Thursday, June 4, 2009

June 4th, 2009

Tokyo, Japan a Luffing Tower Crane being climbed down for dismantle appears to have suffered a hydraulic failure in the climber that caused the boom to collapse killing a worker and person on the ground.
Often tower cranes are climbed down to allow for a smaller truck crane to either reach it or allow for using a smaller truck crane to perform the work which can save tremendous amounts of money. The climb is achieved via a climbing frame that surrounds the mast then connects to the turntable. It is connected to electrical power that runs a hydraulic pump that pushes a ram into climbing dogs (of various designs). The hydraulics are supposed to have check valves in case of hose or pump failure. The check valves should hold the ram in place during a hose change out if it were necessary. From the sound of the description I hear that the turntable fell, crashing hard into the tower below, while being climbed down. This could have been from one or two meters and would have been violent.
So what could have caused the climber to fail? Three causes come to mind. If the Check Valves were not in place or simply weren’t the right size, or the valves failed themselves. This could be the result during massive pump or hose failure. Stranger things have happened, but this would be a new scenario to me and I would want to see the maintenance records on that climber. Were the check valves ever changed out to possibly the wrong ones? The second stand out potential is the climbing dogs slipping. In many designs a person has to physically or mechanically pull the ram in to proper position. If a guy got lazy it could be off and a slip could happen allowing the crash. My third and final suggestion would be climbing dog failure. These structural members are welded into place just like any other piece of the crane. If you had a weld or metallurgical failure, again, this would be the result.
This is an odd scenario. I have 100+ crane accidents on my blog with maybe a dozen climbing accidents and no climber slips that led to this. In New York a tower was thrown off due to a slip, but the result was the tower being thrown off the platform and landing on a passing cab, not killing anyone, luckily. The solution there is to secure the tower to the climber via rigging while climbing. Past similar accident link.
Another possibility, from looking at the pictures, is that the tower crane came apart from the climber. The climbers are either pinned to the turntable, or bolted. This type of accident has happened twice that I know of, in Seattle in 1985 and in Croyden, England in 07. If you do not bolt or pin the turntable to the climber, only balance would hold the turntable on the climber. The idea that this could have happened again is beyond comprehension and murder charges would be the appropriate result. This is simple speculation in looking at the pictures and not based on the stories that I’m reading.
Hopefully we’ll hear the cause of this accident. Climbing a crane is some of the most relaxed work in tower cranes, if you have experience. It’s 15 minutes of fury followed by 30 minutes of trying to stay awake. But the guy running that pump needs to pay attention and every move that you make is critical. Sequencing and experience is critical even though it can seem so simple. The most spectacular accidents happen during climbs. This one may not even be human error, but you must have the right people in place for a climb. If you don’t… Seattle in 85, San Francisco in 89, Manhattan in 08, Hong Kong in 08, New York in 06, etc.


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