Approved code of practice

Appendix 3 - Control of substances that cause occupational asthma

The following is an appendix from the COSHH (control of substances hazardous to health) Approved Code of Practice.  It gives information on the control of substances that cause occupational asthma.



1 - For the purposes of this Appendix:

'Asthma' is characterised by periodic attacks of wheezing, chest tightness or breathlessness resulting from constriction of the airways. A substance is considered to cause occupational asthma if, as a result of exposures in the workplace, it both:

  • (a) produces the biological change known as the hypersensitive state in the airways; and
  • (b) triggers a subsequent reaction in those airways.

2 - 'Cause' does not, in this context, mean triggering an asthmatic attack in a person who has asthma due to another, unrelated cause (occupational or non-occupational). Occupational asthma may be caused by manufactured chemicals or naturally occurring materials, such as fungal spores. The way in which substances cause asthma is the subject of scientific debate, and this Appendix makes no assumption about the mechanism.

Scope of this Appendix

3 - All substances which cause occupational asthma are within the definition of substances hazardous to health for the purposes of the Control of Substances Hazardous to Health Regulations 2002 (COSHH). Therefore the COSHH Regulations and the main COSHH ACOP, of which this Appendix is part, apply and must be observed by employers.

4 - This Appendix applies to:

  • (a) substances listed in Section C of the HSE publication Asthmagen? Critical assessments of the evidence for agents implicated in occupational asthma;
  • (b) any other substances assigned the risk phrases 'May cause sensitisation by inhalation' (R42) or 'May cause sensitisation by inhalation and skin contact' (R42/43) under the Chemicals (Hazard Information and Packaging for Supply) Regulations 2002 (CHIP); and
  • (c) any other substance which the employer's risk assessment has shown to be a potential cause of occupational asthma.

5 - This Appendix does not apply to general environmental allergens such as grass pollens and fungal spores unless the work activity generates them or leads to their occurrence at higher concentrations than are normally present in the general environment. Nor does it apply to substances, eg general dust, where exposure may produce asthmatic symptoms in a person with pre-existing asthma but where the substance itself is not a cause of occupational asthma.

6 - This Appendix applies to employers, the self-employed and employees to the extent that duties under the COSHH Regulations may apply to them.

Assessment of the risk to health created by work involving substances hazardous to health (regulation 6)

7 - The risk assessment should:

  • (a) identify the hazards - which substances with the potential to cause asthma are used or generated by work activity;
  • (b) decide who might be harmed, and how. Which routine and non-routine activities of employees and others are likely to involve exposure? In deciding who might be harmed, it might be prudent to consider also who might be more at risk/vulnerable;
  • (c) evaluate the risks and decide whether existing precautions are adequate or if more should be done. See if exposure can be prevented and, if it cannot, consider the potential risk for each activity. Consider whether the substances identified might be released into the air as a result of the work activity;
  • (d) record the findings – employers with five or more employees must record the significant findings, eg hazards and conclusions;
  • (e) review the assessment and revise it if necessary. Identify all relevant measures to provide adequate control and ensure their combined effectiveness.

8 - Assessment of control measures and good working practices for substances which cause asthma should take account of the seriousness of the health effects which could result from a failure of control. Particular attention should be given to identifying and assessing the controls for any short-term exposures which may involve markedly higher concentrations than the long-term average.

9 - Employers are required by the COSHH Regulations to protect the health of employees who have developed occupational asthma even though they may develop symptoms at very low, even undetectable, levels of exposure.

10 - Employers should review assessments regularly as required by regulation 6(3) of COSHH. There should be arrangements for review of the assessment and control measures in the light of experience or if new information becomes available. It is particularly important that there should be an immediate review wherever a case of occupational asthma is confirmed.

11 - The employer should set out procedures for responding to a confirmed new case of asthma, which may be occupationally related. These should include measures to:

  • (a) protect the person(s) while the cause of the symptoms is investigated;
  • (b) review the assessment and control measures; and
  • (c) report the case to the enforcing authority if a doctor has notified the employer of it in writing. This is required by the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR).

Prevention or control of exposure to substances hazardous to health (regulation 7)

12 - Exposure to substances with the potential to cause occupational asthma should be prevented. If that is not reasonably practicable, the objective should be to control exposure so as to prevent employees and others who may be exposed from developing occupational asthma as a result of exposure to those substances. This will involve considering the potential for short-term peaks of exposure as well as longer-term time weighted averages.

13 - If an individual develops occupational asthma to a substance, their exposure must be controlled to prevent triggering further attacks. Suitable levels are likely to be well below any maximum exposure level, where these exist.

Health surveillance (regulation 11)

14 - All employees exposed or liable to be exposed to a substance which may cause occupational asthma should be under suitable health surveillance. The extent and detail of the health surveillance should be related to the degree of risk identified during the COSHH assessment. There should be appropriate consultation with an occupational health professional over the degree of risk and level of surveillance. Health surveillance should include the maintenance of a health record in a suitable form for each exposed individual.

Information, instruction and training for persons who may be exposed to substances hazardous to health (regulation 12)

15 - Employees should be provided with suitable and sufficient information covering in particular:

  • (a) typical symptoms of asthma;
  • (b) the nature of any substance likely to cause occupational asthma to which they may be exposed;
  • (c) the likelihood that once developed, occupational asthma could be permanent and what happens after further exposures;
  • (d) the procedures for reporting symptoms; and
  • (e) the need to report immediately any symptoms which may indicate that asthma has occurred.

16 - Employers should also give employees proper training, including induction training before they start the job. Appropriate training should be given in respect of:

  • (a) correct use and maintenance of control measures provided;
  • (b) work practices which prevent or reduce the emission of the substance into the atmosphere of both the workplace and the general environment;
  • (c) the use of RPE, where it is used as a control measure, and other control measures to further reduce exposure to the substance; and
  • (d) emergency procedures.

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