Jammed slug, bridged interlock and a taped light curtain on a 150-tonne press
At a press shop running a 150-tonne mechanical press on fan-motor laminations, the operator clears a jammed slug by sliding the fixed front guard aside and reaching under the ram while a helper keeps both hands on the two-hand control. Tool changes on this press are done without lockout; the flywheel is simply allowed to run down. The left-side light curtain has been taped over because it kept tripping, and the fixed-guard interlock switch is bridged with a wire. A hydraulic pump leaks oil across the walking area, and a sound-level meter reads 96 dB(A) at the operator position. No risk assessment exists for the press, and nobody records near misses. The supervisor wants the line restarted immediately because a dispatch is overdue. You are the tool-room trainee standing nearby.
1. Separate the unsafe acts from the unsafe conditions on this press, and state the first three actions you would take before any production restarts.
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Unsafe acts: reaching under a live ram; the helper holding the two-hand control to defeat its purpose; taping over the light curtain; bridging the interlock; carrying out tool changes without lockout. Unsafe conditions: an unguarded point of operation, disabled safety devices, oil on the walking surface, 96 dB(A) noise, no risk assessment and no near-miss register.
First three actions:
- Stop and isolate the press: switch off, lock and tag the isolator, and verify isolation by attempting a start and by checking the flywheel has stopped.
- Barricade the press and clean the oil with absorbent; mark the spill area.
- Remove the tape and the bridge wire, then prove the guard circuit operates by testing the interlock and light curtain function.
The jammed slug is cleared with the ram at bottom dead centre and energy isolated, using a hook or brass rod. Restart only after a documented risk assessment and a safe procedure for jam clearing exist.
2. The light curtain was taped over because it kept tripping. Using the hierarchy of control, explain how this should have been corrected and why PPE ranks last.
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Hierarchy, best first: eliminate the hazard by designing the tool so slugs cannot jam and adding a slug chute; substitute the process, e.g. a press with better ram control; engineer the control, i.e. a fixed interlocked guard, a correctly aligned light curtain, a two-hand control with anti-tie-down and a ram lock; then administrative controls such as a lockout-tagout procedure, permits and training; PPE last.
A nuisance-tripping curtain is a symptom of misalignment, wrong blanking or muting settings, or a worn curtain, and each of those has an engineering fix. The correct response is to realign, re-set the muting, and add a function test at each shift change and after every tool change - never to tape it over. PPE ranks last because it protects only the wearer, depends on correct selection and fit, gives no warning when it fails, and leaves the hazard in place for the next person. An interlocked guard removes the hazard for everyone.
3. State what you would record about this event and what is required for the noise exposure at 96 dB(A).
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Record it in the near-miss register: date and time, press number, people involved, which device was defeated and why, the oil spill, the noise reading, immediate action taken, corrective action with a named owner and a due date, and verification that the interlock now works. Photograph the bridged switch before removing it. Report to the safety officer; a defeat of a guard is a reportable unsafe practice and should be reviewed with the whole shift.
For noise: 96 dB(A) over 8 hours exceeds the 90 dB(A) limit, and with a 3 dB exchange rate the permitted duration at 96 dB(A) is about 2 hours. So either reduce the level or strictly limit time in the area. Actions: engineer the source (silencer, enclosure, anti-vibration mounting, quieter pump), mark and signpost a hearing protection zone, issue ear plugs or muffs of adequate attenuation and enforce their use, start baseline audiometry with annual repeats, and repeat the noise survey after modification. PPE comes after the engineering controls.