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Infrastructure Projects - Construction Technology
A Practical Guide to Construction Techniques and Practice
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Are tower cranes safe? There was a period of time in recent history when there seemed to be a rash of accidents and tower cranes got a great deal of scrutiny and a lot of attention in the public media. I think that had more to do with the fact that it was an extremely busy time in the city, and perhaps a hundred or more of tower cranes were in use. Let's have a look back at some of the most serious incidents. The very building we have been examining, in 2007, there was an accident, a serious accident when a bundle of rebar fell on an office trailer at the site and seriously injured one of the project architects. I have no inside knowledge about the details of that event. I only know what I read in the newspaper. Apparently, the bundle of rebar was being lifted with a nylon sling, which was described as being worn. That's what led to the accident, or that's what was alleged to have been the cause of the accident. I would question the use of a nylon sling in the first place. I would only use a steel sling, and it's a length of steel cable with an eye on each end. You pass that under the load, under the bundle of rebar, and you pass one eye through the other eye and then attach it to the hook of the crane. You make sure that's snug around the bundle. When the crane begins to lift, it tightens the cable and literally chokes the load, and that kind of a cable used that way is actually called a choker. That's how I've been lifting rebar all of my life. That's how I lift a structural steel section. So it's really questionable in my mind as to why anyone would use a nylon sling. And certainly a nylon sling that's worn, so much the worse. |
My point here is this has nothing to do with tower cranes. The crane on the right side of this photo is a conventional crawler crane and could have had the same accident. This is independent of tower cranes. This could have happened with any piece of equipment. It just seems to me that it was poor technique in the first place.
The second event was a real tragedy. It occurred in 2008 where a tower crane fell off the tower and killed several people. Once again, all I know about that is what I saw in the newspaper. It was really difficult to read the details. Apparently, the ring that supports the crane cracked, and the owner knew it was cracked, and he shipped it to China to be repaired. I keep asking myself, how expensive would it be to buy a new ring and save the expense of shipping it to China for repair and shipping it back to New York? I really scratch my head. Nevertheless, he shipped it to China. The fabricator in China alerted him to the fact that he doubted that this piece could be adequately repaired. In spite of that, he was told to continue and perform the repair. The ring was returned to New York. It was placed in service. Shortly thereafter, the crane fell off the tower. Now, of course, that is a tower crane accident, but to condemn tower cranes because of that kind of negligence would really be incorrect. That was a terrible incident, and I think it is just now reaching the courts, and we will have to wait and see what the judgment is in the legal process. The third incident was very recent. It occurred in 2012, just about the time that I'm assembling these classes and a bundle of steel fell from a tower crane at the World Trade Center. I don't think it was the Freedom Tower. I think it was one of the adjacent commercial buildings. Nevertheless, a bundle of steel fell from the crane. That is a very, very recent event. No details at all. It sounds suspiciously like the first incident where the bundle of steel came loose. Maybe they used nylon strings. It's foolish for me to even speculate, but that seems like poor technique, human error and not really attributable to tower cranes. In conclusion, in my opinion, tower cranes are perfectly safe. |