This International Standard provides definitions and equations for the calculation of toxic product yields and the fire conditions under which they have been derived in terms of equivalence ratio and combustion efficiency. Sample calculations for practical cases are provided. The methods can be used to produce either instantaneous or averaged values for those experimental fires in which time-resolved data are available. This International Standard is intended to provide guidance to fire researchers for — appropriate experimental fire data to be recorded, — calculating average yields of gases and smoke in fire effluents in fire tests and fire-like combustion in reduced scale apparatus, — characterizing burning behaviour in experimental fires in terms of equivalence ratio and combustion efficiency using oxygen consumption and product generation data. This International Standard does not provide guidance on the operating procedure of any particular piece of apparatus or interpretation of data obtained therein (e.g. toxicological significance of results).