MSHA - Code of Federal Regulations - 30 CFR 56.4130
30 CFR § 56.4130
Electric substations and liquid storage facilities.
(a) If a hazard to persons could be created, no combustible materials
shall be stored or allowed to accumulate within 25 feet of the following:
(1) Electric substations.
(2) Unburied, flammable or combustible liquid storage
tanks.
(3) Any group of containers used for storage of more than
60 gallons of flammable or combustible liquids.
(b) The area within the 25-foot perimeter shall be kept free of dry
vegetation.
