By Frank Montagna
Firefighters are the structural fire experts. We know about the fire triangle, how to extinguish many different types of fires, and how fire behaves and travels. We know the various types of building construction and what to expect from them in fires. After all, we are firefighters, and you would expect that we would be experts in structural fires. But, do we respond only to structural fires? Of course not. Some of us respond to utility incidents more frequently than to structural fires. You would think that means that we are the experts in utility incidents, but that is not the case. As a new firefighter, I received little training in what to do at utility incidents just as other firefighters around country who, until relatively recently, received little such training. Utility incidents, like structural fires, can be dangerous, even deadly; and just as in structural firefighting, you need to know information that will keep you safe when responding to and operating at these incidents.
When power lines end up in the street, we are called to respond. Do you know the hazards you are facing when you arrive at the incident? A primary wire (high voltage) lying on the ground poses several hazards. It can arc continually, generating enough heat to burn down through the pavement to gas lines, damage them, and ignite the gas. It can whip and bounce around like an angry snake or just lie there looking innocent. It may look innocent, but it is not innocent. Electricity can be flowing into the ground, electrifying it for up to 100 feet from the point of contact. This is known as “step potential.” An unsuspecting firefighter stepping into the charged area could suffer deadly electrocution. To be clear, this is a hazard resulting from high-voltage wires.
If the fallen wire is resting on a metallic fence, the entire fence could be electrically charged. If the fence is attached to a combustible building, the building could ignite as the electricity passing through the fence heats it up. If the building has aluminum siding, the siding could be electrified. A wire on an occupied car poses a dilemma. It is not safe to touch the car or the wire, nor is it safe for the car’s occupant to step out of the car. What can we do? No much without specialized tools and training. The occupant can jump out of the car, not touching the car and the ground at the same time, but what about step potential?
What if you respond to a burning pole-mounted transformer? Should you extinguish it? If we don’t, it is possible for a wire to burn through and fall to the ground, or worse. If it is a primary wire, it might fall onto the secondary wires or cable wires, sending its high voltage into nearby buildings.
The transformer contains dielectric fluid with a flashpoint of around 300˚F. As it burns, the fluid heats up. Putting water into the hot liquid can cause the water to convert to steam, expanding 1,700 times and expelling the burning oil out of the transformer and down onto the engine company operating the hoseline.
An electrical manhole fire can be a spectacular visual and audio event with plumes of thick black smoke, brilliant sparks, thunderous explosions, and flying 300-lb. manhole covers. It is all well and good to cordon off the area from civilians and firefighters and to stand by waiting for the utility experts to respond, but there is an insidious danger to civilians here. The underground fire is generating a witch’s brew of toxic and explosive gases. Deadly and explosive carbon monoxide (CO) is present in large amounts, and it is traveling along underground electric conduit into other manholes, light poles, and even surrounding buildings. It can even migrate into buildings through the soil. Wherever it collects, it creates a toxic atmosphere that can be explosive. Involved buildings will have to be checked for the presence of CO and evacuated and ventilated as necessary.
It might seem like a good idea to operate the building’s main breaker to disconnect it from electric grid, but doing so will create a spark that could ignite the CO collecting inside the breaker box, resulting in an explosion that blows the box off the wall, injuring the firefighter operating the breaker.
The underground electrical system contains transformers in underground vaults. These transformers can contain as much as 500 gallons of transformer oil. When things go wrong here, the oil can ignite, resulting in the same hazardous conditions as a manhole fire with the added problem of a catastrophic and explosive failure of the transformer. Such failures have resulted in six-story flames and flying metal parts of the failed transformer spewing out of the vault.
Here, you will be dealing with hundreds of thousands of volts of electricity. Unlike your home electric system of wires and appliances, you need not touch an electrical conductor to be shocked. If you violate set safe distances, it will reach out and touch you; and it will most likely be fatal. Obviously, there are electrical hazards in a substation. There are also chemical hazards such as sulphur hexafluoride gas (SF6), which, when exposed to high heat (high-voltage electric arcs can exceed 8,0000F) decomposes into hydrogen sulfide gas, which will become hydrofluoric acid when combined with the moisture in your lungs, and a white powder that is a metal fluoride that can scavenge the calcium from your system, inducing a heart attack.
This is just some of the need-to-know information you must have to make intelligent and safe decisions at electrical emergencies. Much of the need-to-know information is not intuitive or obvious. It is tricky. Learning it by word of mouth from the senior man is not the best way to arm yourself with this important information. Instead, get your local utility to provide meaningful classes on the types of incidents to which you respond. Find out what you can do and what you should not do at these responses. Learn the obvious hazards and those that are not so obvious. Much has been written about electricity for electricians. Unfortunately, most of us are not electricians. Find and read what has been written for firefighters on the topic. Conduct regular drills on the do’s and don’ts of electrical response just as you conduct classes on structural firefighting. You will respond to these incidents. Often you will precede the utility experts. You will have to make what may be life-and-death decisions affecting civilians and firefighters. See to it that you have the need-to-know information to help you make good decisions.
FRANK MONTAGNA, a 43-year veteran of the Fire Department of New York, retired as a battalion chief, a position he held for 26 years. He was assigned to the department’s Training Academy, where he was responsible for curriculum and officer development and simulation training. He wrote the department’s gas and electric procedure manuals. He is one of the creators of Fire Engineering’s simulations. He has a BS degree in fire science. He teaches a course for John Jay College based on his book Responding to Routine Emergencies, has published numerous fire-related articles, and frequently lectures on these topics.