Gas safety, hazard and risk management
What this domain tests
This domain asks how you identify, evaluate and control gas hazards, and how you respond when controls fail. Expect questions on risk assessment, gas detection, emergency isolation, purging, permits-to-work and incident reporting under Hong Kong's gas safety regime.
Hazard and risk framework
- Identify hazards: escape, fire, explosion, asphyxiation, carbon monoxide, cryogenic exposure, overpressure and mechanical damage.
- Estimate likelihood and consequence, then rank risk on a matrix. Record the basis for each rating.
- Apply the hierarchy of control: eliminate, substitute, engineer, administrate, then PPE. Engineering controls such as ventilation, excess-flow valves, gas detection and remote isolation are preferred over procedural controls.
- Reduce risk to ALARP. Residual risk must be understood and accepted by the responsible person, not merely ignored.
- HAZID and HAZOP are used for new installations and modifications; QRA supports major hazard decisions but does not replace good design.
Emergency and operational controls
Odorisation, leak surveys, emergency control valves and a clear gas-escape procedure are core. On a reported escape: remove ignition sources, ventilate, isolate at the emergency control, evacuate if necessary, and call the utility and emergency services. Do not operate electrical switches in the affected area. Purge and re-commission only under a written procedure.
Worked example
A district governor has a leak scenario rated likelihood 3 (possible) and consequence 4 (fire or serious injury), giving a risk score of 12 on a 5x5 matrix, ranked high. Adding a gas detector linked to automatic isolation and increasing inspection frequency reduces likelihood to 2, giving a residual score of 8, ranked medium. The engineer must still document the residual risk, verify detector calibration and confirm that isolation fails safe.
Traps that cost marks
- Treating a low probability as no risk and omitting consequence analysis.
- Relying on administrative controls or PPE where engineering controls are practicable.
- Forgetting human factors, maintenance error and simultaneous operations.
- Writing generic controls without an owner, verification method or completion date.
- Failing to report a notifiable incident to the authority within the required time.