Safety, Hazard Control, and Emergency Response
This domain tests recognition, isolation, and response to gas releases, fires, and confined-space hazards.
Core rules
- Detectors read %LEL, not concentration. Calibrate with the target gas or the correct response factor; a methane-calibrated sensor responds differently to propane.
- Alarm setpoints are tiered: low alarm to investigate, high alarm to isolate and evacuate. Do not use a detector as a substitute for ventilation or isolation.
- Emergency response sequence: raise alarm, isolate gas, eliminate ignition sources, ventilate, account for personnel, and do not re-enter without PPE and gas testing.
- Hot work near gas requires a permit, gas testing, fire watch, and positive isolation, not just a closed valve.
- Confined-space entry requires atmospheric testing for oxygen, LEL, and toxics before entry and continuous monitoring.
Worked example
A 10 m × 10 m × 3 m room contains 300 m³ of air. Methane LEL is 5% by volume, so a 5% LEL alarm corresponds to 0.25% methane by volume. 0.25% of 300 m³ = 0.75 m³ of methane. That is a small release-about 0.75 m³ at standard conditions-yet enough to reach the alarm. This is why small leaks in poorly ventilated rooms matter.
Traps
Treating 100% LEL as pure gas leads to grossly wrong evacuation distances. Assuming odorant is reliable fails for new pipe, some industrial gases, and anosmic individuals. Also do not purge into a confined area or use compressed air to disperse gas.