This International Standard presents a screening method for evaluating the heat stress to which a person is exposed. It should be regarded as a method to establish the presence or absence of heat stress. It applies to the evaluation of the effect of heat on a person during a period representative of his or her total exposure over the working day. It does not apply for very short exposures to heat. It applies to the assessment of indoor and outdoor occupational environments as well as to other types of environment. It applies to male and female adults who are fit for work.