The Crusher Chute Blockage
You are the processing plant supervisor. At 10:15 the primary jaw crusher feed chute bridges and the crusher stops. The operator reports the blockage over the radio and says he can clear it 'in two minutes with a bar' from the access platform. The crusher drive is still energised but the feed conveyor interlock has tripped. The plant has no permit-to-work system for chute clearing; the operator has done it 'many times'. A second operator is on the platform above, out of sight of the first. The crusher discharge conveyor is running. The site's isolation procedure requires a lock and key at the MCC, but the MCC is 60 m away and the key is held by the shift electrician, who is on a break.
1. Assess the hazards of the proposed chute-clearing method and state what must happen before any work begins.
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The proposed method is a classic fatality scenario:
- Entanglement and crushing: clearing a blockage from an energised crusher exposes the operator to the jaw, the flywheel and the drive. Even with the interlock tripped, stored energy and unexpected restart are possible.
- Stored energy: a bridged chute can release suddenly, dropping rock and the bar onto the operator.
- Falling from height: the access platform, with the operator leaning over an edge.
- Falling objects: the second operator above, out of sight, could drop material or be struck.
- No permit system: the absence of a formal clearance procedure means no verification that the machine is isolated.
Before work begins:
- Isolate and lock off the crusher and all associated conveyors at the MCC, with a personal lock and key held by the person doing the work.
- Prove dead - try-start and test for zero energy.
- Physically secure the chute against release (e.g. support the bridged material).
- Use a safe clearing method - from a guarded platform, with a proper tool, never by reaching into the crusher.
- Brief both operators, establish radio contact, and ensure the second operator is visible or in communication.
- Complete a permit or the site's equivalent clearance record.
2. The shift electrician cannot be found and production is losing money. What is your decision?
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Stop the job until isolation is achieved. Production loss is not a justification for bypassing isolation. Options in order of preference:
- Locate the electrician or another authorised person with isolation authority - page them, call their mobile, or send someone.
- Use the site's emergency isolation procedure if one exists, which typically allows a competent supervisor to isolate under a documented process.
- Keep the plant stopped and inform the quarry manager of the delay and the reason.
What I would not do is allow the operator to clear the chute with the crusher energised. The 'done it many times' argument is exactly how people are killed - familiarity breeds shortcuts. The decision and the reason for delay are recorded, and the lack of a permit-to-work for chute clearing is raised as a corrective action.
3. Recommend the longer-term controls to prevent recurrence.
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- Introduce a permit-to-work system for entry into crushers, chutes and conveyors, with named isolators and personal locks.
- Engineering controls: fit a properly guarded clearing platform, a hydraulic rock breaker or vibrator to prevent bridging, and level sensors to alarm on high level before bridging occurs.
- Interlock verification: ensure the feed conveyor interlock cannot be reset while anyone is on the platform.
- Training and competence: brief all operators on the clearance procedure; remove the informal 'bar' method.
- Communication: require radio contact and a banksman for any work on the platform.
- Review after any near miss or blockage event.