Evaluation of Lightning Hazards to Munition Storage Handling and Maintenance Facilities with the Use of Advanced Methods for Solutions of Maxwell's Equations

Munition storage, handling, and maintenance facilities consist of a variety of structures. They include buried rebar re-enforced concrete walled igloos of several types as well as above-ground buildings. One of the safety hazards of concern is the protection of these munitions from the effects of lightning. These structures are electromagnetically complex because they consist of a variety of inhomogeneous materials (e.g., concrete with rebar) which may be either conducting or partially conducting. In addition, the structures usually have metallic penetrations such as electrical cables or plumbing, as well as a lightning protection system including an earth-ground of some type. The objective of this paper is to describe how the lightning hazards to such structures can be evaluated using advanced formulations of Maxwell's Equations. The method described is the Three Dimensional Finite Difference Time Domain Solution. It can be used to solve for the lightning interaction with such structures in three dimensions and includes a considerable amount of detail. Examples of lightning strikes to buried igloos and above ground buildings are presented. The results include the voltages and currents induced on conductors which penetrate the facility, as well as the internal electric and magnetic fields. Possibilities for internal arcing are described. These results can then be used to evaluate the possible hazard to materials stored inside. Of special interest is the evaluation of the effectiveness of earth-ground systems and how they affect energy penetration to the facility interior. See also ADA235005, Volume 1. Published in the Minutes of the Explosives Safety Seminar (24th) held in St. Louis, MO on 28-30 August 1990 (p853-866).