Outrigger Sinking on Soft Asphalt
At 15:30 on a 95-degree-F day, a 100-foot aerial is positioned on a newly paved parking lot to reach a third-floor roof. The asphalt is soft; the outrigger pads are 24-inch square. The lot slopes 4 percent down toward the street. The operator sets the right rear outrigger on a pad and the left rear outrigger on a pad. The aerial is raised to 65 degrees with a firefighter on the tip when the tiller operator notices the right rear pad has sunk 1.5 inches and the apparatus frame has shifted. The turntable bubble is still within the level indicator. The aerial is over the roof edge, and the firefighter is working. The driver/operator is at the turntable controls and has not seen the pad.
1. What should the tiller operator do immediately when the pad sinks, and why?
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Signal an emergency stop and tell the aerial operator to stop all movement. Do not wait for the bubble to go out of level. A 1.5-inch sink and a frame shift mean the outrigger is losing bearing and the load is transferring to the other outriggers. With a firefighter on the tip, continued movement could tip the apparatus or cause the aerial to strike the roof edge.
The aerial should be retracted and lowered to the stowed position, and the firefighter should be brought down or moved to a safe egress before anyone inspects the pad. Keep personnel clear of the downhill side and the area under the aerial. The tiller operator should not try to chase the level by adjusting the outrigger while the aerial is elevated; that can make the shift worse. The immediate priority is to remove the elevated load from the unstable outrigger, then assess the ground and the pad.
2. What must be done before the aerial is raised again?
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The aerial must be fully retracted and stowed, and the firefighter must be clear. Inspect the pad and the ground: soft asphalt at 95 degrees has low bearing capacity, and a 4 percent slope adds a lateral component. Reposition to firmer ground if possible, or use larger load-spreading pads and cribbing under all outriggers, not just the one that sank, so the load is distributed.
Re-level the apparatus, set the parking brake, chock the wheels, and deploy the outriggers fully. Verify the bubble and the manufacturer's slope limit. Recheck the pads under load before raising the aerial. If the ground cannot support the outriggers, do not raise the aerial; use a ground ladder or another apparatus. The tiller operator should document the sinking, the weather, the pad size, and the corrective action. Returning to the same setup without changing the load distribution would repeat the hazard.
3. If the hydraulic system fails with the aerial elevated, describe the emergency lowering procedure and the tiller operator's role.
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Follow the manufacturer's emergency lowering procedure. Stop the aerial, clear the area below, and use the manual override or emergency pump to lower the aerial slowly. Do not open hydraulic lines or force the boom. The tiller operator's role is communication and ground control: keep personnel out from under the aerial, confirm the path is clear, and relay commands between the operator and the crew.
If the firefighter on the tip cannot be lowered by the emergency system, use an alternate rescue such as a ground ladder or platform only if it can be done safely. After lowering, tag the apparatus out of service and have the hydraulic system inspected. The tiller operator should not leave the spotter position or the controls unless properly relieved. The priority order is to stop movement, protect the firefighter, control the ground, and then lower the aerial using the approved emergency method.