Understanding lightning protection systems

Scientific advances improve lightning protection for mission critical facilities.

05/17/2017


Learning objectives:

  •  Know the basics of lightning protection systems and the need for them.
  •  Understand the factors that electrical engineers should consider when assessing lightning risk.
  • Apply the codes and standards to specifying lightning protection systems.

Benjamin Franklin demonstrated that an electrically conductive path can safely channel lightning strikes from the top of a building into the earth. His lightning protection system (LPS) has repeatedly proven its effectiveness and has been gradually refined during the past 2 centuries. For ordinary facilities, it assures reliable and affordable protection when designed and installed in accordance with NFPA 780: Standard for the Installation of Lightning Protection Systems.

Yet the lightning protection requirements of many structures exceed those provided by ordinary air terminals (formerly called lightning rods) and grounding. Their vulnerabilities have increased as increasingly sensitive electronics now control vital functions including building security, climate control, data storage and processing, lighting, manufacturing and processing equipment, door hardware and access systems, health care systems, and other critical functions. At the same time, the risk appears to be rising due to the occurrence of more frequent extreme weather events associated with climate change, as lightning accompanies tornadoes and hurricanes as well as thunderstorms.

Lightning poses a Figure 1: A lightning protection system provides a conductive path that can safely channel lightning into the ground. Air terminals, conductors, ground rods, fittings, and other components must be listed under UL 96—Lightning Protection Components. In most steel-framed buildings, structural members can be used as down conductors between the roof and earth. Surge-protection devices must be installed on all power and signal services penetrating the building envelope. Courtesy: East Coast Lightning Equipment Inc.significant risk to buildings and their occupants and contents. It strikes 40 to 50 times per second worldwide, for a total of nearly 1.4 billion flashes a year, with up to more than 200,000 amperes of virtually unimpeded current surging between ionic charges in the atmosphere and the earth. Every region of North America is vulnerable to lightning. On a national scale, lightning causes about as much damage as tornadoes. The scope of this devastation, however, is frequently unrecognized because individual lightning strikes do not attract the media attention that is given to regional disasters. Yet a single lightning strike can be a disaster for a business or community if it disrupts mission critical operations.

Insurance claims for lightning-damaged buildings in the U.S. total more than $5 billion annually. This figure understates the cost because it primarily measures fire and structural damage and overlooks most of the damage to electronic devices and systems. Lightning damage to electronic devices is frequently misattributed to other causes.

Consider, for example, a Level I trauma center that had installed a new backup generator. The generator repeatedly failed routine, monthly checkups, and the hospital made claims against the manufacturer’s warranty. Someone eventually noticed a correlation between equipment failures and thunderstorms in the area, and it was discovered that the generator had not been properly integrated into the building’s LPS. Since remediation, the facility manager reports the generator has not failed again.

Even if an insurance policy paid for damaged equipment, would it cover consequential damages, such as loss of revenue or failure to respond in an emergency? You would not want to be the police or fire chief that is unable to respond to storm-related damage because the very storm fried your communication system.

Risk assessment

A good place to begin understanding your building’s lightning protection needs is with the lightning risk assessment in Annex L of NFPA 780.

The standard recommends lightning protection when a structure’s vulnerability to lightning is greater than its tolerable risk:

  • Vulnerability is determined by lightning-flash density (frequency/area/year based on national weather-service maps) with modifications based on a structure’s area, height, topography, and proximity to taller structures or trees. 
  • Risk is affected by the conductivity and combustibility of the roof and structural system, the value and combustibility of the building, the ease with which occupants can be evacuated, an owner’s attitude toward continuity of operations, and environmental hazards, such as the release of hazardous materials.

Regardless of the calculations, NFPA recommends serious consideration of lightning protection if any of the following factors are present.

  • Large crowds
  • High lightning-flash frequency
  • Tall, isolated structures
  • Explosive or flammable content
  • Irreplaceable cultural heritage
  • Regulatory or insurance requirements
  • Continuity of critical services.

Lightning monitoringFigure 2: The physical plant director of this hospital said he can't accept the risk of lightning damage when someone could be on the operating table. The railings around this rooftop equipment acts as a strike termination device and is used in lieu of conventional air terminals (lightning rods). The cable at the base of the railing is UL-listed for lightning protection and assures electrical continuity with the rest of the lightning protection system. Courtesy: East Coast Lightning Equipment Inc.

Many of the recent advancements in lightning safety were developed for military and space-launch applications. This is understandable because launch facilities, such as those at Cape Canaveral, Fla., are located in areas with intense lightning activity. At such launch facilities, the value of the assets is high, the avionic and aeronautical equipment is sensitive, rockets and their launch structures are tall, and the stakes are enormous when astronauts or other high-value payloads are sitting on top of massive, highly volatile rocket-fuel tanks

This was illustrated in 2011 as Space Shuttle Atlantis sat on Launch Complex 39A (LC-39A) at the Kennedy Space Center. One day before Atlantis was due to make the final voyage of NASA’s Shuttle program, lightning struck near the launch complex, twice. The crucial questions for engineers and officials hoping to keep the launch on schedule were: Where exactly did the lightning strikes hit, and were they close enough to damage the shuttle’s electrical systems?

Two systems were monitoring lightning activity around Kennedy Space Center at the time: the local Cloud-to-Ground Lightning Surveillance System (CGLSS), operated by the Air Force’s 45th Weather Squadron, and the U.S. National Lightning Detection Network (NLDN), a nationwide lightning-detection system owned and operated by Vaisala, a private company.

The systems indicated the lightning events were close to LC-39A, where Atlantis was waiting for launch. But prior NASA investigations had determined that both CGLSS and NLDN produced questionable results: They reported 70% to 80% of lightning strikes and were prone to reporting strikes in locations where they did not actually occur.

In previous cases, lightning strikes in the vicinity of the launch pad would have delayed the launch by up to a week while engineers retested potentially affected systems. This time, however, NASA had the benefit of a new lightning-monitoring system. The system used state-of-the-art, high-speed cameras designed to capture visual evidence of any lightning striking the pad directly or in the nearby vicinity.

Images from the camera showed one strike was outside the LC-39A perimeter and the other struck a water tank. NASA officials had sufficient confidence in the relatively untested system to keep the Atlantis launch a “go.”

Commercial aFigure 3: Lightning can exceed 3 million V and protecting structures and equipment from lightning is not covered in the electrical codes. Lightning protection system (LPS) should be designed and installed by individuals certified by the Lightning Protection Institute and using equipment specifically listed for lightning protection systems. This copper grounding bar is used to create a common ground point where the LPS and the grounds for other building services can be interconnected. Courtesy: East Coast Lightning Equipment Inc.vailability

Technology similar to the surveillance system relied upon to monitor Atlantis on the launch pad has been refined and is now available commercially. The optical lightning-monitoring system uses high-speed, zero-dead-time cameras to detect and record 100% of strikes within a specified surveillance area. The system uses robust, aerospace-grade components that are easily deployed and solar-powered to provide immediate reports that allow timely responses.

Recently, the innovative optical lightning-surveillance system was crucial to the successful December 2016 launch of the Cyclone Global Navigation Satellite System (CYGNSS), allowing the countdown to continue despite fierce lightning at Cape Canaveral Air Force Station just days before the scheduled deployment. CYGNSS contains eight microsatellites that will measure wind speeds over Earth's oceans, increasing the ability of scientists to understand and predict hurricanes. CYGNSS was launched Dec. 15, 2016, by Orbital ATK Inc. using their Pegasus XL rocket—an air-launched vehicle mounted under a modified Lockheed L-1011 aircraft.

Two optical lightning-surveillance systems provided unprecedented precision in determining where lightning struck. Engineers immediately reviewed the data collected and provided conclusive evidence that the aircraft and rocket had not been exposed to lightning-related effects that would endanger the mission.

Commenting on a photograph taken by the system, NASA’s Sean Potter said, “Though the photo gives the appearance of lightning directly striking Orbital ATK’s L-1011 carrier aircraft, the strike occurred approximately 2.5 miles from the aircraft’s location beside Cape Canaveral Air Force Station’s runway. The aircraft and Pegasus XL rocket were surrounded by an overhead lightning protection system designed to protect them had a strike actually occurred in the immediate vicinity; the three masts of the LPS can be seen near the front and aft of the aircraft.”

To augment the LPS, Potter said, “The surveillance system was designed for NASA’s Launch Services Program to document and assess potential deleterious effects of lightning strikes. The lightning-surveillance system provided timely and accurate data that allowed for continuation of the Pegasus XL countdown despite numerous cloud-to-ground lightning strikes recorded that day.” He also said that the contractor, “provided outstanding support and was able to quickly provide information that was helpful in mitigating the concern and moving forward with the launch.”

The optical lightning-surveillance system is proving invaluable to other industries. In the wind-energy industry, for example, a lightning-damaged wind-generator blade can throw the turbine out of balance, potentially causing the entire tower to collapse. By monitoring an entire wind farm, an operator can quickly determine if a particular wind turbine has been struck so it can be safely shut down for maintenance—and possibly avert a catastrophic failure.

In the insurance industry, accurate lightning surveillance allows property owners to document claims that damage is due to lightning and not mechanical malfunction. Similarly, insurance companies can protect against fraudulent claims. Both parties benefit by not having to send investigators into the field for costly forensic work.

The horizontal footprint of a facility is a significant factor in determining vulnerability to lightning. This makes the optical surveillance system particularly valuable to organizations providing services across areas with many high-valued assets, such as airport and harbors, military installations, construction sites, power-generation facilities, and complexes with multiple lightning-vulnerable structures.


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