COSHH Assessment Guide for Construction: What You Need to Know

What Is COSHH?

COSHH stands for the Control of Substances Hazardous to Health. It is a set of regulations under UK law — specifically the Control of Substances Hazardous to Health Regulations 2002 (as amended) — that require employers to control exposure to hazardous substances in the workplace. In construction, hazardous substances are everywhere: cement, silica dust, wood dust, solvents, adhesives, paints, resins, asbestos fibres, diesel exhaust, and dozens more.

A COSHH assessment is a documented evaluation of the health risks from hazardous substances used or encountered during a specific work activity, along with the control measures needed to prevent or reduce exposure. It is a legal requirement, not a best practice suggestion. Failure to carry out adequate COSHH assessments can result in enforcement action from the Health and Safety Executive (HSE), including improvement notices, prohibition notices, and prosecution.

The construction industry has some of the highest rates of occupational disease in the UK. Silicosis, occupational asthma, dermatitis, and cancer linked to workplace substance exposure affect thousands of construction workers every year. Many of these conditions develop over years of low-level exposure, which is why COSHH assessments matter even when the immediate risks seem low.

Legal Requirements Under COSHH Regulations

The COSHH Regulations 2002 place specific duties on employers. These apply to all construction businesses, from sole traders to major contractors. The key obligations are:

• Assess the risks: Identify which hazardous substances are present or will be used, and evaluate the health risks from exposure (Regulation 6).
• Prevent or control exposure: Where possible, prevent exposure entirely by eliminating the substance or substituting a less hazardous alternative. Where prevention is not reasonably practicable, control exposure to below the Workplace Exposure Limit (WEL) using appropriate measures (Regulation 7).
• Use and maintain controls: Ensure that control measures (ventilation, extraction, enclosures, PPE) are properly used, maintained, and tested (Regulations 8 and 9).
• Monitor exposure: Where there is a risk of exposure exceeding the WEL, carry out air monitoring to check that controls are effective (Regulation 10).
• Health surveillance: Where employees are exposed to substances linked to identifiable diseases, provide health surveillance (Regulation 11). In construction, this commonly applies to workers exposed to silica dust, isocyanates, and certain solvents.
• Inform, instruct and train: Provide employees with information about the substances they work with, the risks, and the controls in place (Regulation 12).

These are not optional. They apply to every construction project where hazardous substances are present, which in practical terms means every project.

Common Hazardous Substances on Construction Sites

Construction sites contain a wide range of hazardous substances. Here are the most commonly encountered:

Silica Dust

Generated when cutting, drilling, grinding, or sanding concrete, brick, stone, mortar, and many other construction materials. Respirable crystalline silica (RCS) causes silicosis, a serious and irreversible lung disease, and is classified as a human carcinogen. The Workplace Exposure Limit is 0.1 mg/m³. This is the single biggest substance-related health risk in construction.

Cement and Concrete

Wet cement is highly alkaline (pH 12-13) and causes severe chemical burns to skin. Chromium VI in cement causes allergic contact dermatitis, which is a lifelong condition once sensitised. Dry cement dust irritates the respiratory system. Every bricklayer, plasterer, and groundworker is exposed.

Wood Dust

Both hardwood and softwood dust are hazardous. Hardwood dust is classified as a carcinogen (nasal cancer). The WEL for hardwood dust is 3 mg/m³ and for softwood dust is 5 mg/m³. Carpenters, joiners, and anyone cutting MDF or plywood are exposed daily.

Solvents and Paints

Many construction products contain volatile organic compounds (VOCs) and solvents that cause headaches, dizziness, and long-term neurological damage. Solvent-based paints, varnishes, adhesives, sealants, and cleaning agents are common sources. Isocyanates in two-pack paints and spray foams can cause occupational asthma.

Asbestos

While not a substance you would bring to site, asbestos is frequently encountered during refurbishment and demolition of buildings built before 2000. Asbestos is covered by its own regulations (Control of Asbestos Regulations 2012) but interacts with COSHH. If you disturb asbestos without proper controls, you are committing a criminal offence.

Diesel Exhaust Emissions (DEE)

Plant and equipment on construction sites, including generators, excavators, and dump trucks, produce diesel exhaust containing particulate matter classified as a carcinogen. Poorly ventilated areas such as basements and tunnels present the highest risk.

How to Carry Out a COSHH Assessment: The 5 Steps

The HSE recommends a five-step approach to COSHH assessment, which aligns with the general risk assessment framework:

Step 1: Identify the Hazardous Substances

List every substance that will be used or generated during the work activity. This includes products you bring to site (adhesives, paints, sealants) and substances generated by the work (silica dust from cutting concrete, wood dust from sawing timber, welding fumes). For every product, obtain the Safety Data Sheet (SDS) from the manufacturer — this is your primary source of hazard information.

Do not forget substances generated by the process. Cutting a concrete block with a disc cutter generates silica dust even though you did not bring silica to site.

Step 2: Assess the Risks

For each substance, evaluate who is exposed, how they are exposed (inhalation, skin contact, ingestion), how much exposure occurs, and how often. Consider both the workers carrying out the task and anyone else nearby. The Safety Data Sheet provides hazard classifications, WELs, and health effects. Consider the duration of exposure, the quantity of substance, and whether the work is indoors or outdoors.

Step 3: Decide on Control Measures

Apply the hierarchy of controls in order of preference:

• Elimination: Can you remove the substance entirely? Use mechanical fixings instead of adhesive. Use pre-cast elements instead of cutting on site.
• Substitution: Can you use a less hazardous alternative? Water-based paint instead of solvent-based. Low-chromium cement instead of standard OPC.
• Engineering controls: Local exhaust ventilation (LEV) on cutting equipment. Water suppression for dust. Enclosed mixing systems.
• Administrative controls: Limit exposure time. Rotate workers. Restrict access to work areas. Provide training.
• Personal Protective Equipment (PPE): The last resort. RPE (respiratory protective equipment) must be face-fit tested. Gloves must be appropriate for the specific substance. PPE is always used alongside other controls, not instead of them.

Step 4: Implement and Record

Put the control measures into practice and document the assessment. The written record must include: the substances identified, the health risks, who is at risk, the control measures in place, and any monitoring or health surveillance requirements. If you employ five or more people, the written record is a legal requirement. Even if you employ fewer, keeping a written record is strongly recommended.

Step 5: Review and Update

COSHH assessments are not static documents. Review them when the work activity changes, when new substances are introduced, when monitoring shows controls are inadequate, when health surveillance reveals a problem, or at regular intervals regardless (annually is standard practice). A COSHH assessment that was last reviewed three years ago is unlikely to reflect current conditions.

Record Keeping Obligations

COSHH Regulation 6(3) requires employers with five or more employees to record the significant findings of the assessment. In practice, you should record:

• The date of the assessment and the name of the assessor
• The task and location being assessed
• The hazardous substances identified, with SDS references
• Who is exposed and how
• The control measures in place
• Any monitoring or health surveillance required
• The review date

Health surveillance records must be kept for 40 years from the date of the last entry (Regulation 11(4)). Exposure monitoring records must be kept for at least 5 years, or 40 years if the substance is linked to specific occupational diseases.

How MyQS Generates COSHH Assessments

Creating COSHH assessments for every substance on every project is a significant administrative burden. MyQS automates this by generating project-specific COSHH assessments based on your scope of works. When you create a project and define the trades and activities involved, the system identifies the relevant hazardous substances, references current Workplace Exposure Limits, applies the hierarchy of controls, and produces a professional assessment document ready for review and use on site.

The generated assessments include substance identification, exposure routes, control measures, PPE requirements, emergency procedures, and monitoring recommendations. They are specific to your project, not generic templates. You review, adjust if needed, and download as a PDF for your site files. This ensures compliance without hours of manual document preparation.

Frequently Asked Questions

Do I need a separate COSHH assessment for every substance?

Not necessarily. You can group substances if they are used in the same task and the exposure route, risks, and control measures are similar. For example, a single COSHH assessment might cover all water-based paints used on a decoration task. However, substances with significantly different hazard profiles should have separate assessments. Silica dust and a solvent-based adhesive require different assessments because the risks and controls are fundamentally different.

Who is qualified to carry out a COSHH assessment?

COSHH Regulation 6(2) states that the assessment must be carried out by a "competent person." This means someone with sufficient training, knowledge, and experience to understand the hazards, interpret Safety Data Sheets, and select appropriate control measures. There is no specific qualification required by law, but IOSH or NEBOSH training is common. For complex situations involving high-risk substances, you may need specialist occupational hygiene advice.

What are the penalties for not having COSHH assessments?

The HSE can issue improvement notices requiring you to carry out assessments within a set timeframe, or prohibition notices stopping work until assessments are in place. Prosecution for COSHH failures can result in unlimited fines and, in serious cases, imprisonment. Beyond the legal penalties, the human cost of occupational disease caused by uncontrolled substance exposure is immense and entirely preventable.