Definition(s)
Action Integral
The joule or ohmic heating energy dissipated per unit resistance at the lightning attachment point. The action integral is measured in A2s (amperes-squared seconds), which is the same as JΩ-1 (joules per ohm) (Rakov and Uman, Lightning: Physics and Effects, p. 277).
Source: API RP 545 Recommended Practice for Lightning Protection of Aboveground Storage Tanks for Flammable or Combustible Liquids, First Edition, October 2009. Global Standards