Lightning Safety

Contents

• Introduction
• Notice Summary
• Applicability
• Description
• Events Summary
• Lightning Season
• Figure 1. Lightning-Related ORPS
• Risk Analysis
• Figure 2. Lightning-Related ORPS Reports By Site
• Lightning Protection Systems
• Lightning Testing Systems
• Lightning Testing Systems
• Conclusions
• Lightning Standards and Codes
• References
• Notices Previously Issued

Introduction

This notice is one in a series of publications issued by the Office of Nuclear and Facility Safety to share nuclear safety information throughout the Department of Energy complex. For more information, contact Richard L. Trevillian, Office of Operating Experience Analysis and Feedback, Office of Nuclear and Facility Safety, U.S. Department of Energy, Washington, DC 20585, telephone (301) 903-3074. This Safety Notice should be processed as an external source of lessons- learned information as described in DOE-STD-7501-95, Development of DOE Lessons-Learned Programs.

Safety Notices are distributed to U.S. Department of Energy Program Offices, Field Offices, and contractors who have responsibility for the operation and maintenance of nuclear and related facilities, and to other organizations involved in nuclear safety. Written requests to be added to or deleted from the distribution of Safety Notices should be sent to: Christine Crow, RPI, 20251 Century Blvd., Germantown, MD 20874 or by fax, (301) 540-2499.

The ESH Office of Information Management maintains a file of Safety Notices and supporting information. Copies can be obtained by contacting the Office of Information Management at (301) 903-0449 or by writing to the Office of Information Management, U.S. Department of Energy, EH-72/Suite 100, CXXI/3, Washington, DC 20585.

Notice Summary

Lightning Strikes the Empire State Building

DOE facilities have been struck by lightning numerous times, causing equipment damage and adversely affecting facility safety and operations. This notice contains information about the safety and operational impact of lightning strikes and actions that can be taken to minimize damage.

Applicability

This notice applies to all DOE facilities. It should be processed as an external source of lessons learned information as described in DOE-STD-7501-95.¹ The Office of Nuclear and Facility Safety encourages DOE managers to examine their lightning protection programs, equipment, and procedures in view of this information.

Description

At any time, some 2,000 thunderstorms are occurring around the world, creating approximately 100 lightning strikes every second. In the United States alone, lightning causes the majority of forest fires and over $2 billion in property losses. Lightning is also the leading weather-related killer in the United States, causing from 100 to 200 deaths every year.²

Lightning is essentially an electric discharge of very large magnitude that can accompany

atmospheric upsets such as storms, volcanic eruptions, and small nuclear explosions.

It can have electrical currents ranging up to 200,000 amps, temperatures to 30,000 degrees Kelvin, and can travel at 35,000 to 100,000 kilometers per second.

Damage from lightning strikes can result from the energy of the initial strike or from secondary effects, such as fires, electrical ground faults, or power loss. Not included in the dollar value of direct property damage are lost-time costs associated with work stoppages from responding to false alarms or loss of electrical power and the possibility of undetected damage to safety-critical alarms and sensors.

Events Summary

On June 29, 1995, at the Sandia National Laboratory, a lightning strike disabled part of the security alarm system communications network. Security personnel sealed affected vaults and initiated patrols. Except for one data loop, all repairs were completed within an hour. On June 30, technicians experienced additional problems with the security computer. Because alarm reporting was questionable, security patrols again sealed and patrolled the affected vaults.

Technicians re-initialized the computer and returned it to operation within five hours.³

Investigators determined that the root cause of the initial failure was inadequate grounding of the electrical power distribution system. This allowed the lightning strike to damage several components in the security alarm communications network and resulted in partial loss of the system. Information overload from the failed data loop caused the second failure.

Investigators determined that the failure occurred despite a $40,000 investment in improving lightning protection for the alarm network in 1991. The supplier of the 1,500 communications transponders in the alarm system stated that, because of the grounding problems, the lightning protection built into their product would not be effective.

Laboratory personnel started a $37 million power system modernization project in March 1994. The project is scheduled for completion in January 1998. An electrical safety committee identified 23 buildings with inadequate grounding. As part of the modernization project, electrical distribution system grounding problems are being corrected as new power feeds are supplied to each building. Until the upgrades are completed, communication systems in the buildings that have not been modernized will have an elevated risk of damage from a lighting strike. Other lightning protection methods have been tried without success. However, these upgrades should mitigate future lightning-related problems in the security alarm system communications network.

On May 17, 1991, the West Valley Site experienced a sitewide loss of electrical power because a lightning strike destroyed a lightning arrestor at the main plant stepdown transformer. All emergency equipment initially responded as expected; however, two steam supply boilers shut down because of low boiler feedwater supply. As a result, the steam-driven, main ventilation system backup blower and the backup plant air compressor also shut down. Because of these failures, emergency personnel declared an Unusual Event in accordance with the site emergency plan.⁴

Electricians inspected the main plant stepdown transformer and discovered no damage other than the destroyed lightning arrestor. After about four and one-half hours, maintenance workers returned the main ventilation system to service, and emergency personnel declared an end to the Unusual Event.

Electricians examined the high voltage electrical distribution system in November 1990 and identified degradation in the ground insulation of one phase. Two planned outages to perform maintenance, including repair of the degradation, were canceled because of inclement weather and other higher priority work. Following this event, in June 1991, electricians inspected and replaced numerous insulators and ground cables. Planners established a preventive maintenance schedule to periodically examine and maintain the insulators and ground cables in the electrical distribution system.

This event illustrates the importance of preventive maintenance for lightning protection and electrical distribution systems. Lightning protection equipment can degrade over time or after suppressing numerous strikes. The degraded equipment can suddenly fail without warning. Deficiencies such as failed surge arrestors or degraded insulation can cause ground faults and electrical distribution system failures.

On August 4, 1995, at Fernald, lightning struck and damaged transmission lines for the sitewide alarm system. The system monitors all fire, environmental, and radiological detection alarms. As a result, facility communications center personnel relied on local alarms and physical walk-through inspections to ensure safe conditions. Personal computers used to interact with the mainframe computer were damaged, as were local fire alarm data-gathering panels. There was no significant impact to onsite or offsite personnel as a result of this event.⁵

The lightning strike knocked one of the support wires off the primary site radio tower. The charge entered the fire alarm wiring system and destroyed all electronic components in the local fire alarm data-gathering panels in two buildings.

Two additional strikes damaged control cards in local fire alarm data-gathering panels. The assistant emergency duty officer restricted some site operations until service was restored to the computer system. Fire watches and walk-through inspections were completed every two hours on facilities that did not have local alarms on monitoring equipment. Damage to the system was approximately $50,000.

Recovery from the strike was expedited by implementation of plant contingency plans and available spare parts purchased as a result of lessons learned from previous lightning strikes. The system was 99 percent operational within 10 hours of the initial damage. There were enough spare parts to completely rebuild the two local fire alarm data-gathering panels and replace the damaged personal computers.

Lightning Season

Facility managers should be most concerned with lighting strikes during the late spring, summer, and early fall. In the continental United States, the second and third quarters of the year usually have the most lightning activity. Centers of thunderstorm activity shift from one area of the country to another during the year, generally moving southward with the sun during the winter. About half of the storms for the entire year occur during June, July, and August.⁶

Operating Experience Analysis and Feedback Engineers (OEAF) reviewed the ORPS (Occurrence Reporting and Processing System) database for lightning-related occurrences and found that 89 percent of the events occurred during the second and third quarters of the year. Figure 1 shows the quarterly distribution of lightning-related ORPS reports from 1991 to the second quarter of 1996.

Figure 1. Lightning-Related ORPS Reports By Quarter(1)

Risk Analysis

Lightning risk analysis considers the consequences of a lightning strike and its likelihood of occurrence. Plants that contain high-energy systems or components such as explosives would have an elevated risk because of the potential damage from a detonation. The most expensive lightning strike in U.S. history occurred at Lake Denmark, New Jersey, on July 10, 1926, when lightning struck a Navy ammunition depot. The resulting fires and explosions killed 19 people and destroyed property valued at $17 million (1996 dollars).⁷

The most accurate indicator of lightning strike frequency is ground-flash density. This is the number of times lightning will strike an area the size of a square kilometer in a year and is expressed as number of flashes/km2/year. The number of annual thunder days (number of days in a year that thunder is heard in an area) also provides an indication of how much lightning a region can expect. Thunder is caused by the energy of lightning rapidly ionizing and heating the air along the path of a strike. The air expands radially in all directions faster than the speed of sound. This abrupt expansion of air is similar to the expansion of gases from an explosion. Air is pushed aside, causing the sound waves known as thunder.

A map of the sites that reported the most strikes during this period is shown in Figure 2.

The Pantex Plant in Texas has a high lightning risk because of the high-energy explosives stored onsite and its location in an area that has a high ground-flash density. During the three-year period from 1991 to 1993, there were over 600 lightning flashes at the Plant.

Pantex engineers designed a detailed lightning protection system that, along with administrative procedures, thoroughly protects the weapons stockpile.⁸ Ensuring that warheads and their components can withstand lightning strikes requires multiple physical barriers to block the transfer of energy from the strikes to critical components and materials.

Instruments and control systems at many facilities are also vulnerable to damage and lightning-induced malfunction. Earlier generations of electrical and electronic systems used vacuum tubes, relays, and analog and computation devices that were more immune to the effects of lightning than are today's solid-state, microprocessor-based systems. Brief overvoltages caused by lightning strikes and man-made transient voltages can immediately destroy low-power, solid-state components, such as computer chips, or can weaken them to the point that they fail months after a lightning event.⁹

Figure 2. Lightning-Related ORPS Reports By Site

Recommendations

Proper lightning protection design accepts a strike as inevitable, provides a controlled path for the current to follow, and minimizes the development of hazardous potential differences. A comprehensive lightning safety program should be site-specific.

The National Lightning Safety Institute recommends a comprehensive lightning mitigation program that integrates six key safety elements.¹⁰

• Authentication—Senior managers need to adopt a policy statement that expresses a serious attitude toward lightning safety. This means creating realistic budgets, developing adequate maintenance and inspection programs for lightning protection equipment, and keeping comprehensive records.
• Detection—Conditions conducive to lightning must be identified before lightning actually strikes. This includes purchasing specific equipment that will gather data, report it, and alarm as lightning conditions change.
• Education and Training—Managers need to integrate lightning safety into the overall safety plan. This includes conducting safety seminars and posting safety tips on bulletin boards, shelters, machinery, vehicles, and other conspicuous places. Employees who work indoors should be included in safety efforts because telephones and other alternating current equipment can induce shocks as a result of indirect or distant lightning strikes.
• Notification—Site notification systems should include audible or visual warnings of lightning alerts. Lighting strike scenarios should be included as part of the site evacuation and response plan. Periodic drill exercises should include lightning events.
• Protection—Personnel need to be provided with safe shelters. Critical capital assets must be identified and commensurate protection provided. All power and data lines, main panels, and subpanels should be provided with surge protection. Bonding, grounding, and shielding should be specific for the buildings, climate, and type of soil. Backup power supplies must be provided for critical components and systems.
• Testing—Engineers need to consider modern diagnostic testing methods to verify the performance of lightning- conducting devices as well as the general path of lightning through structures. Radio frequency testing and other techniques can help engineers forecast the effects of lightning on their facilities.

Lightning Protection Systems

Lightning protection is frequently a standard design feature for new projects or buildings. Each building has its own characteristics that require special design review. Soil conditions, building height and configuration, type of structure, and vulnerability of equipment and occupants must be evaluated.

Inspection of lightning protection systems should be performed periodically. The National Fire Protection Association¹¹ recommends inspecting systems annually. In some areas, where severe climatic changes occur, the inspection should be performed semiannually. Complete in-depth inspection should be performed every three to five years. Lightning protection systems need to be maintained because they can lose their effectiveness through corrosion, weather-related damage, and lightning strikes.

First-level protection of structures is provided by the lightning grounding system. All electrically conductive paths that penetrate the building must be shielded and bonded to the lightning grounding system externally at the point of entry. To protect the components housed inside, all electrical conductors should pass through surge arrestors located inside the structure as close as possible to the point of entry.

The use of low-impedance materials is essential. Aluminum wiring should be avoided because it may melt. Gradual bends (minimum 8-inch radius) should be adopted to avoid flashover problems. When down-conductors are located near people, non-metallic warning signs and barriers are recommended to isolate the area for at least a meter.

Connector bonding should be thermal, not mechanical, where possible. Mechanical bonds are subject to corrosion and mechanical damage, both of which reduce their effectiveness. Frequent inspection and resistance measuring of mechanical connectors are recommended.

Ordinary fuses and circuit breakers operate much too slowly to respond to lighting-induced transients; therefore, staged protection against induced or secondary voltages is recommended. This includes (1) protecting the main panel (alternating current power) entry, (2) protecting all secondary distribution panels, and (3) protecting all valuable plug-in devices, such as computers, printers, alarm and control systems, and fax machines. Incoming data and signal lines (telephone, coaxial, and modem) and electric sources secondary to the main structure (for example, well heads, remote security alarms, CCTV cameras, and high-mast lighting) must also be protected.

Lightning Testing Systems

Low-voltage radio frequency testing can be performed to determine the effectiveness of a lightning protection system. A network analyzer continuously emits signals in the range of 10 kHz, which includes the radio frequency spectrum of a lightning stroke. The signals are amplified and applied to the facility lightning down-conductors and conductive penetrations. As the signals travel through the down-conductors, they pass through sensing coils, which send a sample of the applied signals back to the network analyzer. A measurement coil sends signals back from the area being tested, and the network analyzer compares the two signals. The low voltage data is mathematically scaled up to the higher voltages associated with lightning strikes to determine how the protection system will respond to an actual strike. This method allows engineers to model the worst-case lightning effects on the facility and analyze the adequacy of the lightning protection system.

Personnel Safety

Data provided by the National Lightning Safety Institute indicates that 10 percent of lightning strike victims die; 25 percent of the survivors suffer serious long-term after- effects. Some of the more common after-effects include:

Memory Deficits and Loss 52%

Sleep Disturbance 44%

Attention Deficits 41%

Dizziness 38%

Easily Fatigued 37%

Numbness/Paralysis 36%

Stiffness in Joints 35%

Depression 32%

This data emphasizes the effects of a lightning strike and should encourage everyone to practice lightning safety. The following safety tips can enhance personal safety during thunderstorms.

· If outdoors, seek shelter; get indoors or in an all-metal car (except a convertible), truck, or van with the windows shut.

· Avoid bodies of water and all metal objects.

· Get off the high ground; avoid solitary trees, hilltops, cliff faces, caves, and open spaces.

· If caught away from shelter during a lightning storm, adopt the lightning safety position—stay away from other people; take off all metal objects; and crouch with feet together, head bowed, and hands on knees.

· If indoors, avoid plumbing and other penetrating conductors; stay away from open doors and windows.

· Hang up the telephone and take off head sets; turn off appliances, computers, power tools, and television sets—lightning can strike electric or phone lines and result in a shock.

Everyone should also practice the "flash-bang" method of measuring lightning distance, which involves counting the time from seeing the flash to hearing the thunder. For each 5-second count, lightning is approximately 1 mile away. At the count of 15 (approximately 3 miles) immediate action is recommended.

Conclusions

Lightning protection in an absolute sense, is essentially impossible. Lightning can overcome any defense man can conceive. A hazard mitigation approach to lightning safety is a prudent course of action.

Organizations should adopt a lightning safety policy and integrate it into their overall safety plan.

All employees should receive appropriate training designed to develop a realistic awareness of personal lightning safety. Employees who work indoors should be trained because telephones and other indoor electrical equipment can be a source of shocks. Employees working outdoors must understand the nature of the lightning hazard as well as appropriate safety measures.

Lightning Standards and Codes

DOE O 420.1¹² provides guidance on natural phenomena hazards mitigation, including lightning, for DOE facilities. The Order states that contractors/operators at new sites shall conduct a natural phenomena assessment commensurate with a graded approach to the facility. For existing sites, the contractor/operator shall review and update the natural hazards assessments as necessary and shall conduct a review of the natural hazards assessment at least every 10 years.

MIL-HDBK-419A¹³ provides guidance for grounding, bonding, and shielding electronic equipment and facilities. The handbook is approved for public release, and distribution is unlimited.

NFPA 780¹⁴ provides guidance for the installation of lightning protection systems. Some of the issues addressed in the standard include installation requirements, a risk assessment guide, and ground measurement techniques.

References

1 DOE-STD-7501-95, Development of DOE Lessons Learned Programs.

2 National Lightning Safety Institute, 891 Hoover Ave., P. O. Box 778, Louisville, CO 80027-0778.

3 ALO-KO-SNL-NMSEC-1995-0003, "Partial Outage of the North Security Alarm System."

4 ID--WVNS-CF-1991-1003, "Site Power Outage - Due to Lightning Strike."

5 OH-FN-FERM-FEMP-1995-0089, "Loss of Honeywell System Due to Weather."

6 The Lightning Book, Peter E. Viemeister, 1972, The MIT Press, Cambridge, MA.

7 "Pictatinny Arsenal Historical Overview," Internet Address http://www.pica.army.mil/ pica/about/history.html#top3

8 SAND93-2517 UC-706, "Evaluation of the Electomagnetic Effects Due to Direct Lightning to Nuclear Explosive Areas at Pantex."

9 Science and Technology Review, May 1996, Lawrence Livermore Laboratory.

10 "The Lightning Safety Problem," Richard Kithil, President National Lightning Safety Institute, 891 Hoover Ave., P. O. Box 778, Louisville, CO 80027-0778.

11 National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

12 DOE O 420.1, Facility Safety.

13 MIL-HDBK-419A, Military Handbook Grounding, Bonding and Shielding For Electronic Equipments and Facilities. Naval Publications and Forms Center, 5801 Tabor Avenue, Philadelphia, PA 19120-5099.

14 NFPA 780, Standard For Installation of Lightning Protection Systems, 1995 Edition. National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

Notices Previously Issued

• Technical Notice 94-01, "Guidelines For Valves in Tritium Service," September 1994.
• Safety Notice 91-1, "Criticality Safety Moderator Hazards," September 1991.
• Safety Notice 92-1, "Criticality Safety Hazards Associated With Large Vessels," February 1992.
• Safety Notice 92-2, "Radiation Streaming at Hot Cells," August 1992.
• Safety Notice 92-3, "Explosion Hazards of Uranium-Zirconium Alloys," August 1992.
• Safety Notice 92-4, "Facility Logs and Records," September 1992.
• Safety Notice 92-5, "Discharge of Fire Water Into a Critical Mass Lab," October 1992.
• Safety Notice 92-6, "Estimated Critical Positions (ECPs)," November 1992.
• Safety Notice 93-1, "Fire, Explosion, and High-Pressure Hazards Associated with Drums and Containers," February 1993.
• Safety Notice 93-02, "Control of Temporary Modifications," September 1993.
• Safety Notice 94-01, "Contamination of Emergency Diesel Generator Fuel Supplies," July 1994.
• Safety Notice 94-02, "High-Efficiency Particulate Air Filters," August 1994.
• Safety Notice 94-03, "Events Involving Undetected Spread of Contamination," September 1994.
• Safety Notice 94-04, "Uninterruptible Power Supplies," November 1994.
• Safety Notice 95-01, "Decision Analysis Techniques," August 1995.
• Safety Notice 95-02, "Independent Verification and Self- Checking," September 1995.
• Safety Notice 95-03, "Lessons Learned Programs," October 1995.
• Safety Notice 95-04, "Post-Maintenance Test Programs," December 1995.
• Safety Notice 95-05, "Department of Transportation Non- Conformances by Vendor Shippers," December 1995.
• Safety Notice 96-01, "Chemical Spills During Loading," April 1996.
• Safety Notice No. 96-02, "Risk-Based Analysis of Electrical Hazard," May 1996.
• Safety Notice No. 96-03, "Compressed Gas Cylinder Safety," June 1996.

This Notice is one in a series of publications issued by the Office of Nuclear and Facility Safety to share nuclear safety information throughout the Department of Energy complex. For more information, contact Richard Trevillian, Office of Operating Experience Analysis and Feedback, Office of Nuclear and Facility Safety, U.S. Department of Energy, Washington, DC 20585, telephone (301) 903-3074. This Safety Notice should be processed as an external source of lessons-learned information as described in DOE-STD-7501-95, Development of DOE Lessons-Learned Programs.

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Safety Notices are distributed to U.S. Department of Energy Program Offices, Field Offices, and contractors who have responsibility for the operation and maintenance of nuclear and related facilities, and to other organizations involved in nuclear safety. Written requests to be added to or deleted from the distribution of Safety Notices should be sent to Christine Crow, RPI, 20251 Century Blvd., Germantown, MD 20874 or faxed to, (301) 540-2499.

The HSS Information Center maintains a file of Safety Notices and supporting information. Copies can be obtained by contacting the Info Center, (301) 903-0449, or by writing to HSS Information Center, U.S. Department of Energy, EH-72/Suite 100, CXXI/3, Germantown, MD 20874.

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(1) OEAF engineers screened the ORPS database using the Narrative search "lightning" and found 406 occurrences. OEAF engineers validated the occurrences and determined that 260 were actual lightning strikes.