From MSHA accident file…
The two (10) ten-inch metal pipes being removed were part of a closed-loop chiller system that had been abandoned. One pipe supplied chilled water underground (supply and shown as blue in the drawing), and the other returned water to the surface (return and shown as red in the drawing).
The chiller pipe system ran from the “chiller buildings” on the surface to the 1600-foot underground level.
Both the supply and return pipes had isolation valves. However…
- One set of isolation valves on the SUPPLY AND RETURN sides was located approximately sixty feet away from the accident location and was only reachable by a lift or ladder. The investigators found these valves CLOSED.
- The CLOSED valves on the return pipe near the thrust block, along with the closed isolation valve on the return line 60 feet away from the accident location, left water trapped in the return chiller pipe and pressurized by up to 1,600 feet of water column all the way back to the surface.
- If full, this entrapped water column pressurized the return chiller pipe with an estimated 700 pounds per square inch of water pressure due to gravity. The investigator was unable to determine how much water was in the pipe at the time of the accident.
- The mine operator had an established procedure for hazardous energy isolation of air, water, and discharge lines.
- The procedure required miners to identify and isolate all energy sources, turn off and lock the main feed valves, and open relief valves to release stored energy.
- On the day of the accident, the miners did not follow these steps before removing the pipe. The accident investigator determined this contributed to the accident.
NOTE: I disagree with MSHA’s comments regarding root cause and contributing factors. The improper energy isolation that caused the release of 700 psi water is the root cause; not being tied off in the lift and the water knocking the miner out of the lift was a contributing factor.
CLICK HERE for the MSHA report