By Administrator Separating fact from fiction about metal roofs and construction Lightning is a frequently experienced weather peril and a known risk for many structures. Yet lightning remains a misunderstood weather hazard and myths persist about lightning protection; especially where metal construction or roofing is concerned. Here are a few common myths associated with lightning… Continue reading Lightning Protection Systems
By Administrator
Separating fact from fiction about metal roofs and construction
Lightning is a frequently experienced weather peril and a known risk for many structures. Yet lightning remains a misunderstood weather hazard and myths persist about lightning protection; especially where metal construction or roofing is concerned. Here are a few common myths associated with lightning and metal construction:
Myth: A metal roof will increase the likelihood of lightning striking a structure.
Fact: The probabilities of lightning striking a metal-roofed structure are no more or less than lightning striking any other kind of structure. A metal roof does not attract lightning, nor does it protect a structure against lightning.
Myth: A protection system is not needed for a metal roof since the metal will disperse lightning’s energy safely through a structure
Fact: Metal buildings are typically constructed of thin section metal, which is generally considered mechanically continuous, not electrically, and doesn’t have sufficient thickness to serve as a capable lightning conductor. A metal roof does not provide an adequate path to take lightning’s harmful electricity safely to ground.
Myth: Lightning protection systems are only needed for wood or masonry structures, not modern day metal construction buildings.
Fact: Metal roofing is often thought of as a low risk option that can prevent lightning fires. In reality, lightning does hit and damage unprotected metal construction buildings. The November/ December “Firewatch” report (NFPA Journal) details a lightning fire to a single-story, wood-frame barn equipped with a metal-covered roof and metal walls. The report described Ohio firefighters arriving at the scene to find the barn completely engulfed in flames with the metal roof collapsing. The barn stored $2.5 million in farm equipment and was not equipped with lightning protection, fire detection or a suppression system.
Myth: Today’s metal roofed structures are grounded and at less risk for lightning.
Fact: Lightning can travel through structural steel Nearly every construction project today incorporates measures for energy conservation and sustainability. Today’s project owners demand state-of-the-art “earth friendly” products and technologies for both the physical structure and the building systems. When working with earth friendly products and green technology, designers need to consider the unique threats that lightning strikes pose. When the goal is to build a structure with a longer life span and a smaller impact on the environment, the wisdom of protecting that structure from lightning damage should not be underestimated. A lightning fire, which will typically destroy the roof and attic of a structure, is hardly an earth friendly event. Even if there is no direct strike or fire, nearby lightning strikes frequently cause damage to electronic systems. In many cases, surge induced damages are not covered by property insurance policies. Prior to the age of electronics, the threat to structures from lightning strikes was primarily fire related. The low resistance pathways that lightning protection systems provide prevent the energy of a lightning strike from igniting structural fires. The introduction of low voltage wiring and electronically controlled building components presented a new vulnerability to lightning. To address these concerns, lightning protection standards were updated during the 1990s. Additional provisions for grounding and augmented criteria for lightning arrestors and surge protection devices were added to protect building electronics. The “green building” era presents yet another level of lightning vulnerability. Fire prevention is a green initiative in its own right, since burning structures present a serious hazard to the atmosphere and rebuilding after a preventable fire increases a structure’s energy footprint substantially. Many eco-friendly building components, such as bamboo flooring, cedar shingles and resin countertops are both flammable and costly to replace. A lightning framing and reinforcing rods in concrete walls or flooring. On the outside of the structure, lightning can travel along conductive metal vents, roof drainage elements and external supports as it seeks a path to ground. Once inside the structure, lightning can travel through the electrical, communication, or data wiring, along with plumbing, gas or process piping systems. Most structures have an electrical system ground, communications system ground and a data system ground, which are designed to handle current flow, but are not designed to accommodate grounding for a lightning strike. Lightning can carry a 30,000 amp or larger electrical surge-which is why a lightning strike to an unprotected structure can be disastrous.
While lightning receives little media attention, a recent 9/11 Opinion Survey conducted by disaster safety firm Cote & D’Ambrosio revealed that it is a serious concern for U.S. consumers. When asked to rate their concerns about natural disasters, the highest number of consumers were very or somewhat concerned about lightning strikes (62 percent), as compared to other hazards such as: flooding, tornadoes, hurricanes, ice storms, earthquakes, hail storms and wild fires. Consumer concerns about lightning are well-founded, as the Insurance Information Institute
(I.I.I.) reported that lightning strikes cost more than $1 billion in insured losses in 2010 with claims up nearly 15 percent from 2009.
Unlike threats posed by tornadoes, hurricanes or floods, lightning’s incredible electrical power can be controlled on a specified path. The highly conductive materials used in a lightning protection system provide a low resistance path for lightning’s harmful electricity. When the protection network is in place, a lightning strike is intercepted and directed to ground without impact to a structure or its contents. Without the presence of the protection system, lightning will fight its way through nonconductive building materials like isolated metal, wood, brick, rubber membranes, glass, plastic, etc., as it seeks its way to earth ground. The resistance it encounters will produce heat, fires and even explosions, as these building materials are not designed to provide a safe path to ground for lightning. Providing a safe path to ground is the objective of the lightning protection system design.
The concept behind lightning protection is relatively simple, but requirements for installation are specific and often complex. The 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 Standard requirements), is published by the Lightning Protection Institute (LPI), as a quality control resource for installation and materials. A complete lightning protection system includes the following elements:
• A network of prominent strike termination devices
• A network of ground terminations (ground electrodes)
• A network of conductors or qualified structural steel framing members to interconnect strike and ground terminations
• Interconnections/bonding with other metallic grounded building systems
• Surge protection devices on all incoming power, data and communication lines
• Inspection service to verify standard compliance and quality assurance
Failure to make proper provisions for any of the elements involved in installation can result in inadequate protection. LPI is a nonprofit, nationwide group founded in 1955 to promote lightning safety, awareness and protection education. A new LPI-IP Inspection program now provides on-site lightning protection inspection services.
“The LPI-IP provides the most thorough inspection program on the market,” explains Tim Harger, program manager for the LPI Inspection Program. “Obtaining a Certified Master Installation Certificate will ensure that your metal building meets all national lightning protection safety standards and quality control measures.”
Kim Loehr is the communications director for the Lighting Protection Institute in Maryville, Mo. LPI conducts certification and educational programs and is a leading resource for lightning protection information and system requirements. Visit www.lightning.org for more information.
