Wednesday, May 20, 2009

May 20th, 2009

Malta Self-Erecting tower crane being used to pour concrete collapsed and landed across two buildings. The crane was being ran with a remote control which is very common for self-erectors. Most also have cabs. While there could be structural or soil or limit malfunction issues with this crane, it's also possible  that there was operator error. Notice that the tower has fallen over with the jib and I'd point towards the boom (luffing) rope. Over and over when a structural failure happens the mast still stands. 
If I were to train an operator on a self erector, it would be from the cab of the crane. Being smooth is important to running the crane in a safe manner. Self-erectors move so much that a guy in the cab will learn to run smooth unless he has a death wish. They can take the intended loads, but the getting the feeling of the crane bouncing while operating will teach a guy to respect the needs of the crane more than the needs of the crew asking him to go faster and faster. Being able to yank on controls does not make you a good operator. When you get the loads swinging, especially when the load is fluid like a CMU wall mix (grout) would be for this site, the pendulum of the load and sloshing of the concrete could tip the crane even if it were structurally sound. Overturning moments must be respected on Self-erecting tower cranes. It's fine to run the crane with the remote, but you still have to be smooth and accelerate and decelerate with respect.  

Sunday, May 10, 2009

May 9th,2009

Calgary Alberta, Canada. A rigging accident has killed a man  in Calgary working on a highrise in conjunction with a tower crane. Concrete panels were being moved. The panel weighed approximately 4000 lbs. 
I'm having difficulty in understanding exactly what happened. It's aresult of journalists writing about construction, so I'm going to go at this in two ways. I know some Canadian Safety workers read this so if and when you get better details, please add them or contact me and I'll post what you get. 
The common claim between articles is that the form slipped out of the rigging.  Guys love to rig using "basket" rigging practices. It's quick and easy and you look like you are fast. While chokes take longer, weaken the rigging capacities, and it annoys people to do it, I prefer this method of rigging. Basket rigging allows the load the freedom to fall out of the rigging. If you are hoisting outside of a building from the ground to the top of a 20 story and don't have a lot of real estate to work with, if you hang up on anything with a basket the load can be ripped out. If you have a choke in place the load has a much better chance ot remaining locked in. 
If you use a choke the center of gravity is not as critical a componenet  because the rigging is less likely to run. They mention winds here as having come up. If you get into winds with an uneven load in a basket and it starts to spin, the load running becomes much more likely. Proper planning for the job will allow you to get rigging with sufficient capacity to allow chokes on any load.
The other potential cause here would be a lifting eye or rigging failure. Beyond consistently checking and inspecting your rigging, I don't have much to add here without specific information. 
I don't think that this comment will apply here, but since we are talking about concrete panels... They are often stuck to the deck or wall. on modern cranes operators should get used to what a piece weights because he's going to hoist it over and over. You should not be freeing the load with the crane. The carpenters, or whomever, should be sure that the load is loose by the operator having the approximate weight then the load should be Burke barred or levered to assure that it isn't stuck or break it loose. The load should also be lifted slowly until you are certain no nails or tie wire is still attached and not about to hang up. 
A man is dead, and we are likely able to improve as a result of it. We owe it to his memory to find out what it is that we need to do better to prevent the next death.  

Thursday, May 7, 2009

A friend of mine whom erects tower cranes here in Seattle stopped by for coffee one day last week. He brought along some pictures that I think are worth sharing. It's a tower crane that had a trolley sheave seize. They found the problem during a dismatle process and it had not been reported. It really points out the importance of inspecting your crane regularly. I once saw an operator that literally wore a harness while operating his tower crane. I never could understand how he was able to run the crane safely while being so afraid of heights. Just as importantly, he could not inspect his crane. When I say inspect, I cannot imagine not walking the jib weekly. To inspect sheaves I'll put a shoulder under the rope, push it off the sheave and give it a spin. noticable wobbles or noises cause me to look further. 10 seconds to prevent this problem. As a side note, it's irresponsible and against manufacturer recommendations to not inspect the entire crane prior to each shift. What I'm getting at is jumping on the crane from the highest point on the building is both stupid and illegal. I only wish that I had pictures of a crane that had base pins that had nearly fallen out of their holes because the operator never inspected it.
These pictures also show the importance of paying attention to your crane. There would have been telltale noises that this was happening when the bearing was failing. Then you would have been able to hear the rope sawing through the sheave. Then you would have heard and seen the rope jump from the sheave to the pin and fishplate. Then you would have seen the rope jump and slacken up when it fell 3 feet after sawing through the pin. Then you would have heard it sawing into the diamond plate on edge. This isn't difficult, it's just paying attention to something being different. When I was an operator I had a bearing going bad and it only showed under heavy loads. The technician disagreed. So I brought up my tools, called him back out and dismantled it while he was there. The metal under the bearing was oblonged and wasn't properly supporting the race. I picked out the right sheave with a small problem from the seat. That was on my first crane. I don't see an excuse for this operator and the danger here is hardware raining out of the sky. Pay attention to your rig and inspect them before you kill someone.