Preventing Transformer and Substation Fires With Below-Grade Secondary Containment



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Indian Point Energy Center, Site of Transformer Fire (Photo: Associated Press)

On May 9, 2015, an electrical transformer at the Indian Point Energy Center, a nuclear plant located about 40 miles outside of New York City, caught fire. Though actions were swiftly taken to shut down the plant, some 16,000 gallons of dielectric fluid is still unaccounted for; an unknown amount has been confirmed to have spilled into the Hudson River. That same day in Old Town Fort Collins, Colorado, a transformer housed underground caught fire in a bustling shopping and dining area, causing nearly all the businesses in the immediate vicinity to lose power for a couple hours. In Candor, North Carolina, a transformer exploded in the early morning hours of May 6, 2015, forcing nearly 2,000 Duke Energy customers to get ready for work … in the dark.

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Transformer fires are of serious concern, as they seem to happen more and more. Perhaps this is in part due to aging equipment in older substations, but that’s not always the case. The transformer at Indian Point has only been in service since 2007. Though the number of transformers that catch fire vary by location and environment, a 2010 study by Berg & Fritze claimed 730 transformer explosions in the U.S. annually. T&D World Magazine estimated that 2.4% to 4% of all transformers can be expected to cause a fire during the average 40-year service life. Since oxygen, heat, and fuel, the three main components or elements necessary for a fire to burn (as illustrated in the FIRE TRIANGLE), are typically present when transformers fail or explode, that estimate could be very accurate.

Great Balls of Fire!

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A Fireball Forms as a Transformer Explodes

Fires at transmission and distribution substations present unique response challenges for fire fighters and first responders. The blazes are often a fearsome concoction of flames, heat, explosions, high-voltage electricity, oil ignition and dispersion, and possible harm to those fighting it, if they’re unaware of how to deal with a fire in electrical switchgear. When on fire, the substation and the immediate vicinity around it create a hazardous environment. Substations generally contain transformers, energized electrical equipment and large quantities of oil, some of which may contain polychlorinated biphenyls (PCBs). (At older substations that have not been or were unable to be retrofilled, PCBs and other harmful contaminants may be present not only in the oil, but also in the water runoff and smoke.) As the fire heats up, porcelain bushings and capacitors could explode, adding flying shrapnel and flaming oil to an already chaotic scene.

For this reason, utilities are encouraged to take a proactive approach to mitigating hazardous and destructive fires, as outlined in the IEEE Standard P980—2013: Guide for Containment and Control of Oil Spills in Substations. Section 7.0 provides a guideline for containment with substations from fires, warning that in places where the oil-filled device is installed in an open pit (not filled with stone), there is the possibility of a pool fire. If the pooled oil catches on fire, the equipment will likely be destroyed.

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It seems like it would be common sense for utilities to try to avoid the destruction of their important and expensive electrical equipment, but according to the 1992 IEEE survey, only a few utilities altered their secondary containment practices because of a pool fire possibility. Those that do address the concern employ active or passive quenching systems, or drain the oil to a remote pit. Active quenching systems include foam or water spray deluge systems; passive systems include pits filled with crushed stone, which tend to be the most common and effective fire quenching system.

Don’t Fight Fire with Fire

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Above grade containment units, such as this concrete pit, offer the ideal environment to ignite a hazardous fire

Most above grade level secondary containments, such as concrete pits, composite walls, or earthen berms, create a moat-like area within the containment that provides all of three of the elements vital for a successful transformer fire start and burn – oxygen, fuel and heat.

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A transformer burns at a SDG&E substation in 2010

“The average temperature of a class B fire is roughly 1,800 degrees Fahrenheit,” says Anthony Natale, a Senior Specialist of the ConEdison Emergency Response Group and a leading expert on transformer fires. In fact, the heat – or more specifically, the rate at which heat is generated by fire, also called the heat release rate – is what really defines the size and intensity of a transformer fire. “The heat release rate looks at the size of the pool fire,” continues Natale. “The incidents that cause a transformer to tear open creating a large surface pool fire will generate considerably more heat.” The combination of pooled fuel, oxygen in the air, and heat creates an ideal environment for a violent inferno.

However, below-grade secondary containment solutions, such as the C.I.Agent Geomembrane Liner Systems, are able to remove two of the three elements in transformer fire situations. As the flaming oil passes downward through the stone, the stone cools the oil and ignition is lost. In addition, there isn’t enough oxygen present in the stone to support the flames. Therefore, the fire is quenched.

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Backfilling with stone during an Installation of below-grade C.I.Agent Geomembrane Liner System

In passive systems with crushed stone, IEEE recommends no less than 12” of stone to extinguish the oil if on fire. Smaller stone is more effective, ¾” to 1½” is recommended. While larger stone permits quicker penetration by the oil, its size makes it less effective as a quenching stone. The Geomembrane Liner works best when backfilled with clean, washed stone free of dirt and fines, averaging ¾” to 1½” in size.

Putting Out the Fire

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Implementing fire quenching containment measures can also affect how long it takes first responders to contain the flames. “If you have an effective suppression system, it can be contained within 2 minutes,” says Natale. However, he warns not to place the suppression system too close to transformer. “The initial blast blows apart the system and water never reaches the fire but fills up your containment moat eventually carrying PCB laden oil away with it,” thus further damaging the environment.

For the past few years, Natale and the Emergency Response Group at ConEdison have lead a vigilant initiative to educate traditional fire operations in New York City on how to best attack fire in an electric station. “The main issue is that the fire services don’t see these often enough to be good at them,” he explains. “They are low frequency high hazard incidents. As such, they leave after the fire is out, not considering there are internal pockets of fire within the transformer still going.” He cites the recent incident at Indian Point Energy Center as an example. “The bank reignited a short time later,” after the fire department had left the site.

Anthony Natale, a 15 year veteran of ConEdison and key member of its Emergency Response Group, is an expert in managing high-hazard emergencies. He is responsible for managing the full gamut hazards and response tactics necessary to produce favorable outcomes in utility based emergencies. His dedicated research and development work has ushered in significant changes and improvements in response to electric transformer fires and fire fighter safety.

 

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