MSHA - Code of Federal Regulations - 30 CFR 77.208
30 CFR § 77.208
Storage of materials.
(a) Materials shall be stored and stacked in a manner which minimizes
stumbling or fall-of-material hazards.
(b) Materials that can create hazards if accidentally liberated from
their containers shall be stored in a manner that minimizes the dangers.
(c) Containers holding hazardous materials must be of a type
approved for such use by recognized agencies.
(d) Compressed and liquid gas cylinders shall be secured in a safe
manner.
(e) Valves on compressed gas cylinders shall be protected by covers
when being transported or stored, and by a safe location when the cylinders
are in use.