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Federal regulators in Philadelphia are looking at unsafe ground conditions as a suspect in Monday's tragic aerial lift accident, which killed the machine operator and injured three bystanders. Ground conditions are a major safety issue around these machines, industry experts caution.

Before we begin dissecting the details, let's clear the air about aerial work platforms, or AWPs. Despite reports claiming otherwise, Most AWPs are designed to be driven from the platform. That's the whole point, so you don't have to move ladders or scaffolds and risk injuring yourself on the way up or down. The one that fell in Philly could be driven with the boom extended, no problem, sources tell us.

Here's what else we know: The worker was using a JLG 1250AJP--a 125-ft-tall AWP--to inspect the masonry of the city's First Presbyterian Church.
The "ultra boom" aerial, which costs about $180,000 and weighs about 20 tons, tipped over when the operator drove it over a plastic vault cover on the sidewalk, catching one of the wheels.

Early reports characterize the cover as a "grate" or a "manhole," but an investigator with the U.S. Occupational Safety and Health Administration tells us that the composite cover looks like a "concrete" lid—something that may not instantly set off a red alert to an AWP operator. The investigator is not drawing any conclusions but notes that workers should "make sure to check the area where they are going to run an aerial lift. The type of ground they are on, and the stability of the ground."

Guy Ramsey, who publishes Lift and Access magazine, says that aerial lift operators commonly use the public way but are not always trained to assess its stability. "These window washers and painters and glaziers drive up on sidewalks all the time," he tells us. "I've been around these machines since the beginning of the [AWP] industry, and I would never think to look to find out whether there was some kind of cavity or room or something underneath the sidewalk."

Ramsey says he would like to know how common these plastic vault covers are. Like cranes, aerial work platforms are highly engineered vehicles that require attention to the training of the operator, the maintenance of the machine and the site on which it stands. In his 2004 review of JLG's 1350SJP, a similar machine to the one that fell in Philly, Ramsey describes the dangers in chilling detail:

When you step into the platform of a boom lift, let alone one that can be driven from 135 feet in the air, you start to think about a lot of things. Is the operation area flat and REALLY firm? Is the wind too strong? Was the unit properly tested and serviced? Is my life insurance paid up? Once you have satisfactorily answered these questions, it's time to slip on the body harness."

Unsafe ground conditions should be on every employer's radar screen and a part of an operator's basic training, adds Tony Groat, executive director of AWPT, a Schenectady, N.Y.-based safety institute, and former vice president of NES Rentals.

"The best practice is to go to your supervisor and say, 'This thing weighs a lot. If this ground won't hold it, then I know there is going to be a problem,'" says Groat.

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Still, ground conditions are frequently ignored or sidestepped, he and others admit. We snapped the above photo on a jobsite in Chicago a few years back. Does this look like engineered cribbing?