7.1 — What is COSHH?

COSHH stands for the Control of Substances Hazardous to Health. The COSHH Regulations 2002 require employers — and self-employed persons — to assess the risks from hazardous substances used at work and to implement appropriate controls to protect workers and others who may be affected.

In mould remediation, COSHH applies to the biocidal and fungicidal treatments used to kill and remove mould, as well as to the mould itself, which is a biological hazard. Every substance you use at work that could cause harm must be covered by a COSHH assessment.

7.2 — The Eight Steps of COSHH

The HSE sets out eight steps for COSHH compliance. For a mould remediation business, these translate as follows:

• Step 1: Assess the risks — identify all hazardous substances used (biocides, fungicides, cleaning chemicals) and assess the risk of harm from each
• Step 2: Decide what precautions are needed — use the hierarchy of controls to determine appropriate measures
• Step 3: Prevent or adequately control exposure — eliminate hazardous substances where possible; substitute with less hazardous alternatives; use engineering controls and PPE
• Step 4: Ensure that control measures are used and maintained — PPE must be worn; equipment must be maintained and inspected
• Step 5: Monitor the exposure — for most remediation chemicals, monitoring is not required; for high-risk substances, air monitoring may be needed
• Step 6: Carry out appropriate health surveillance — monitor operatives for signs of sensitisation or occupational ill health
• Step 7: Prepare plans and procedures for accidents, incidents, and emergencies — spillage procedures, first aid, emergency contacts
• Step 8: Ensure employees are properly informed, trained, and supervised — all operatives must understand the hazards and controls for every substance they use

7.3 — Safety Data Sheets (SDS)

A Safety Data Sheet (SDS) is a standardised document provided by the manufacturer of every hazardous chemical product. It contains all the information you need to use the product safely and to complete your COSHH assessment. You must obtain and read the SDS for every product you use before using it for the first time.

The 16 Sections of an SDS

7.4 — Completing a COSHH Assessment

A COSHH assessment must be completed in writing for every hazardous substance used in your work. It does not need to be complex, but it must be specific to the substance and the task.

What a COSHH Assessment Must Cover

• Product name and supplier
• Hazard classification — from Section 2 of the SDS
• Who may be exposed — operatives, other workers, building occupants
• How exposure can occur — inhalation, skin contact, ingestion, eye contact
• Existing controls — ventilation, dilution, containment
• PPE required — specific to the product, from Section 8 of the SDS
• Emergency procedures — spillage, first aid, from Sections 4 and 6 of the SDS
• Disposal — from Section 13 of the SDS
• Assessment date and review date
• Assessor name and signature

7.5 — Chemicals Used in Mould Remediation

The main categories of chemical used in mould remediation are biocidal treatments, fungicidal washes, and surface preparation products. Each has specific hazards that must be understood before use.

Biocidal Treatments

Biocidal products are regulated under the Biocidal Products Regulation (BPR) and must be authorised for use in the UK. Common active ingredients include quaternary ammonium compounds (QACs), hydrogen peroxide, sodium hypochlorite (bleach), and benzalkonium chloride. Key hazards include skin and respiratory sensitisation, eye damage, and environmental toxicity.

Fungicidal Washes

Fungicidal washes are designed to kill mould on surfaces. Many contain the same active ingredients as biocidal treatments but at different concentrations. Always check the product label and SDS — do not assume a lower concentration means a lower hazard.

Sodium Hypochlorite (Bleach)

Bleach is widely used as a mould treatment but has significant limitations and hazards. It is corrosive at higher concentrations, produces chlorine gas if mixed with acids or ammonia-based products, and can damage porous surfaces. It does not penetrate porous materials effectively and is not suitable as a standalone treatment for significant mould contamination.

Encapsulants and Sealers

Encapsulants are applied after treatment to seal treated surfaces and prevent regrowth. Many contain fungicidal additives. Hazards include solvent vapours (in solvent-based products) and skin sensitisation. Ensure adequate ventilation when applying solvent-based encapsulants.

7.6 — Safe Handling and Dilution

Many biocidal products are supplied as concentrates that must be diluted before use. Incorrect dilution is a common cause of both chemical incidents and treatment failure.

Dilution Principles

• Always follow the manufacturer's dilution instructions exactly — do not estimate
• Add concentrate to water, not water to concentrate — this reduces the risk of splashing concentrated product
• Use calibrated measuring equipment — do not use food or drink containers
• Label all diluted solutions clearly with the product name, concentration, and date of preparation
• Do not store diluted solutions for longer than the manufacturer recommends — many biocides degrade rapidly once diluted
• Wear appropriate PPE when handling concentrates — the hazard is significantly higher than for diluted solutions

Safe Storage

• Store chemicals in their original containers with labels intact
• Store in a cool, dry, well-ventilated area away from direct sunlight and heat sources
• Keep chemicals away from food, drink, and animal feed
• Store oxidising agents (e.g. hydrogen peroxide) separately from flammable materials
• Ensure storage areas are locked and inaccessible to children and unauthorised persons
• Maintain a chemical inventory and check for expired products regularly

7.7 — Spillage and Exposure Incidents

Despite best practice, chemical spillages and exposure incidents can occur. Having clear procedures in place before they happen is essential.

Spillage Procedure

• Evacuate the immediate area and prevent others from entering
• Don appropriate PPE before attempting to deal with the spillage
• Contain the spillage using absorbent material (sand, vermiculite, or proprietary spill kits) — do not use paper towels for corrosive or oxidising products
• Collect contaminated absorbent material and place in a sealed waste bag for disposal as chemical waste
• Wash the affected area with large quantities of water
• Ventilate the area thoroughly
• Record the incident and review your COSHH assessment

Exposure Incidents

• Skin contact: Remove contaminated clothing immediately. Wash affected skin with large quantities of water for at least 15 minutes. Seek medical attention if irritation persists.
• Eye contact: Irrigate immediately with clean water for at least 15 minutes, holding the eyelid open. Seek urgent medical attention.
• Inhalation: Move to fresh air immediately. If breathing is difficult, seek emergency medical attention. Do not re-enter the contaminated area without appropriate respiratory protection.
• Ingestion: Do not induce vomiting. Seek emergency medical attention immediately. Take the SDS with you to the hospital.

7.8 — Biocidal Products Regulation (BPR)

The Biocidal Products Regulation (BPR) controls the placing on the market and use of biocidal products in the UK. Only authorised biocidal products may be used professionally for mould treatment. Using an unauthorised product is illegal and may expose you to liability if harm results.

What This Means in Practice

• Only purchase biocidal products from reputable suppliers and check that they carry a UK BPR authorisation number
• Use products only for the purposes stated on the product label — using a product for an unauthorised purpose is illegal
• Follow label instructions for dilution, application method, dwell time, and re-entry interval
• Keep records of the products you use, including batch numbers, for traceability

Key Terms — Module 7

Module 7 Summary

• COSHH Regulations 2002 require a written assessment for every hazardous substance used at work — including all biocidal and fungicidal products used in mould remediation.
• Safety Data Sheets provide the information needed to complete COSHH assessments — obtain and read the SDS for every product before first use.
• Common chemicals in mould remediation include QAC-based biocides, hydrogen peroxide, sodium hypochlorite, and encapsulants — each with specific hazards.
• Never mix bleach with other chemicals — the reaction produces toxic gases that can cause severe respiratory injury.
• Follow manufacturer dilution instructions exactly, label all diluted solutions, and store chemicals correctly in their original containers.
• Have clear spillage and exposure incident procedures in place before they are needed — first aid information is in Section 4 of the SDS.
• Only use UK BPR-authorised biocidal products and follow label instructions for application, dwell time, and re-entry interval.

Version 1.0 — August 2026