COSHH Comprehensive Guide

Hazardous substances are those substances that can cause harm to health, and may include:

  • Those used during work processes (such as glues and paints).
  • Those produced by work activities (such as fumes, vapours and mists).
  • Those which occur naturally (such as dust, gases and germs).

Learn more about welding fumes and metalworking fluids by visiting our dedicated FAQ page on Welding Fumes and Metalworking Fluids

Exposure to toxic chemicals

What are their routes of entry?

Hazardous substances have several routes of entry into the body, where they can cause harm. The most common routes of entry for health hazards include:

  • Absorption, which is when a substance comes into contact with the skin and is absorbed. This can lead to skin irritation and conditions such as dermatitis.
  • Inhalation, which is the most common route of entry, is when a substance is breathed in. This can be very dangerous because it makes it easy for a substance to reach the lungs, where it has access to a person’s bloodstream and many of their organs.
  • Ingestion, which is when a substance enters the mouth and is swallowed. This is not a common route of entry, and is usually the fault of poor working practices (such as a workplace failing to extract airborne dust) or poor personal hygiene (such as a person failing to wash their hands before eating food).

What are their effects?

Contact with a hazardous substance can have a range of effects that are classified as one of the following:

  • Acute: These are short, rapidly-occurring effects caused by a single or short term exposure, such as asthma-type attacks, nausea and fainting. 
  • Chronic: These are gradual, often irreversible illnesses caused by prolonged or repeated exposure to hazardous substances, such as cancers and respiratory diseases.

The specific effects that a hazardous substance has will depend on its nature but, because these effects can take many years to develop, it is often difficult to establish a definitive link between a substance and an illness. This is why many dangerous materials, such as asbestos, were used extensively for as long as they were.

How can I tell that a substance is hazardous?

There are a number of ways to tell that a substance is hazardous. One such way is by looking at its packaging.

The EU’s Globally Harmonised System (GHS) and the UK’s Classification, Labelling and Packaging (CLP) Regulations both set out a series of pictograms that must be present on a substance’s packaging if it poses a hazard to health. These pictograms are as follows:


Physical Hazard Pictograms

Physical and health

Physical & Health Pictograms


Health Pictograms


Environmental Pictograms

Alongside pictograms, any hazardous substance that is being supplied for use at work must come with a Safety Data Sheet (SDS). This sheet will outline the hazards associated with a specific substance, making it easier to assess and control the risks that the substance poses in a specific workplace.

What is COSHH?

COSHH, or the Control of Substances Hazardous to Health Regulations, are a set of regulations designed to protect people from coming into contact with hazardous substances and experiencing ill health as a result. They cover all substances that are hazardous to health except asbestos, lead and radioactive substances, which are all covered by their own legislation.

The COSHH Regulations impose duties on employers to protect employees and others who may be exposed to substances hazardous to their health, and require employers to control exposure to such substances. They also offer a framework that employers can use to build a management system to assess the health risks associated with hazardous substances, and implement effective control measures.

What does COSHH require from employers?

When hazardous substances are considered for, or are in, use at a place of work, the COSHH Regulations impose certain duties on employers to prevent or reduce workers exposure to hazardous substances. They must do so in several ways:


Employers must undertake a suitable and sufficient assessment of the health risks created by work which is liable to expose their employees to substances hazardous to health and of the steps that need to be taken by employers to meet the requirements of these regulations (regulation 6).


Employers must prevent, or where this is not reasonably practicable, adequately control the exposure of their employees to substances hazardous to health. If exposure cannot be prevented, Workspace Exposure Limits (WELs), which are specified by the HSE for certain substances, must not be exceeded. 

When preventing inhalation specifically, control should be achieved by means other than personal protective equipment where possible. If personal or respiratory protective equipment is still required, then it must conform with HSE standards (regulation 7). 


Employers and employees must make proper use of any control measures provided (regulation 8). Employers must also regularly maintain any installed control measures, keep suitable records (regulation 9) and review their systems of work.


Monitoring must be undertaken of any employee exposed to certain substances (listed in schedule 5 of the regulations) or in any other case where monitoring is required for the maintenance of adequate control or the protection of employees. Records of this monitoring must be kept for at least 5 years, or 40 years where employees can be identified (regulation 10).

Also, health surveillance must be provided to any employees who are exposed to certain other substances (listed in schedule 6), and records of this surveillance must be kept for at least 40 years after the last entry (regulation 11).


Emergency plans and procedures must be prepared to deal with accidents or incidents involving exposure to hazardous substances beyond normal day-to-day risks. These should include details of any warnings and communication systems used to alert people immediately after any incident occurs.


Employees who may be exposed to substances hazardous to their health must be given information, instruction and training sufficient for them to know the health risks created by the exposure and the precautions which should be taken (regulation 12).

Assessing the risks

One of the main duties that the COSHH Regulations places on employers is to complete a COSHH risk assessment. This is used to identify any relevant hazardous substances that an employee may come into contact with, and establish how to adequately control exposure to them.

What is covered by COSHH?

Not all hazardous substances are covered by the COSHH Regulations. 

  • A COSHH assessment is required for the following:
  • A COSHH assessment is NOT required for the following:
    • A substance that does not have any warning symbols on the container (such as bottled water).
    • Biological agents which are not directly used in the workplace (such as an influenza virus).
    • Hazardous substances which are subject to their own individual regulations (asbestos, lead or radioactive substances). 
Toxic chemicals

How do I complete a five step COSHH assessment?

A COSHH assessment is very similar to a risk assessment, but it applies specifically to hazardous substances. The HSE suggests that a five step process is used to complete a COSHH assessment, which is outlined below:

Step 1: Gather information about the substances, work and working practices.

  • Identify the hazardous substances present, or likely to be present, in the workplace, and the number and type of people present in the workplace.
  • Gather information about the hazardous substances, including the quantity of the substances used.
  • Identify the hazards that these substances pose by reviewing labels, material safety data sheets, HSE guidance and published literature.
  • Decide who could be affected by the hazardous substances and the possible routes of entry to people exposed (such as inhalation, ingestion or absorption).

Step 2: Evaluate the risks to health either individually or collectively.

  • Evaluate the risks to health, which will involve establishing the duration and frequency of the exposure that a person has to the substances.
  • Evaluate the level of exposure. For example, it may be appropriate to determine the concentration and length of exposure that a person has to any airborne dusts, gases, fumes or vapours.
  • Consider any Workplace Exposure Limits, and whether they are currently being breached.
  • Consider whether existing and potential future exposure presents a risk to health.

Step 3: Decide what needs to be done to control the exposure to hazardous substances.

  • Evaluate the existing control measures, including any PPE, for their effectiveness (using any available records of environmental monitoring) and compliance with relevant legislation.
  • Decide on any additional control measures that are required.
  • Decide what maintenance and supervision is required to ensure that the control measures are effective.
  • Plan what to do in an emergency.
  • Set out how exposure should be monitored.
  • Decide what health surveillance is necessary.
  • Decide what information, instruction and training is required.

Step 4: Record the assessment.

  • Decide if the assessment must be recorded (an organisation must record the findings of a COSHH assessment if it has five or more employees).
  • Decide on the format of this record.
  • Decide on how the record will be stored and made available to those who require it, such as employees and visitors.

Step 5: Review the assessment.

  • Decide when a review is necessary (which will usually be after a set period of time, or after a significant change in working practices).
  • Decide what needs to be reviewed.

What are workplace exposure limits?

Workplace exposure limits (WELs) are set by the HSE in its ‘EH40 Occupational Exposure Limits’ publication. They dictate how much of a substance an employee can be exposed to before new or additional control measures are required.

If an employee is exposed to a greater concentration of a hazardous substance than the workplace exposure limit allows, additional control measures must be implemented to reduce their exposure. Failing to do so is dangerous for employees, and can have significant legal consequences.

What is health surveillance?

A COSHH assessment may determine that employees must undergo health surveillance, which is a regular system of ongoing health checks.

Health surveillance is important for:

  • Detecting ill health at an early stage.
  • Providing data to help employers evaluate health risks.
  • Enabling employees to raise concerns about how work affects their health.
  • Highlighting issues with workplace control measures and risk assessments.

Controlling the risks

The objective of the COSHH Regulations is to prevent ill health caused by exposure to hazardous substances. In doing so, employers are expected to develop suitable and sufficient control measures that control said exposure.

To help with this, the HSE has produced the eight principles of good practice that outline how control measures should be determined and maintained:

  1. Design and operate processes and activities to minimise the emission, release and spread of substances hazardous to health.
  2. Take into account all relevant routes of exposure - inhalation, skin absorption and ingestion - when developing control measures.
  3. Control exposure by measures that are proportionate to the health risk.
  4. Choose the most effective and reliable control options which minimise the escape and spread of hazardous substances.
  5. When exposure control cannot be achieved, provide suitable personal protective equipment.
  6. Check and review regularly all elements of control measures for their continuing effectiveness.
  7. Inform and train employees on the risks from the substances they work with and the control measures required to minimise the risks.
  8. Ensure that the introduction of control measures does not increase the overall risk to health and safety.

What is the hierarchy of control?

The COSHH Regulations require:

‘The prevention or adequate control of exposure by measures other than personal protective equipment (PPE), so far as is reasonably practicable, taking into account the degree of exposure and current knowledge of the health risks and associated technical remedies’

An effective way of determining which control measures should be implemented is the hierarchy of control, which lists the forms of control measure from most to least effective:


Elimination is the safest and most effective method of control, and is usually achieved by changing the process completely (such as using a brush applied paint rather than a spray paint).


If a substance cannot be eliminated, the next best alternative is to substitute it with something safer. For example, using a water-based paint poses less of a risk to health than an oil-based one.

Engineering controls

Engineering controls may involve the use of a wide range of equipment, such as on-gun solder fume collectors, dust hoods, fume cupboards, and spray booths. Regardless of how they operate, all engineering controls will be designed to: 

  • Collect or contain the contaminant.
  • Reliably keep it away from the worker.
  • Keep exposures below the workplace exposure limit.

Supervisory controls

Supervisory controls include systems of work, effective communication and training. Some examples of supervisory controls include:

  • Reduced the time spent exposure to hazardous substances.
  • Reduced the number of workers exposed to hazardous substances.
  • Prohibiting eating, drinking and smoking in areas where hazardous substances are in use.
  • Ensuring rules, such as the use of PPE, are strictly enforced.


Personal protective equipment (PPE) can only be used as a control measure as a last resort. This is because it does not eliminate the hazard, and relies on good user training, the availability of the correct equipment at all times, good supervision and strong enforcement.

Still have more questions? Consider visiting our FAQ and answers about COSHH.

At Commodious, we offer a COSHH Awareness course that provides learners with all the information they need on COSHH. Successfully completing this course will also provide learners with an IIRSM-approved COSHH Awareness certificate: