Blind Loading Over a 2.4 m Wall on a Shared Radio Channel
An excavator is loading 20-tonne dump trucks over a 2.4 m concrete wall. The operator's eye level cannot see the truck bed, so a signaler stands on the far side. The signaler is 12 m from the machine on the edge of a haul road used by an articulated truck every four minutes. All crews share one radio channel, and the operator can hear a second signaler giving instructions to a different excavator. The signaler is new to the site, wears high-vis but has no air horn, and the hand signals are partly in shadow from the low afternoon sun. The operator's left track is 1.2 m from a drainage ditch. During the first cycle the signaler waves the bucket over the wall while the radio says 'hold, hold, hold' for another machine, and the operator also sees a worker walking behind the truck.
1. What must be agreed and set up before the first bucket goes over the wall?
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Communication:
- One designated signaler for this machine, agreed by name and identifiable (a distinct vest colour or 'signaler' marking). Two signalers on one channel is the failure mode already developing here.
- A dedicated channel or talk-group, with a call sign for the machine, tested before the first cycle.
- Standard hand signals from the site's signal chart, plus an emergency stop signal and a horn acknowledgement.
- The rule that any stop signal, from anyone, is obeyed, and that an unclear signal means stop.
Positioning and site:
- The signaler stands where they can see both the bucket and the truck bed, can be seen by the operator, and is outside the swing radius and the truck path, with an escape route. The haul road edge at 12 m is not automatically safe.
- Mark the signaler's stand; keep the ditch edge clear, with the left track at least 1.5 m back or the blade set as a support.
- Agree the truck spot position, the loading sequence, and what happens if the radio fails - usually a stop and a face-to-face reset.
- Give the signaler an air horn or whistle if they are ever in a blind spot.
2. The hand signal says 'swing' and the radio says 'hold'. What do you do, and what is the reasoning?
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Stop. Release the levers, keep the bucket clear of the wall and the truck, sound the horn, and set the safety lock lever.
Reasoning:
- The 'hold' may not be for this machine, but on a shared channel the operator cannot prove that. Acting on a guess is exactly how the wrong machine moves.
- A signal is valid only from the designated signaler, and only when the operator is sure it is meant for them. A wave seen through shadow, from a new signaler, on a channel carrying another crew, does not meet that test.
- A worker is walking behind the truck - an independent reason to hold the bucket where it is.
Then: radio 'machine X stopping, who is holding?' on the dedicated channel, and confirm verbally who the instruction was for. Do not resume until the signaler confirms clearly on the dedicated channel or face to face. Log the near miss. The operator owns the consequence of the swing, so the conservative action is the correct one.
3. How should the signaler be positioned, and what safer alternative would you propose for this blind lift?
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Position: on the operator's side and in view, outside the house swing radius plus bucket reach, never between the machine and the wall, never in the truck's path, on a marked stand with a clear escape route. From there the signaler must see the bucket and the truck bed at the same time - if they cannot, the signaler cannot do the job.
Safer alternatives, in order of preference:
- Reposition the machine so the operator can see the truck bed directly over or around the wall. Removing the blind lift removes the whole communication dependency.
- Fit a camera or a mirror on the wall so the operator has direct sight of the bed, and use the signaler only as a backup.
- Alter the task - load from the other side, use a ramp or a lower section of wall, or use a different loading point.
A second signaler at the wall is not an improvement: two voices on one channel recreates today's conflict.
Also fix the sun angle (reposition or use a visor) and keep plant and spoil back from the ditch edge. Blind lifting should be a designed last resort, not a daily method.