Headaches in a Basement Plant Room
Two operatives are breaking out a 3 m × 1.2 m section of concrete slab and cutting a 250 mm chase in the plant room of a retail unit. The room is 6 m × 4 m, below ground, with no windows; the only access is a single door and a stairwell. Mechanical ventilation is installed but not yet commissioned. They are using a petrol cut-off saw and a 25 kg petrol breaker. After about 50 minutes the younger operative says he has a pounding headache, feels dizzy and sits down on the step; his face is flushed and he is short of breath. The older operative, who has had a headache since the previous afternoon, tells him to 'get a bit of air and come back in'. The fuel can has just been refilled inside the room beside the door, with the saw still hot. Both wear glasses, ear defenders, gloves and boots. There is no gas monitor, no RPE, and no mobile signal in the basement.
1. What is the most likely explanation for the two men's symptoms, and what should happen in the next ten minutes?
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The picture points strongly to carbon monoxide poisoning from petrol engines running in an enclosed space. CO is produced by incomplete combustion, binds to haemoglobin far more readily than oxygen does, and starves the body of oxygen. Headache, dizziness, flushing, breathlessness and confusion are classic, and the older man's headache since the previous afternoon suggests exposure built up over more than one shift rather than a one-off event.
Next ten minutes:
- Stop both machines and get both men out of the basement into fresh air, using the stairs, without re-entering for tools or the fuel can.
- Do not send the younger man back in after a breather - that is the mistake in the scenario.
- Call 112/999 for the symptomatic man. CO casualties can deteriorate quickly, and anyone with breathlessness, confusion or reduced consciousness needs oxygen and assessment.
- Keep both casualties at rest and warm, and do not let either drive. Exertion increases uptake, and the older man should also be assessed even though he says he is fine.
- Send someone up to the site entrance to meet the ambulance, because there is no mobile signal below ground.
- Tell the site manager, and treat this as an incident to be recorded and investigated, not a bad morning.
One affected person can be a coincidence; two in the same room points to the atmosphere.
2. Why is 'get some air and come back in' dangerous, and why does the fact that no one could smell anything change nothing?
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Why the advice is dangerous: stepping outside relieves the symptom but does not remove the carboxyhaemoglobin. On room air the half-life of CO in the blood is measured in hours; on high-flow oxygen it falls sharply. So the man would feel a little better, go back down, and continue accumulating CO on top of a burden that has not cleared. The headache would return and the next step could be collapse in a room with one door, no signal and no one watching.
Why smell is irrelevant: CO is colourless, odourless and non-irritant. It gives no warning at all - no smell, no taste, no eye sting. The only 'warning' is the symptoms themselves, by which point people are already affected. The faint petrol smell that might be noticed comes from fuel, not from CO, and its absence or presence tells you nothing about CO levels. The refuelling inside the room beside a hot saw also released petrol vapour and created a fire risk, which is a second reason the practice is unacceptable.
The wider point: the exam expects you to recognise that an atmosphere that has made two people ill is a hazard to everyone who enters, including the person sent down to fetch the tools. Nobody should re-enter until the job has been re-planned and the space checked.
3. Re-plan the job so the same thing cannot happen again. Give at least four controls, in order of preference.
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1. Eliminate the petrol engines indoors. Use 110 V electric or hydraulic plant - a hydraulic breaker fed from a power pack sited outside, and an electric saw with water suppression or dust extraction. This removes the CO source entirely and is the only control that does not depend on behaviour.
2. If petrol plant is genuinely unavoidable, engineer the ventilation. Forced ventilation with a fan and duct delivering clean air to the work face and extracting to outside, running for the whole task and for a period after, plus CO monitors worn by each operative with alarms set at action levels. No refuelling inside the room, ever - fuel up outside, engine off, away from ignition sources.
3. Limit and control the exposure. Shorter work periods, engines off when not cutting, a second person stationed outside the door as a safety watcher, and a reliable means of communication - radios or an air horn, because there is no mobile signal below ground. Agree a rescue plan before anyone goes down.
4. Administrative and PPE back-up. A trained first aider on site, a written briefing on CO symptoms and the instruction to report headaches immediately, and dust controls for the silica risk from cutting concrete - water suppression plus FFP3 respiratory protection with face-fit testing.
Record the incident, review the risk assessment and method statement, and brief the whole crew on what changed and why.