Lightning protection: for field storage

Ground Warrior, August, 2008 by Chris Batchelor, Christopher Karabin, Steve Lengquist, Mike James

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How Powerful is Lightning? Each spark of lightning can reach over five miles in length, soar to temperatures of approximately 50,000 degrees Fahrenheit, and contain 100 million electrical volts. Lightning Is A Random, Chaotic And Dangerous Fact Of Nature

At any given moment, there are 1,800 thunderstorms in progress somewhere on the earth. This amounts to 16 million storms each year! We know the cloud conditions needed to produce lightning, but cannot forecast the location or time of the next stroke of lightning. There are lightning detection systems in the United States and they monitor an average of 25 million flashes of lightning from the cloud to ground every year!

Lightning strikes at ammunition storage areas are not uncommon. The most famous and most costly single bolt of lightning occurred on July 10, 1926, in northern New Jersey. This bolt struck the Naval Ammunition Depot at Lake Denmark, triggering a series of explosions that ended in a major catastrophe. All buildings for half a mile were destroyed, debris fell 22 miles away, and 16 people lost their lives.

Since the Lake Denmark explosion vast improvements in Lightning Protection Systems (LPS) have been made. LPS standards are outlined in NAVSEA OP 5 Volume I and National Fire Protection Association (NFPA) 780. These standards provide invaluable information on the installation of an LPS on magazines and operating buildings however, provide little information for the protection of ammunition stored in a tactical environment.

The Marine Corps/Navy constantly trains with ammunition and explosives in a tactical environment. This training is invaluable in preparing Marines/Sailors in their primary mission which, is to close with, and destroy the enemy by fire, and maneuver. This mission is primarily achieved by the employment of ammunition and explosive ordnance. To accomplish this, Marines and Sailors on the battlefield must have direct access to their ammunition and explosive ordnance. The sterile storage and operating conditions enjoyed at Naval Installations are not available during contingency operations at forward operating bases.

In the inherently dangerous combat environment, ammunition and explosives are often stored, handled, packaged and transported in a manner not compatible with their design, in order to support mission needs. The result of a lightning strike at a combat storage area is heightened due to the condition of the ammunition, unpackaged and in a ready to fire configuration. The operational environment is fast paced and sometimes safety is sacrificed in order to accomplish the mission. Accomplishing the mission is critical, but loss of life and property can also lead to mission failure through destruction of essential assets. Loss of ammunition assets due to a lightning strike could have catastrophic effects and jeopardize the success of the mission. While it is not practical to install an LPS at every operational location where ammunition and explosives are stored, consideration must be given to locations where major ammunition supply points (ASP) are constructed at forward operating bases (FOB). The intent of this paper is to provide a means to install a Lightning Protection System for the most common types of materials used to construct an ASP, field barricades or HESCO Barriers. This system has been adapted from NFPA 780. This design meets the intent of NFPA 780 and NAVSEA OP-5.

In the interest of minimizing the equipment and supplies required to install an LPS, the design has been limited to use 1/0 bare copper cable and 10 foot ground rods. In addition, this guidance should only be applied to barricades that have span across the cell less than 60'. For the purpose of this design, an LPS can be defined by three distinct subsystems, (1) Air Termination/ Strike Intercept, (2) Down Conductors or Current Carrying/Controlling, and (3) Earth Electrode System/Grounding.

1. The Air Termination system is commonly comprised of air terminals or lightning rods. Lightning rods are generally arranged in an array pattern over the structure to be protected. The array is spaced to conform to the 100' rolling ball method to ensure coverage and protection for the structure. This design intends to implement standard 10 foot ground rods as air terminals to minimize the number of components needed to be stocked for a field deployed unit.

2. The Current Carrying system is designed to provide multiple paths for the lightning currents to follow to ground. The current carrying system is sized and installed to minimize the impedance from the air terminals and the earth electrode system.

3. The Earth Electrode System (EES) is intented to dissipate the lightning current safely in the ground, thereby preventing damage to the structure. The EES must provide a low impedance connection with Earth with sufficient capacity to quickly dissipate the lightning current into the Earth.

All bonding and electrical connections must conform to NAVSEA OP-5. Electrical testing and inspection for the systems shall conform to guidance provided in OP-5.