Compressed Air, a Trolley Jack and a Dust Cloud: The Rear Brake Job
A 2013 2.4 L diesel pickup is booked in for rear brake shoes and a leaking wheel cylinder. The workshop has three bays. The roller shutter is open only about 1.5 m because of rain, and the ceiling fan is switched off. The air line runs at 8 bar with no dryer or filter. An apprentice who joined three months ago jacks the rear axle with a 2-tonne trolley jack on the concrete floor, leaves the jack under the axle and removes both wheels, stacking them face-down beside the bay. He then cleans the dust out of the drum and off the backplate with a blow gun, producing a visible cloud that drifts into the next bay, where a colleague with diagnosed asthma is working. He wears a face shield but no respirator. The leaking wheel cylinder has left a pool of brake fluid under the left rear wheel, and the fluid drained so far sits in an open pail that already contains used engine oil.
1. List the unsafe acts and unsafe conditions in this scene, then rank the three highest risks and justify the ranking.
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Unsafe acts and conditions present
- Vehicle supported only by a trolley jack, with both wheels removed and no axle stands.
- Compressed air at 8 bar used to blow brake dust into the open workshop.
- No respiratory protection; the air line has no dryer or filter, so it also carries oil and water mist.
- Brake fluid spilled on the floor and drained into an open pail mixed with used engine oil.
- Poor ventilation: shutter almost closed and fan off.
- Inexperienced worker performing the task unsupervised.
Ranking (severity × likelihood)
- Jack-only support. Severity is fatal or permanently disabling; likelihood rises every minute the vehicle is up, because a hydraulic seal is a single point of failure with no backup. Nothing else here can kill as quickly.
- Dust cloud. Severity depends on lining composition, which is unknown, and on the asthmatic colleague who is an immediate sensitive receptor; a respirable cloud in an enclosed bay makes exposure near-certain. Latency of lung disease makes it easy to dismiss, which is why it ranks high.
- Brake fluid spill and mixed waste. Slip risk is immediate and the environmental consequence is a legal one. It ranks below the first two because the harm per event is usually an injury rather than a fatality, but it must be fixed before work continues.
2. Set out the correct sequence and controls for removing the drum, cleaning the assembly and replacing the wheel cylinder, including PPE and waste handling.
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Before lifting
- Chock the front wheels, crack the rear wheel nuts on the ground, and confirm the jacking point from the manual. Jack, then lower onto a pair of axle stands rated above the vehicle's rear axle load, placed under the axle tube. Lower the jack so the weight sits on the stands, and leave the jack touching as a backup. Slide the removed wheels flat under the sill.
Dust control: do not blow it
- Dampen the assembly with a water mist or use a brake washer, then wipe with a damp cloth; or extract at source with a HEPA brake vacuum. If compressed air is unavoidable, use the lowest pressure with extraction at the nozzle, never a free jet across the bay.
- PPE: nitrile gloves, sealed safety glasses, P2 respirator (fit-checked), coveralls. The asthmatic colleague stays out of the bay until the cloud has cleared.
- Bag the cloth and vacuum filter as contaminated waste.
Wheel cylinder
- Clamp or plug the brake line, remove the cylinder, clean the backplate with brake cleaner (not solvent), fit the new cylinder, bleed in the correct sequence, and check pedal feel and for leaks.
Spill and waste
- Absorb the floor spill with granules, sweep and bag it. Brake fluid goes into a labelled, closed container for a licensed hazardous-waste contractor. Never mix it with used engine oil and never to the drain.
3. As the senior technician, what do you say and do at the moment you see this, and what follow-up is required?
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Immediate action
- Stop the job calmly and without humiliating him: "Hold on, let's get that on stands before anything else." Getting the axle onto stands comes first, before any explanation, because the hazard is live.
- Explain the reason, not just the rule: a jack holds by a seal that can let go; stands hold mechanically. Show him the correct stand position on the axle tube and let him do it while you watch.
Follow-up
- Report it in the workshop hazard/near-miss record, including the dust and the mixed waste, and notify the supervisor. The employer has a general duty to provide a safe system of work, information, instruction, training and supervision, and an untrained worker on this task is a supervision failure, not only his mistake.
- Check his induction record and put him with a competent buddy until he is assessed.
- Fix the equipment issues: service the air line with a dryer/filter, stock P2 respirators and a brake vacuum, and set a rule that the shutter stays open when engines or dust are present.
- Hold a five-minute toolbox talk on jacking and brake dust for the whole bay, and check the waste containers are labelled and segregated.