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Author Topic: 120-volt Electrocution Mystery  (Read 3801 times)

Mike Sokol

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120-volt Electrocution Mystery
« on: April 08, 2014, 04:38:39 pm »

Here's an article from EC&M Magazine about a worker electrocuted by 120-volts, and nobody is sure exactly why or how he was killed. But it's an important lesson about maintaining safety around even "low-voltage" 120-volt circuits.

Mike Sokol

The Case of the 120V Electrocution Mystery
Oct 1, 2007 - Michael S. Morse | Electrical Construction and Maintenance


Although often dismissed by industry veterans and novices alike as trivial, working in proximity to live 120V circuits leads to the untimely and unexpected death of many workers each year (see Lessons in Low Voltage on page 22). What many electrical workers don't realize is that any 120V shock is potentially lethal and surviving such an event should be viewed as a bullet dodged rather than something
 
Although often dismissed by industry veterans and novices alike as trivial, working in proximity to live 120V circuits leads to the untimely and unexpected death of many workers each year (see Lessons in Low Voltage below). What many electrical workers don't realize is that any 120V shock is potentially lethal — and surviving such an event should be viewed as a bullet dodged rather than something that simply comes with the territory. No one starts their day anticipating they will be a decedent by sunset. Unfortunately, this is the story of an electrical field technician who did not dodge the 120V bullet and paid the price with his life.

The scene

The day started like any other for this field technician, who was working for a company that routinely installed temporary electrical power systems at various construction sites.

The circuits installed were typically 2-phase, low-voltage (120/240V). Power was delivered to temporary wooden power poles using heavy extension cords, which were connected using twistlock-type connectors. The cords ran between the permanent power source that was owned by the electric utility and the first temporary pole in the series of poles. Given the need to drive multiple large loads associated with tools on construction sites, minimizing the distance from power source to load was always a concern on these sites. Shorter distances translated to lower voltage drop along the line. If the voltage at the load was too low, the tools would not perform as needed.

The accident


On the day of the incident, the victim was asked to disconnect one source from a pole (previously set up by his company) and connect a series of temporary poles to a closer power source (also set up by his company).

Upon arriving at the scene, the man and his supervisor walked through the site, inspecting the work area. First, the technician was to perform a live cutout of the more distant power source, thus de-energizing and isolating a series of poles. This task entailed placing a ladder against one pole, climbing the ladder, and cutting the two live 120V phases, the neutral, and finally cutting the ground, presumably with wire cutters. Doing this work “live” meant that any equipment connected upstream of the cutout on the live sequence of poles would not suffer a power interruption.

With the supervisor watching, the victim, who was not wearing insulated gloves, successfully cut out the live circuit. Based on testimony from his supervisor, the technician was then supposed to separate a male and female twistlock connector in a sequence of power cords, thus breaking a live connection to the closer power source and leaving a de-energized cord that was to be connected to the recently de-energized series of temporary poles. The next step was to place a ladder on the pole where the new connection was to be made and remove the insulating electrical tape on the wire-clamps from the (now de-energized) wire coming from the upstream pole (where the successful live cutout had just been completed). Finally, the victim was to connect the ground, neutral, and two phases coming from the power cord. Upon completion of the connection process, he was instructed to reconnect the twistlock and energize the sequence of poles from the closer power source.

After observing the live cutout, the supervisor went about other business for only a few minutes. Upon his return, he noticed the technician was not at the top of the pole (where he was supposed to be making the new connection). Soon thereafter, he heard moaning and quickly found the victim at the bottom of the ladder in apparent distress. Although the supervisor immediately called 911, and help arrived as soon as possible, the man died at the scene.

A lawsuit quickly ensued, with the estate/family of the decedent suing the owner of the construction site. I was retained by the plaintiff's counsel as a forensic expert to examine all of the evidence, reconstruct the accident scenario, and explain to what extent the decedent had contributed to his own death.

The investigation

Although the utility had no ownership or liability, the first technical person on the scene was a troubleman from the power company. He made several initial assessments. First, he noted that the ladder was fiberglass; therefore, it would not have provided a pathway to ground. The ground wire to the new source at the top of the pole had been properly connected. Upon inspection, he found that the insulating tape covering the wire-clamps from the line just cut out (the old source) to the pole had been removed, but the clamps were still connected to the wires leading to downstream poles.

On the new line to be connected, he noticed that the neutral (white) was cut but not stripped or connected. One phase (red) was cut and fully stripped back approximately 1 inch. The other phase (black) was cut with the insulation slid a short distance back but still intact on the wire. He measured the voltage on the exposed phases at 120V. Subsequently, per testimony by the supervisor, the twistlock that was supposed to break the live connection from the new source was still connected, thus explaining why the wires at the top of the pole were live.

Continuing the investigation, OSHA offered additional analysis, including the following clues. Pieces of electrical tape were observed on the ground at the foot of the pole. The missing piece of red insulation was not found at the base of the pole or anyplace else for that matter. A pair of insulated wire cutters was found at the base of the ladder, some distance away from the base of the pole.

The body of the decedent was found face down with his feet close to the bottom of the ladder and his head facing away from the ladder. Revealing a single burn in the middle of the decedent's chest, the autopsy also noted that there were no injuries consistent with a fall from any significant height as might be expected in a fall from a ladder.

The findings

There was no doubt that this case involved an electric shock. The question was one of contributory negligence. The defense's theory appeared to be that contrary to the supervisor's instructions the decedent had chosen to work on a live wire, had failed to test the wire with a multimeter (as would have been good practice), and had begun to make a live connection. Next, they alleged he made contact with an energized phase while using the wire cutter, received a shock, and fell from the ladder, ultimately dying from electrically induced ventricular fibrillation.

From a forensic perspective, this case remained somewhat of a mystery, based on several circumstances. The lack of wounds consistent with a fall from the height necessary to work on the wires was troubling to say the least. In addition, no one took pictures of the placement of the wires before the investigation began. The wire cutter found on the ground was not at the base of the pole, as would have been anticipated if it had been dropped immediately following the shock. The handle of the wire cutter was insulated. Although tape, (presumably removed from the wire clamps), was found at the base of the pole, the stripped insulation from the red phase was nowhere to be found. This raised the question as to whether or not the wire had been stripped previously — or if the decedent had in fact even been working on the wires at the time of the electrical contact. In my opinion, had he been the one who stripped the red wire, the red piece of insulation would have been found somewhere.

At autopsy, less than 50% of all deaths caused by low-voltage contact are found to have burn injuries. The lack of burns delineating either entry or exit points are thus not definitive unto themselves. The single burn observed could have been an entry, an exit, but given its appearance, I thought it might have even been both, caused by close proximity between entry and exit points. It was quite possible that in climbing the ladder the decedent had not yet even begun work on the wires, and that two wires had contacted his chest, thus causing the burn and fibrillating his heart. Still, there was the issue of the lack of wounds from a fall. I also felt that the placement of the decedent's body was not consistent with a fall from the top of the ladder.

Despite the fact that there were no witnesses to the actual event, after considering all of the evidence present — and considering the probability of certain unknown factors — I concluded there was no evidence to suggest that the decedent had actively been working on the wires at the time of the electrical contact. Furthermore, I concluded that immediately following the electrical contact, the decedent was conscious long enough to climb down the ladder before falling in the position he was found as if exiting the ladder. As to the wire cutter at the base of the ladder, I believe it was either dropped or fell from his tool belt as he stumbled at the bottom of the ladder. Although no one can say for sure, there is a very good probability that it was not dropped directly from the top of the ladder.

Ultimately, I felt it was impossible to demonstrate to the legal standard that the decedent had actively contributed to his own demise. Independent of my other findings, I offered no comment regarding why the wire had not been disconnected at the twistlock. That was beyond my scope.

Like so many cases, because this case did not go to trial, we will never know how a jury would have viewed the evidence or weighed the opposing input from experts, such as myself. Unfortunately, I suppose only the decedent truly knows what happened on the ladder that day.

The lesson to be learned here is that no one is immune from the dangers of 120V — and that the next contact may be lethal. Given this reality, electrical workers should never develop a complacent attitude when working on or around 120V circuits.

To help prevent future accidents, anyone doing this type of work should hold regular tailgate meetings to emphasize the need for safety around live circuits. No circuit should ever be considered de-energized until tested. More specifically, circuits should be tested, procedures followed exactly as specified, and training should never minimize the risk from 120V. All live contacts — even those made with 120V circuits — should be made using personal protective gear. Following these safety tips goes a long way toward preventing more workers from becoming a tragic statistic.

Morse is a researcher and consultant who serves as a full professor of electrical engineering at the University of San Diego.


Sidebar: Lessons in Low Voltage

According to the U.S. Bureau of Labor Statistics, 278 workers lost their lives in 1999 as a result of on-the-job electrocutions. This number accounted for almost 5% of all job-related deaths. Among work-related electrocutions (1992 to 1999), approximately one-third were linked to high-voltage (power line) contacts. A large percentage of the remaining on-the-job electrocution deaths were from low-voltage contacts.

While almost all high-voltage contacts result in burns and hospitalization, very few low-voltage contacts result in any injury requiring treatment. Therefore, they go unreported and are lost from statistical evaluation. Ironically, the two most likely outcomes from low-voltage contact are either no injury at all or death (from electrically induced ventricular fibrillation.) What we can learn from these statistics is that no one should have a false sense of security when working in proximity to live 120V circuits.
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Jonathan Johnson

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Re: 120-volt Electrocution Mystery
« Reply #1 on: April 10, 2014, 11:11:05 pm »

Remember this:

No circuit should ever be considered de-energized until tested.

I dodged a bullet once. I was working in a live panel and a moment of carelessness gave me a jolt to remember.
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Mike Sokol

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Re: 120-volt Electrocution Mystery
« Reply #2 on: April 11, 2014, 12:38:56 am »

Remember this:

I dodged a bullet once. I was working in a live panel and a moment of carelessness gave me a jolt to remember.

It only takes a second of inattention to kill you. My dad would always want to watch me work in his live service panel while chatting about everything non-related, but I always told him to be quiet unless he wanted to see me electrocuted. He finally shut up until I was out of the panel. And since I teach a lot of seminars with live/hot gear on the table in front of me, I have to be doubly careful when students ask questions. Even though I have it all GFCI protected, it's still possible to get between the hot and neutral lines which the GFCI breakers won't recognize as an unbalanced ground fault. Of course, I never let any students near my demonstration table since it only takes a second to do something deadly. I'm super careful with this, but there's always the unplanned move that bites you. There are old electricians, and bold electricians, but there are very few old AND bold electricians. You've gotta respect this voltage stuff or it will kill you.
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John Halliburton

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Re: 120-volt Electrocution Mystery
« Reply #3 on: April 12, 2014, 10:08:12 am »

I was always taught that "Low Voltage" is 24v or less.  Also, always keep one hand behind your back when working in a panel.  Not always possible, but it drives home the point to not create a path, especially across your chest.

Anything else demands undivided respect and attention to procedure.

Even though I won't use it much, I added an Extech CT70 to my arsenal of test gear at the beginning of the year.

Best regards,

John
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Jonathan Johnson

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Re: 120-volt Electrocution Mystery
« Reply #4 on: April 12, 2014, 07:38:26 pm »

I was always taught that "Low Voltage" is 24v or less.

The term "Low Voltage" seems to be subjective. If you regularly work with utility lines, "low voltage" might be anything less than 480V. If you regularly work with 120/240V service, "low voltage" might be anything less than 90V. While some standards may define "low voltage," as used in trade lingo it can mean different things to different people.

Given the right conditions, even 12V can be deadly.

Also, keep in mind that pro audio circuits can have significant nominal voltage: 48V phantom power or 70V speaker lines (nominally) for example. Analog telephone circuits -- which are generally considered "low voltage" -- typically have a ringing voltage of 90-105V. I've gotten tickled by a phone line when it rang as I was touching it.

Just because it doesn't say "120V" doesn't mean you shouldn't be careful.
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Mike Sokol

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Re: 120-volt Electrocution Mystery
« Reply #5 on: April 12, 2014, 09:11:29 pm »

Just because it doesn't say "120V" doesn't mean you shouldn't be careful.
Even 30 volts AC (at 60 Hz) under the right conditions (you're totally wet and your body resistance is down around 1,000 ohms) can induce 30 mA of current through your body. If you get shocked hand-to-hand with just 20 mA, you can't let go of the wires, and if you're shocked with 30 mA of current for several seconds, that's all it takes to put your heart into fibrillation. Without CPR and a defibrillator you'll be dead in 5 minutes. Any shock, no matter how small, should be taken seriously.
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Stephen Swaffer

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Re: 120-volt Electrocution Mystery
« Reply #6 on: April 12, 2014, 10:46:14 pm »

Another practice I find myself following more and more the longer I work with electricity is to avoid touching anything that is energized in normal operation-even if power has been isolated.

I upgraded/repaired 5 services this week- from 240v/1P/100A to 480V/3P/3000A.  In every case, power was disconnected by the POCO, but except for the big one, I don't think my skin ever touched anything that could have been or would eventually be energized.  Granted, the gloves I was wearing were not voltage rated-but they were dry leather and would have afforded some protection.  If bare handed, I was usually using needlenose, etc to handle the wire.  Again, not the same way I would do "hot work"-but an added level of protection against an oversight "I thought it was off."  I honestly get nervous and hesitate if I ever am forced to touch a metal part that is normally energized-just a very uncomfortable feeling!  There is almost always a way to avoid touching stuff that can bite (unless you are working inside a piece of gear such as an amp, etc-but that is a different story altogether). 
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