49 CFR §393.69

1. (a)A fuel system that uses liquefied petroleum gas as a fuel for the operation of a motor vehicle or for the operation of auxiliary equipment installed on, or used in connection with, a motor vehicle must conform to the “Standards for the Storage and Handling of Liquefied Petroleum Gases” of the National Fire Protection Association, Battery March Park, Quincy, MA 02269, as follows:
   1. (1)A fuel system installed before December 31, 1962, must conform to the 1951 edition of the Standards.
   2. (2)A fuel system installed on or after December 31, 1962, and before January 1, 1973, must conform to Division IV of the June 1959 edition of the Standards.
   3. (3)A fuel system installed on or after January 1, 1973, and providing fuel for propulsion of the motor vehicle must conform to Division IV of the 1969 edition of the Standards.
   4. (4)A fuel system installed on or after January 1, 1973, and providing fuel for the operation of auxiliary equipment must conform to Division VII of the 1969 edition of the Standards.
2. (b)When the rules in this section require a fuel system to conform to a specific edition of the Standards, the fuel system may conform to the applicable provisions in a later edition of the Standards specified in this section.
3. (c)The tank of a fuel system must be marked to indicate that the system conforms to the Standards.