Hopefully somebody can help me answer this question. If it is necessary to use a fire safe ball valve (approved to API 607) on a gas tank as a second closure what approval is required for the 1st closure valve (internal foot valve) if any? If the the internal footvalve does not need to be firesafe what is the justification for it?

I think that depends on your local regulations and the design codes and standards mandated by the local authorities.

The justification might be required (or thought as) 'redundancy' in this case simply an extra added safety :- two closed valves in series are safer than one.

Apart from this and the comments from others above, I have one more remark:

as most accidents have an element of human error: two valves in series will not contribute to added safety if one of them are left permanently open...

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