From these accidents, the following phenomena and conclusions have been preliminarily drawn:
1) Most of it occurs at high liquid level, and direct lightning and induction lightning cannot be ruled out;
2) Combustible gas accumulates in the secondary sealed cavity and reaches the explosion limit range;
(3) The conductive sheets are all "covered";
4) Large external floating roof oil tanks have no high and medium frequency lightning current shunt facilities, and no medium and low frequency lightning current shunt facilities.
5) Current measures still have loopholes in lightning protection design and management, such as unqualified grounding resistance, inconsistent contact resistance between conductive sheet and tank wall, etc.