If you work with cement, cutting concrete, welding steel, or applying adhesives and sealants, you are handling substances that can harm health. The Control of Substances Hazardous to Health Regulations 2002 (COSHH) require UK employers to assess these risks and put controls in place before work begins. Construction ranks among the highest industries for occupational lung disease, skin disease, and cancer linked to substance exposure, according to the Health and Safety Executive (HSE). Understanding COSHH is not a box-ticking exercise—it is essential to keeping your workforce safe.

What Does COSHH Cover on Construction Sites?

COSHH applies to any substance hazardous to health. In construction, this includes:

  • Dusts: Respirable crystalline silica from cutting, drilling, or grinding concrete, stone, bricks, or mortar; wood dust from joinery; cement dust from mixing and pouring.
  • Chemicals: Cleaning products, paints, solvents, fuels, adhesives, waterproofing agents, and laboratory reagents.
  • Fumes: Welding fumes containing manganese and hexavalent chromium (classified as a Class A carcinogen since 2019); soldering fumes; vehicle exhausts in enclosed spaces.
  • Vapours and mists: From solvents, fuels, paint thinners, sprays, machining coolants, and chemical cleaning.
  • Gases: Asphyxiating gases such as nitrogen and argon in confined spaces; industrial gases in healthcare and laboratories.
  • Biological agents: Bacteria, viruses, and fungi encountered in demolition, sewage work, or agriculture.

Notable exceptions include asbestos, which falls under the Control of Asbestos Regulations 2012, and lead, which has dedicated regulatory frameworks. However, many construction tasks—mixing mortar, spraying isocyanate-containing paints, sanding wood, or welding—generate hazardous substances that COSHH directly governs.

What Is a Workplace Exposure Limit?

A Workplace Exposure Limit (WEL) is the maximum legal concentration of a hazardous substance in the air that a worker can be exposed to over a specified time period. Think of it as a speed limit for the air your team breathes: exceeding it increases the risk of illness.

WELs are set by the HSE based on scientific evidence about the concentration at which substances start to cause harm. They form a cornerstone of COSHH compliance. Employers must prevent exposure or, where that is not reasonably practicable, reduce it to below the WEL. The HSE publishes these limits in document EH40, which lists WELs for hundreds of airborne substances.

In practice, a WEL represents a point on a scale of exposure below which, according to current scientific knowledge, no harm to worker health is expected from day-to-day inhalation exposure. Staying below this ceiling is non-negotiable—breaching a WEL is a legal failure, not just a technical one.

What Does a COSHH Assessment Cover?

Every employer must carry out a COSHH assessment before workers are exposed to hazardous substances. The assessment identifies what the substance is, who is at risk, and how exposure can be controlled. Key elements include:

  • Substance identification: What is the substance, its form (dust, vapour, liquid), and which Safety Data Sheet applies?
  • Who is at risk: Operatives directly using the substance and others nearby who may be exposed.
  • Route of exposure: Inhalation, skin contact, ingestion, or injection.
  • Workplace Exposure Limit: The HSE-set limit from EH40 for airborne substances.
  • Control measures: Following the hierarchy of control—eliminate, substitute, engineering controls (such as local exhaust ventilation), administrative measures, and respiratory protective equipment (RPE).
  • Emergency arrangements: Spillage response, first aid for exposure, and fire or explosion risk.

COSHH assessments are typically referenced within Risk Assessment and Method Statements (RAMS) under the "Substances" section. The RAMS sets out which substances are used in the work activity; the COSHH assessment provides the detailed substance-level risk evaluation. A well-prepared RAMS package includes both documents together.

Common Construction Substances Requiring COSHH Assessment

Several substances appear repeatedly across construction sites and demand careful control:

  • Silica dust: Generated from cutting, drilling, grinding, or sanding concrete, stone, bricks, or mortar. Respirable crystalline silica is a known carcinogen.
  • Cement: Cement dust and wet cement can cause skin sensitisation and dermatitis due to hexavalent chromium content.
  • Wood dust: Both hardwood and softwood dust from cutting and sanding. Hardwood dust is a recognised carcinogen.
  • Isocyanates: Found in spray paints, foam insulation, and polyurethane flooring systems. Isocyanates are respiratory sensitisers.
  • Welding fume: Metal fume containing manganese and hexavalent chromium, classified as a Class A carcinogen.
  • Lead: In pre-1978 paint, lead sheet roofing and flashing, and lead pipes.
  • Solvents: Present in adhesives, paints, sealants, and cleaning products.

For more on chemical product safety, see our guide on Safety Data Sheets and CLP labelling of construction chemicals.

The Compliance Framework: What You Must Do

COSHH compliance is systematic and demands more than knowing the numbers. Employers must:

  • Risk assessment: Identify hazardous substances on site and determine how, when, and where workers might be exposed.
  • Control measures: Implement practical strategies to reduce exposure—better ventilation, process changes, substitution with less hazardous alternatives.
  • Monitoring: Regularly measure the concentration of airborne substances to verify that controls are working and WELs are not being breached.
  • Record keeping: Maintain detailed records of assessments, monitoring results, and implemented control measures.
  • Information and training: Ensure workers understand the risks, the controls in place, and how to use personal protective equipment correctly.
  • Health surveillance: Where necessary, arrange medical monitoring for workers exposed to certain high-risk substances.

For further reading on the classification and labelling of chemically technical products and their regulatory requirements, consult our article on biocides and pot preservatives in construction chemical products.

Practical Take-Away for the Site

COSHH is not a paperwork burden—it is a legal and practical tool to prevent serious, often irreversible, health harm. If your project involves cutting, grinding, welding, painting, gluing, or mixing, you are working with hazardous substances. Identify them, assess the risk, control exposure below the WEL, and document everything. The HSE enforces these requirements rigorously, and non-compliance can result in enforcement notices, prosecution, and civil claims. More importantly, effective COSHH management protects the people who do the work.