Grounded in reality- truths about electrical safety

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By Bill Shewan

Frequently, I will be asked to participate in some function or another to "preach the word" of worker safety - and in particular, electrical safety. What I find so interesting are the almost universal misunderstandings regarding basic electrical theory, and due to this, an almost universal confusion about how to work safely near electricity. Now, before I continue, let me state that there are many workers who have likely forgotten more about electrical theory than I will ever know. I meet them every day in my work, and it's because of these people that I have come to appreciate some of what I will attempt to impart to you now.

 
Recently, I found myself in a parking lot in front of a Canadian Tire store. I was there to talk to those that would listen, about educating their children on electrical safety. You know the talk: don't fly your kites near power lines, don't climb over the fence that says "High Voltage," don't try to break open the locked transformer sitting on your front lawn, etc. During my talk, I use a unique demonstrator, built to represent a typical small town setting, complete with a transmission tower and aerial device (bucket truck to some). I manipulate this tool with simple push/pull rods to enable the conductive pieces to contact exposed wires, creating small electric arcs. The "spark" gets everyone's attention - a tough thing to do with the kids that I'm trying to reach - and although making sparks says nothing about electrical safety, it does allow me to talk to my captured audience and slip in my subliminal safety message. Want to hear something that might surprise you? The kids always get the message. The parents, unfortunately, are not so easily tricked.

 Tough concept (smart kid)

At these demonstrations I do not throw out technical terms at the already wary viewers. I have never used the word "equipotential" during any public awareness campaign. I talk about it nonetheless, and I am relentless. At the end of my parking lot demonstration, portable generator still humming in the background, I asked a young girl who might have been five years old a not-so-simple question:

 "Can you think of something that touches an electrical wire, but doesn't get hurt?" I inquired.

 "Sure." She bluntly stated. "A bird."

 "Say! That's right! Now, do you think you can tell me why the bird doesn't get hurt?"

 "Sure." She remarked, "Because the bird only touches one potential."

No, I'm not kidding.

  There is something about this well-known phenomenon that, once explained, kids will have no qualms about accepting as fact. Adults, on the other hand, remain dubious. As with most of my talks, I do my best to engage the parents. In the case of the little girl at Canadian Tire, her father had this to say (and I paraphrase to protect the innocent): "So, the bird must be protected by the covering on the wires, right?" It's a question that I hear at every showing.

 "Well sir, actually, no. The bird is standing on a bare conductor. Most of the overhead conductors around are bare."

 "So, the bird is standing on a live wire, then?" He asks incredulously.

 "Yes, that's correct."

 
This line of conversation usually forces me to bring up the concept of equipotential work zones - although again, I do what I can to stay away from that vernacular. I have found that mentioning it is about the quickest way to clear a room I've yet discovered.

 Instead of really understanding that electricity can pass through us, many adults find credulity in the beliefs that birds are either floating above the conductors, have bizarre insulative properties in their feet or some inherent resistance to electrical flow that we humans do not yet possess. I believe workers must have similar beliefs, because asking them to prepare for the possibility of allowing electrical energy into their work zones is often met with more than a little skepticism.

 I make light of these comments to illustrate this fact: often, it is safer to permit electrical energy into a work zone, than to try and insulate yourself and your work environment from it. Getting back to the precocious little girl for a moment, you may be wondering if she really knows what electrical potential is. Honestly, I don't know - but what I can say with surety is she knows that if something touches an electrical circuit and also touches the ground (a different potential) then that something will cause electricity (specifically current) to flow through it to the ground. And she also knows that this is bad.

 Okay, enough anecdotes. You are reading to learn, and I am writing to hopefully trick some of you into doing just that. In particular, the people I hope to reach with this article are those who work on the fringe - the fringe of electrical hazards. You are the workers who may trim trees, or paint signs, or wash streetlights. And you are certainly workers who use excavation equipment - directional drilling or boring. And there's another group that I am becoming very familiar with: hydrovacuum operators. What do these fringe workers have in common? Or, what should they have in common? They should all know what an equipotential work zone is, and if they work around electrical conductors, they should all know how to use one.

 
I am going to focus on hydrovacuum work environments for the rest of my article. It is an environment that I am more familiar with than some of the others and because it is something you will be seeing much more of in the very near future. The concepts apply to a wide range of work environments within the electrical industry and on the fringe of it.

 Hazards below

Hydrovacuum vehicles are becoming more prevalent in utility settings and are used extensively in other industries where time and a delicate touch make their use necessary. One of the most popular applications for these vehicles is in helping utilities expose underground plant (electrical, gas, fibre, etc.) This is often referred to as "daylighting," a rather appropriate term coined by a particular hydrovac operator, Badger Daylighting Incorporated. The problem with daylighting - exposing underground plant to the daylight - is that it is a "blind" operation. Even if the equipment locates the utility plant for you, there's no guarantee that the locates will be completely accurate, nor is there any guarantee as to the condition the buried plant will be in. Splices and nicks on cable are not uncommon. Whether one is using a hydrovacuum setup or digging with a pick and shovel, there is an increased risk of cutting into plant when it has been previously weakened or damaged. Experienced hydrovacuum operators know what they're doing and know how to prevent such accidents. Proper water pressures, nozzle types, work procedures and PPE all come into play in order to ensure a safe work environment.

 
Even so, accidents have occurred whereby underground, energized conductors have been "cut" and deadly energy flows have entered these muddy, wet, difficult, work environments. Do you think that a pair of rubber gloves will be of much help here? Think again. Fringe workers are often exposed to electrical energies, but due to the nature of their work, the use of traditional insulative protective barriers are not enough to thoroughly protect them.

 Here is the crux of the problem surrounding fringe workers: the unconditional reliance on all things rubber. Rubber gloves, mats, line hose and bucket liners are wonderful pieces of equipment when used properly and maintained to uncompromising standards. In these types of fringe environments, however, rubber protective equipment is only one small piece of a much more important system - the equipotential system.

Coexisting with live current

Think about a worker that you see every day in the summer - a road construction jack hammer operator. What would happen to that worker if he or she were to accidentally break through an underground concrete duct and contact energized underground plant? A messy, contaminated environment where the point of contact to the tool might not be just the worker's hands but could include the forearm, shoulder, thigh and chest. Even if the worker were just holding the hammer with his or her hands, the leather work glove is not intended to provide any degree of insulation for that worker. In short, there would be trouble. Also, when this type of accident occurs, the fault or "short circuit" current will not be limited to contacting the worker using the tool - another common misconception. There will be a potential rise in the form of a gradient, surrounding that work zone, starting at the initial point of contact. In other words, any worker in the vicinity of the fault will be at risk.

 
This is one of the reasons that utility personnel take advantage of specialized equipment such as the insulated aerial device. The boom of these vehicles has been dielectrically tested. It is insulative. If the boom of the vehicle were to contact energized, overhead conductors, someone casually leaning at the base of the truck would not be harmed.

 What about the workers in the bucket? Think about the bird sitting on a wire again. The workers in the bucket (using approved work methods that I will not venture to discuss today) will experience a potential rise. Yes, the workers and the portion of the boom above the insulation will become energized. Also, like birds on wires, these workers will be safe. Utility workers have used equipotential concepts in many work practices for years. Many fringe workers may find themselves exposed to risks similar to those of utility personnel, but without the necessary knowledge, training, experience or equipment necessary to use these equipotential work zones. Clearly, this needs to be addressed, and fortunately, some people have already been working on the problem.

 Ian Munro of Badger Daylighting was kind enough to allow us to witness the setup of an equipotential work zone, using Badger's hydrovacuum vehicles (seen in the accompanying photos). These vehicles were never designed to meet the exacting standards of a certified aerial device and moreover, even if they did meet these standards originally, the amount of water and mud that gets sprayed around in a typical daylighting scene would negate most, if not all, of the insulative properties of the truck. This type of work needs protection from inadvertent electrical contacts, and the protection needs to be durable enough to control the hazards created by the work itself. Would rubber protective equipment fill this need? Clearly not. Rubber protective equipment is tested and inspected prior to use. This type of equipment loses much of its insulative properties, however, when wet and otherwise contaminated. In fact, with rubber gloves, the worker may be lulled into a sense that he or she is protected from electrical shock. In environments like these, something else has to be in place.

 
If you notice the photo showing the hydrovac truck setup on page 18, you will see that there is a protective mat on the ground. Do not be fooled: this is not rubber. It is not insulative - but conductive. With a simple bonding procedure (using approved and tested equipment, of course) workers on the mat, called a portable ground gradient mat - would see a rise in potential if a fault should occur. As with our experienced utility workers in the aerial device, our hydrovac operators would become energized to the same potential as the conductive mat and all of the components metallically connected, during an inadvertent contact situation.

 You might still be wondering about all of that water and mud. This slurry is conductive of course, but as long as the workers remain on the gradient mat - wet or not - they will remain in a safe work zone. The same cannot be said of work practices relying on rubber. If you are someone working on the fringe, do yourself a favour and investigate these equipotential work zones in earnest.

Something to ponder:

Another favourite question of mine during a demonstration is this one for the parents. You've seen or heard about vehicles that knock over hydro poles and the conductor is left arcing away as it flails around on the vehicle. You've been told from many different agencies over the years that the safest thing for you to do is remain in the vehicle. Right? Okay, now why is that? If you are thinking that your steel-belted, graphite infused and dirt encrusted rubber tires are insulating you, you are not alone. In this scenario you would be safe in your vehicle, but certainly not because of your tires. Think about what we've discussed here. Think equipotential. If you are already thinking equipotential then great, you were easier to trick than I thought!

 Bill Shewan is technical communications consultant at The Electrical & Utilities Safety Association of Ontario. Special thanks to Ian Munro, safety & fleet manager, Badger Daylighting Inc.

 Editor's note: The Electrical & Utilities Safety Association offers material and training to help you learn about, create and maintain, equipotential work zones. These are not just for the utility professionals, but for anyone working on or near underground and overhead plant. Visit the association's Web site at www.eusa.on.ca or e-mail Bill Shewan at bill.shewan@eusa.on.ca.