Multi Gas Monitor Alarm Setpoints
Multi Gas Monitor Alarm Setpoints are programmed concentration thresholds on a multi-gas detector that trigger warning and danger/evacuation alarms for atmospheric hazards like oxygen deficiency/enrichment, combustible gas, carbon monoxide, and hydrogen sulfide. These setpoints are selected by a qualified person based on hazard assessment, exposure limits, and work tasks, with the first alarm typically set below the occupational exposure limit to warn workers before conditions become unsafe.
On a shop floor, multi-gas monitor alarm setpoints are used as early-warning controls, not just passive meters. Workers wear detectors in the breathing zone, verify alarms during bump testing, and program values to match specific hazards like oxygen displacement, solvent vapors, weld gases, or cleaning chemicals. For confined spaces and permit-required entries, devices are configured to alarm before exposure above the site's action level or occupational exposure limit, enabling crews to isolate, ventilate, evacuate, or upgrade respiratory protection as needed. Typical practice includes setting an initial warning alarm at 5 ppm H₂S and a full alarm at 9 ppm H₂S for oil and gas work, with explosive gas alarmed at 10% LEL.
- Using factory defaults without site-specific review instead of setting alarms from the hazard assessment and applicable OEL/STEL/ceiling limit.
- Setting the low alarm too high, which reduces warning time; WorkSafeBC advises the first alarm should be below the OEL, often around 50% of the OEL as a starting point.
- Treating bump tests as calibration or skipping verification; a bump test only confirms sensor/alarm response and does not measure accuracy, while failed bump tests should trigger full calibration.
What is the relationship between OEL, STEL, and alarm setpoints?
The alarm setpoint should generally be anchored to the hazard hierarchy used by the site: an early warning below the exposure limit, with a higher alarm at or near the level requiring evacuation or immediate control action; WorkSafeBC references OELs that include 8-hour TWA, 15-minute STEL, and ceiling limits.
What are the standard oxygen alarm thresholds?
Many multi-gas monitors use 19.5% O₂ as the low alarm for oxygen deficiency and 23.0% or 23.5% O₂ as the high alarm for oxygen enrichment, depending on the device and site procedure.
What is the common combustible gas alarm point?
A widely used early alarm is 10% LEL, with escalation above that depending on the procedure and hazard assessment; WorkSafeBC oil and gas guidance explicitly uses 10% LEL as a full alarm point for explosive gas.