement or prohibition notices, prosecution, significant fines, imprisonment, and civil claims for damages.
Best Practice for Ongoing Compliance
Maintain an up-to-date COSHH register and review assessments annually or after any significant change. Provide refresher training for all relevant staff, inspect control measures regularly, and act promptly on any deficiencies identified during monitoring or health surveillance. Store monitoring and surveillance records securely for the required retention periods.
Conclusion
COSHH offers a structured and practical framework for controlling hazardous substances in the workplace. When risk assessment, control measures, WEL monitoring, and health surveillance are applied together, and supported by accurate SDS information and emergency readiness, the result is a safer, healthier, and legally compliant workplace.
More Information
If you need further guidance please contact us on 033 33 215 005 or at info@wirehouse-es.com.
References
Health and Safety at Work etc. Act 1974. Available at: https://www.legislation.gov.uk/ukpga/1974/37
Control of Substances Hazardous to Health Regulations 2002 (as amended). Available at: https://www.legislation.gov.uk/uksi/2002/2677/contents/made
HSE (2020) Control of Substances Hazardous to Health (COSHH). Approved Code of Practice and guidance L5 (6th edition). Available at: https://www.hse.gov.uk/pubns/books/l5.htm
HSE (2023) COSHH: A brief guide to the Regulations. INDG136 (rev6). Available at: https://www.hse.gov.uk/pubns/indg136.htm
HSE (2024) Workplace health and disease statistics (including COSHH-related illnesses). Available at: https://www.hse.gov.uk/statistics
HSE (2020) EH40/2005 Workplace Exposure Limits (4th edition). Available at: https://www.hse.gov.uk/pubns/books/eh40.htm HSE (2004) COSHH Essentials: Easy steps to control chemicals. HSG97 (2nd edition). Available at: https://www.hse.gov.uk/pubns/books/hsg97.htm
