If you look, you will probably find that you have an electric substation in your response area. Have you responded to it? Have you entered it? Do you know the dangers that are waiting for you inside the substation’s gates? If you were to respond to it for a fire or another emergency, would you be able to operate safely to extinguish the fire or mitigate the emergency? These are questions that you should answer before your first response to an electric substation.
Substation Overview
Electricity is produced at generating stations and routed to electric substations for distribution. There are two types of substations—transmission and distribution. Both act as transportation hubs for power. The differences between a transmission and a distribution substation are the voltage present and the destination of the electricity.
Voltages May Vary
Transmission substations typically receive high-voltage electricity that is stepped down or reduced by passing through a transformer—for example, a 345,000-volt feed might be stepped down to 138,000 volts. Following this voltage reduction, power then is routed to a distribution substation, which receives the 138,000-volt feed and steps it down further before routing it to various distribution networks. Common voltages leaving a distribution network are in the 13,000- to 33,000-volt range, but they can vary from area to area. To accommodate the end user, further voltage reduction occurs in small-area substations and, finally, by pole-mounted or underground transformers in the field. Commercial voltages range from 270 volts to 460 volts; standard residential voltage is 120/220 volts.
Overhead Clearance and Exposed Conductors
What most of us know about electrical safety we learned in our homes. For instance, a Romex®1 cable is insulated electrical wiring sheathed in plastic, whereas BX cable is insulated wiring sheathed in a metal jacket. In some applications, insulated wires are run in conduit. If you were to come in contact with these wires or the conduit, the insulation would protect you from the electrically charged wire. As a result, you may think that you have to touch an electrical conductor to get hurt. This, however, is not true when dealing with high voltages. Substations use a high-voltage, open-air conductor—called “bus”—which resembles a three-inch conduit pipe. The metal pipes running through the overhead areas of a substation are the conductors and electricity. There are no wires inside the pipe. The electricity is carried on the pipe’s outside skin.
Safety from Overhead Electric Bus
Just knowing what an electrical conductor looks like will not keep you safe in a substation. Because of the high voltages involved, you need not touch an electrical conductor to be harmed. If you get close enough, the electricity will reach out and touch you in the form of a high-temperature electrical arc. The potential for an electrical arc becomes greater as voltage increases. For this reason, the safety distances you must observe for electrical conductors increase with the voltage, as noted in Table 1. The proper clearance from the overhead bus is calculated for each station, and conductors are positioned accordingly, using a conservative distance to ensure the safety of anyone walking through a station. For 345kV, a safe distance of 18 feet has been established. To stay safe from the electric bus inside a substation, do not climb, and do not carry tools above your shoulder.
Safety from Ground-Level Electrical Hazards
The overhead bus is not the only electrical hazard present in a substation. Many electrical hazards are found at ground level also. Safety from these hazards is maintained by restricting access to them and by placing the hazard behind locked doors, cages, and fenced-in areas. Capacitor banks reside in cages, providing a buffer zone between you and the exposed electrical conductors. Circuit breakers are housed in locked cubicles to eliminate the chance of anyone’s casually entering into these areas. Lightning arrestors and various other electrical components may be found behind fences. Substations can have two battery rooms containing a number of lead acid batteries, connected in series, and similar to large car batteries. They will be in a room with a locked door. Do not ignore the posted warning signs. Remaining on the outside of these locked doors, gates, and fenced areas will keep you safe.
Chemical Hazards
The typical chemicals found in substations include dielectric fluid, transformer oil, Edisol XT, sulfuric acid, and sulfur hexafluoride. All but sulfuric acid serve to insulate and cool the electrical conductors
Dielectric fluid, a mineral oil, is used to cool and insulate underground transmission feeders. This nonpolychlorinated biphenyl (PCB) oil resembles cooking oil and has a flash point of 350°F and an autoignition temperature of 795°F. Note that electrical arcs can produce temperatures up to 7,000°F to 10,000°F and can easily ignite oils used for insulation or cooling.
Transformer oil is the generic name given to the oil used to insulate and cool transformers. Its flash point is approximately 300°F. Historically, this is where PCBs have been found. Over the years, utility companies have successfully worked to remove the carcinogenic PCBs from their system through a process called “retrofilling.” This is somewhat similar to changing the antifreeze in a car: The old product is drained, and the new product is put in. Unfortunately, there are certain oil-filled components that cannot be retrofilled and have no sampling ports. Their PCB content is unknown. As a result, when we respond to fires or other emergency conditions, we should assume the oil is contaminated with PCBs until sampling proves otherwise. Wear personal protective equipment (PPE) to protect against potential dermal and respiratory exposure to PCBs.
Test leaking oil or oil involved in fire to determine if it is contaminated with PCBs. Representative samples can be obtained once the area is made safe. In most cases, test results will not be available until well after companies have taken up from the scene. Anyone contaminated by the smoke and liquid should, as a precaution, decon prior to leaving the location to avoid spreading contaminants to the apparatus, the firehouse, or their homes.
Edisol XT is a viscous insulating oil used in capacitor banks. It is nonPCB oil and has a flash point of 284°F. Material safety data sheet (MSDS) information indicates that dermal exposure results in skin irritation, consistent with most petroleum exposures. Note that older capacitor cans may contain PCBs.
Sulfuric acid is contained in the lead/acid batteries used in the backup power source for the facility. Substations typically have two battery rooms, each containing 30 to 40 car-type batteries. Each battery holds five to 10 gallons of acid with a 30- to 40-percent concentration. Exposure to sulfuric acid under normal conditions presents a dermal hazard, but more significant issues arise when the product is exposed to heat. Sulfuric acid mist can produce serious, if not fatal, injuries to responders who fail to protect against respiratory exposure.
Make note of posted warning signs.
Note that the carbon monoxide (CO) detectors used by the fire service have shown false CO readings in battery rooms. The sensors in these units are cross-sensitive to the hydrogen released when the batteries charge. In one case, personal monitoring devices indicated 50 parts per million (ppm) of carbon monoxide in a substation’s battery room. Additional testing revealed that it was actually hydrogen with a concentration of 1,500 ppm. (The lower explosive limit for hydrogen is 30,000 ppm.)
Sulfur hexafluoride gas is used to insulate and extinguish arcs in circuit breakers and other electrical components. Under normal conditions, it is an odorless and colorless gas that is five times heavier than air and presents an asphyxiation hazard in below-grade confined spaces. If exposed to high heat, thermal decomposition of the product produces two hazardous by-products, hydrogen fluoride gas and metal fluorides.
Hydrogen fluoride gas (HF) gives off a rotten egg smell and is a desensitizer. Continued exposure to it may make it seem as if it has dissipated. It is also a respiratory hazard that when mixed with water, say, in your lungs, produces hydrofluoric acid.
Metal fluoride, a white talcum powder-like substance, is a dermal hazard, and exposure to it produces a sunburn-type effect on the skin. In addition, the ions in fluoride are calcium scavengers; they will eat through the skin and aggressively attack the bones. It also leaches calcium from your system and can trigger a heart attack. The key to successful treatment is early recognition of the symptoms of exposure and obtaining medical attention in a timely manner. MSDS information recommends flushing with copious amounts of water and using calcium gluconate, a gel that impedes the effects of the process.
Response Tactics
Because of the hazardous environment found in substations, firefighters must resist their natural tendency toward aggressive tactics. These incidents require specialized knowledge, close control of operating personnel, and a heightened sense of caution. The first responding officers must closely supervise their firefighters to ensure their safety. All firefighters operating at the scene must be aware of the potential dangers and act to safeguard themselves from those dangers. When you respond to incidents at these sites, your utility should provide you with a representative with the specialized knowledge that will enable you to safely operate at a substation incident.
The depth of these underground feeders varies based on geological conditions of soil and rock. The general range is from 24 inches to 72 inches.
Initial Actions
When called to a substation, do not force entry. Instead, survey the substation from the exterior. Entering and moving around in a substation unescorted exposes you to the hazards mentioned above. Here are some guidelines that will help keep you safe at substation incidents.
Wait for the utility representative.Some substations are staffed 24/7; others are not. If there is a fire or an emergency at a staffed substation, a utility representative should come out to meet you. If the utility representative does not come out to meet first-due companies in a reasonable time, he may be actively engaged in mitigating the emergency and hazards, he may be injured, or the site may be unoccupied at the time of the incident and the representative may be en route from a neighboring station.
(6) Distribution substation transformers contain between 15,000 and 25,000 gallons of oil, whereas transmission station transformers contain 35,000 to 45,000 gallons.
If a utility representative is not present, call your local utility. If a number is not posted on a sign on the exterior of the gate, your dispatcher should have a master list of such locations and be able to contact the utility. Since utilities routinely electronically monitor these facilities for problems, it is likely that a representative already will be on the way by the time you arrive and call.
Protect exposures outside of the substation, but do not direct water into the substation without first consulting with the utility representative. If a substation fire is exposing residential or commercial neighbors, set up lines or large-caliber streams for exposure protection. It is safe to put water on the threatened exposures.
Do not apply water directly on electrical equipment inside the substation without first consulting the representative. He will tell you what is energized and where you can safely apply water. For a fire inside the substation, you must decide which extinguishing agent is safe, where to position the apparatus, and the safe standoff distance for applying the stream. Once again, the utility representative’s expertise will be invaluable.
Prepare to supply the sprinkler system. Substations have a deluge sprinkler system, but coverage is typically limited to the transformers. The sprinkler system has its own water supply, which may be augmented by an external siamese connection. If there is a water main break or if a fire pump fails, the utility may ask that you augment its system. Be guided by your utility representative’s advice as to whether to supply the siamese and at what pressure.
Exposure to PCBS and Other Contaminants
The following practices will help to contain exposure to contaminants for responders and civilians:
Because of the possibility of a PCB spill and the presence of PCBs and other contaminants in the smoke, wear full PPE, and attempt to operate away from the smoke and water runoff or any liquid spills by staying uphill and upwind if possible. Use your self-contained breathing apparatus even in light smoke.
If practical, contain the water runoff or liquid spills by channeling the liquid away from civilians and firefighters.
You may have to evacuate exposures if it is possible that they have been exposed to PCB-contaminated smoke.
Consider decontamination after being exposed to any smoke, oil, or water runoff because it may be contaminated. It is better to do this as a precaution instead of taking the chance of spreading the contamination to the apparatus, the firehouse, or your own home.
Overall Safety Precautions
The basic rules for enforcing electrical safety at substation incidents are simple and as follows:
1 There is no safe action you can take inside the substation until a qualified representative arrives. Wait for him, and confer with him.
2 Observe and respect the posted warning signs.
3 Don’t climb, and you will maintain the necessary clearance from the overhead conductors—in other words, stay on the ground, and you’ll stay safe.
4 Avoid bringing metal or partially metal tools into the substation, and do not carry tools projecting over your shoulder. Carry all tools below the shoulder so that you do not reduce the allotted safe clearance distances. Note: Even a wooden or fiberglass hook can conduct the high voltages found in substations.
5 Even raising ladders outside the substation may not be safe. If you are considering raising aerial ladders or tower ladder buckets outside of a substation, you must still maintain the safe clearance horizontally from the substation’s exterior fence line. High-voltage electrical equipment may be just inside a fence or a wall. Placing a ladder against or an aerial platform near or over that fence or wall can violate the safe standoff distance, putting firefighters in danger of electrocution. It is best to leave the aerial devices bedded until after consultation with the utility representative.
6 Only the incident commander should give the order to put water onto or near electrical equipment inside of a substation, and this should only be done after consultation with the utility representative. When considering hose or large-caliber stream operations, you must consider the path that the water takes from the hose or appliance to the fire. Is there any live electrical equipment in the path or alongside of it? If your stream can contact it, measure your safe distance from that point.
7 Always operate as if PCBs or other contaminants are present in the smoke, oil, and water runoff; decon as a precaution.
8 Consult with the utility representative on the hazards and safety of proposed tactics.
