Grinder, Jack and Air Line: Prioritising Hazards in a Two-Wheeler Workshop
In a two-wheeler workshop in Howrah, three mechanics share one bench grinder. The 150 mm grinding wheel has a 3 mm chip near its edge, the tongue guard is set 8 mm from the wheel, and the work rest is 5 mm away. An apprentice sharpens a screwdriver on the side of the wheel without goggles. Nearby, a Maruti 800 is held up by a 2-tonne hydraulic jack on an oily concrete floor; no axle stands are visible. A mechanic uses a compressed-air gun at 8 bar to blow dust from motorcycle rear brake shoes; the workshop door is closed and the air line has no water trap. The workshop has one 5 kg CO2 extinguisher near the door and a first-aid box with expired antiseptic. The owner asks you to audit the workshop before a vocational practical class visits next week.
1. Rank the three most serious hazards in this workshop and justify your ranking using likely severity and probability.
Read the worked answer
Rank by risk, not by how untidy the workshop looks: risk ≈ severity × probability.
- Chipped wheel, side-grinding and no goggles - highest. A 150 mm bonded wheel running at normal speed can burst. The 3 mm chip concentrates stress, and side-grinding loads the wheel in a direction it was not designed for. The apprentice is exposed every time the grinder runs, and eye or head injury can be permanent or fatal.
- Vehicle on a jack alone, on oily concrete - second. The jack may be rated at 2 tonnes and the car may be light, but oil reduces friction, concrete can crack, and there are no axle stands. A fall onto a person working underneath is a crush injury with high severity and a high probability because the task is being done now.
- 8 bar air used on brake dust - third. It creates immediate eye and air-injection risk and spreads respirable brake dust in a closed room with no water trap. The chronic harm is serious, but the per-task injury probability is lower than for the grinder and the jack.
The expired antiseptic is a minor issue by comparison; it does not drive the ranking.
2. State the immediate actions you would take before the class visits, including what must be taken out of service.
Read the worked answer
Take the grinder out of service first: remove the plug or lock the isolator and tag it. Replace the chipped wheel, fit the correct guard, set the tongue guard to within about 2 mm of the wheel and the work rest to within about 3 mm, and prohibit side-grinding. Provide goggles and a face shield, and train the apprentice before any further use.
For the car, lower it, clean the oil, and raise it again only with axle stands under the body or suspension points; the jack is for lifting, not support. Do not allow work underneath until the stands are fitted.
Ban dry air-blasting of brake dust. Provide a wet-cleaning or HEPA vacuum method, PPE, and open ventilation. Replace the expired first-aid items, check the CO2 extinguisher tag and weight, and remove all three unsafe practices from the practical-class area before students arrive.
3. Describe a safe procedure for cleaning brake dust from the motorcycle brake shoes.
Read the worked answer
Assume the dust may contain asbestos or other harmful fibres. Do not dry-brush it and do not use the 8 bar air line.
- Wear an approved respirator, eye protection and gloves; keep other workers away.
- If possible, wet the assembly gently with a fine water mist to suppress dust, or use a dedicated HEPA vacuum nozzle close to the shoe.
- Remove the shoes and clean them in a controlled area, not over the open workshop floor.
- Wipe residues with a damp disposable cloth and place all cloths, dust and old shoes in a sealed bag for proper disposal.
- Clean the drum and backplate with the same wet or vacuum method, then dry the braking surfaces so no oil or water remains.
- Wash hands and face before eating or drinking, and clean the area afterwards.
The reasoning is to stop dust becoming airborne at the point of generation; once it is in the air, a closed door and no water trap make exposure worse.