Ask almost anyone, and you'll get the same answer. The distribution power lines with which we share our world carry a lethal dose of energy. Ironically, from the perspective of most who toil and live their lives below the extensive electrical distribution network, there is little fear and almost no perceived risk. Despite the known danger that power lines pose to humans, we also know that the “air isolation” between us and the power lines keeps us safe from harm.
For the few whose work brings them directly or indirectly closer to the wires overhead, the risks are real — and the danger is always imminent. The crew of a moving company, charged with the task of transporting a metal shed under power lines one winter day, learned this lesson firsthand. Unfortunately, it came a little too late — after the move went terribly wrong, leaving one individual dead and another injured.
Considerable planning had gone into moving the large metal industrial shed, which measured 40 feet by 100 feet. At the time of the move, several parties played a part in coordinating the operation, including an electric company lineman, cable company employee, employees of the road commission, and a police escort. The building was elevated on two steering dollies at the rear and a tow dolly at the front. Everyone involved was aware of the presence of the overhead 14.4kV power line that obstructed the move.
The power line was located where the shed was to be turned from the original site onto the road. Prior to moving the structure across the path of the power line, the lineman dropped the neutral to the ground. The cable company dropped its line and built a protective guard over the cable. An energized phase was left in its elevated position with the intent that the building would traverse underneath it.
The lineman was positioned in an elevated bucket so as to observe the passage of the building under the power line. While passing under the wire, the team believed the building would also need to execute a turn. The rear (steerable) wheels of the building could only be controlled by manual ratchets located under the building. Due to some winter weather a few days prior to the move, snow was on the roof of the shed. Therefore, no final inspection of the roof was conducted.
The move began as planned, with the building brought into position near the power line. The lineman was in place. Spotters were observing the move. The building began to pass under the power line. At some point soon thereafter, however, two individuals associated with the moving company assumed positions under the building so as to steer the rear wheels. (There was conflicting testimony about whether or not those individuals had been ordered away from the building by the power company employee.)
When approximately 75 feet of the building had passed under the power line, there was a flash of light. At this time, the order was given for the building to stop moving. A previously unnoticed 3-foot-tall antenna on the roof of the building had made contact with the energized phase. Electricity had been conducted down through the building to the steering wheels and into the two men controlling the steering ratchets.
One man was pronounced dead at the scene; the other survived the electrical contact and was taken by ambulance to the hospital. Even with the risk that the building might still be energized, witnesses went under the structure to offer assistance to the injured pair. Interestingly enough, no one could describe the state of the man who died for the first 15 to 20 seconds following the contact.
As is often the case in these types of contacts, an official investigation was conducted. It was concluded that the rule that requires 10 foot air isolation between power lines and humans (or conductive pathways to humans) had been violated.
Had such spacing been maintained, even the unobserved 3-foot antenna would not have contacted the power line, and no injury would have occurred. The lineman testified that he had warned the owner of the moving company, prior to the move, to keep all individuals out from under the building while passing under the wire — and that he had yelled to individuals under the building to get out during the move and observed them heeding his warnings. (This conflicted with testimony from the owner of the moving company.)
The family of the decedent sued the power company and moving company. I was hired as an expert consultant for the plaintiff (decedent's family) for the purpose of discussing the effects of electricity on the decedent and to answer the question of whether or not he had felt pain in the 15 to 20 seconds that could not be accounted for by way of witness testimony.
The shock was analyzed based on the physical evidence and witness statements. The decedent was found unconscious with burns to his right hand. He was wearing gloves and steel toed boots.
Assuming that the voltage to ground from the power line was 7,200V, the metal building provided a good conductive pathway to the decedent, and the current rapidly breached the decedents gloves, shoes, and skin, a body resistance of 500 to 1,000 ohms was used to calculate (by way of Ohm's law) a current through the decedent of between 7A and 14A. Witness statements and physical evidence suggested that the contact duration would have been less than 1 second. The building was being turned and was moving a few feet per second (1 mph = 1.4 feet/second). An arc would have been drawn to the antenna when it was a fraction of an inch from the wire (because the dielectric breakdown of air is 30,000V per centimeter). Furthermore, the arc would have extinguished shortly after the antenna burnt through or when the antenna was spaced enough distance from the wire by the motion of the building such that an arc could not be sustained.
This line of thinking is consistent with witness statements regarding the sudden flash of light, suggesting a brief electrical contact. The burn pattern was also consistent with this theory. The obvious current pathway was from the entry point right hand to the decedent's feet to ground, which would be considered a non-head-involved contact.
Accepted data regarding the effects of electricity on the human body would predict that the current was of a significant enough level to cause sustained contraction of the heart muscle (currents over 1 ampere). Upon cessation of the current, the heart would most probably have fibrillated, resulting in loss of consciousness within 15 to 20 seconds.
Regarding the issue of pain during the contact, the accepted view is that the decedent would have been oxygenated and cognizant of his world prior to the shock — and that since the shock did not impact his brain, this level of cognizance would have remained for some period of seconds following the shock. Although oxygen delivery to the brain would have ceased when the heart was impacted by the current, it is probable that the decedent was sufficiently oxygenated for a duration long enough to be cognizant of the pain from the shock impacting his nerves, the pain from the electrically induced burns, and possibly pain from electrically induced muscle contraction. Some literature even suggests that some individuals in similar situations have a cognizance of their impending death. Although pain is subjective, there is no question that the pain from this scenario would have been extreme.
The case ultimately settled for an undisclosed amount. Like most of the electrical injury cases that I have reviewed over the years, this was an avoidable death for several reasons. Had a final inspection been made of the roof of the shed, the antenna should have been discovered, and no injury would have occurred. The presence of snow made the risk of such an inspection seem to exceed the perceived benefit. Had a minimal air gap of 10 feet been maintained, or had the power line been briefly de-energized or temporarily shielded, no injury would have occurred. Furthermore, had the lineman perhaps been more vigilant in his observations — and had the operation not been allowed to proceed when individuals were under or in proximity to the building — there would have been no injury.
Although the issue of warnings was in dispute, had proper warnings been given and followed, no injury would have occurred. In my experience, I've found that the most important reason to have clearly developed rules and protocols in these situations is because, when executed properly, they can prevent the unforeseeable from being so obvious in hindsight, as was the case in this tragic accident.
Morse is a researcher and consultant who serves as a full professor of electrical engineering at the University of San Diego.