Acetylene cylinder leak and an unguarded 230 mm grinder
At a school workshop, the gas store is a 2 m × 3 m room shared with paint cans. An acetylene cylinder is lying on its side with the regulator still fitted, and there is a faint acetone smell. The oxygen cylinders are chained upright beside it. Outside, eight learners are in a 6 m × 8 m bay. One learner is about to cut 40 mm × 40 mm box section with a 230 mm angle grinder. The guard has been removed to reach into the corner, the extraction fan is off, and the nearest face shield is 10 m away. The grinder is marked 6,500 rpm and the disc is rated 6,600 rpm. The store temperature is 34 °C. The supervisor asks you to take charge before any more work starts.
1. State your immediate actions, in order, before any further work is allowed. Explain why each action comes in that order.
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Put people first, then remove ignition sources, then deal with the gas. Stop the grinding, take the grinder out of service and move learners away from the store. Do not switch electrical equipment on or off in the bay; isolate at the remote distribution point if safe. Open doors and ventilate, but avoid creating sparks or using naked flames. Treat the acetone smell as a possible cylinder or regulator leak until proved otherwise, because acetone is the solvent in acetylene cylinders and a leak can form a flammable atmosphere. Warn the supervisor, restrict the area, and call the gas supplier or a competent person. Only after evacuation and ignition control should a trained person in PPE approach the cylinder with soapy water. The order protects people first, prevents ignition second, and avoids disturbing a leaking cylinder until the area is controlled.
2. How would you make the acetylene cylinder and the store safe? Include the checks you would carry out and the storage rules you would apply.
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Do not use a flame to look for leaks. With the area ventilated and ignition sources removed, a trained person applies soapy water to the valve, regulator connection and hose fittings; bubbles show the leak. If the leak is at the valve and cannot be stopped by closing it, do not move the cylinder unless it is essential; evacuate, ventilate, contact the supplier and keep ignition sources away. Acetylene must be used upright and should stand upright for at least 30 minutes before use if it has been lying down, so the acetone can settle. Secure cylinders with chains or straps, keep valves closed when not in use, fit flashback arrestors, and keep oxygen and acetylene separated by at least 3 m or a fire-resistant barrier. Remove paint cans and other combustibles from the store. Keep the store ventilated and below the cylinder supplier's recommended temperature; 34 °C in a small room is already a warning sign.
3. Set out the controls you would require for the grinding task and explain how you would verify them before work restarts.
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The guard must be refitted before the grinder is used; an unguarded 230 mm disc can throw fragments and cause severe injury. Check that the disc is correct for metal, free from cracks, and rated at or above the machine speed: 6,600 rpm is acceptable on a 6,500 rpm machine, but a lower-rated disc is not. Require a face shield plus safety glasses, hearing protection, and no loose sleeves or dangling cords. Switch on the extraction, clamp the box section so both hands are free, and screen other learners from sparks. Check the cable, plug, RCD and dead-man switch. Verify by a supervisor's checklist: guard fitted and secure, disc speed and condition confirmed, extraction running, PPE worn, workpiece clamped, area clear. The learner should demonstrate the check before the first cut, and the grinder should be tagged out if any item fails.