"This Standard addresses the details of construction@ performance@ and testing of portable@ mobile@ and stationary electrical gas-detection instruments operating at ambient temperatures and pressures used to provide a warning of the presence of toxic gases in air. Instruments used to detect flammable (explosive) concentrations of toxic gas(es) when the LEL exceeds the TLV are excluded. Hereafter@ the term ""instruments"" will refer to ""gas-detection instruments."" Parts of the instruments may be installed or operated in hazardous (classified) locations. Reference Annex B@ Item 1@ for applicable ranges for specific instruments. This Standard applies to mains-connected instruments rated at 250 V nominal or less@ and to portable@ mobile@ and stationary battery-powered instruments. This Standard applies to instruments suitable for use in an ambient temperature range indicated in Annex B@ Item 2. This Standard addresses instruments that provide at least one detection range that includes the short-term exposure limit (STEL) as listed by the current NIOSH or ACGIH documents. This Standard does not address laboratory- or scientific-type instruments used for analysis or measurement in process control and process monitoring applications@ instruments intended for residential purposes@ or instruments with full-scale gas concentration ranges that do not include a level covered by paragraph 2.4 above. NOTE ?C The user should specify instrumentation that will provide a higher level of accuracy than the minimum tolerances of this Standard if required by the application risk. The user should be aware of environmental effects on both the instrument and the toxic gas. The effects are not intended to be evaluated by this Standard. Purpose This Standard provides minimum performance requirements of electrical instruments for the determination of toxic gas content in air in order to enhance the safety of personnel. ISA-RP92.0.02@ the companion Recommended Practice for this Standard@ establishes user criteria for the installation@ operation@ and maintenance of toxic gas-detection instruments."