Methane monitors are mounted on the massive, 30-foot-long continuous miners because explosive gas can collect in pockets near the roofs of mines. Methane can be released as the machine cuts into rock and coal. The spinning carbide teeth that do the cutting send sparks flying when they cut into rock. The sparks and the gas are an explosive mix, so the methane monitor is designed to signal a warning and automatically shut down the machine when gas approaches dangerous concentrations.
Because the monitor continually shut down the machine:
On Feb. 13, an electrician deliberately disabled a methane gas monitor on a continuous mining machine because the monitor repeatedly shut down the machine.
Three witnesses say the electrician was ordered by a mine supervisor to “bridge” the automatic shutoff mechanism in the monitor.
There is some discussion as to whether the monitor was malfunctioning and shutting the machine down when it should not have or whether it was shutting down due to actual methane in the air. People in many industries willfully disable aids meant to keep them safe and malfunction is only one of the variables that affects the behavior (granted, it’s likely a big one). Here is one example from agriculture, collected for NIOSH through the FACE database program*:
A 26-year-old Hispanic male knitting machine operator died when he was crushed by moving parts within the knitting machine as he tried to make an adjustment. The victim opened a safety gate and jammed a needle in the “on” button that allowed the machine to operate with the safety gates open.
Last, in at least this one case the safety cut-off contributed to an accident.
On June 4, 2004, a 47-year-old co-owner of a recycling business was run over and killed by a Gradall telescopic boom lift (rough-terrain forklift) while he was working underneath it. He had been operating the Gradall, and had shut it down when he momentarily exited the vehicle. When he returned to the machine, he found it would not restart. The Gradall had a safety interlock that prevented starting from the ignition switch while in gear. The contractor was apparently unaware of this safety feature. He checked the batteries, and then crawled underneath the cab area and reached up into the engine compartment with a screwdriver. The screwdriver made contact between the two terminals on the starter, effectively jump-starting the engine and bypassing the safety mechanism that prevented ignition while in gear. The Gradall started and moved forward. The parking brake was not set. The back left tire rolled over the contractor.
In short, I admire but do not envy the designers who have to create these dangerous systems. Their users are inventive, under pressure, and different from each other in countless ways. Designing safety sounds easy (one can imagine “just make it shut off when they aren’t using it,”) but the answers seem far from being so simple. Many of the examples I have seen from other industries show quick and easy ways to bypass a safety system.
- Machinery automatically cuts off after 8 seconds when there is no weight in the driver’s seat. Worker keeps a heavy tool bag nearby to put on the seat when the worker wants to check on things outside the cab.
- Same system as above – worker tries to jump out of cab and complete task in less than 8 seconds.
- Worker cannot reach objective with lap safety bar in place, a bar that must be down for machinery to operate. Worker lifts bar then puts it back down across empty seat and reaches for objective with machinery running.
There does seem to be a difference in premeditation in the examples I’ve come across and the idea of hiring an electrician to specifically and more permanently remove a guard from a safety system.
*I have posted on the FACE program before. It is a valuable repository.
Photo Credit NIOSH on Flickr