Hazardous substances (COSHH) safety

The Control of Substances Hazardous to Health Regulations (COSHH) requires that risks arising from substances that are hazardous to health are prevented or controlled (where prevention isn't reasonably practicable).

If you're responsible for work that may expose people to harmful substances you will need to make sure you have carried out a COSHH assessment before work starts.

COSHH assessment

A COSHH assessment is like a risk assessmentrisk assessmentrisk assessment. It's the careful examination of the hazardous substances in your workplace that could cause people to suffer harm and ill health. The key to a good assessment is making sure you have up to date information about the substances, the work and the working practices in your area of responsibility. This information can inform you on the best risk controls to either eliminate or reduce exposure so far as is reasonably practicable.

Once the COSHH assessment is completed, make sure you implement the control measures and communicate the assessment findings to the people at risk.

1. Identify the substances present or likely to be

The first step is to find out what harmful substances are in your area of responsibility. Here are some suggestions to get you started.

  • Walk around your workplace. What hazardous substances are there? Where are they? Think about chemicals, products or mixtures, fumes, dusts, vapours, mists, liquids, gases and asphyxiating gases. Also, biological agents, germs that cause diseases and nanotechnology.
  • What tasks could lead to exposure? Include the intended use and by-products, storage, handling, transportation, waste disposal, cleaning and maintenance in your task list. Think about the activities carried out, such as pouring, packing, weighing or dilution. Consider possible emergency situations, e.g. the accidental release of a substance or a spillage.
  • Are there any areas of concern? Think about accidents or near misses involving hazardous substances.

Specialist advice


There are some hazardous substances that are covered elsewhere. They are biological agents (Essex users only) and radioactive substancesradioactive substancesradioactive substances.

2. Identify the substance hazards

Once you have identified your substance you need to find out how it's harmful to health. If it's a chemical, the safety data sheet and hazard label provide information on the hazards and the handling, storage and emergency measures needed. They are provided by the supplier and must be up to date. Industry information will help in gathering information about biological agents or natural products like flour and wood dust.

In the past, people wrongly assumed the safety data sheet was the COSHH assessment. This is incorrect. The COSHH assessment is a product of the substance’s hazard information, how you are exposed and your control measures to reduce the risk.

Safety data sheets and labels have pictograms, signal words, hazard statements (phrases that describe the nature of the hazard) and precautionary statements (phrases that describe recommended measures to prevent harm) which follow a standard international labelling system.

Substance categories 

Substances that fall into categories need certain actions to control exposure.

  • Substances listed in EH40 Workplace exposure limits (.pdf)
  • Carcinogens or mutagens (Regulation 2 and lists in Schedule 1, COSHH Regulations (.pdf)). Hazard class 'Danger' carcinogenicity category 1A and 1B, 'Danger' germ cell mutagenicity category 1A and 1B and 'Danger' reproductive toxicity category.
  • Substances classified as 'Danger' acute toxicity category 1, 2 and 3, specific target organ toxicity (STOT SE) category 1.
  • Substances classified a 'Warning' acute toxicity category 4 and STOT SE category 2, ‘Danger’ aspiration toxicity category 1.
  • Substances classified as 'Danger' skin corrosion category 1A, 1B and 1C and ‘Warning’ skin irritation category 2.
  • Substances classified as 'Danger' eye damage category 1 and ‘Warning’ eye irritation category 2.
  • Substances classified as 'Danger' respiratory Respiratory sensitiser Category 1 and Subcategory 1(A) and 1(B) and 'Warning' Skin sensitiser Category 1 and Subcategory 1(A) and 1(B).

3. Find out who could be exposed and how

Understanding how people are exposed to the substance and how it enters the body can inform you on the range of control measures needed to reduce exposure. Hazardous substances can enter the body by:

  • ingestion
  • inhalation
  • absorption through skin and other body membranes
  • accidental injection

Once you know the routes of entry, consider the number and types of people who could be harmed through direct or indirect exposure. Direct exposure is when someone knowingly handles the substance or is aware that it's present as part of their work activity. Indirect exposure might happen when someone is exposed through an unrelated activity, such as cleaning, maintenance, responding to an emergency situation or working nearby and is unaware of its presence.

In both cases, the nature of exposure needs to be assessed by establishing the likelihood and the frequency of exposure. Also, the levels people are exposed to and for how long. Additional consideration must be made for people especially at risk people especially at risk people especially at risk.

4. Control measures and health surveillance

Now you know the risk posed by the substances in your workplace and the nature of exposure, choose control measures to prevent or adequately control exposure.

Control measures

When considering control measures, think about how you can reduce the likelihood of exposure and the harm and consequences if exposure occurs. Include control measures for emergency situations as well. It's recommended you consider control measures in order of priority and effectiveness.

  • Eliminate the substance. If you don’t need it or don’t use it, safely remove it from the workplace.
  • Substance substitution. This is using alternative substances that are less hazardous or using another process that doesn’t create a hazardous form.
  • Engineering controls that enclose the process using full and partial enclosures.
  • Extract emissions at source, for example, local exhaust ventilation (LEV). LEV needs periodic thorough examination and testing and records kept.
  • Limit the number of people in harm’s way as much as possible. This can be authorised people only and permit to work procedures
  • Provide personal protective equipment.
  • Training for employees. The people at risk get the right information at the right time to stay safe. Refresher training.

You will also need to consider what else is required to make sure your control measures are maintained, inspected and replaced when they are damaged or expired. In some cases, you will need to arrange for monitoring to be carried out to ensure your control measures are working well.

Health surveillance

Health surveillance involves ongoing health checks designed to detect ill-health effects from specific identified hazards. It is required when:

  • there is a disease associated with the substance in use (e.g. Asthma, Dermatitis, Cancers);
  • it is possible to detect the disease or adverse change and reduce the risk of further harm;
  • the conditions in the workplace make it likely that the disease will appear.

If you use or create substances that are respiratory or skin sensitisers or potential carcinogens, health surveillance will be required unless control measures are robust enough to prevent exposure. If you rely on personal protective equipment to control exposure, health surveillance will be required.

Your COSHH risk assessment should identify whether health surveillance is required. Find out more about the types of health surveillance required and the purpose of health surveillance.

If you need help with COSHH risk assessment you can contact the Health and Safety Advisory Service.

If you think you may need health surveillance for your hazardous substances email the Occupational Health Service ohquery@essex.ac.uk for advice.

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