A bright flash followed by a loud boom in the evening usually means one of two things in the summer: lightning or fireworks. This article is about the former. If you live in the northwestern United States, you can skip this article, as the probability of a lightning strike can be as low as 0.1 strikes per square kilometer per year in the Pacific Northwest, contrasted with the Southeast where it is just a matter of how close.

Statistics collected and published by the National Fire Protection Association show that there have been 4,000–5,000 home fires started by lightning over the past few decades, even as the overall number of residential fires has significantly decreased. Most homes aren’t equipped with a lightning protection system (LPS). An LPS that follows the guidelines of NFPA 780, Standard for the Installation of Lightning Protection Systems, provides a network of low-resistance paths to safely intercept lightning’s destructive electricity and direct it to ground, preventing it from damaging the structure or injuring occupants.

Locally this summer, a homeowner using a power tool in his garage during a thunderstorm was electrocuted from a lightning strike that coupled into the electrical system, resulting in him being hospitalized. While the family was just feet away in the kitchen, a bolt entered through the outside porch light, destroying the door jamb, numerous receptacles and other devices in the house, including the Wi-Fi router and HVAC, and filling the house with smoke—but fortunately, no fire. 

When it struck this home, a lightning bolt entered the building’s electrical system through the outside porch and blew apart the door jamb. The homeowner was using a power tool and was hospitalized for electrocution.

How does lightning work?

A bit of background into how lightning operates might be helpful when determining how to dodge the bolt. Lightning is nature’s way of neutralizing an excess amount of positive and negative charges in the clouds and earth. 

An excess of opposite charges either within the thunderstorm cloud or between the cloud and earth triggers a rapid discharge of electricity. For cloud-to-ground lightning, a stepped leader makes its way from the cloud toward the earth. As it gets near, leaders go up from the earth. Many leaders don’t make a connection. But when they do, it’s like placing a heavy-gauge wire between two terminals of an extremely high-voltage battery. This path allows a massive amount of energy to be released, hence the bright flash, which is usually 2–4 strokes of 30–40A of 50–500 MV just milliseconds apart to several points on the earth. The energy can cause induced voltage into power lines or the earth as a pathway into a structure, or a direct strike to wires or structures. 

Lightning that entered the home’s electrical system destroyed several receptacles.

While NFPA 780 and UL 96A, Installation Requirements for Lightning Protection Systems, provide guidance on dodging a bolt, they are more likely to be used when designing and constructing a new facility. Creating a zone of protection by installing a lightning rod protection system would be a significant deterrent, but they aren’t commonly seen except on skyscrapers and old barns. It’s a great two-fold approach, though: the system bleeds off the charge built up so it isn’t attractive to the opposite charge in the cloud, and, if the leader does come its way, it provides a path into the earth around the structure, not through it.

What to do about it

It is common for lightning to get into a structure through what penetrates the structure’s shell. The most obvious is the power lines from the utility company. Since the distribution system is a likely place to pick up either induced or direct strike energy, a properly selected and installed surge suppression system can minimize that source. These aren’t merely the power strips that are often just used to have more places to plug in all the information technology equipment. 

Rooftop photovoltaic (PV) systems are another source of entry. Read up on Article 250 on grounding and bonding and Article 690 on PV systems, and install lightning protection components, including surge protection devices (SPD) specifically designed for PV systems, in accordance with UL 96A. 

Another bolt of lightning caused irreparable damage to this Ford Ranger’s fuse box.

Communication lines from landlines and cable providers can open the door for lightning. As with power lines, properly rated SPDs should be properly installed to close that door. Then there are all the tentacles reaching out from inside the structure. The circuits running out to the pool, detached garage, patio lighting and koi fish pond pump are more attractive to the bolt than the wooden structure. These require proper grounding and SPDs to close the portals. 

Turning off electronic equipment and other devices isn’t as effective as in the past, because many have “soft start” or “sleep” modes so they can be remotely turned on, and therefore aren’t really off. Other good suggestions to help dodge the bolt during a storm include not using wired electric tools or equipment such as vacuum cleaners, not taking a shower or doing the dishes (if the pipes are metal) and not standing by the window or on the front porch. 

However, the old adage that it’s safe to stay in a vehicle during a storm because it has rubber tires doesn’t jibe with the fuse box of the Ford Ranger in the picture at left, which was destroyed by another stroke of the bolt that hit the house. It hit the tire, which went flat, then came up through the brake line and into the fuse box. The truck is not really fixable. 

Header image: When it struck this home, a lightning bolt entered the building’s electrical system through the outside porch light. All images courtesy of Nicole Chew.