What is lightning and how is it caused?
Between 2003 – 2007, Zurich church customers incurred 945 lightning strikes costing millions of dollars of losses and untold hours of interruption of church ministries. This means that each week, 3-4 churches Zurich insures are struck by lightning, with an average claim cost of $12,500. The costliest lightning strike occurring within the past two years resulted in a $3.9 million total church loss. Exposures to lightning strikes are most prevalent in the Southeast and Midwest states, with losses occurring mostly in Florida, Mississippi and Texas. Interesting enough, scientists are not exactly certain how lightning works, or with any degree of certainty just where and when it will strike. We do know that lightning is an enormous electrostatic discharge, similar to the type of static electric shock you can receive while walking on carpeting and touching metal surfaces.
Key exposures:
All parts of the U.S. are susceptible to lightning strikes. Taller buildings, particularly churches with spires or steeples and properties located on hilltops, have an increased risk of receiving a lightning strike. Geography can also add to the risk of exposure.
According to the National Oceanic and Atmospheric Administration (NOAA), the highest frequency of cloud to-ground lightning over the entire year exists in Florida between Tampa and Orlando. This is due to the frequent presence of a large moisture content in the atmosphere at low levels (below 5,000 feet), as well as high surface temperatures that produce strong sea breezes along the Florida coasts. The western mountains of the U.S. also produce strong upward motions and contribute to frequent cloud-to-ground lightning. In addition to this, there are high frequencies along the Gulf of Mexico coast westward to Texas, the Atlantic coast in the southeast U.S. and inland from the Gulf. Regions along the Pacific west coast have the least cloud-to-ground lightning.
Thus, it is not just the energy of a surge that has to be considered, but the frequency of surges. Lightning is hazardous to equipment when the strike is very close and also at great distances. The intense electric and magnetic fields surrounding a strike will induce a high voltage charge at a distance of 300 feet in just three feet of wire and will still induce hundreds of volts at a distance of one-half mile. This is why equipment failures occur during a storm, when no evidence of a strike is apparent in the immediate area.
Although it cannot be precisely predicted where lightning will strike, there are some factors that increase the risk of a lightning strike. These include:
- Prior lightning damage
- Structures that are located or isolated in open areas, on top of hills and/or near a large body of water
- Structures that are located in areas that have a high number of thunderstorms
- Buildings that have trees overhanging the roof
- Buildings that are constructed with a metal, brick, or stone chimney, with metal ridge vents, or with aluminum siding
- Buildings that have no surge protection
Where and how often does lightning usually strike?
Lightning strikes the ground somewhere in the U.S. nearly every day of the year. Thunderstorms and lightning occur most commonly in moist warm climates. Data from the National Lightning Detection Network shows that over the continental U.S., an average of 20 million cloud-to-ground flashes occur every year. Around the world, lightning strikes the ground about 100 times each second or eight million times a day.
Related articles:
Lightning protection
Lightning safety
Surge protection
Lessons of loss
The information in this publication was compiled by Zurich Services Corporation from sources believed to be reliable. We do not guarantee the accuracy of this information or any results and further assume no liability in connection with this publication, including any information, methods or safety suggestions contained herein. Moreover, Zurich Services Corporation reminds you that this publication cannot be assumed to contain every acceptable safety and compliance procedure or that additional procedures might not be appropriate under the circumstances. The subject matter of this publication is not tied to any specific insurance product nor will adopting these procedures insure coverage under any insurance policy. ©2008 Zurich Services Corporation