49 CFR §193.2905

1. (a)The following facilities must be surrounded by a protective enclosure:
   1. (1)Storage tanks;
   2. (2)Impounding systems;
   3. (3)Vapor barriers;
   4. (4)Cargo transfer systems;
   5. (5)Process, liquefaction, and vaporization equipment;
   6. (6)Control rooms and stations;
   7. (7)Control systems;
   8. (8)Fire control equipment;
   9. (9)Security communications systems; and
   10. (10)Alternative power sources.
2. (b)Ground elevations outside a protective enclosure must be graded in a manner that does not impair the effectiveness of the enclosure.
3. (c)Protective enclosures may not be located near features outside of the facility, such as trees, poles, or buildings, which could be used to breach the security.
4. (d)At least two accesses must be provided in each protective enclosure and be located to minimize the escape distance in the event of emergency.
5. (e)Each access must be locked unless it is continuously guarded. During normal operations, an access may be unlocked only by persons designated in writing by the operator. During an emergency, a means must be readily available to all facility personnel within the protective enclosure to open each access.