The Sidewalk Vault and the Restricted Quadrant
At 02:10 you position a 100-ft rear-mount aerial ladder at a three-story garden apartment with fire through the roof and a resident reported trapped at a second-floor window on the right-rear side of the building. The street is 22 ft wide with a 5 percent crown. Your first spot puts the right-rear outrigger over a sidewalk utility vault whose cover sits 3 ft from the curb, and a fence limits the left side to a 14-ft spread. The placard allows a 500-lb tip load fully supported and 250 lb with the right-rear jack short, with short jacking permitted only when the aerial works over the left-front quadrant. The cab level reads 3 degrees of cross slope against a 5-degree limit. Reaching the window needs about 78 ft of extension at 68 degrees. Moving 40 ft down the street clears the vault but drops the rated tip load to 350 lb at that extension.
1. Which position do you take, and what facts decide it?
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The rescue objective controls the answer. Short jacking is not simply a capacity penalty here; the placard restricts the whole operating envelope to the left-front quadrant when the right-rear jack is short. The trapped occupant is on the right-rear side, so the restricted envelope cannot reach the objective at all. That removes the original spot regardless of the 250-lb rating.
So you reposition 40 ft down the street and plan the operation around the 350-lb tip load at 78 ft. Two firefighters in full PPE run roughly 480 lb before you add tools, which exceeds 350 lb. That forces a deliberate configuration: one rescuer plus the victim plus minimal tools per trip, a second trip for the other rescuer, or a ground ladder for the second firefighter. The lesson the exam is testing is that the load chart and the envelope restriction are both absolute limits, not advice, and the tactical objective has to be matched to them before the boom comes off the bed.
2. What must be verified before the aerial leaves the bed at the new position?
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Work through the stabilization sequence in order, because each step invalidates the next if skipped:
- Apparatus placement: wheels chocked, parking brake set, transmission in the proper position per the manual, and the aerial positioned so the tip will not pass near energized overhead conductors within the required minimum approach distance.
- Ground bearing: all four outrigger pads on undisturbed, competent surface. On a crowned street, a downhill pad may hang in air; crib only enough to achieve firm bearing, and never stack cribbing to manufacture level beyond the manufacturer's slope limit.
- Level verification: read the truck's own level indicator at the turntable, not the cab bubble alone, and confirm you are inside the placarded limit.
- Full deployment confirmation: jacks pinned or locked as designed, pads fully seated, interlock lights showing.
- Personnel clearance: nobody in the stabilizer sweep before and during deployment, and a spotter watching the pads while the boom loads.
- Function check and load chart: raise, rotate and extend through a short cycle, verify quadrant, then confirm the 350-lb rating applies to the direction you will actually work.
3. If the incident commander orders you back to the first spot, how do you handle the 3-degree crown and the vault?
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The 3-degree cross slope is inside the 5-degree limit, so it is not by itself a reason to refuse. On a crowned street the practical problem is pad contact: the downhill jack can unload or the uphill jack can take an uneven share. The correct fix is a small amount of cribbing to get solid bearing, not building a level platform under the truck. If leveling to operate would require cribbing beyond the manufacturer's slope allowance, the answer is to relocate, because the outriggers and frame were not designed to carry a truck perched on timber.
The vault is the harder call. A vault cover is not a structural bearing surface for an outrigger; it is designed for foot traffic. If the spot is unavoidable, the pad must bridge to the vault walls or to solid pavement outside the cover, with cribbing sized for the actual jack load, which for a heavy aerial with the boom extended can run into the tens of thousands of pounds per jack. If you cannot confirm the vault's construction and capacity, refuse the spot, tell the IC why, and document the refusal and the reason.