b'Steep Slopeof lightning protection system if it is equal to or greaterlisted for ordinary electrical service are not safe for than 3/16 inches (4.8 mm) in thickness and is electricallylightning protection.continuous, or made electrically continuous Finally,wemustrecognizethatmetalroofingMetal Nonmetallic Combustible Seeking the path of least resistance from sky tohas to protect a building against rain, wind, snow,Structure Roof Roof Roofground, lightning will arc or side-flash from conductorssunlight and other meteorological conditions. WhenMetal 0.5 1.0 0.5into electrical, plumbing, HVAC, structural membersinstalled in conjunction with an LPS, metal roofingNonmetallic 1.0 1.0 1.0and other metallic systems if electrical potential is notcan also withstand lightning, one of natures mostCombustible 2.0 2.5 2.0equalized between all grounded systems. Similarly,dangerous hazards. LPS requires its own grounding system that mustFor more information about lightning protection, be bonded to other grounding systems, such as thesee bit.ly/LPSresources. A lightning protection system is ground for the buildings electrical power.recommended if buildings exposure Air terminals are not highly visible from the ground.Note: Some of the photos used in this article have beento lightning exceeds tolerable risk as Aluminum air terminals can be as slim as 1/2 inchesenhanced to make lightning protection equipment morecalculated based on the following:diameter, just 10 inches tall and set up to 24 inches invisible. In actual installations, the thin air terminals are from roof edges. Light colored air terminalseitheroften difficult to see from normal viewing distances.BE Exposure Criteria:aluminum or plated copperreflect and blend into Lightning Flash Density:the sky. Exposed cables on the roof should be locatedJennifer A. Morgan is secretary/treasurer at East Coast Lightning Equipment Inc.,This is the average cloudon the less visible face of a roof and against the ribs inand Education Coordinator of the Lightning Safety Alliance (LSA).to ground lightning flashesmetal roofing to minimize visibility. per-square kilometer perComponents of a lightning protection system mustMichael Chusid, RA, FCSI is an advocate for improvements in building materialsyear as based on localcomply with UL 96Standard for Lightning Protec- and design practices. The authors are LSA-certified to present continuing educa- meteorological data or thetion Components and be listed by UL. Componentstion programs about lightning protection. Contact them at info@ecle.biz.Average U.S. LightningFlash Density Map fromAD HERE the National LightningNFPA 780 SIMPLIFIED RISKDetection Network. Whiledensity varies, every state inASSESSMENT CRITERIAthe Country is at risk.Equivalent Collection Area:This is essentially based on Without a lightning protection system, the lightning the footprint of a building attached to the building along the metal parapet. It then adjusted by the height of arced into the steel reinforcing in the wall, shattered the grout-filled masonry units, and created hazardous falling the building. The larger and debris. The power continued to wreck havoc on its way to taller a building, the greater ground. Photo courtesy of Mr. Lightning.its exposure.Tolerance Criteria: Value of building contents. Construction coefficient based on conductivity and combustibility ofstructure and roofing: Ease of evacuating building occupants. Continuity of service requirements and environmental consequences.Regardless of the outcome of the risk assessment, protection should be given serious consideration if any of the following are factors: Large crowds. Continuity of critical services. High lightning flash frequency. Tall isolated structure. Explosive or flammable materials. Irreplaceable cultural heritage. Statutory, regulatory and insurance requirements.Every state is vulnerable to lightning (even Alaska and Hawaii, not shown on map). Low risk is not the same as norisk, and designers should conduct a lightning risk assessment for each structure. Graph courtesy of Vaisala.32 www.mrca.orgMidwest Roofer2.25x9.875.indd 3 8/23/17 3:34 PMBE_Winter18_MetalRoofingFeature.indd 30 1/17/18 11:46 AMBE_Winter18_MetalRoofingFeature.indd 31 1/19/18 11:35 AM'