Hazard identification and risk assessment in confined spaces
This domain tests whether you can build a hazard picture before entry and turn it into a proportionate risk assessment. The exam favours scenarios where the obvious gas hazard hides engulfment, isolation or rescue hazards.
Hazard families
- Atmospheric: oxygen deficiency from rusting, combustion, bacterial action or displacement; oxygen enrichment from leaking oxygen lines or welding; flammable gas or vapour such as methane in sewers or solvent vapour in tanks; toxic gases such as hydrogen sulphide in sewage, carbon monoxide from engines, chlorine, ammonia and welding fume; dust.
- Physical: engulfment by grain, sand or sludge; entrapment by agitators or moving machinery; falls from height; electrical contact; heat, noise, vibration, poor lighting, traffic, flooding and slips.
- Biological: leptospirosis from rat urine in drains, tetanus, hepatitis and moulds. Chemical contact and fire or explosion also belong in the picture.
Assessment that stands up
Identify the hazard, its source and who may be affected; consider normal, abnormal and emergency conditions and adjacent activities. Evaluate likelihood and severity, then apply the hierarchy: avoid entry (camera, robotic cleaning), eliminate, engineer (isolation, ventilation), administer (permit, training), and use PPE last. Record the assessment and review it when the task, conditions, equipment or people change. The assessment must also test whether rescue is feasible.
Worked example
A team plans a visual inspection of a 3 m sewage manhole. A weak answer lists "toxic gas". A strong answer identifies hydrogen sulphide and methane from sewage, oxygen deficiency, sludge engulfment, falling, traffic and leptospirosis; it states the worst credible case and the controls: isolate flow, ventilate, test top, middle and bottom, full-body harness and tripod, standby, barriers and hygiene. It also asks whether a camera can avoid entry. The reasoning is that controls follow from the credible outcome, not from the label on the space.
Traps that cost marks
- Producing a hazard list with no risk evaluation or control selection.
- Ignoring oxygen enrichment and flammable risk while focusing on toxicity.
- Treating "no smell" as evidence of safety; hydrogen sulphide deadens smell.
- Failing to review the assessment after rain, flow change or a change of task.
- Copying a generic assessment from another site.