COSHH · Mandatory · Pre-Construction

COSHH Assessment — General Site

The General Site COSHH Assessment identifies hazardous substances commonly encountered across construction activities and establishes baseline control measures. It covers dust, cleaning chemicals, fuels, and commonly used construction materials. This assessment provides the overarching framework under which substance-specific COSHH assessments sit.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. COSHH Regs 2002 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	COSHH Regulations 2002 (Regs 6, 7, 8, 9, 10, 11, 12) + Health and Safety at Work Act 1974 (Sections 2, 3) + Management of Health and Safety at Work Regulations 1999 (Regulation 3)
Who conducts it	The employer (or a competent person appointed by the employer) must carry out the assessment. The assessor must have sufficient knowledge of the work process, the substances involved, and the principles of risk assessment.
Frequency	Before work with a hazardous substance begins; reviewed annually as a minimum; reviewed immediately when there is reason to believe the assessment is no longer valid (e.g. change of substance, process, or control measure)
WEL (general)	Respirable dust: 4 mg/m³ (8-hr TWA); Inhalable dust: 10 mg/m³ (8-hr TWA). Substance-specific WELs are listed in EH40 and take precedence where they exist.
8 Principles	Schedule 2A of the COSHH Regulations sets out the 8 Principles of Good Practice for the control of exposure to substances hazardous to health. These form the hierarchy of control.
Prosecution example	A Bristol construction company was fined £100,000 after workers were exposed to hazardous substances without adequate COSHH assessments or controls in place.
SDS requirement	The Safety Data Sheet (SDS) is the starting point for identifying hazards but is not itself a COSHH assessment. The SDS provides information on hazards, exposure limits, and recommended controls, which must then be applied to the specific work activity in the COSHH assessment.

1. What Is a COSHH Assessment?

A COSHH assessment is a structured evaluation required under Regulation 6 of the Control of Substances Hazardous to Health Regulations 2002 (COSHH). It identifies the hazardous substances present in a work activity, evaluates the risk of exposure to workers, and determines the control measures necessary to prevent or adequately control that exposure. The assessment must be suitable and sufficient — meaning it must be specific to the work being carried out, not a generic document copied from another site or project.

COSHH applies to a broad range of substances: chemicals, products containing chemicals, dusts, fumes, vapours, mists, gases, biological agents, and any other material that can harm health through inhalation, skin contact, ingestion, or injection. On a construction site, common COSHH substances include cement, silica dust, wood dust, welding fumes, paints, solvents, adhesives, resins, asbestos fibres (where encountered), and man-made mineral fibres.

The legal duty under Section 2 of the Health and Safety at Work Act 1974 requires the employer to ensure, so far as is reasonably practicable, the health and safety of employees. Regulation 3 of MHSWR 1999 requires a suitable and sufficient risk assessment. COSHH Regulation 6 makes this obligation specific to hazardous substances: no work that is liable to expose any employee to a substance hazardous to health shall be carried out unless the employer has made a suitable and sufficient assessment of the risk and of the steps that need to be taken to meet the requirements of COSHH.

COSHH assesses exposure, not just the substance

A common misunderstanding is that a COSHH assessment is simply a record of what substances are on site. In fact, COSHH requires an assessment of the exposure — how workers come into contact with the substance, by what route (inhalation, skin, ingestion), for how long, at what concentration, and under what conditions. The same substance can present very different risks depending on the work activity. Cement in a sealed bag presents minimal risk; cement being mixed in a confined space presents a serious inhalation and skin contact risk. The assessment must address the specific exposure scenario, not just identify the substance.

2. The 8 Principles of Good Practice (Schedule 2A)

Schedule 2A of the COSHH Regulations 2002 sets out the eight principles of good practice for the control of exposure to substances hazardous to health. These principles form the hierarchy of control and must be applied in order. The assessment must demonstrate that higher-order controls have been considered before resorting to lower-order controls such as personal protective equipment.

Principle	Description	Construction example
1. Design and operate processes to minimise emission, release, and spread	Select work methods and processes that inherently produce less exposure.	Use pre-mixed concrete delivered by chute rather than mixing dry cement on site. Use water-based paints instead of solvent-based where technically feasible.
2. Take into account all routes of exposure	Consider inhalation, skin absorption, ingestion, and injection — not just the most obvious route.	Cement presents both an inhalation risk (dry dust) and a skin contact risk (wet alkaline burns). Both routes must be assessed and controlled separately.
3. Control exposure by measures proportionate to the health risk	The level of control must match the severity and likelihood of the health effect.	Silica dust (a known carcinogen, WEL 0.1 mg/m³) requires more stringent controls than general inhalable dust (WEL 10 mg/m³).
4. Choose the most effective and reliable control options	Prefer engineering controls (elimination, substitution, enclosure, LEV) over procedural controls and PPE.	On-tool dust extraction on a concrete cutter is more effective and reliable than relying on an operative to wear RPE correctly throughout a shift.
5. Where adequate control cannot be achieved by other means, provide PPE in combination with other controls	PPE is the last resort, not the first. Where PPE is needed, it supplements other controls rather than replacing them.	An operative cutting concrete uses on-tool water suppression (engineering control) plus RPE (PPE) — not RPE alone.
6. Check and review regularly all control measures	Controls must be maintained, tested, and reviewed to confirm they remain effective.	LEV systems must be tested at least every 14 months under COSHH Regulation 9. RPE must be examined and maintained, and face-fit testing must be repeated.
7. Inform and train all employees on the hazards and controls	Workers must understand what substances they are exposed to, what the health effects are, and how the controls work.	Toolbox talks on cement burns, silica dust, and the correct use and limitations of RPE. Training records retained.
8. Ensure that the introduction of control measures does not increase the overall risk	A control measure that reduces one risk must not create or increase another.	Using LEV in a confined space may create a negative pressure environment that draws in contaminants from elsewhere. The control must be considered in context.

RPE is the last resort, not the first line of defence

Respiratory protective equipment (RPE) sits at the bottom of the hierarchy of control. Principle 5 requires that RPE is only used where adequate control of exposure cannot be achieved by other means — elimination, substitution, engineering controls (enclosure, LEV), or procedural controls. Where RPE is required, it must be suitable for the substance and concentration, face-fit tested to the wearer, maintained, and used correctly. Relying on RPE as the sole control is a common enforcement action trigger because it depends entirely on correct selection, fit, maintenance, and wearer compliance.

3. What the Assessment Must Cover

A COSHH assessment must be systematic and comprehensive. The following table sets out each element that a suitable and sufficient assessment must address. Omitting any element renders the assessment inadequate and non-compliant with Regulation 6.

Element	What it means	Common failure
Substance identity	Full product name, chemical name(s), CAS number(s) where applicable. The SDS provides this information.	Recording only the trade name without identifying the hazardous chemical components (e.g. "PVA adhesive" without identifying the vinyl acetate monomer content).
Hazard profile	Classification of the substance: what health effects it can cause (irritant, corrosive, sensitiser, carcinogen, toxic, etc.), and the routes of exposure (inhalation, skin, ingestion).	Copying H-statements from the SDS without translating them into plain language that workers can understand.
Who is exposed	Identify all persons who may be exposed — not just the operative using the substance but also those nearby (bystander exposure), those who enter the area after use, and maintenance personnel who may encounter residues.	Assessing only the primary user and ignoring bystander exposure or exposure during clean-up and disposal.
Exposure route	How workers are exposed: inhalation of dust, fume, vapour, or mist; skin or eye contact (liquid, paste, dust); ingestion (hand-to-mouth transfer); injection (high-pressure systems).	Assessing inhalation only and ignoring skin exposure, which is the primary route for many construction substances including wet cement, epoxy resins, and isocyanates.
WEL / OEL	The workplace exposure limit from EH40 (or the manufacturer’s recommended OEL if no statutory WEL exists). The assessment must state the relevant limit and assess whether exposure is likely to exceed it.	Not recording the WEL, or recording it but not assessing whether the work activity is likely to produce exposure at or above the limit.
Current controls	The controls currently in place: elimination, substitution, engineering controls (LEV, enclosure, water suppression), procedural controls (restricted access, reduced exposure time), and PPE.	Listing controls that are aspirational ("LEV will be provided") rather than confirmed as in place and functioning.
Adequacy of controls	A judgement on whether the current controls are sufficient to prevent or adequately control exposure. This is the core of the assessment.	Stating "controls adequate" without any reasoning or evidence, particularly where the only control is RPE.
Actions required	Where controls are not adequate, the specific actions needed to achieve adequate control — with responsible person and target date.	No action plan where the assessment identifies that controls are inadequate. The assessment identifies the gap but does not close it.
Health surveillance	Whether health surveillance is required under Regulation 11. Health surveillance is required where there is a reasonable likelihood that a disease or adverse health effect associated with exposure may occur under the conditions of work despite controls.	Not identifying that health surveillance is required — particularly for silica (lung function), cement/epoxy (dermatitis), isocyanates (respiratory sensitisation), and wood dust (respiratory surveillance).

4. Common Mistakes

Using the Safety Data Sheet as the COSHH assessment

The SDS is a manufacturer’s document that provides information about the substance in general terms. It is not a COSHH assessment. A COSHH assessment must evaluate the specific exposure in the specific work activity on the specific site. The SDS is the input to the assessment, not the assessment itself. Filing the SDS and claiming "COSHH assessment done" is one of the most common compliance failures on construction sites and is routinely cited in HSE enforcement actions.

Producing generic assessments that do not reflect actual site conditions

A COSHH assessment copied from a template or another project without being adapted to the actual work conditions, substances, quantities, exposure durations, and controls on the current site is not suitable and sufficient. The assessment must reflect the reality of how the substance is used on this site, by these workers, under these conditions. Generic assessments fail because they do not identify the specific exposure scenario and therefore cannot identify the specific controls needed.

Not reviewing the assessment when work conditions change

A COSHH assessment is not a one-time document. It must be reviewed whenever there is reason to believe it is no longer valid: when the substance changes, when the work method changes, when the environment changes (e.g. moving from outdoor to enclosed work), when exposure monitoring shows levels approaching the WEL, or when health surveillance identifies early signs of ill health. As a minimum, assessments should be reviewed annually. Failure to review is a breach of Regulation 6(3).

Relying on RPE as the sole control measure

RPE sits at the bottom of the hierarchy of control (Principle 5 of Schedule 2A). Using RPE as the sole control measure is only acceptable where it can be demonstrated that all higher-order controls have been considered and are not reasonably practicable. In most construction scenarios, engineering controls such as water suppression, on-tool extraction, or LEV are available and must be implemented before or alongside RPE. HSE inspectors routinely challenge assessments where RPE is the only control listed.

Not identifying substances produced by the work activity itself

COSHH applies not only to commercial products and chemicals brought onto site, but also to substances generated by the work process. Cutting concrete produces respirable crystalline silica. Welding produces metal fumes. Grinding produces fine metalite dust. Burning treated timber produces toxic gases. These substances will not appear on an SDS because they are not purchased products — they are by-products of the work activity. The COSHH assessment must identify and assess these exposures as well as exposures to purchased substances.

5. Related Documents

The general COSHH assessment forms the foundation for all substance-specific assessments on a construction project. The following documents are directly related and should be cross-referenced.

Document	Relationship
C6 — COSHH Assessment: Silica Dust	Silica dust requires a substance-specific COSHH assessment due to its carcinogenic classification and low WEL (0.1 mg/m³). The general COSHH assessment identifies silica as a site hazard; the C6 assessment provides the detailed controls for cutting, grinding, and drilling activities.
C7 — COSHH Assessment: Wood Dust	Wood dust is a respiratory sensitiser (hardwood dust is also a carcinogen). The general COSHH assessment identifies wood dust as a site hazard where joinery or carpentry work is carried out; the C7 assessment details the specific WEL, LEV requirements, and health surveillance.
C8 — COSHH Assessment: Welding Fumes	Welding fumes are now classified as carcinogenic (IARC Group 1). The general COSHH assessment identifies welding fume as a site hazard; the C8 assessment provides the specific controls including LEV, RPE selection, and health surveillance requirements.
C13 — Hazardous Materials Register	The hazardous materials register is the site-wide record of all substances hazardous to health present on site. It provides the starting point for identifying which COSHH assessments are needed and ensures no substance is overlooked.
C14 — SDS Register	The SDS register holds the safety data sheets for all commercial chemical products on site. These provide the hazard information, WELs, and recommended controls that feed into each COSHH assessment.

6. Frequently Asked Questions

Who is legally responsible for the COSHH assessment?▾

The employer is responsible. Under Regulation 6 of COSHH 2002, the employer must not carry out work that is liable to expose employees to substances hazardous to health unless a suitable and sufficient assessment of the risk has been made. The employer may appoint a competent person to carry out the assessment on their behalf, but the legal duty remains with the employer. On a construction site, each contractor is responsible for the COSHH assessments relevant to their own work activities. The principal contractor has a duty under CDM 2015 to ensure that contractors have adequate COSHH arrangements in place but is not required to produce assessments for work carried out by other contractors.

Is a COSHH assessment required for brief or occasional exposure?▾

Yes. There is no exemption for short-duration or infrequent exposure. COSHH Regulation 6 applies to any work that is liable to expose an employee to a substance hazardous to health. A brief exposure to a highly toxic substance (e.g. isocyanate spray mist) can cause irreversible health effects. The assessment must evaluate the exposure based on the actual conditions — if the conclusion is that the risk from a brief exposure is low and no additional controls beyond those already in place are needed, that is a valid outcome of the assessment. But the assessment itself must still be carried out.

What records must be kept?▾

COSHH Regulation 6(4) requires that the significant findings of the assessment are recorded and retained. For assessments involving substances that may cause cancer, asthma, or genetic damage (e.g. silica, hardwood dust, isocyanates), exposure records must be kept for 40 years. For all other substances, there is no specified retention period but records should be kept for the duration of employment plus a reasonable period (typically 5-10 years). Health surveillance records under Regulation 11 must be kept for 40 years from the date of the last entry.

When is health surveillance required?▾

Health surveillance is required under COSHH Regulation 11 where: (a) an employee is exposed to a substance listed in Schedule 6 (which includes substances causing occupational asthma, dermatitis, and other specific conditions); or (b) there is a reasonable likelihood that an identifiable disease or adverse health effect will result from the exposure. In construction, the most common triggers are: exposure to silica dust (lung function testing); exposure to cement, epoxy resins, or other skin sensitisers (skin surveillance for dermatitis); exposure to isocyanates (respiratory surveillance including lung function and symptom questionnaire); and exposure to wood dust (respiratory surveillance). The employer must ensure that appropriate health surveillance is in place and that records are maintained.

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