Thursday, June 18, 2009

June 16th, 2009

Montreal, Quebec A story from last year about an erector death left me a little confused. A gentleman has pointed me to a link that helps clear it up. It's a report by the government as to how the accident happened. They have video animations which I will link to here.
The crane shown is a Piener 405 or 415. The crane was being disassembled. They were taking off the outer jib when it shifted, coming back and striking the erector in the head and pinned him to the top chord of the jib. You have to imagine that this piece weighs possibly 30,000 lbs, depending on length. The jibs rarely come in level, and often you don't want them to. You want to be able to make one connection, adjust the piece and make the next connection as it's easier to make a double connection, or single connection then allow the metal or gravity do the rest of the lining up.
During disassembly it's the same process in reverse. The jib is not coming out level. The crew that I worked on would hoist the piece sometimes mutiple times until we liked how it was positioned just off of the ground. Then we would paint mark the rigging locations and note, 10 feet tip heavy, or 10 feet "butt heavy" (flattering term, no?). The intention was that the dissasembly crew could visualize how this jib is going to free up and know that the rigging points are correct.
In the computer animation here, and here, you see the jib come up and strike the man. Note how the jib moves out then comes back and hits him. Here's how that happens on a Piener. That connection at the top of the lower chords has some flat bar that extends over the connection. So the male connection from the outer jib has a little area where it could hang up if the mobile crane is under-boomed. The jib is horizontal (nuetral) instead of tip heavy. As the guys get the piece free, it shifts nearly instandly and since the crane was under-boomed itcame back and hit the worker.
My suggestions are the same as my first blog, plus some more. #1, Use a B&O (Backing Out) hammer to drive pins on tower crane jibs. #2, after the pins are removed and before the B&O is removed, a sleever bar or Spud wrench needs to be in the hole to control the load. You move the mobile until the piece floats and you do not remove that tool until it floats, period. #3, the Mobile crane operator should be aware, or the "phone man" in the air should ask if the crane is under or over boomed if questions arise. Fianlly, #4 Mark you jib pick points and the attitude at which the peice flys naturally using those pick points. As a back up a guy can take a 15 foot rope, tie the horizontal members together by looping the rope twice, then twist the free ends until it is snug. If the piece jumps then the person can start to loosen the twist and manually float the piece. You'd be surprised how effective this is.
The report does not change the fact that this death was preventable. With a tool in the hole, the phone man should have seen that the piece was not moving, asked the ground man if it were over boomed, then boomed down until it pops free. At that point you adjust the hoist until it floats, pull the tools and the mobile crane now safely has the piece.
Crane work is unforgiving. If you think that you are on a crew that is unskilled, you probably are. If it takes you more than a day to put up the average crane, quit today. I see things travelling around to cities all over the US and simply shake my head. Someone on the site must know what they are doing, and they are incharge, period. Please, use the proper tools. Contact me if you don't know how to do it.
Thanks to the person whom sent me the link. Updates are part of what I'd like to get so that this blog is as accurate as possible. Journalists don't know what they are talking about in this arena and any solid info only makes us better, and safer.

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