Lightning protection systems on trial
Few events are as awesome as witnessing a lightning strike or seeing the damage it can produce. Nevertheless, when the subject is lightning protection systems, some of the most recent drama has been created by man rather than nature. It involves challenges to — and the defense of — lightning rod technology that traces its roots to Benjamin Franklin's kite-flying experiments in 1752. In simple terms, the debate centers on whether it is better to attract lightning and dissipate its energy into the ground, or to create a zone of protection intended to repel it.
Lightning protection is "a fairly contentious industry," observes Arthur Cote, senior vice president of the Quincy, Mass.-based National Fire Protection Association (NFPA), which has issued specifications for lightning protection systems since 1904. Its NFPA 780 is the most widely used standard for specifying these systems.
Cote notes that lightning protection industry members predominantly adhere to the traditional "Franklin rod" type of system covered by NFPA 780. From that group has evolved proponents of "early streamer emission" (ESE) systems, an enhanced version of a lightning rod system that is claimed to be more effective. "This has been an ongoing debate for some time," Cote adds.
NFPA was requested to develop a standard for ESE technology. The standards organization decided not to take such action, on the basis that sufficient scientific evidence had not been presented to justify its technical validity. During these deliberations, the technical validity of NFPA 780 was also questioned. NFPA considered withdrawing the standard unless an independent review could establish a valid scientific basis for it.
NFPA's Standards Council decided last October to issue the 2000 edition of NFPA 780. Its decision was based in part on a report by a group of federal scientists and engineers who emphasized that this standard is relied upon as the basis of lightning protection systems around the world.
Elaborating on its decision, the Standards Council said: "The consensus of the scientific literature, field testing, et cetera, is that the conventional, or Franklin, systems, in the venue of the NFPA 780 standard, are highly effective when properly installed and adequately maintained."
Applications are broadening
Lightning protection systems traditionally have been installed on tall buildings and in recent years are more commonly found on low-rise buildings as well, according to Chuck Ackerman, president of Winsted, Conn.-based East Coast Lighting Equipment Inc. This broadening of applications is a result in part of the proliferation of electronic equipment that is susceptible to lightning damage. The larger the building, the greater is its exposure, he notes.
An Underwriters Laboratories (UL) Master Label installation, which covers the owner in terms of liability, generally should be specified, according to Curt Stidham, marketing manager of Harger Lightning and Grounding, Grayslake, Ill. An integrated system includes grounding and good bonding of individual components, as well as surge protection for electric circuits and equipment. Design professionals should work with the lightning protection contractor. Electrical engineers normally are not involved with the details of a system, although they should know its impact on a building's overall electrical system — for example, where a system's conductors should be located to prevent damage to computer equipment.
The incorporation of a lightning protection system is often the result of an owner's desire to reduce "downtime" in his facility. However, lightning protection systems are typically one of the first items eliminated when project budgets are cut.
Lightning rods typically extend 12 inches to 18 inches above the roof and are made of copper, says Randy Duke, a vice president of the M/E/P engineering firm of Cosentini Associates. However, aluminum rods are used if the roof flashing is aluminum, in order to prevent corrosion from an interaction between dissimilar metals.
Not fully protected
Reebok International's headquarters in Canton, Mass., (BD&C, January 2001) has a traditional UL Master Label lightning protection system. However, lightning rods were not initially installed on the building's emergency generator enclosures. "We got hit by lightning," recounts Douglas Noonan, Reebok's director of corporate real estate. "We're unsure whether it struck the utility line or the generator housing. It blew out elevator control panels, transfer switch control circuits and pump controllers and damaged the generator controls — all minor stuff, but the total damage amounted to about $25,000. That oversight has been corrected, and there have been no subsequent problems. We're believers in lightning protection." He says that Reebok's system is serviced annually to inspect for damaged rods and loose connections.
When lightning strikes a power line, it can impact all buildings served by that line. Frank Klusek, chief electrical engineer with Philadelphia-based A/E Kling Lindquist, specifies surge protection of 300,000 amps for service switchgear (the average lightning strike is about 30,000 amps). This is designed to take a lightning stroke that enters through an overhead utility line and direct it into the ground.
A different approach
The concept behind a traditional lightning protection system is to attract lightning and channel its energy into the ground, where it will be dissipated. A charge transfer system, on the other hand, takes the opposite approach by attempting to prevent lightning from entering protected zones. This type of system is marketed by Boulder, Colo.-based Lightning Eliminators & Consultants Inc. The company's Dissipation Array System (DAS) utilizes thousands of 4-in.-high stainless-steel wires, or "points," installed in various configurations, including along a building perimeter, and connected to a 21/2-in. diameter copper ground rod.
When a thunderstorm moves into an area, a ground charge is induced. The ion-producing "points" create a current flow to the surrounding air, removing the storm-induced charge on the protected site and transferring it to air molecules above the site. The intent of the DAS system is to prevent strikes by lowering the voltage difference between the ground and the charged cloud from which lightning could originate.
Jerry Kerr, marketing director of Lightning Eliminators, concedes that lightning rod-based systems prevent physical damage and fire, but argues that they cannot eliminate secondary effects that can damage electronic circuits and equipment. "A more than 200-year-old technology is not really appropriate for high-tech buildings," he says. "Our system does not allow a strike to touch the protected facilities — period. We provide a written guarantee that the building or site will not be struck."
Metal objects on a roof are grounded into a lightning protection system.
Strike-free for 18 years
Federal Express installed a DAS system at its Memphis International Airport operations center in the mid-1980s. "At first we had doubts about DAS, but the system works," says Federal Express Senior Project Manager Larry Marsh. "We thought if we could eliminate half of the strikes, it would be useful. Eighteen years later, to my knowledge, there hasn't been one strike."
Kerr says office building owners typically have left concerns about lightning protection to their tenants. But today's tenants may have valuable electronic equipment and thus want to know about the adequacy of their building's lightning protection system. Some building owners are now marketing the DAS system as part of their project, he says.
Specifiers say they are reluctant to specify a charge transfer system because it is not recognized by NFPA. They also express concern that the wind could blow the ionized air away from the site it is intended to protect.
Although there is currently no standard for charge transfer systems, the Institute of Electrical and Electronics Engineers (IEEE) has appointed a committee to develop one. Balloting on a draft is expected to occur this spring.
Florida, with an average of 19.7 lightning flashes per square mile, is the state with the most recorded lightning strikes, according to Tucson-based Global Atmospherics, which maps and records lightning activity. Near the bottom of the list is California, which recorded only 0.50 flashes per square mile. High lightning activity is found along the Front Range of the Rocky Mountains, along the Gulf Coast and in the area stretching from Georgia to the Northeast United States.