Control of Substances Hazardous to Health (COSHH)

What are substances hazardous to health?

COSHH defines them as:

  • Substances officially classified as toxic, harmful, irritant or corrosive. These should carry an appropriate orange and black pictogram on the container, although some proprietary or imported substances may not;
  • Substances with workplace exposure limits;
  • Dusts of any kind in substantial concentrations;
  • Biological agents (harmful micro-organisms); and
  • Any other substances that creates a risk to health, e.g. pesticides, allergens.

What does the law require when working with substances hazardous to health?

  • Assessment of risks - identify the hazards from manufacturer’s data sheets, detailed information on the container, or other sources e.g. literature;
  • Identification and implementation of the precautions needed to prevent or control exposure;
  • Making sure that staff work in accordance with the safe working procedures and maintaining any equipment used to control exposure;
  • Informing, instructing and training staff in control measures and emergency procedures; and
  • Monitoring that the system of control is working properly.

Assessing the risks

You need to:

  • Decide how the substances are used - this includes their storage and disposal and look at the process and see what actually happens, not what is supposed to happen; check whether any vapours or dusts are released.
  • Determine who might be exposed and how - can the substance be breathed in, swallowed e.g. by putting contaminated fingers in the mouth or absorbed through skin.
  • Check the effectiveness and use of existing precautions.
  • Decide whether exposure could occur as a result of an accident e.g. a spillage.
  • Make sure your assessment covers any risks arising out of cleaning and maintenance.

You must record your assessment in writing (except in very simple cases, e.g. when following clear instructions on a container).  If you are working in a laboratory, unless you are using standard precautions a specific COSHH assessment form should be used for written assessments.   

Assessments should be reviewed if anything changes and at least every five years.

NEW GUIDANCE SCoP 08 Working with Hazardous Substances

Please refer to the new Safety Code of Practice SCoP 08 for the University Guidance on COSHH and specifically drafting a COSHH Assessment.  Refer to this document is you are required to carry out a COSHH Assessment.  Please note, staff should be competent to carry out the assessment.  For further guidance refer to SCoP 08.


  1. COSHH Assessment Form (word editable)
  2. COSHH Assessment Form (pdf)

Controlling the risks

You must prevent exposure to hazardous substances if it is reasonably practicable to do so.  You could change the work you are doing, use a safer substance or use a safer form of the same substance eg if the chemical causes harm by inhalation, you could use a pellet form instead of a powder.

If you cannot prevent exposure, you need to ensure adequate control, using the following precautions (in order of priority):

  • use appropriate work processes, systems and engineering controls, and provide suitable work equipment and materials e.g. use processes which minimise the amount of material used or produced, or equipment which totally encloses the process;
  • control exposure at source (e.g. local exhaust ventilation), and reduce the number of employees exposed to a minimum, the level and duration of their exposure, and the quantity of hazardous substances used or produced in the workplace;
  • provide personal protective equipment (e.g. face masks, respirators, protective clothing), but only as a last resort and never as a replacement for other control measures which are required
If you have any doubts about the effectiveness of controls (and in some specific cases), you may need to monitor exposure or carry out health surveillance.

For further details please contact Safety Services