COSHH assessment guide for construction sites

What COSHH covers on construction sites

COSHH applies to any substance that can cause ill health through inhalation, skin contact, ingestion, or injection into the body. On construction sites, this covers two categories:

• Products brought to site: Paints, adhesives, sealants, cleaning chemicals, fuels, oils, resins, and any other product with a safety data sheet (SDS) indicating hazardous properties.
• Substances generated by work activities: Silica dust from cutting or grinding concrete, stone, or brick. Wood dust from cutting timber. Welding fumes. Lead dust during refurbishment of older buildings. Asbestos fibres during demolition or strip-out (though asbestos has its own separate regulations under CAR 2012).

The regulations require employers to: prevent exposure where reasonably practicable, or adequately control exposure where prevention is not possible. The hierarchy of control runs from elimination (do not use the substance at all) through substitution, engineering controls, administrative controls, and finally personal protective equipment (PPE) as the last resort.

Common hazardous substances in construction

These are the substances that appear most frequently in construction COSHH assessments:

• Silica dust (RCS): Respirable crystalline silica is generated whenever concrete, stone, brick, morite, or sandstone is cut, drilled, ground, or demolished. Long-term exposure causes silicosis, an irreversible lung disease, and is linked to lung cancer. The workplace exposure limit (WEL) is 0.1 mg/m3. This is the single most significant COSHH risk on most construction sites.
• Cement: Wet cement is alkaline (pH 12-13) and causes chemical burns and contact dermatitis. Dry cement dust is also an irritant. Cement dermatitis is one of the most commonly reported occupational skin diseases in construction.
• Wood dust: Hardwood dust is classified as a carcinogen (Group 1). Softwood dust causes respiratory sensitisation. The WEL for hardwood dust is 3 mg/m3 and for softwood dust is 5 mg/m3.
• Solvents: Found in paints, varnishes, adhesives, and cleaning products. Effects include headaches, dizziness, and long-term neurological damage. Some solvents are also flammable, creating dual risks.
• Isocyanates: Used in polyurethane spray foams, some paints, and adhesives. Isocyanates are the leading cause of occupational asthma in the UK. Once sensitised, a worker may react to extremely low concentrations.
• Lead: Encountered during refurbishment of pre-1960s buildings (lead paint, lead pipework). The Control of Lead at Work Regulations 2002 apply additional requirements on top of COSHH.

The COSHH assessment process

A COSHH assessment must be "suitable and sufficient." For construction, this means:

1. Identify the hazards: List every substance used on site and every process that generates hazardous substances. Collect safety data sheets (SDS) for all products. Identify processes that create dust, fumes, or vapour.
2. Identify who is exposed: Not just the person using the substance, but anyone nearby. A worker cutting concrete creates a dust cloud that affects everyone in the area. Consider whether members of the public could be exposed at the site boundary.
3. Evaluate the risk: Consider the toxicity of the substance, the amount used, the duration and frequency of exposure, and the effectiveness of any existing controls. Refer to workplace exposure limits where they exist.
4. Decide on controls: Apply the hierarchy of control. Can the substance be eliminated or substituted? Can the process be changed to reduce exposure? What engineering controls (LEV, water suppression, enclosure) are needed? What PPE is required as a last line of defence?
5. Record the assessment: Document the findings, the control measures, and who is responsible for implementing them. The assessment must be accessible to workers and supervisors.
6. Review regularly: Assessments must be reviewed when substances change, processes change, or there is reason to believe they are no longer valid. An annual review is good practice even if nothing has changed.

Assessments can be grouped where the substance, the task, and the controls are the same. For example, you might have a single assessment for "cutting concrete and masonry" that covers silica dust exposure across multiple activities, rather than separate assessments for each trade.

Control measures

The hierarchy of control applied to common construction COSHH risks:

• Elimination: Use pre-cast or pre-cut materials to avoid on-site cutting. Specify water-based products instead of solvent-based. Design out the need for hazardous processes where possible.
• Substitution: Replace high-silica materials with lower-silica alternatives. Use low-isocyanate spray foams. Choose low-VOC paints and adhesives.
• Engineering controls: Water suppression on cutting equipment (reduces silica dust by up to 90%). Local exhaust ventilation (LEV) on dust-generating tools. On-tool extraction for wood dust. Enclosed mixing areas for cement.
• Administrative controls: Restrict access to areas where hazardous work is taking place. Rotate workers to reduce individual exposure time. Schedule dusty work when fewer people are nearby.
• PPE: RPE (respiratory protective equipment) appropriate to the substance and concentration. Chemical-resistant gloves for cement and solvent handling. Face shields for splash risks. PPE must be face-fit tested for RPE and maintained properly.

PPE should never be the primary control. An HSE inspector who sees workers relying solely on dust masks while dry-cutting concrete will want to know why water suppression or on-tool extraction is not being used.

Record keeping: the 40-year rule

COSHH record keeping catches many construction employers off guard. The rules are:

• COSHH assessments: Must be recorded and kept for at least five years, or longer if the assessment relates to substances with long-latency health effects.
• Health surveillance records: Where health surveillance is required (for example, lung function testing for workers exposed to silica dust, or skin checks for cement handlers), the records must be kept for 40 years from the date of the last entry. This applies to individual worker records.
• Exposure records: Records of workplace exposure monitoring (air sampling results) must also be kept for 40 years where the substance can cause cancer or chronic disease.

The 40-year retention period reflects the fact that diseases like silicosis, mesothelioma, and occupational cancer can take decades to develop. A worker exposed to silica dust in 2026 may not develop symptoms until 2050. The employer (or their successors) must be able to produce records of exposure and health surveillance for that entire period.

For construction companies, this means COSHH records cannot live in paper files in site cabins that are dismantled at the end of a project. They need to be in a system that outlasts individual projects and can be retrieved decades later.

AttendIQ stores compliance documents against each worker's profile in a centralised, searchable system. While COSHH assessments are typically managed at the project level, linking health surveillance records and training certificates to individual workers ensures that records follow the worker, not the project. When you need to show an inspector (or a court) what exposure a worker had and what health surveillance was carried out, the records are there.

Training and awareness

COSHH requires employers to provide information, instruction, and training to workers who may be exposed to hazardous substances. For construction, this should cover:

• What hazardous substances are present on the site and what risks they pose.
• The control measures in place and why they must be followed.
• How to use engineering controls (water suppression, LEV) correctly.
• How to use, fit-test, and maintain RPE and other PPE.
• What to do if controls fail or an exposure incident occurs.
• Health surveillance requirements and the importance of attending appointments.

COSHH awareness should be part of every site induction. Workers need to know the specific COSHH risks on that particular project, not just generic information about hazardous substances. If the project involves extensive concrete cutting, the induction should cover silica dust risks, the water suppression systems in use, RPE requirements, and the dust-free zones.

Training records should be kept alongside COSHH assessments. If a worker later develops an occupational disease, the employer will need to demonstrate that training was provided and that the worker was made aware of the risks and the controls.