UL 920001 2021 pdf download – Performance Requirements for Toxic Gas Detectors.
3.25 spot-reading apparatus: apparatus intended to be used for short periods of time as required (typically 5 min or less). 3.26 sample-draw: a method to cause deliberate flow of the atmosphere being monitored to a gas-sensing element. 3.27 signal-processing detector head: an apparatus intended to be incorporated with separate signal processing, data acquisition, central monitoring, or other similar systems in which the apparatus provides a conditioned electronic signal or output indication to systems of the aforementioned type that typically process information from various locations and sources including, but not limited to, gas-detection apparatus. 3.28 span: the algebraic difference between the upper and lower values of a range. 3.29 stabilization: state when three successive readings of an apparatus, taken at intervals equal to the maximum t(90) value defined in Annex A (Item 5), indicates no changes greater than the accuracy value defined in Annex A (Item 2). 3.30 stationary apparatus: a gas-detection apparatus intended for permanent installation in a fixed location. 3.31 (TLV-)STEL, (Threshold Limit Value-) Short-Term Exposure Limit: a 15-minute Time-Weighted Average (TWA) exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the Threshold Limit Value – Time-Weighted Average (TLV-TWA). 3.32 test gas: toxic gas diluted with clean air or inert gas to a known concentration within the test-gas tolerance stated in Annex A, Item 1. 3.33 transportable apparatus: apparatus not intended to be portable, but which can be moved readily from one place to another. 3.34 (TLV-)TWA, (Threshold Limit Value-) Time-Weighted Average: the time-weighted average concentration for a normal 8-hour work day in a 40-hour work week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. 3.35 toxic gas: toxic gases, for the purpose of this standard, are gases that may cause significant acute health effects at low concentrations.