Control Of Substances hazardous to Health Print

What you should be aiming for…

The COSHH regulations are 'goal setting' and recognize the fact that risk cannot always be eliminated. The aim is therefore to reduce the risk of exposure to hazardous substances to a tolerable level. This is achieved using the COSHH hierarchy of control.

Overview of the COSHH hierarchy of control

Regulation 7 of COSHH requires you to consider a hierarchy of control measures to ensure that exposure to substances hazardous to health is adequately controlled. The levels of the hierarchy are listed in priority order and must be considered and applied in this order. Each level of the hierarchy should be applied in a way that is appropriate to the activity and consistent with the risk assessment and each should only be considered after consideration of the ones above it. Most situations require several levels of the hierarchy to be used in order to adequately control the risk associated with exposure. In this way, residual risks should be dealt with by the next level of the hierarchy.

The hierarchy of control is as follows:

  • Eliminate the use of the hazardous substance wherever possible - is it possible to replace it with a less hazardous substance for example?
  • Enclose the process to reduce the potential for exposure to the hazardous substance wherever possible
  • Control the exposure of the substance at source using engineering means (such as local exhaust ventilation system - LEV)
  • Provide adequate protective equipment (such as respiratory protective equipment - RPE)

Expected standards of control are greater for substances that are classed as sensitizers, carcinogens or are particularly toxic.

There is a legal requirement to have local exhaust ventilation thoroughly examined at least every 12 - 14 months, or as frequently as dictated by a competent person. The competent person should draw up a schedule of thorough examination, which could be more frequent than the minimum, taking into account the demands of the process (for example, LEV in dusty environments may require more frequent examination). Similarly, there is a requirement to ensure that RPE is maintained in a suitable condition to ensure continuing effectiveness.

The Control of Substance Hazardous to Health (COSHH) Regulations of 1988, consolidated in 1994, amended in 1996, 1997 and 1998, 1999 and further consolidated in 2002 are the main piece of legislation covering control of the risks to employees and other people arising from exposure to harmful substances generated out of or in connection with any work activity under the employer's control.  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.

In terms of the regulations, a substance hazardous to health is:
  • one that has already been classified as being very toxic (T+), toxic (T), harmful (X), corrosive (C) or irritant (Xi) under the Chemicals (Hazard Information and Packaging) Regulations or CHIP (The Approved Supply List).
  • or a substance which has been assigned exposure limits
  • or a substance that is carcinogenic, mutagenic or toxic to reproduction
  • or a biological agent
  • or dust in substantial concentrations in air and
  • any substance not mentioned above but which creates a hazard to health comparable to those mentioned above


As with all other regulations building on the Health and Safety at Work etc. Act, legal duties under COSHH are laid primarily on employers and it is their duty to see that proper systems of work and management are in place.  Many of the duties that employers owe to their employees who may be affected by the employer's activity.

Duties on 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 does apply, forbidding the misuse of anything provided in the interests of health, safety or welfare.

What COSHH Requires

Complying with COSHH involves:
  • assessing the risks to health arising from hazardous substances at work and deciding 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

Preventing or Controlling Exposure

Employers must ensure that the exposure of employees to hazardous substances is either prevented (i.e. no exposure) or adequately controlled.  If it is reasonably practicable, exposure must be prevented by changing the process or activity so that the hazardous substance is not required or generated, or replacing it with a safer alternative (especially important if the substance is a carcinogen), or using it in a safer form.  If prevention is not reasonably practicable, exposure must be adequately controlled by one or more of the measures outlined in the regulations e.g. total enclosure of the process, suitable ventilation etc. (If total enclosure is not practicable for a carcinogen then all the other methods of control mentioned in the Regulations must be used.)

Adequate control of volatile or airborne substances can be assessed by reference to the set Exposure Limits.

Adequate control also means having systems in place to deal with emergencies, spills and disposal.

Only as a last resort should personal protective equipment be used as a means of protection. (However, the routine wearing of laboratory coats and safety glasses is generally regarded as a basic measure to minimize risks from foreseeable hazards - it is not reasonably practicable to provide other means of protection for workers and especially for their eyes.)

Ensuring that Control Measures are Used and Maintained

Employees are required to make proper use of control measures and to report defects and employers must take all reasonable steps to ensure that they do so. Employers must also ensure that the equipment is kept in efficient working order and good repair and that it is tested regularly.

Monitoring Exposure and Health Surveillance

Monitoring of the concentrations of hazardous substances in the air must be carried out in certain circumstances e.g. where there could be a serious risk to health if control measures failed or deteriorated. 

Where the assessment has shown this to be necessary e.g. use of a substance known to cause Cancer then health surveillance must be carried out.