An asphalt plant is a fairly complicated arrangement of ducts, drums, silos, conveyor belts, and one BIG burner. In one drum, the sand, rocks, and molten oil are heated and churned together to make the hot mix that is then held in a silo until it is shipped to the job. The silos are insulated and will hold the temperature for several hours. In many of the largest plants, there is a system of hoppers and conveyors that move the sand and rocks to the burner; in smaller plants the hoppers are fed by a front-end loader that brings the material from piles on the plant site. That is a hustling job.
When it is running at full capacity, an asphalt plant is semi-organized chaos...loaders and workers on the ground dashing around, trucks lined up and trucks moving under the silos to load, trucks moving out of the plant onto the road, and trucks coming into the plant to pick up a load or to dump material to feed the plant. It is a dusty place.
Periodically the plant is shut down, cooled off, serviced, and cleaned out. At least once a year the major components are disassembled and thoroughly cleaned. One part of the plant that needs regular maintenance and cleaning is called the "bag house"...a compartment filled with filter bags that are supposed to help control the dust in the air. But the ducts that bring the air into the bag house are usually only cleaned annually.
Told you all that (and believe me, that is the barest of Readers' Digest versions of the operation) so I could tell you this:
I was working for an Asphalt paving company a few years ago. It was time for the new plant to have its first annual tear-down for thorough cleaning and maintenance. We had hired a local 12-Ton mobile crane to come over and lift some of the components off their mountings. The crane operator seemed to know his stuff and soon got set up to lift the duct off the bag house. The duct is about two feet in diameter, twenty-some feet long with curves on each end and made of a pretty heavy-gauge steel. The bosses were guessing that the duct was well within the crane's max weight limit...and it should have been. Once the rigging was set for the lift and all the attaching bolts were un-attached, someone pointed out that the line from the crane was not exactly perpendicular. Everyone eye-balled it and the operator said it would be okay; it might swing a little when it broke free but it would be controllable. Two guide ropes were attached and two of the laborers were assigned to hold the ropes and steady the duct once it was in the air.
The operator put tension on the line and everyone took one more look to ensure it was all right, then they all cleared out of the area and the operator started the lift. At first all that happened was the cable got tighter and tighter. Then with a snap, the duct broke free, swung toward the crane, and then swung away from the crane. The rear of the crane was lifted off the ground, there was a creaky, trembling, tearing sound, and the crane pulled all the way over, the boom smashing into the burner and bag house, the duct crashing to the ground in a huge cloud of dust.
There was silence once the parts settled, and no one moved for what seemed like hours but was more like a few seconds; then pandemonium broke out all over the plant. The boys on the guide ropes were smart enough to drop them and run so they were a hundred yards away, safe and sound. The control house and all the work spaces were quickly searched to make sure no one was hurt. Then one of the bosses asked where the crane operator was. No one could see him. There was momentary panic as everyone ran to the cab of the crane to find the operator. He wasn't there. Then one of the smaller loader operators ( he was there mixing soils for landscape customers) rolled up to see what was going on. Some one asked him if he had seen the crane operator and the loader kid said, "Yeah, I gave him a ride down to the gate; he seemed to be in a hurry to get out of here."
It turned out that the operator immediately got out of the crane, went to the gate (luckily he got a ride) went across the highway to the gas station and called his wife to come get him 'cause he was "off work".
It really wasn't funny at the time...there were thousands of dollars worth of damage (could have run into the millions) and that was really lucky. No major structural damage was done and the plant was reassembled and in operation in short order. The cause of the problem was the tons of dust that had accumulated in the duct causing the crane to be over-loaded, coupled with the fact that the cable wasn't straight, a major no-no in a heavy-lift operation. But it was funny to me that the operator knew instantly that his working days for that crane company were over, so he just walked out and left, leaving a monster mess and damage behind.
I watched that locomotive bite the dust in Africa on the docks and it was this story that was the first thing that jumped into my mind. I wonder if that Gabonese rigger just turned around and walked on off the dock...