Recap
Prior to allowing qualified electrical workers to cross into the RAB or MAD, one of two conditions must first be in place. Either the worker is insulated from the exposed energized part, or the exposed energized part is insulated from him. These two mandatory actions clearly establish the fact that entering the RAB or MAD is no different than making intentional contact with the energized parts.
But let’s also recall that the purpose of the shock boundaries is to prevent unintentional or inadvertent contact with the energized parts.
Technically speaking, only one or the other is required to be selected at a minimum, but electrical safety best practices should consider deploying both whenever feasible. Adding two effective barriers in series will further reduce the possibility of accidental contact. Obviously, this will be on a case-to-case basis, but it is practical in most cases.
Avoid Contact – A Simple Concept or Confusing Directive?
With this in mind, let’s start peeling back the onion skin of “Avoid Contact” and its relationship with and how it can exacerbate risk when working near low voltage hazards.
When we review the various OSHA or NFPA® 70E® tables for their respective MAD or RAB distances, we see that all of them require a physical air gap between the worker and the energized part, except for one. That one departure from an actual distance to an ambiguous statement is the MAD and RAB titled, “Avoid Contact.”
OSHA and the NESC uses “Avoid Contact” as their MAD for the voltage range of 50 volts to 300 volts, while NFPA 70E, being more conservative, throttles back “Avoid Contact” voltage threshold from 50 to a maximum of 150 volts for the RAB. When using the OSHA or NESC voltage range for “Avoid Contact,” common, albeit very hazardous, voltages fall into the parameter, mainly 208, 240 and 277 volts. But if we select NFPA 70E, then the highest industrial voltage exposures would be reduced to 120 VAC and 130 VDC circuits.
What Does “Avoid Contact” Mean to You?
So, this begs an important question: What does “Avoid Contact” mean to you?
If you’re like most electrical workers, foremen, supervisors, electrical engineers or safety professionals, you will probably default to something like, “Don’t touch it” or “I won’t touch it.” If this is your answer, you’re not alone.
During all my electrical safety training classes, I make it a point to ask students this exact same question, and invariably every one of them will reply, “Don’t touch it.” There are several reasons for this position. The two most common reasons are probably because they were either taught this by tenured co-workers or came to the verdict on their own interpretation. Their subsequent conclusion makes sense because without an official definition of “Avoid Contact” in the standards or codes, the worker is left to interpret the phrase from their understanding of basic English.
When the word “Avoid,” which is defined as “to keep away from,” is coupled with “Contact,” which means “a junction or connection of two parts,” then the logical conclusion is, “Don’t touch it!” This explains why so many highly skilled individuals consistently come to the same, albeit incorrect, verdict.
If we take a moment to ponder what “Don’t touch it” is really communicating, we quickly realize it is nothing more than a warning to “Be careful.” However, being careful through situational awareness is not an effective barrier between life or death.
Low Voltage Can Lead to a False Sense of Safety
Some readers may be thinking to themselves, “One hundred twenty volts isn’t that dangerous because I’ve been hit by it and nothing really bad happened to me.” How many of you have ever uttered the words, “It’s only 120 volts?” I’m guessing nearly all of us have at one time or another in our careers, including myself, the author of many electrical safety publications.
This position is especially common with veteran utility electricians and linemen, who normally work around what we call primary voltages, meaning equipment energized at medium voltage, such as 4.16kV, 12.5kV, 13.8kV, 14.4kV, 24kV, 36kV, etc.
Because utility electricians work on “BIG voltage,” our lack of respect for “little voltage” can lead to error precursors like overconfidence, complacency, taking shortcuts, putting our guard down and a host of others, thus leading us to take unnecessary risks due to an inaccurate risk perception.
This dangerous mindset is reinforced when nothing bad happens following a job where the work was completed in a timely manner. This questionable success without consequences further perpetuates the lowering and reduction of our tolerance of the risks, especially when supervisors reward high producers while they turn a blind eye to the unsafe methods used to accomplish production.
The slow progression of change in our behaviors results in a willingness to accept greater risks and is often called the “normalization of deviance” or simply “drift” within human performance circles, where things that were once deemed unacceptable gradually move towards a culture that now accepts it as normative, thus “acceptable” and “safe.”
Low Voltage Hazards
No one will argue that as the voltage increases the subsequent risk of shock also increases, but at the same time no one should ever believe working on lower voltage circuits is safe or without risks. For this reason, all regulations and standards in the US universally establish 50 volts as the starting point for electrical shock.
But even for circuits energized at less than the official 50-volt threshold, the regulations or codes never claim they are safe or “not hazardous” or that they won’t cause injury. Interestingly, our neighbors to the north in Canada have a lower threshold of 30 VAC, according to CSA Z462, Workplace Electrical Safety.
While electric shock is unlikely from such very low voltages, there remains the hazards of electrical burns or explosions as identified by OSHA 1910.333(a)(1) and 70E 110.2(B), Exception Number 5.
For example, the electric potential of a 12 VDC car battery may not be able to push much current through hands with a dry skin resistance of approximately 1kΩ, but if you short a wrench across the two poles, you’ll see just how much heat energy a standard automotive battery can release.
Twenty-four volts DC from a small, fused power supply is completely different than twenty-four volts DC from a battery bank. The bottom line is, if a voltage exists, then there is some level of threat to your health and safety. A risk assessment is necessary to help determine the likelihood and severity of that threat.
Less Than 50 Volts Is Hazardous – A Personal Story
I recall an incident many years ago when a co-worker and I were working on a large negative (-) 48 VDC power distribution rack for telecommunications equipment fed by several battery chargers in parallel and connected to a medium sized battery bank.
If you are familiar with this type of DC system, the positive (+) pole is the intentionally grounded conductor circuit, with the negative (-) polarity used as the ungrounded circuit. This results in all non-current-carrying metal parts, such as cable trays, enclosures, equipment racks, etc. being referenced to the positive (+) polarity.
Since the nominal system is officially less than 50 volts, (nominal 48 volts but with a floating voltage of around 54 volts and an equalized voltage well above 60 volts), our safety rules didn’t mandate the use of Class 00 rubber gloves, insulated tools, or any other electrical PPE. In fact, the unwritten safety rules were, “Just be careful when working with power.”
What About Electrical Tape? Doesn’t That Increase Protection?
But, like all good safety-minded technicians, I always wrapped the shank of my prized Klein screwdrivers with two wraps of Scotch Super 33+ electrical tape, which has an insulating value of 600 volts. Using two overlaying half wraps obviously gave my screwdrivers a voltage rating of at least 1.2kV, because 600 + 600 = 1200, right?
Wrong! Why? Because we cannot take any safety credit when using electrical tape on standard hand tools. If it doesn’t carry the ASTM F1505 and/or IEC 60900 certification, then it is not an insulated hand tool.
Now, back to the story. My co-worker had borrowed my #2 Phillips long-shanked screwdriver to secure screws into the frame of a 23-inch equipment rack which housed the two large, energized DC buses, one for positive (+) and the other for negative (-) terminations. The tip of the screwdriver was in contact with the head of the screw which now placed it at the positive (+) polarity, but the screwdriver’s shank was inadvertently in contact with the outer edge of the negative (-) bus.
Because of the electric tape covering the shank, nothing initially happened – until my co-worker started turning the screwdriver. As the shank rotated against the sharp edge of the negative (-) bus, it finally cut through the tape layers, and you can guess the outcome. This direct short circuit from a huge source of electrical energy caused a large arc that nearly blew the screwdriver’s shank in half, along with making a gouge in the bus.
Looking Back
Thankfully, he wasn’t hurt, mainly because he was wearing heavy duty leather work gloves which protected his hands from burns and, more importantly, he was wearing ANSI Z87.1 safety glasses. The lenses of his safety glasses were pocked with several small particles of molten metal embedded in them. His cotton shirt also had several small burn holes.
Can you imagine the serious injuries, including permanent blindness, if he wasn’t wearing basic PPE, or if his shirt was made of a highly flammable and meltable fabric like polyester? All this damage from a circuit that was energized under OSHA’s and 70E’s official threshold of 50 volts only proves that electricity is dangerous regardless of the voltage. OSHA cites several fatalities and serious injuries during welding activities and automotive work from very low voltages below 50 volts.
Fatality Data of ‘Low Voltage’ Contact
When we review OSHA’s Final Rules, we discover that twenty-six qualified electrical utility workers died from inadvertent contact with “only 120 volts” from 1984 to 1996. More recent data, provided by the Electrical Safety Foundation International (ESFI) from 2011 to 2022, documents thirty workers who lost their lives from contacting voltages ranging from 110 to 120 volts, twenty-three deaths from 208 to 240 volts, and sixty-two fatalities from 270 to 300 volts.
But let us not forget that most of the fatalities that occurred with 208-volt or 240-volt systems were very likely a phase-to-ground exposure, meaning the actual voltage that caused the fatality was a 120-volt contact. This is also true of some of the 480-volt fatalities, where the phase-to-ground voltage is 277 volts.
The ESFI data further reveals an additional 807 deaths from electricity where the voltage was not identified in the accident reports. Of these 807 fatalities, we can assume a good number were caused by voltages between 50 to 150 volts, or 50 to 300 volts. In that short eleven-year span, a total of 922 people lost their lives to electricity, most from low voltages in the range from 110 to 300 volts.
ESFI statistics also show the most common location for workplace electrical fatalities occurred in private residences (37%), as illustrated in Figure 5. The normal voltage exposure in residences is in the 120- to 240-volt range, placing these deaths at OSHA’s MAD of “Avoid Contact.” The data clearly shows lower voltages are claiming a significant number of lives annually in the workplace.
This finding is further supported by NFPA 70E, Informative Annex K – General Categories of Electrical Hazards, which validates the misunderstanding of the hazards from low voltage with the following statement:
“A corporate case study examining electrical injury reporting and safety practices found that 40% of electrical incidents involved 250 volts or less, and were indicative of a misperception of electrical safety as a high voltage issue.”
My point here is to emphasize how extremely hazardous lower voltages can be to the health and safety of employees, which is exacerbated when workers either don’t understand or choose to ignore this truth.
Conclusion
We must remember electrical energy is hazardous regardless of voltage. Sadly, many people have lost their lives following a low voltage accident. Starting in Part 4, we will continue with the problems caused by the term “Avoid Contact” when used as the RAB or MAD, along with some suggestions that will help to mitigate the risks and challenges.
