UL 920001-2021 pdf free download.Performance Requirements for Toxic Gas Detectors.
4.4 Alarm signal
4.4.1 Continuous-duty apparatus If alarm devices, output contacts, or alarm signal outputs are provided as part of fixed or continuous duty portable apparatus and are intended to operate when a potentially hazardous gas concentration is detected, they shall be of a latching type requiring a deliberate manual action to reset within the gas detection system. Where the outputs are connected to an integrated or auxiliary system the means of latching and resetting may be incorporated into these systems. If two or more set or alarm positions are provided, the lower may be nonlatching – based on user preference. NOTE – The integral or latching device may reside in software.
4.4.2 Factory default alarm settings
All gas-detection apparatus and stand-alone control units with alarm functions that are factory set at default values shall be identified by marking and/or a product document, and the factory default alarm setting shall be at or below the ACGIH TLV, NIOSH REL, OSHA PEL or specified level required by the local authority where the product will be used.
4.4.3 Stand-alone apparatus
All stand-alone gas-detection apparatus and stand-alone control units shall include alarm or indication. Signal processing heads, approvable under this standard, are designed as components of a data- acquisition, central-monitoring, or similar system in which the alarm and malfunction are inherently part of the system, and hence gas alarm functions are not separately required as part of the detecting head.
4.4.4 Portable apparatus
All portable gas-detection apparatus shall be provided with a distinguishable trouble signal indicating low- battery condition, and the nature and purpose of this indication shall be explained in the manual. This trouble signal shall operate for a minimum of 10 minutes, during which time no false alarms are permitted and the ability to accurately detect gas and generate alarm(s) shall not be compromised. 4.5 Fault signals 4.5.1 Fixed and transportable apparatus Fixed and transportable apparatus shall provide a fault signal in the event of power failure to the apparatus, short circuit in connection to any sensor, loss of continuity in one or more of the wires to any sensor or sensing element, loss of electrical continuity of any gas-sensing system, or the manufacturers specified down-scale indication not to exceed 10% of the measuring range. NOTE – It is desirable to provide a trouble signal for a gas-sensing element failure.
4.5.2 Sample-draw gas-detection apparatus Sample-draw gas-detection apparatus shall be provided with flow-proving devices that produce a trouble signal in the form of a contact transfer or signal transfer in the event of flow outside the manufacturer’s stated flow-rate range.UL 920001 pdf download.