Aprimary function of the building enclosure is to protect structures, their contents, and occupants from the variations and extremes of weather. Wind, precipitation, air temperature, and humidity are readily recognized as atmospheric phenomena that must be considered in the design of building systems, especially when they manifest in their more extreme forms, such as tornados, hurricanes, blizzards, floods, and life-threatening temperatures. However, lightning—the “most underrated weather hazard,” according to the National Weather Service1—is often overlooked in the design and maintenance of a building enclosure, even though it occurs throughout the United States on a daily basis (Fig. 1). This omission may be because the typical concept of the building enclosure is limited to the thin envelope of materials used for wall and roof assemblies. However, a broader understanding is that a building enclosure is a system that mitigates and balances differences between internal and external environmental forces; in this definition, the building enclosure includes lightning protection systems. Lightning occurs when the difference between electrical charges in the atmosphere and the earth are sufficient to overcome the electric insulation of the air. When this occurs, a massive discharge of static electricity, with a potential difference of millions of volts and a current of tens of thousands of amperes, passes between sky and ground and through anything—such as a building—located between the two poles. Lightning passing through a building can harm occupants or disrupt building operations by causing fire, structural damage, and damage to building contents and equipment (Fig. 2). Today, the stakes are greater than ever before for two reasons: (a) the data-driven and electronic devices we rely on to operate enterprises and critical building systems are highly vulnerable to damage by electrical surges, and (b) climate change is increasing the risk of severe storms (Fig. 3). Most building codes have abrogated their responsibility for public health, safety, and welfare by failing to include lightning protection. Instead, the design team and consultants must take it upon themselves to evaluate the need for lightning protection under their professions’ standards of care. Fortunately, lightning protection systems provide effective and affordable mitigation against lightning damage when designed, installed, and inspected in accordance with recognized standards. This article discusses some of the fundamentals of lightning protection systems and will help you understand the factors used to determine whether a particular structure requires lightning protection. RISK A lightning protection system should be used when a structure’s vulnerability to lightning is greater than the tolerable risk. A weather-related metric, lightning flash density, is the first vulnerability factor listed in the National Fire Protection Association’s NFPA 24 • IIBEC Interface September 2021 Figure 1. Cloud-to-ground lightning flashes occurred over 170 million times in the United States in 2020, making lightning one of the most frequent types of severe weather events. Photo credit: Photographer: Larry McNish. 780: Standard for the Installation of Lightning Protection Systems2 annex on “Lightning Risk Assessment.” Density, the yearly number of cloud-to-ground lightning strikes per square kilometer, can be based on local records or nationally compiled isopleth maps showing average densities over a multiyear period. Though density in some regions is low, there is no part of North America that is free from lightning risk (Fig. 5). Moreover, climate- driven changes may justify assuming a building’s exposure to lightning will be higher than historic data suggest. For example, counties in 12 states experienced a 100% increase in lightning density in 2020 compared to previous five-year averages, 3 which may suggest that the unprecedented “lightning complex” wildfires in California in 2020 are a harbinger of lightning devastation to come.4 (A “lightning complex fire” occurs when multiple fires started by lightning merge into a single, large blaze.) Other factors affecting vulnerability are a structure’s area and height, topography, and proximity to taller structures or trees. The level of tolerable risk, the other side of the assessment equation, is affected by the conductivity and combustibility of the roof and structural systems, the value and combustibility of contents, the ease of evacuation, the owner’s attitude toward operational continuity, and environmental hazards. An online lightning risk calculator based upon NFPA’s simplified risk assessment protocols is available.5 The calculations can be performed in fewer than 15 minutes, without special skills or knowledge, and will generate a report stating whether a lightning protection system on a project is required or optional. The report can be shared with clients and used as the basis for decision making (Fig. 4). NFPA2 recommends a lightning protection system if any of the following are concerns: large crowds, continuity of critical services, high lightning flash frequency, buildings that are taller than nearby structures, isolated structures, explosive or flammable content, irreplaceable cultural heritage, or regulatory or insurance requirements. September 2021 IIBEC Interface • 25 Figure 3. When lightning struck this radio station, it surged throughout the broadcasting equipment, destroying gear worth thousands of dollars and knocking the station off the air. Photo credit: Courtesy Mark Persons/Radio World. Figure 4. Online calculators simplify lightning risk assessments based on NFPA 780 protocols. Credit: East Coast Lightning Equipment Inc. Figure 2. Lightning ripped through the masonry wall of this unprotected church on its way to ground. Photo credit: James H. Robinson / Science Photo Library. SYSTEM BASICS The cost of installing lightning protection is modest, and a system will last the life of a structure with minimal maintenance. Despite spurious claims made by some manufacturers, lightning cannot be diverted away from a structure. Instead, a lightning protection system provides multiple low-resistance paths on which lightning can safely pass through a building (Fig. 6). In addition to complying with NFPA 780, lightning protection systems must be designed, installed, inspected, and maintained in accordance with these nationally recognized standards: • Lightning Protection Institute’s LPI 175: Standard of Practice for the Design—Installation—Inspection of Lightning Protection Systems6 • Underwriters Laboratory’s UL Standard 96A: Installation Requirements for Lightning Protection Systems7 • CSA Group’s CSA B72: Installation Code for Lightning Protection Systems8 (applicable in Canada) A complete system (Fig. 7) includes five primary types of components: • Strike terminations: Air terminals (formerly known as “lightning rods”) rise at least 10 in. above a roof to provide a contact point for electrical charges approaching a building. NFPA requires air terminals to be located at 20 ft on-center maximum along ridges, parapets, and other high points on a building. A “rolling sphere” analysis will determine where air terminals are also required on rooftop equipment, along eaves, and within the field of the roof. (Figure 8 presents an illustration of rolling sphere analysis; an animated video explaining rolling sphere analysis is available.9) Metal building elements such as railings and ladders can also be used as strike termination devices if they meet requirements set forth in the national standards. 26 • IIBEC Interface September 2021 Figure 5. Every part of North America, including portions not shown on this isopleth map, is vulnerable to lightning strikes. Credit: Vaisala. Despite spurious claims made by some manufacturers, lightning cannot be diverted away from a structure. • Conductors: Air terminals are typically interconnected via large braided or twisted multistrand copper or aluminum cables that lead to the ground. Referred to as “conductors,” these cables can be installed in direct contact with combustible materials and do not require thermal or electrical insulation. Weather-resistant, through-structure penetration devices may be required where conductors penetrate roofing or walls. Metal structural members can also be used as conductors if they meet requirements set forth in the national standards. • Bonding: Lightning can side flash from one metallic building system to another as it seeks a path to ground. To prevent this, the electrical, structural, plumbing, and other grounded systems in a building must be interconnected with the lightning protection system so their electrical potential is equalized. Conductor cables are typically used to make the connections. • Grounding: A lightning protection system must have multiple ground points spaced apart from each other. Ground rods, driven at least 10 ft (3 m) into the earth, are the most common grounding method. Other methods, such as a ground loop of conductor cable around the building’s foundation, can be used, depending on soil conductivity and ground conditions. • Surge protective devices: Lightning can travel through power, data, and other electrically conductive lines. Surge protective devices are located where lines enter a building and interrupt sudden power spikes caused by lightning. In addition, a vast variety of connectors, fasteners, and accessories are required to install a complete system. Lightning protection system components must be listed for compliance with UL 96: Lightning Protection Components.10 Note that September 2021 IIBEC Interface • 27 Figure 7. A lightning protection system is part of the building enclosure that protects the structure, its contents, and occupants from lightning damage. Credit: East Coast Lightning Equipment Inc. Figure 6. At the Broadmoor Mountain Camp above Colorado Springs, Colo., air terminals are connected to ground via a network of lightning conductors. Photo credit: Mr. Lightning. products designed for normal electrical current are undersized and are not suitable for use in lightning protection systems. Lightning protection system components are typically made of highly conductive copper or aluminum and should be selected based on compatibility with adjacent materials. For example, copper cannot 28 • IIBEC Interface September 2021 Figure 10. Example of damage to a lightning protection system due to rooftop maintenance. When this rooftop exhaust was serviced, the air terminal that should be on top of the dome was lost and the conductor cable was frayed and became detached from the HVAC unit. Photo credit: Smokestack Lightning, Inc. Figure 9. The recently completed U.S. Olympic & Paralympic Museum needed special attention to detailing to integrate the lightning protection system into the curving, faceted cladding system. Photo credit: Mr. Lightning. Figure 8. In a rolling sphere analysis, lightning is modelled as a 300-ft-diameter sphere rolling across a building envelope. Lightning can attach to the structure anywhere it is touched by the sphere. The air terminals, shown in green, rise above the building and are spaced to prevent the sphere from making contact with the building. Photo credit: Scientific Lightning Solutions LLC. be in contact with steel and aluminum because of galvanic action, and aluminum should not be embedded in concrete. DESIGN AND INSPECTION On most projects, it is not necessary for the design team or consultants to design the lightning protection system. Instead, project specifications should require compliance with national standards and delegate system design to a firm specializing in lightning protection systems. It is recommended that this firm’s staff should include an individual with Lightning Protection Institute Master Installer/Designer or Master Installer certification. Installation of a lightning protection system is significantly different from installing electrical power systems, and few electrical contractors are qualified to do lightning protection work. It is also recommended that the specification require the lightning protection system to be inspected and certified by the Lightning Protection Institute Inspection Program.11 The building owner should have the system recertified at least every three years and whenever additions to or modifications of the building occur. CONSULTANT’S ROLE Weather conditions, including lightning, are integral to a holistic assessment of a building enclosure. In new construction, this type of evaluation begins with the consultant’s asking the client whether a lightning risk assessment has been performed or if it should be included in the scope of work. Consultants might also be requested to prepare project specifications, a task made simpler by using guide specifications available from the Lightning Protection Institute12 and leading lightning protection component manufacturers. However, some lightning protection projects will require early and close collaboration with a lightning protection specialist. For example, special attention to detailing was needed to integrate the lightning protection system into the curving, facetted cladding system of the recently completed U.S. Olympic & Paralympic Museum in Colorado Springs, Colo. (Fig. 9). When consulting on a building with an existing lightning protection system, it is prudent to find out whether the lightning protection system has a current inspection report. While lightning protection systems are strong and robust, they do experience ordinary wear and tear and can also be damaged during maintenance of rooftop units (Fig. 10). Problems can also arise when new equipment is installed outside of the lightning protection system’s zone of protection (Fig. 11). Coordination is especially important on reroofing, remodeling, and maintenance projects (Fig. 12). A lightning protection system specialty contractor should remove the existing lightning protection components before roof work begins to protect reusable components and mark and preserve through-roof penetrations. After a new roof is installed, the lightning protection contractor can reinstall, modify, and extend the lightning protection system to ensure the system qualifies for recertification. September 2021 IIBEC Interface • 29 Figure 11. Example of a problem caused when new equipment is installed outside of the lightning protection system’s zone of protection. When the surveillance camera was installed, a lightning protection specialist should have been brought in to install an air terminal on top of the camera and connect it to the lightning protection system. Photo credit: Boston Lightning Rod Co. Inc. FINAL CONSIDERATIONS Consultants interested in a better understanding of lightning protection systems can avail themselves of free continuing education programs offered by the Lightning Safety Alliance.13 Whether or not a project has a lightning protection system, weather gets the final word. Lightning can travel long distances before it attaches to the earth’s surface, so it is wise to heed the National Weather Service’s advice: “When thunder roars, go indoors.”14 REFERENCES 1. National Weather Service. n.d. “Lightning Safety.” Accessed July 31, 2021. https://www.weather.gov/jetstream/lightning_safety. 2. National Fire Protection Association (NFPA). 2020. NFPA 780: Standard for the Installation of Lightning Protection Systems. Quincy, MA: NFPA. 3. “Lightning Like Never Before: Annual Lightning Report 2020,” Vaisala, 2021, https://www.vaisala.com/sites/default/files/documents/WEA-MET-Annual-Lightning-Report-2020-B212260EN-A.pdf. 4. “In the West, Lightning Grows as a Cause of Damaging Fires.” The New York Times, 2020-10-3-23, https://www.nytimes.com/interactive/2020/10/23/climate/west-lightning-wildfires.html. 5. East Coast Lightning Equipment. n.d. “Lightning Risk Calculation Guide.” Accessed July 31, 2021. https://ecle.biz/lightning-risk-assessment-guide. 6. Lightning Protection Institute (LPI). 2020. LPI 175-2020: Standard of Practice for the Design—Installation—Inspection of Lightning Protection Systems. Libertyville, IL: LPI. 7. Underwriters Laboratory (UL). 2016. UL Standard 96A: Installation Requirements for Lightning Protection Systems. Northbrook, IL: UL. 8. CSA Group. 2020. CSA B72: Installation Code for Lightning Protection Systems. Toronto, ON, Canada: CSA Group. 9. East Coast Lightning Equipment. n.d. “Rolling Sphere.” Accessed July 31, 2021. https://ecle.biz/lightning-protection/rolling-sphere. 10. UL. 2016. UL Standard 96: Lightning Protection Components. Northbrook, IL: UL. 11. Lightning Protection Institute Inspection Program. n.d. Accessed July 31, 2021. https://lpi-ip.com. 12. Lightning Protection Institute. n.d. “Specs and Tools.” Accessed July 31, 2021. https://lightning.org/specs-and-tools. 13. Lightning Safety Alliance. n.d. “Continuing Education.” Accessed July 31, 2021. http://lightningsafetyalliance.org/education.html. 14. National Weather Service. n.d. “Lightning Safety Tips and Resources.” https://www.weather.gov/safety/lightning. Please address reader comments to elorenz@iibec.org, including “Letter to Editor” in the subject line, or IIBEC, IIBEC Interface Journal, 434 Fayetteville St., Suite 2400, Raleigh, NC 27601. 30 • IIBEC Interface September 2021 Jennifer Morgan is co-owner of East Coast Lightning Equipment and education coordinator of the Lightning Safety Alliance. She can be reached via www.ecle.biz. Jennifer Morgan Michael Chusid, RA, FCSI, has published numerous papers on integrating lightning protection into buildings and can be reached via www.BuildingProduct.guru. Michael Chusid, RA, FCSI Lightning Protection Institute (www.lightning.org) is a national organization that establishes standards and guidelines for the design, installation, and inspection of lightning protection systems. Figure 12. Roofers can damage a lightning protection system during reroofing or roof maintenance. In this photo, conductors and air terminals are carelessly strewn across the lower roof, which could damage the components. For example, the kink in the conductor, visible in the lower right corner of the photo, violates the minimum bending radius required by industry standards and can allow lightning to “jump” off the cable. Photo credit: Guardian Lightning Protection.
