How to handle hazardous substances

The Control of Substances Hazardous to Health Regulations (COSHH) requires every employer to identify the substances in use at the workplace and to ‘assess’ whether they present a ‘risk’. The assessments must be recorded and any risks prevented or controlled. However, the subject of COSHH often gives rise to concerns by those responsible for its implementation. But, for most basic work activities, COSHH is not and need not be, overly complicated.

The main objective of the Regulations is to reduce occupational ill-health by setting out a simple framework for controlling hazardous substances in the workplace.

As with all other regulations, legal duties under COSHH are laid primarily on employers and it is your duty to see that proper systems of work and management are in place.

Duties on your employees include making proper use of any control measures, following safe systems of work, abiding by local rules and reporting defects in safety equipment. Non-employees have no specific duties under COSHH but the requirements of the Health and Safety at Work etc. Act do apply, forbidding the misuse of anything provided in the interests of health, safety or welfare.

What does COSHH Cover?

COSHH covers substances which can cause ill-health. They can be used directly in work, e.g.  paints or cleaning materials; or arise from the work waste products; or occur naturally, e.g. fungal spores in agriculture, legionella.

Hazardous substances can be found all sorts of work environments factories, offices, quarries, mines, farms, offshore installations, pipelines, shops, swimming pools, etc. – and unless the right precautions are taken, they can threaten the health of workers and others exposed to them.

What COSHH Requires

Complying with COSHH involves:

  • assessing the risks to health arising from hazardous substances at work
  • identifying what precautions are needed
  • preventing or adequately controlling exposure
  • ensuring that control measures are used, maintained, examined and tested
  • if necessary, monitoring exposure and carrying out health surveillance
  • ensuring that employees are properly informed, trained and supervised



‘Suitable and sufficient’ assessment includes identifying the hazardous substances that are likely to be encountered, evaluating the risks they present to health, finding out how much and how often the substances are used, how hazardous they are and what are the exposure routes and finally making a decision on the action needed to prevent exposure or to reduce it as far as is reasonably practicable. This will also include the actions to be taken in an emergency, to clear up any spills and to safely dispose of any residues. Except for the most trivial cases, the conclusions of this assessment must be recorded, made readily accessible and reviewed regularly. A sample form is available to download on our website.

Entry or Exposure Routes

Major routes of exposure are through the skin (topical), through the lung (inhalation) or through the gastrointestinal tract (ingestion). In general, inhalation is likely to cause more damage than ingestion, which, in turn, is more harmful than skin exposure.

Skin Absorption

This is the least likely route of penetration as the natural thickness of the skin plus its natural coating of grease and sweat provide some protection against chemicals. However, some materials are capable of penetrating intact, healthy skin, such as corrosive substances.


Gases and vapours, aerosols and fumes are readily inhaled and may cause harm anywhere in the respiratory system and may also be absorbed into the bloodstream. But, inhalation of particles depends upon their size and shape – the smaller the particle, the further into the respiratory tract it can go, such as asbestos fibres entering the lungs.


Airborne particles that are eventually swallowed are the most likely source of ingested chemical. Otherwise, ingestion of potentially toxic substances is likely to be accidental on contaminated food, drink or make-up. Once absorbed through the stomach or intestine, the route to excretion may be complex and damaging.

Adverse effects may be local or systemic:

Local effects occur at the site of exposure e.g. corrosives and often irritants.

Systemic Effects occur at a target organ or at a site remote from the point of contact following absorption and distribution around the body.

Some substances produce both effects.

Adverse effects may also be acute or chronic:

Acute effects are immediate such as the effect from inhaling chlorine.

Chronic effects are much slower, often cumulative following repeated exposures. Chronic effects can be the most difficult to avoid because damage may not become evident for many years.

COSHH is a useful tool of good management which sets out basic measures that you and sometimes your employees must take. These are set out in the Health and Safety Executive (HSE) leaflet ‘COSHH: A brief guide to the Regulations’ available from the HSE website.

If you, as an employer, fail to adequately control hazardous substances, your employees or others may become ill. Effects from hazardous substances range from mild eye irritation to chronic lung disease or, on occasions, death.

Download a COSHH Risk Assessment Template