Thousands of lightning strikes occur in the U.S. every year, and each strike has the potential to injure people and damage property. According to Underwriters Laboratories (UL), lightning accounts for more than $1 billion annually in structural damage to buildings in this country. What’s not reported is the loss of business, downtime and liability when business or commercial tenants are forced to shut down to repair lightning damage. Property owners who have witnessed lightning’s destructive power understand the need to protect personnel, structures and contents. Unlike threats posed by other forces of nature, lightning’s incredible power can be controlled on a specified path.
Even though statistics for lightning damage are staggering, it remains one of the most underrated weather hazards. Fortunately, engineers and risk assessment professionals have long understood the importance of lightning protection systems and the benefits from the enhanced grounding these systems provide for a variety of structures, equipment and roof types. Risk prevention has encouraged specification of lightning protection systems for all types of structures; especially critical facilities such as power plants, hospitals, emergency service buildings and fire stations. The probabilities of lightning striking a metal-roofed structure are no more or less than lightning striking any other type of structure, yet questions often arise about metal roofs attracting lightning or providing built-in protection against lightning. The facts are, without the presence of a professionally installed lightning protection system, any structure will be vulnerable to lightning-with or without a metal roof.
Fire stations are routinely equipped with metallic roofing and siding systems designed to fulfill the mechanical function of weather exclusion. Unfortunately, these metal roofs are not designed for electrical continuity or to provide structural lightning protection. The anchoring sections of roofing and siding systems are not constructed to carry current because, in most situations, the thickness of the metal used is insufficient to provide a guaranteed path for lightning. Assessing the need for lightning protection typically involves comparing the expected lightning frequency with the tolerable lightning frequency risk-which means weighing the lightning probability against its consequence to life and environment. Naturally, critical structures like fire stations cannot afford to be vulnerable.
The good news is that fire stations in particular are seeing fewer lightning-related losses thanks to a safety initiative that is providing lightning protection systems for these at-risk structures. The Lightning Protection Institute (LPI) began the “Building Lightning Safe Communities” (BLSC) initiative two years ago in an effort to provide lightning protection resources for the public in the fire safety community.
Since then, LPI-member firms have donated approximately $200,000 in lightning protection systems for fire stations in Colorado, Connecticut, Florida, Illinois, Michigan, Missouri and Texas. These systems help protect fire personnel, structures and sensitive communications equipment against lightning.
“Lightning caused serious problems for our fire station and diminished our ability to respond when it took out our generator, phone and pager system,” says Mike Johnson, assistant fire chief for the Sni Valley Fire Protection District in Oak Grove, Mo. According to Johnson, the station suffered two separate lightning incidents in the span of several months that caused approximately $30,000 in lightning losses. The Sni Valley station features a standing seam metal roof that is now equipped with a lightning protection system donated and installed by LPI-member firm, Preferred Lightning Protection Inc., Maryville, Mo., in conjunction with the BLSC campaign. The $25,000 lightning protection system required a significant design effort and took a week to install.
The highly conductive materials used in a lightning protection system provide a low resistance path for lightning to travel without resistance. When the network is in place, a lightning strike is intercepted and directed to the ground without impact to a structure or its contents. While the concept behind lightning protection is relatively simple, requirements for installation are specific and often complex.
The single best way to ensure proper system design and installation is to specify compliance with nationally recognized safety standards for lightning protection. The LPI-175 Standard of Practice (based on NFPA 780 and UL 96 requirements) is published by LPI as a resource to help ensure quality control for lightning protection installation and materials. A complete lightning protection system includes:
- A roof network of prominent strike termination devices
(rods). - A network of ground terminations (ground electrodes).
- A network of conductors or qualified structural members interconnecting the strike and ground terminations.
- Bonding with other grounded building systems.
- Surge protection on all incoming power, data and communication lines.
Failure to make proper provisions for any elements outlined in the safety standards during design or installation can result in inadequate protection. The NFPA safety standard provides industry guidelines for inspection and maintenance to ensure that age, roof damage or modifications to the structure do not degrade a system.
“Lightning protection is a must for fire safety facilities and we are extremely grateful for our system and to Preferred for their generous donation,” says Johnson. “The Sni Valley station has not suffered a single lightning loss since the lightning protection system was installed.”
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Kim Loehr is the communications director for the Lightning Protection Institute (LPI), Maryville, Mo. LPI is a nationwide nonprofit organization founded in 1955 to promote lightning protection education, awareness and safety. To learn more, visit www.lightning.org. Information about follow-up, third-party inspection services can be found at www.lpi-ip.com.