Computational assessment of mitigation of lightning-induced oil tank fires

Lightning strikes on oil tanks at oil storage facilities can result oil tank fires that lead to major financial losses. These oil tank fires appear to be caused by the large inductively generated electric fields in the gap between the floating roof and the sides of the oil tank. It has been proposed to eliminate these large electric fields through adding electrical shorts across the gap between the walls of the tank and the roof. However, some assessment of efficacy of these shorts is needed to have confidence in this methodology.

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Preliminary Results

VORPAL was used to do some preliminary calculations, computing the induced electric fields for a 30 cm computational resolution (understandably inadequate). These computations show qualitatively that adding shorts can result in a favorable reduction of the electric field in the gap. Animations produced from VORPAL data with and without the short appear below.

These are results from two different simulations, both with a lightning strike of the same form. The lightning current profile is shown in the upper left corner. On the left is a non-shorted oil tank, while on the right is the shorted tank. As the lightning strike progresses, surfaces of constant electric field are shown. The magnitude of the electric field is shown in the upper right, with the end of the scale being 1 MV/m. The simulations show that the peak electric field in the gap approaches 1 MV/m with no mitigation, but remains below 0.2 MV/m with when a short circuit is added.