Very challenging job!

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Very challenging job!

Post by MGC » Mon Apr 04, 2016 7:50 pm

We received a call to go Folkestone waste treatment works and deal with an incident where a laden skip weighing somewhere between 15-18T had fallen from an overhead crane after the lifting cables failed. It struck the raised loading platform on the way down and the rear of the skip carried on falling to the lower level, which is approx. 10m down. It hit 2 skips that were in the process of being loaded, damaging the roofs badly. One of the skips lifted up, appearing as if it was going to overturn and allow the falling container to land sideways in the basement. The water treatment works is a very complex building with many high pressure pipes, valves, tanks and electronics strewn just about everywhere. A skip falling against any of this equipment could be catastrophic. The worst scenario would be to rupture one of the large pipes, this could allow the vast tanks that are behind the incident to fill the lower levels.

The large mobile lifting gantry can travel backwards/forwards. It has a winch carriage fitted which can motor from side to side as well as raising the load. This is all controlled by an operator, usually from a viewing window in a nearby office. The winch and its carriage were unserviceable following the incident.

Apparently, another operator had viewed the situation previously and stated the container could not be lifted in a laden condition. He advised that the load must be removed before it was lifted out of the way. We were asked if we could come up with a solution as load removal was really not desirable. Cutting of the container would be required with this method. Hot work in this kind of environment is totally unsuitable. It could have been cold-cut but this again had its own problems. The container was not stable and even if it were to be supported via another means, it would have meant that men had to not only cut the box in several places, but they would have to be close by to remove the load. The load is a very dense material, being compressed waste from the treatment plant. It has a damp consistency quite like wet peat and is also very heavy.

I do agree that to remove the load would obviously have made the job very easy, and also reduced any risks involved, but that wasn't what the customer was asking.

We attended with the 1075 and carried out a survey of the building, situation etc. Several issues were immediately obvious; there was a question over the capacity of the raised area where the trucks normally collect the skips/containers. The vehicles moving the waste operate at a max. of 32T whilst the 1075 weighs nearer 35T, and that's without increasing loads via lifting etc. We spent some considerable time looking carefully at the structure of the platform and asking questions. No definitive answer could be found, but it was substantially built and a plan was being hatched where the load would be shared over another part of the building.

The platform had a steel deck covering the concrete structure. Although this helps with strength etc, it was going to work against us once the legs were lowered on the 1075. It is a narrow structure which does not leave sufficient room for full leg extension, but as we weren't lifting over the side we felt we had enough room. There was very little height overhead, meaning that the boom of the 1075 had to work at a relatively low elevation, thus reducing its capacity. As mentioned before, the structure was narrow so another problem identified was even if the container were to be lifted, the 1075 would be placed exactly in the spot where the container would need to be moved to. Moving any further forward than the few feet we allowed from the edge of the platform would make any effort the 1075 could provide both totally out of line and inadequate.

Attention was then focused on the gantry. It was rated at 20T, substantially built but spanned a very broad area. Obviously the wider you go with the beam, the higher the likelihood of overloading when placing weight in the centre. We wanted to use the gantry as an anchor point from which we could rig a means of lifting the rear of the container. Ideally we would have used both beams. Only the rear beam had a small access platform that we could use to gain access and set up some of the rigging. To use both beams would have meant that we would have had too low a sling point if we wanted to set up blocks giving enough height to reach the platform.

The gantry was sent further back into the building and we set up two 12 inch slings with packing etc beneath them to prevent cutting on the sharp edges. Shackles and blocks were added before it was sent in the opposite direction where the cables etc where attached, being very close to the 1075. The initial plan was to rig 3-to-1 from the 1075's top winches. 3 falls of cable on each side beginning with 1 from either winch that would begin its fall by the gantry. More time spent thinking and calculating resulted in another change. We felt that this would have had a problem where the gantry, even though anchored to the rear of the container, would have tried to move towards the 1075 and effectively drop the load again. Although it was particularly awkward to rig, you will see the images show the cables coming from the 1075, to the rear of the skip and then turning uphill where the 3 part line would connect between the container and the gantry. This method provided advantages in as much as the 3 part line only provided lift, the single cables coming from the 1075 not only aided lift but they pulled the container in an uphill direction.

The drag winch was set up to give some stability and a tractive effort to the front of the container. The lift began and the trapped containers were soon released. The 2nd vehicle was summoned to provide better anchorage for the rotator and it was also placed to provide assistance at a later stage in the plans.

Disaster struck whilst rigging up in that one of the auxiliary winches blew a pipe – something you don't need to happen when you're already up against it! The covers etc were removed, the pipework altered and modified temporarily to prevent further leakage, one winch isolated and the work then continued.

A very slow and tense lift then took place, everyone being blatantly aware that any errors could result in a disastrous situation. As the lift continued, it was necessary to keep tension on the drag winch in order to pull the container closer to the rear of the 1075. There was substantial weight on the twisted rails beneath the container at the point where they rested upon the stop plinth at the end of the platform. The under-lift was used, along with 2 short sleeper sections, to aid reduction of friction at this point. It was a case of constantly altering blocks, rigging etc at the back of the rotator to enable forward movement as the lift progressed. Fortunately, we had assistance from an operator who moved the gantry forwards in very small increments as the cable angles altered.

Eventually, the container was at a position where it could be slid onto the platform. We were relieved to see that our measurements were correct. There was only about 7inches left between the upper and lower blocks that were stationed on the gantry/container. As the deck offered little resistance to sliding steel, we raised the legs slightly on the 1075, left the under-lift on the deck surface, dumped the suspension on the 1075 and with a driver releasing the parking brake, it was all winched forwards until the container was safely on the platform.

We have done many challenging jobs before, but there aren't many that will test your nerve as this did.


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