Design for Safety
- Created: Tuesday, 03 September 2013 11:12
- Published: Tuesday, 03 September 2013 11:12
By Randy Logsdon
I woke up shortly before the alarm would have jolted me from my sleep. After some reflexive stretching, I slipped out from under the covers and carefully walked around the corner to the bathroom. The hotel room was still dark, and I reached inside the bathroom doorway to feel for the light switch. One has a sense of where it should be.
It seems to be such an innocuous installation – a duplex outlet (GFCI equipped) and two toggle switches parallel with each other. The faceplate is secure, there is no exposed wiring. It looks like a workman-like installation. But this time, still only half awake, I sensed something that I did not expect.
As I reached for the light switch, the heel of my hand brushed against the duplex outlet. “Not to worry,” one might say. The energized parts are recessed and it is equipped with GFCI protection.
Still, I was not satisfied, and for two reasons. The first is that the installer could easily have reversed the order such that the electrical outlet was third in the sequence away from the doorway. That way reaching for the light switch would limit the risk inadvertent contact with the outlet. Second, why was a safety guy reaching blindly into the dark (clearly an Eyes-On failure)?
The latter (a behavioral issue), I can control and work on improving. The first reminded me of an incident years ago that ended tragically. That incident also involved a choice made during an installation, among other factors.
At a quarry, a plant utility man was servicing a bin conveyor. A bearing mounted behind a sprocket for the chain-drive head pulley was to be lubricated. LOTO was not performed. The utility man did de-energize the equipment using a control switch located in a control booth with direct line-of-sight to the lube point on the bin conveyor.
A stepladder was needed to reach the grease fitting. (You can already see where this is going.) As the utility person was retrieving the ladder and preparing to access the bearing, a truck pulled up and blocked the line-of-sight between the bin conveyor and the control booth.
The bearing could have been mounted with the grease fitting pointing any one of four directions. In fact, it had been installed such that to reach the fitting, one was forced to reach between the top and bottom sections of chain and behind the sprocket. Another employee, after stepping into the control booth, noticed that the bin conveyor was not operating.
Knowing that it was supposed to be in operation, he activated the bin conveyor without checking – without asking why. The utility man’s hand was caught by the chain and carried around the sprocket, resulting in severe damage to the hand and permanent disability.
We can discuss the relative impact of each factor leading to this incident: LOTO, communication, positioning of the truck, start-up without checking or warning, and the installation of the bearing housing. In reality, there were several layers of protection, and each one failed. Had any single one of those protections succeeded, the man’s hand would not have been injured.
So that explains why I have that uneasy feeling about the light switch/duplex installation. Two layers of protection failed in my case – the position of the duplex and my careless action in reaching without looking. Fortunately, in my case there were four layers. The remaining two, the GFCI and the recessed contacts were not faulty.
Positioning of controls, anticipated noise generation, potential leaks, clean-outs, disconnects, lube access, parts replacement, and dozens more. How would an injured person be extricated from the 5th level of a screen plant? Can one person easily remove the guard for maintenance? How does one reach a light fixture to change the bulb? These issues can be most effectively addressed in the planning stages.
But even during repair or replacement, consider how something as simple as the orientation of a bearing housing, or the location of a duplex outlet can affect the risk of operation. It may be a small risk, but it also may be the one that saves your life.