Investigating Lightning Fire Claims

While structural fires as a direct result of lightning are rare, they do occur, and it’s important to get all the facts from the scene before you make a claim decision. Because of the properties of lightning, damage from a strike may be found in multiple, unrelated areas throughout a structure. Even if the origin and cause of a fire loss seems obvious, skipping the investigation could prolong the life of a claim and fail to get all the necessary information for an accurate settlement.

When lightning causes a structural fire, the damage can affect building materials, the electrical wiring, and other essential systems.

According to the National Fire Protection Association (NFPA), local fire departments respond to an estimated average of 22,600 lightning-related fires each year, about 19% of which are residential structures. A certified fire investigator knows what evidence to look for to confirm whether lightning is the cause of loss and can determine whether another expert is needed to evaluate further damage in a structure, giving you what you need for confident next steps.

How Lightning Causes Structural Fire

A typical lightning bolt (also referred to as a strike or stroke) is powerful, carrying about 10,000 to 30,000 amperes and reaching 15,000 to 60,000 degrees Fahrenheit. The hotter a bolt, the more likely it is to cause a structural fire. “Hot lightning” contains a continuing current, meaning that electrical charge flows for a longer period of time and generates more heat. When this lightning strikes, its increased heat and longer lifespan create more opportunities for ignition.

Lightning most often strikes a high point on a structure then travels through the building seeking the most efficient way to ground. The more conductive a material is, the less likely it is to ignite due to lightning. Wood roof framing, insulation, and other poor conductors catch fire easily as lightning travels through the roof structure and attic toward more conductive pipes, wiring, and ventilation systems. 

Insulation and wood framing are poor conductors of electricity and therefore vulnerable to fire damage from lightning seeking a path to ground.

Once the current reaches the wires, the lightning’s heat commonly burns through them, which poses an ignition hazard along the circuit. A certified fire investigator can identify not only the origin and cause of the fire but also the need for other experts, such as an electrical engineer, to confirm all damage caused by the lightning. 

In one investigation in which an electrical engineer followed up on a lightning fire, the lightning was found to have struck the top of the metal vent cap. The current travelled along the metal vent to the gas log fireplace, then followed the Corrugated Stainless Steel Tubing (CSST). Electrical energy from the lightning strike in the CSST arced to a nearby grounded metal object. The heat generated by the lightning was sufficient to melt a hole in the thin wall of the tubing, allowing gas to escape and ignite.

A hole created by lightning in a CSST pipe released gas into the house, where oxygen in the air and heat from the lightning caused the gas to ignite.

To learn how a lightning strike can damage HVAC equipment and how an expert assessment can help, check out this case study from HVACi.

Assessing the Damage

Before a fire investigator makes a recommendation for an electrical or structural assessment, they need to confirm the origin and cause of the fire. What do the experts look for when they’re conducting these evaluations?

As with all investigations, the scientific method and NFPA guidelines drive the investigation process. The expert should get statements from any witnesses, though these might not always be available. Weather data can confirm if lightning occurred in the area around the date of loss; data from up to several hours before the reported time of loss should be considered, since lightning-caused fires can sometimes burn undetected in hidden spaces. Finally, the investigator will take physical evidence into account. 

Because of lightning’s force and heat, the point of origin includes heavy charring and, in this instance, a hole created as the lightning current sought a path to ground.

Structural Evidence

The point on the structure where lightning hits is often high and may exhibit heavy charring or even a hole in the building. Investigators should also note the state of metallic or conductive rooftop components that penetrate into the house, like plumbing vents, flue pipes, and chimney caps. Damage to these elements may include melting or deformation, which isn’t typical in most fires. 

Tracing the Path 

It’s important to note that the location where lightning strikes isn’t always the point of origin. An investigator should assess all potential energy-to-ground paths, including the branch circuit wiring systems, plumbing systems, ventilation ducts, and other metallic elements. Items that wouldn’t normally electrically energize may show evidence of arcing as a result of a lightning strike. 

Direct and indirect lightning strikes also tend to overload household electrical systems. Certified fire investigators should check the circuit breakers of a structure reported to have sustained lightning-related fire damage and document any electronically powered items that no longer function. These damages, in conjunction with other physical evidence, can be indicators of a fire caused by lighting. 

For more information about common cause and evidence of electric wiring fires, check out this article.  

While a lightning fire may seem straightforward, a certified fire investigator’s job extends to more than just confirming the cause of loss. They can also identify potential electrical, structural, or ventilation system damage and recommend other professionals familiar with these items and systems. For the expertise of the Donan fire investigation team and the interdisciplinary experts who support them, submit an assignment today.