For what you are discussing, the only mandatory requirements are those in OSHA 1910.106 paragraph (b)(2) and OSHA 1926.152 paragraph (I)(2)(vi). OSHA reg's apply to US facilities, and you can access them on the internet. The two reg's I mention have an elevation requirement (12') which applies to storage tanks that are "adjacent to buildings or public ways", therefore they only apply to a limited number of tanks in a refinery or chemical plant.
There is a big difference between a combustible liquid and a flammable liquid - you are clear that this is only combustible ? For example, diesel is classified as being combustible for cases where anything in its near environment does not enable it to exceed 55-60degC; when T > 60degC, it is classified as flammable for its service application.
So does this liquid become flammable with any equipment or environment it may come into contact with inside the building if the tank does overflow?
