Lightning Protection - Inherently Protected Above Ground Tanks

[Shells]

NFPA 780 states that metallic structures containing flammable substances that are electrically continuous and tightly sealed to prevent the escape of liquids, vapors and gases of 3/16" thickness or greater shall be inherently self protecting against lightning strikes. I am dealing with a tank that meets the criteria by design and currently does not have any dedicated lightning protection. There is a grounding ring around the tank. I have 2 questions:
1. Is a calculation of Lightning Strike Frequency/Threat of Occurrence still required to validate if lightning protection is required? I am not sure that one was done during the design phase.
2. By design, the tank is tightly sealed however over time we have developed some very small leaks (hydrocarbon) at random locations. I am just wondering if this could warrant a reevaluation of the need for lightning protection.
Any thoughts or advice on this would be appreciated.

Thanks

 

[paulengr]

The point is that you have a huge grounded surface at the bottom of the tank so adding grounding straps and such is a waste of time and money. You can’t measure it directly and NFPA is simply stating the obvious. Don’t care if you have leaks, etc.