Definition of hazardous substances

The COSHH Regulations define the following as hazardous substances:

(a) Chemicals or mixtures of chemicals listed in Annex VI of the Classification, Labelling and Packaging of Substances and Mixtures Regulations (the  CLP Regulation)[1], and for which an indication of danger is specified as very toxic, toxic, harmful, corrosive or irritant.

(b) Substances that have been assigned a Workplace Exposure Limit (WEL)[2]. These are listed in the HSE publication EH40, which is published annually.

(c)  Any kind of dust, if its average concentration in air exceeds the levels specified in COSHH (i.e. >10mgm-3 of inhalable dust or 4mgm-3 of respirable dust, as time-weighted average exposures over an 8 hour period)

(d) Biological agents that are directly connected with work (e.g. those used in laboratories) or a work activity or process (e.g. Legionella bacteria from water cooling towers).

(e) Any other substance that is hazardous to health, but which does not fall into the above categories. This category includes:

  • carcinogens and mutagens
  • asphyxiant gases
  • some pesticides
  • products or by-products of chemical reactions
  • carbon nanotubes and other nanomaterials.

[1] European Regulation (EC) No 1272/2008 on the classification, labelling and packaging of substances and mixtures came into force on 20 January 2009 in all EU Member States. The full provisions of CLP are being phased in over a lengthy transitional period but will be fully in force by 1 June 2015. The CLP Regulation adopts the United Nations’ Globally Harmonised System (GHS) for the classification and labelling of chemicals.  Further information on CLP and GHS may be seen in Appendix 5.


[2] The COSHH (Amendment) Regulations 2004 introduced the concept of the WEL and discontinued the use of maximum exposure limits (MEL) and occupational exposure standards (OES), which were familiar from earlier versions of COSHH.