Gas Detection, Emergency Procedures and Safety Management in Non-Domestic Premises
This domain tests the plant-room safety layer: detectors, alarms, emergency controls and the management system that keeps them working.
Detection
Natural gas detectors mount high level; LPG detectors mount low level. Combustible gas detection typically alarms at a low percentage of the lower flammable limit and takes action at a higher level - for example alarm at about 10% LFL and shut-off at about 20% LFL, following the design and the standard. Carbon monoxide detectors protect occupied space, not the gas pipe. Sensors need calibration and bump testing, and the head must be placed where the gas will actually accumulate, not where the cable is convenient.
Emergency procedure
On a gas escape: do not operate electrical switches; isolate at the emergency control valve; ventilate only if it is safe to do so; evacuate and prevent ignition; call the emergency services, the gas network operator or LPG supplier, and report through the required channels. For LPG, keep people out of basements and pits where vapour may have collected.
Safety management
Permits to work, risk assessments, lockout/tagout, hot-work controls and confined-space procedures apply to gas plant. Contractors must be briefed on the emergency shutdown and the location of isolation points.
Worked example
Staff smell gas in a basement plant room containing LPG-fired equipment. The correct response is to evacuate, avoid switches and naked flames, isolate at the external emergency control valve if safe, and call the supplier and emergency services. A handheld combustible gas detector reading at floor level confirms heavy vapour; nobody should enter to "find the leak" without emergency arrangements.
Traps
Mounting natural gas detectors at low level; using a combustible gas detector as a CO monitor; relying on smell; entering a basement without breathing apparatus or emergency backup.
Exam focus
Detector placement and set points, emergency sequence, isolation points and permit controls.