Pre-Use Inspection Finds Four Safety-Critical Defects
At 06:30 you begin the pre-use inspection of a 2019 crawler dozer that has done 6,400 hours. The machine is booked for a two-hour slot pushing clay into a stockpile in a busy earthworks compound, where pedestrians and dumpers cross the haul route. During the walkaround you find: the right track has 45 mm of sag against a specification of 20–30 mm; the tilt-cylinder hose has a 25 mm bulge with a slight oil weep; the cutting edge measures 15 mm against a new thickness of 30 mm, and two plow bolts are loose; the rear-left ROPS mounting bolt is missing; the seat belt has a 40 mm frayed section; and the horn does not sound. The supervisor says the two hours are critical and asks you to 'top up the track and get on with it-we'll book it in at lunch'.
1. Sort the findings into stop-work, fix-before-use and monitor categories, and explain the reasoning for each.
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- Stop-work: the missing rear-left ROPS mounting bolt. A ROPS is only effective as a complete, correctly torqued assembly; one missing bolt loads the remaining mounts and can let the structure fail in a roll-over. Also stop-work: the frayed seat belt over 40 mm, because it may not restrain the operator, and the tilt-cylinder hose with a 25 mm bulge and weep, because a sudden burst releases hot hydraulic oil at pressure and the blade can drop.
- Fix-before-use: the horn and the loose cutting-edge plow bolts. The horn is part of the site's warning system in a compound with pedestrians; loose bolts can let the edge move or break away. Track tension at 45 mm is outside the 20–30 mm specification and must be corrected before work, not merely monitored.
- Monitor with a written record: the cutting edge at 15 mm against 30 mm new. That is 50% worn, but whether it is condemnable depends on the manufacturer's wear limit; measure it, record it, and check the manual. It may be serviceable if the bolts are correctly torqued and the edge is not cracked.
A defect is not downgraded because the machine is needed. The category decides whether it can move at all.
2. What do you do about the supervisor's instruction, and what records and communication are needed?
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I would not operate the machine. The instruction to ‘top up the track’ does not address the ROPS bolt, the seat belt, the hose or the horn, and starting the shift would put me and nearby pedestrians at risk.
Actions:
- Park on level ground, lower the blade and ripper, apply the parking brake, remove the key and fit a ‘DO NOT OPERATE’ tag.
- Tell the supervisor clearly which defects are stop-work and why; ask for the machine to be booked into maintenance immediately.
- Record each defect in the pre-use inspection/defect log with location, measurement and photo where possible. A verbal report is not enough.
- Sign the checklist only as ‘not fit for use’, not as fit.
- If the supervisor insists, escalate to the site manager or health and safety adviser and ask for a replacement machine.
The two-hour slot is a planning problem, not a reason to override a safety-critical defect.
3. Why is ‘just top up the track’ not a safe fix for the track tension, and how should it be adjusted?
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Track tension is a specified assembly setting, not a pressure to guess at. Over-tensioning loads the idler bearings, seals and track pins, and can cause overheating and premature failure; under-tensioning lets the track jump the sprocket or derail, especially in reverse or on soft clay. At 45 mm sag the track is already loose.
The adjustment should be made:
- On level ground, with the machine in the specified position and the track cleaned of packed clay.
- Using the manufacturer's measuring point and gauge, to the 20–30 mm specification.
- With the correct grease gun and relief valve; the track tensioner is hydraulically loaded, and loosening the fitting can release grease under pressure, which can inject into skin.
- By checking for a leaking tensioner seal or a damaged idler while the area is accessible.
If the track will not hold the setting, the machine has a defect that needs maintenance, not a top-up.