A COSHH assessment is a legal requirement under Regulation 6 of the COSHH Regulations and an essential part of managing health risks from hazardous substances in the workplace. It helps employers identify substances hazardous to health, understand how workers may be exposed, and determine whether appropriate control measures are in place.
For organisations dealing with chemicals, dusts, fumes, vapours, biological agents, or other harmful substances, a suitable and sufficient COSHH risk assessment can provide valuable evidence of how workplace exposure risks should be identified and managed.
This can also become important when investigating workplace exposure claims. Where a worker develops an illness that may be linked to exposure to a hazardous substance, historical COSHH assessments, exposure monitoring, health surveillance records, and other workplace documentation may help establish what substances were present, the intended safe system of work, and whether documented controls reflected the physical reality of the task.
So, what is a COSHH assessment, what should it contain, and why can it matter when assessing an alleged workplace exposure?
What is a COSHH assessment?
COSHH stands for the Control of Substances Hazardous to Health. The COSHH Regulations 2002 require employers to assess the health risks created by work involving hazardous substances. Under Regulation 7, employers must prevent exposure or, where prevention is not reasonably practicable, adequately control it.
A COSHH assessment is a specific risk assessment concerned with managing hazardous substances. Under Regulation 6, it must be carried out before hazardous work begins. It evaluates the substances present, how they are used or generated, who could be exposed, the realistic exposure routes, and the control measures required to achieve adequate control under the law.
The assessment should reflect the actual work being carried out, not simply describe the properties of a substance. A safety data sheet (SDS), for example, can provide important information about chemical properties and recommended precautions. But it does not assess how that substance is then used in a particular process.
COSHH assessments are required across a wide range of industries and working environments. They apply to obvious chemical hazards such as solvents, paints, and cleaning products, as well as dusts, fumes, vapours, mists, and biological agents generated by work processes.
The regulations define a substance hazardous to health broadly. This includes substances classified as hazardous chemicals under the GB Classification, Labelling and Packaging Regulation (CLP), biological agents, substances with an approved workplace exposure limit (WEL), and dusts or other substances that create a health risk because of their properties or the way they are used.
The assessment is intended to provide a practical operational baseline for controlling exposure on the shop floor, rather than simply being a document demonstrating that paperwork has been completed.
What substances are covered by COSHH?
COSHH covers a much wider range of hazardous substances than simply chemicals supplied in labelled containers.
Depending on the workplace and the processes involved, this may include cleaning products, solvents, paints, adhesives, resins, dusts, fumes, gases, vapours, mists, and biological agents. Examples include flour dust, wood dust, welding fume, respirable crystalline silica, solvent vapours, and substances containing isocyanates. Under Regulation 2, COSHH also covers dust of any kind if present in substantial concentrations in the air.
Some of the most dangerous substances are created by work processes rather than brought into the workplace as finished products. Cutting or grinding stone generates respirable crystalline silica dust. Welding produces toxic metal fume, while sanding timber or composite materials releases fine dust into the working environment. Because these process-generated contaminants do not arrive with a manufacturer SDS, employers frequently overlook them, which is a common failure mode in exposure claims.
These process-generated substances must be identified and evaluated with the same rigour as purchased chemicals.
Biological agents also fall within COSHH, including microorganisms that can cause infection, allergy, or toxicity.
Under Regulation 5, certain hazards are explicitly excluded from COSHH because they are covered by dedicated legislation, including asbestos, lead, and radioactive materials. Understanding which substances fall under COSHH, how they arise during physical work, and why they pose health risks is an essential first stage of an assessment.
What does a COSHH assessment include?
A suitable and sufficient assessment needs to consider the physical circumstances in which hazardous substances are actually used, generated, handled, stored and disposed. Under Regulation 6(2) of COSHH, the assessment must evaluate specific statutory criteria.
This starts with identifying hazardous substances. Relevant information may come from product labels, SDS, technical specifications, and observations of the work process. Crucially, the assessment must also identify substances generated during the work itself, such as dusts, mists, or thermal fumes.
The next step is to understand how exposure could occur. Exposure routes include inhalation, skin absorption across the dermal barrier, direct contact damage, and secondary ingestion. The assessment should evaluate the physical task, including operational frequency, duration, chemical quantities, application temperatures, and process energy.
It should also identify who could be exposed. This includes direct operators, maintenance workers, contractors, facility cleaners, and colleagues sharing the room air. Vulnerable individuals, including young persons and pregnant or breastfeeding workers, require specific consideration where applicable.
The potential health hazards must be evaluated. Depending on the substance, these include acute irritation, chemical burns, irritant or allergic contact dermatitis, occupational asthma, specific target organ damage, or long-latency diseases such as cancer.
A COSHH assessment must then determine the required control measures. Under Regulation 7 and Schedule 2A Principles of Good Practice, controls must follow the statutory hierarchy. Employers must prioritise elimination, substitution, and collective engineering controls at source, such as enclosure or local exhaust ventilation, before relying on administrative procedures. Personal protective equipment should only be specified to manage residual risk.
Where existing controls are insufficient, the assessment must identify the additional measures needed to achieve adequate control under the law.
The assessment must also detail how controls are verified in practice. This includes defining Workplace Exposure Limits, exposure monitoring requirements, statutory 14-month examination intervals for extraction systems, daily pre-use checks, health surveillance arrangements, and formal review triggers.
How are hazardous substances assessed?
A COSHH assessment is not simply a matter of deciding whether a substance is hazardous. While the hazard is fixed by the chemical properties of the material, the operational risk depends on how the work is carried out and the extent of human exposure.
Identifying the hazards
The first stage is identifying which hazardous substances are present and understanding what harm they can cause. Safety data sheets provide vital baseline information for supplied materials, including hazard statements, classification codes, and manufacturer recommendations. However, the assessment must look beyond the SDS to identify contaminants generated by the process itself, such as dusts, welding fumes, or thermal degradation vapours.
Evaluating exposure and process energy
Once the intrinsic hazards are identified, the assessor must evaluate the realistic pathways, duration, and intensity of exposure. This requires examining the physical energy applied during the task. A volatile solvent stored in a sealed container presents minimal exposure risk, but that same solvent heated in an open bath, atomised as a spray, or wiped across a broad metal surface evaporates rapidly into the breathing zone.
The assessment must evaluate both normal running conditions and foreseeable non-routine activities, including equipment cleaning, maintenance, and waste handling. It should consider everyone sharing the workspace air, not just the primary operator. Where airborne concentrations cannot be reliably estimated from process parameters, exposure must be quantified through occupational hygiene air monitoring and benchmarked against statutory Workplace Exposure Limits rather than assumed.
What control measures should a COSHH assessment identify?
Under COSHH Regulation 7, employers have an overarching duty to prevent exposure. Where prevention is not reasonably practicable, employers must adequately control exposure.
This means that simply providing personal protective equipment must never be treated as an acceptable default or a primary solution.
Under Regulation 7 and Schedule 2A, control measures must follow a strict statutory hierarchy. Employers must first evaluate elimination or substitution with a less hazardous substance or process. Where hazardous substances remain, control must be achieved at source through collective engineering controls. These include total enclosure, automated handling, and local exhaust ventilation. For high-hazard substances such as carcinogens, mutagens, and respiratory sensitisers, Regulation 7(5) specifically requires total enclosure of the process unless that is shown not to be reasonably practicable.
Administrative controls provide supporting protection through safe operating procedures, restricted access to hazardous areas, reduced exposure durations, and workforce training.
Personal protective equipment (PPE), including respiratory protective equipment, chemical gloves, eye protection, and protective overalls, may also be required. However, under the law, personal protection is restricted to managing residual risk where higher-order engineering controls cannot achieve adequate control on their own.
The assessment must explain the required controls, how they reduce exposure, and the measurable checks needed to confirm they remain effective. This includes defining statutory maintenance, examination, and testing under Regulation 9, such as the mandatory fourteen-month thorough examination for local exhaust ventilation systems.
This distinction between written controls and physical performance is critical when investigating workplace exposure claims. The mere existence of a COSHH assessment does not prove that exposure was adequately controlled. An expert will evaluate whether the controls specified in the assessment were physically installed, properly used, routinely inspected, and backed by objective evidence such as maintenance records, test reports, and air monitoring data.
Exposure monitoring and workplace exposure limits
For some hazardous or high-risk substances, workplace exposure limits provide a reference point for controlling airborne exposure.
The Health and Safety Executive’s EH40 Workplace Exposure Limits publication sets out WELs for substances hazardous to health. Long-term exposure limits generally relate to an eight-hour reference period, while short-term exposure limits may apply to substances where brief periods of exposure can present a significant risk.
Where a COSHH risk assessment indicates that monitoring is necessary to ensure adequate control, exposure monitoring may be required. This can help establish the concentrations to which workers are actually exposed and whether existing exposure controls are working as intended.
Monitoring can be particularly relevant where exposure levels are uncertain, where hazardous or dangerous substances are used in significant quantities, or where the consequences of exposure could be serious.
Historical exposure monitoring can also provide useful evidence when investigating workplace exposure claims. Results may help establish what exposure levels were present at a particular time, although their significance depends on the substance, the monitoring circumstances, and how closely those circumstances match the work being considered.
When is health surveillance required?
Health surveillance forms an integral part of chemical risk management and should be implemented where a suitable and sufficient risk assessment identifies a residual risk to employee health.
Under COSHH Regulation 11, health surveillance is a statutory requirement where four specific conditions are met simultaneously:
- The work involves an identifiable disease or adverse health effect;
- There is a reasonable likelihood that the disease or effect could occur under the particular conditions of the work;
- Valid clinical techniques exist to detect early signs of the condition; and
- The screening technique itself presents low risk to the worker.
Depending on the hazards involved, this includes routine programmes such as regular skin inspections for work-related dermatitis, respiratory symptom questionnaires and spirometry lung function testing for occupational asthma, or biological monitoring for specified substances.
Health surveillance should not be confused with general medical screening. Crucially, health surveillance is not a control measure that prevents exposure. It does not stop a substance entering the body. It is a clinical detection mechanism designed to identify early biological harm when workplace controls fail.
Where health surveillance identifies an adverse health effect or occupational disease, the employer has a mandatory duty under COSHH Regulation 11(5) and Regulation 6(3) to review the risk assessment, re-evaluate existing engineering controls, and review the health of other workers carrying out the same task.
In workplace exposure claims, historical health surveillance records are a critical source of evidence. Under Regulation 11(3), employers are legally required to retain these health records for at least 40 years. In litigation, an expert will examine these records to establish whether early symptoms were identified during employment, whether clinical results triggered a timely investigation of the workplace, and whether the employer took appropriate action to protect the workforce from progressive harm.
How often should a COSHH assessment be reviewed?
A COSHH assessment must never be treated as a static, one-off document.
Under COSHH Regulation 6(3), employers have an absolute legal duty to review an assessment immediately if there is reason to suspect that it is no longer valid, or if there has been a significant change in the work to which it relates.
In workplace operations, relying solely on an annual calendar review is a common pitfall. While periodic administrative reviews are helpful, Regulation 6(3) requires dynamic, event-driven reviews. A formal review is mandatory whenever there are changes in substances, process chemistry, application methods, operating temperatures, batch sizes, or workspace layouts.
A review must also be carried out immediately following an incident, a chemical spill, an engineering control failure such as an unsatisfactory extraction test, or an adverse finding from health surveillance. Any of these events indicates that the assumptions in the original assessment may no longer hold true.
COSHH assessments must also take account of workers who may be more vulnerable to hazardous substances, including pregnant or breastfeeding employees, young or inexperienced workers, and individuals with relevant respiratory or skin conditions. Where an employee provides written notification of pregnancy, has recently given birth or is breastfeeding, Regulations 16 to 18 of the Management of Health and Safety at Work Regulations 1999 require a prompt individual reassessment. In a COSHH context, particular attention should be given to reproductive and developmental toxicants, substances that may pass into breast milk, lead and Category 1 carcinogens.
This distinction becomes pivotal when investigating historical workplace exposure claims. Exposure often occurs over months, years, or decades, during which manufacturing methods, ventilation systems, chemical formulations, and exposure limits evolve. An assessment prepared in 2015 cannot be assumed to describe working conditions that existed in 2005, nor can it reflect altered tasks in 2020.
In litigation, an expert must establish the exact document version control and determine which specific assessment applied during the claimant’s period of alleged exposure. Tracking the historical evolution of the employer’s assessments demonstrates what was known about the risk at each stage, and whether changes in the physical process were evaluated contemporaneously or ignored.
COSHH assessments and workplace exposure claims
A COSHH assessment is a primary piece of contemporaneous evidence when investigating a workplace exposure claim, but it is only one component of the overall evidential picture.
In civil litigation, claims alleging occupational illness from hazardous substances tend to turn on two distinct issues, whether the employer breached the required standard of care, and whether that breach caused the claimant’s condition. A contemporaneous COSHH assessment is central to the first question. It demonstrates the employer’s state of knowledge at the material time, showing what chemical hazards were recognised and what control measures were deemed necessary.
However, a COSHH assessment is fundamentally a document of intent. It sets out the planned safe system of work, but it cannot prove what actually occurred on the workshop floor. The existence of a signed assessment does not establish that controls were operated correctly, that extraction was maintained, or that protective equipment was properly fitted and worn.
For this reason, the COSHH assessment must be tested against corroborating physical evidence. An expert will cross-reference the written assessment against safety data sheets, local exhaust ventilation test reports, maintenance records, air monitoring data, health surveillance records, and witness statements from workers.
The quality of historical documentation varies considerably. Older assessments may describe a process in broad generalities, or they may fail to capture non-routine tasks, equipment wash-downs, maintenance, and process deviations where peak exposures frequently occur.
A forensic evaluation of a workplace exposure claim therefore requires examining the complete factual matrix. The mere existence or absence of a written COSHH assessment should never be treated as conclusive proof of whether an employer met their legal duties or whether actionable exposure occurred.
What can a COSHH assessment tell an expert?
For an expert investigating a workplace exposure claim, a COSHH assessment provides vital evidence of the employer’s contemporaneous state of knowledge and their approach to managing chemical risks at a particular point in time.
It establishes what substances the employer identified as hazardous, which tasks were recognised as creating exposure, the anticipated exposure routes, and the control strategy deemed reasonably practicable at the material time.
Comparing successive assessments over time can also help establish whether chemical formulations, operating temperatures, production volumes, or engineering controls evolved during an individual’s employment.
However, an assessment must always be evaluated in its operational context. A document may record that local exhaust ventilation was provided, for example, but an expert will examine commissioning reports, maintenance logs, and statutory fourteen-month thorough examination records under Regulation 9 to determine whether that extraction system was properly designed, positioned, and achieving effective capture velocity in practice.
Similarly, where an assessment lists PPE as a control measure, an expert will evaluate whether that equipment was both adequate and suitable. This includes verifying whether gloves provided tested permeation breakthrough resistance against the specific chemicals under BS EN ISO 374, whether tight-fitting respirators were supported by valid face-fit testing certificates under HSG53, and whether operating conditions compromised equipment performance.
Crucially, what an assessment omits can be just as informative as what it records. If an assessment failed to identify process-generated fumes, ignored co-located workers sharing the room air, or lacked measurable operational review triggers, this provides significant evidence regarding whether the employer met the required standard of care.
This forensic distinction between documented intention and verified workplace reality is essential when reconstructing historical exposure.
When COSHH assessments are incomplete or unavailable
Not every workplace exposure investigation has access to a complete set of contemporaneous COSHH records.
Assessments may have been replaced following process modifications, historical paperwork may have been lost during company reorganisations, or older files may describe working conditions in terms too generic to assist the court.
The absence of a COSHH assessment confirms a failure of planning under Regulation 6, but it does not, on its own, prove that hazardous exposure occurred or establish medical causation. Conversely, an employer cannot assume that the absence of historical records prevents a claim from succeeding, particularly where statutory records that should have been retained have been lost. Similarly, a modern assessment cannot be relied upon to explain physical conditions that existed ten or twenty years earlier.
Where documentation is incomplete or unavailable, an expert must reconstruct historical working conditions using corroborating technical evidence. This forensic process combines occupational hygiene science with engineering analysis.
An expert evaluates historical purchasing records, material safety data sheets from the relevant era, plant layout drawings, and witness accounts detailing task duration and frequency. Where airborne measurements were never taken, exposure can often be modelled mathematically by evaluating process energy, application temperatures, chemical evaporation rates, and ventilation capacities. These estimates are then benchmarked against the statutory standards, Workplace Exposure Limits, and scientific knowledge in force at the material time.
Retrospective exposure reconstruction requires an understanding of both the physical behaviour of the substance and the operational reality of the engineering process in which it was used.
Why competent COSHH assessment matters
Under the COSHH Regulations and HSE Approved Code of Practice L5, assessments must be carried out by individuals with sufficient training, knowledge, and experience to understand the hazards, the physical release mechanisms, and the practical execution of the work.
Competence also involves recognising the boundaries of individual capability. Where tasks involve complex chemical mixtures, exothermic reactions, or specialised engineering controls, a competent assessment is rarely a solitary desk task. It requires collaboration between the operatives performing the work, line management, and technical specialists such as internal chemists, ventilation engineers, or occupational hygienists.
A generic or software-driven assessment that merely copies hazard statements from a safety data sheet without evaluating how substances are physically manipulated may not satisfy the legal requirement to be suitable and sufficient. In workplace exposure claims, producing a generic assessment can actively undermine the defence, providing evidence that the employer failed to properly evaluate the specific risks of the task.
A competent assessment must be specific to the workplace and the task. It should identify intrinsic chemical endpoints, evaluate the applied process energy, establish objective verification criteria for engineering controls, and set measurable operational review triggers.
This level of technical rigour is vital when historical records are scrutinised during litigation. A clear, process-based assessment demonstrates that the employer applied their mind to the work, providing valuable contemporaneous evidence that they met the expected standard of care.
Why COSHH assessments matter beyond compliance
A COSHH assessment does not only satisfy a statutory duty. It defines the operational boundaries of a safe system of work, bridging high-level risk governance with practical shop-floor containment.
When implemented effectively, a task-based assessment protects workers from long-latency, irreversible illness while protecting the organisation from operational disruption, regulatory enforcement, and civil compensation claims.
In workplace exposure claims, accurate contemporaneous assessments and supporting documentation provide direct evidence of whether an employer applied their mind to the work and maintained an active health and safety management system. For legal teams investigating alleged industrial illness, these records help establish whether working practices, chemical handling, and exposure controls fulfilled the expected standard of care.
How Finch Consulting can support workplace exposure assessments
Finch Consulting has more than thirty years of experience providing multi-disciplinary technical consultancy and independent expert witness services across high-hazard, manufacturing, and scientific sectors.
Our specialists assist duty holders, solicitors, insurers, and loss adjusters by conducting forensic investigations into chemical and workplace exposure disputes. We evaluate historical COSHH documentation, plant engineering, local exhaust ventilation performance, and occupational hygiene records to determine whether exposures were prevented or adequately controlled.
Where litigation arises, Finch provides independent expert opinion under Part 35 of the Civil Procedure Rules, acting on claimant, defendant, or single joint instructions. Our experts evaluate the material state of knowledge, assess the physical reality of the process, and deliver rigorous, objective reports addressing breach of duty, standard of care, and technical causation.
Frequently asked questions
Is a COSHH assessment a legal requirement?
Yes. Regulation 6 of the Control of Substances Hazardous to Health Regulations 2002 requires employers to carry out a suitable and sufficient risk assessment before allowing any work that could expose employees or other people to hazardous substances. Where an employer employs five or more staff, the significant findings of the assessment must be formally recorded.
What is the difference between a COSHH assessment and a safety data sheet?
A safety data sheet is a product document provided by a chemical manufacturer, outlining intrinsic hazards, classification codes, and general handling advice. A safety data sheet is not a risk assessment. Furthermore, safety data sheets do not exist for process-generated hazards such as welding fumes or mineral dusts. A COSHH assessment evaluates the actual task, examining how substances are physically manipulated, realistic exposure pathways, who may be affected, and the specific engineering controls required on the shop floor.
Who can carry out a COSHH assessment?
A COSHH assessment must be carried out by a competent person with sufficient training, practical knowledge, and experience to understand the hazards and the work activity. Competence also involves recognising the limits of personal expertise. For complex chemistry, exothermic reactions, or specialised extraction systems, assessments should be completed collaboratively with input from operators, line managers, and technical specialists such as occupational hygienists or ventilation engineers.
Does a COSHH assessment need to be reviewed?
Yes. Under Regulation 6(3), employers have an absolute legal duty to review an assessment immediately if there is reason to suspect it is no longer valid, or if significant changes occur in the work. Assessments must be updated following process changes, chemical substitutions, engineering control failures, adverse health surveillance results, or workforce vulnerability changes such as a worker declaring pregnancy. For workplace exposure claims, establishing which specific historical version applied at the material time is critical.
Can a COSHH assessment be used as evidence in a workplace exposure claim?
Yes. A contemporaneous COSHH assessment provides vital evidence regarding the employer’s state of knowledge at the material time, showing which substances were recognised as hazardous and what control strategy was planned. However, an assessment is a document of intent and does not prove that controls were operating effectively on the day. An expert witness will test the written assessment against corroborating physical evidence, including statutory ventilation test records, equipment maintenance logs, air monitoring data, health surveillance files, and witness testimony.