This International Standard specifies general requirements for construction, testing and performance, and describes the test methods that apply to portable, transportable, and fixed equipment for the detection and measurement of toxic gases and vapours in workplace atmospheres and other industrial and commercial applications. This International Standard is applicable to continuously sensing equipment whose primary purpose is to provide an indication, alarm and/or other output function the purpose of which is to indicate the presence of a toxic gas or vapour in the atmosphere and in some cases to initiate automatic or manual protective action(s). It is applicable to equipment in which the sensor generates an electrical signal when gas is present. This standard applies to two types of equipment: • Type HM (Health Monitoring) ‘occupational exposure’ equipment: For occupational exposure measurement, the performance requirements are focused on uncertainty of measurement of gas concentrations in the region of Occupational Exposure Limit Values (OELV). The upper limit of measurement will be defined by the manufacturer in accordance with 4.2.1.