A fellow crew member's comment on "getting static" while working near a 115kV air switch goes unheeded and results in an electrician's death.
Engulfed in flames, the electrician fell to his death from a power pole. The reason: While holding the blades of an open 115kV air switch, he made contact with the energized line side of the switch. His family hired our firm to do a forensic engineering analysis to uncover the circumstances leading up to his death.
To ensure an accurate investigation, we quickly set out for the site to prevent evidence modification or tampering. Time was also critical because eyewitnesses tend to be silent when a stranger arrives at the scene late.
Within hours of arrival, we met the family's attorney and asked for copies of the initial investigative report and 8-in. by 10-in. color photos taken at the time of the tragic incident. We wanted to verify the site was in almost the same condition as it was at the time of the accident. We proceeded to interview the other electricians-all members of the same working crew. Since all were qualified and experienced in working with high-voltage systems, we determined this wasn't the error of an unqualified person contacting live parts.
We also arranged to turn off the power at the accident location. While observing the site and equipment, we wanted to replicate as much as possible the actions of those involved at the scene during the time of the accident.
A 115kV potential is "non-forgiving." Thus, we used procedures allowing us to verify the system was isolated and would remain off during our inspection. (Many over-eager investigators have compromised their own safety when attempting to reconstruct an accident.)
Failure to follow correct procedures is fatal. Based on our review of the facts contained in the accident report and reinforced by our interviews with other crew members, we knew the actions of all parties up to the time of the actual fatal accident. For example, we learned the victim (let's call him Smith) knew one of his crew members commented on "getting static" while working in the area where the accident occurred. This may have been the "warning" of induction from the energized portion of the high-voltage switch. Smith's fatal error was to ignore these comments, rather than taking them as a warning of potential lethal danger. Instead of ignoring this warning, he should have used a glow stick to verify the presence of any voltage. He should have also ensured a properly grounded system was in place. Instead, Smith climbed to the "A" frame platform and his eventual death.
When we tested the operating characteristics of the 115kV switch's manual control handle and operating rods, we noted the blades require 12 turns to travel from the fully opened to fully closed position. The operating rods are the mechanical control portion of the switch mechanism and are located on the "A" frame platform. They link and control the switch from the ground level handle. The handle doesn't provide any warning to people on the ground as to the exact position of the switch's rotating live blades, which are located on the upper platform. The rotating action of the switch's blades is supposed to free the unit from ice.
We then reviewed the coroner's report, which revealed the majority of the fault current tracked across and through Smith's clothing, going to ground through the switch's operating rods, upon which he was standing.
We reviewed several standards used in high-voltage installations including ANSI C-2 (National Electrical Safety Code), ANSI C29.9 (Wet Process Porcelain Insulators), C37.30 (IEEE Standard Requirements for High-Voltage Air Switches), and NEMA SG-6 (Power Switching Equipment).
The result of our forensic research was a comprehensive report. It didn't reduce the family's pain, but it did help implement the following changes in operating procedures. * Revised work rules that identify safety techniques for all people working in proximity of live parts. * Recommended changes in selection of switch controls to provide ground- and switch-level visual assurance of the rotating blades' position relative to the operating handle. * Safety training seminars.
This case resulted in a better manual that addressed operating procedure and provided guidelines for purchasing safer disconnect switches in the future. All parties gained useful information, but they paid a tragic price for it.
This writer remembers one of his first forensic investigations: A woman, working at a fountain soda counter, injured herself by getting a severe shock when she touched the metal casing of an electric mixer. We learned almost all of her co-workers had complained to the manager about their fear of that mixer. They all received minor electrical shocks. The woman had the misfortune of touching the mixer and a stainless steel sink at the same time. This writer recalls how easy it was to determine the cause of the problem by simply reversing the wall plug polarity and then testing with a meter.