Byline: Michael A. Santilli
Firefighters know very little about electricity, but they must deal with its harms on a daily basis. To handle electrical incidents safely, they must understand how electricity works. Many people are killed because they touch live wires they thought were dead, which should be a firefighter’s first lesson – all power lines should be considered live until confirmed otherwise by the power company.
The generation of household or commercial electricity is similar to an alternator in a car. The alternator is turned by a belt from the engine and generates 12 volts of electricity to keep the car operating and the battery charged. The power that is supplied to homes, businesses and industries is generated in a similar fashion. Water is boiled to make steam, which turns a turbine that is connected to a generator by a shaft. The generator puts out voltage, or the pressure of the electricity; amperage is the volume. This relationship is similar to water in a pumper that pumps 1,500 gallons at 150psi.
For electricity to flow there must be a completed circuit, much like a car radio, which needs a positive and a negative wire to work. Power flows from the battery through the radio and back to the battery. Remove either wire and the radio stops working. Electrical power in a home or business works basically on the same principle. There is a hot and a neutral wire. The hot wire brings power from the generating station to the house and the neutral returns it back. This neutral wire is connected to the ground at certain intervals.
The neutral and ground wires work together as the return path back to the generating station. This is why when wires fall from utility poles they may arc to the ground. When this happens, it is known as a fault or short. Electricity is always trying to complete the circuit.
When responding to calls of flickering lights or a power outage in half the house, firefighters must be very careful what they touch and what action they take.
Open neutrals can be one of the most dangerous situations responders can be faced with. This is when the neutral wire (the return wire) is broken going to the structure. When this happens the electricity does not have a complete circuit and the power will try to find another way to complete it, possibly through a water pipe or a small ground wire that can’t handle the amperage. Wires will heat up and start fires in any combustible material that they’re in contact with.
Once electricity is generated, it must get from the generating station to the end user. This is done by transmission and distribution systems. The difference between the systems is the operating voltages that are present. Transmission voltages can be as high as 750,000 volts, whereas distribution voltages are from 4,000 to 35,000 volts, depending on where the receiver is located in the country. When you compare these voltages to the 120 volts at the wall receptacle where you plug in your lamp or coffee maker, there’s a big difference.
For those of you who have been shocked when you touched a live wire, I’m sure it wasn’t pleasant and something you would like to avoid in the future. What you felt was most likely 120 volts. The voltage and amperage from only one 7-watt Christmas tree light bulb is enough to kill depending on how it passes through your body.
Calls for assistance
When fighting fires in structures, it is not recommended to pull the meters. The preferred method of turning power off is to turn off the circuit breakers. Also, pull the fuses out in the panel if possible. Then turn off the main circuit breaker or pull out the main cartridge fuses. Crews should note if any breakers have tripped or any fuses have blown. This could be a clue as to what started the fire.
If this can’t be accomplished, the power company should be called to cut the loops at the house or street pole or disconnect the cables at the ground-mounted transformer. Removing the meter should be the last resort. When meters are pulled from their sockets under heavy load, severe arcing and explosive damage can result.
The local power company should be called as soon as possible. Much like the fire service, it is important to give the first responders accurate information as to the problem and what equipment is involved. The more information they have, the faster they can respond with the appropriate equipment.
In some commercial and industrial occupancies, removing the meter won’t shut off the power. These meters work on an inductive principle, meaning that the total amount of power doesn’t go through the meter as in a residential house. In this case, the power company should be called early in the incident to properly shut off the power. Caution also should be used when turning switches and breakers off without the presence of a plant maintenance person or supervisor. Some processing equipment must be shut down in a proper sequence. Just turning the power off often can make the situation worse.
Incident commanders and company officers should be aware of what a clear and safe distance is from any downed wires. The standard should be two poles on either side of a downed wire or a pole on fire. These utility poles hold thousands of pounds, and the strain on the lines can be great if the integrity of just one pole is compromised and starts to lean.
The following are general precautions for handling electrical emergencies:
*Always wear protective clothing.
*Be aware of overhead power lines when using ground ladders and metal hand tools.
*When on any scene where power lines are down, note any tingling in your feet. This is a sign that the ground around the wires is charged.
*Watch for wires that are down on metal fences. Electricity will conduct along the entire length.
*Have the electricity turned off in a building as soon as possible for the safety of the firefighting crews.
*Look up. Aerial truck operators must use caution when placing ladders and towers in service on the fire scene.
*Consider all downed power lines equally dangerous, whether arcing or not.
*Don’t cut any downed power lines. Call the local power company.
*When wires are down in the area, check the homes and businesses in the affected area for secondary damage.
*When power must be turned off to perform a rescue, assign one firefighter with a portable radio to stay at the switch or circuit breaker to prevent anyone from turning the circuit back on prematurely.
Electricity can be very unpredictable and dangerous, so treat it with respect and caution. A Firefighter Electrical Awareness class is available by calling Firehouse Electrical Services at 440-724-1004 or e-mailing Fhelectric@comcast.net
Michael A. Santilli is a licensed electrician. He also is a retired assistant chief.
COPYRIGHT 2004 PRIMEDIA Business Magazines & Media Inc. All rights reserved.
COPYRIGHT 2004 Gale Group