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On December 15, Emeritus Professor Les Hale of Penn State University presented a paper at the 2000 AGU fall meeting in San Francisco calling into question the validity of certain computer codes and mathematical formulations used to evaluate the threats of disruption of avionic equipment or even explosions due to lightning strokes in shielded enclosures such as computer boxes, aircraft hulls, or deep underground facilities. He asserts that lightning-related electric fields rapidly applied to metallic shielding, usually sheet metal, will penetrate much more deeply than predicted by the mathematical concept of skin depth or by commonly-used FDTD (Finite Difference Time Delay) computer codes, readily coupling into the enclosures.