49 CFR §174.300

1. (a)Class 3 (flammable liquid) materials may not be loaded, transported, or stored in a rail car equipped with any type of lighted heater or open-flame device, or in a rail car equipped with any apparatus or mechanism utilizing an internal combustion engine in its operation.
2. (b)A truck body or trailer which is loaded with a Class 3 (flammable liquid) materials and equipped with a lighted heater or any automatic heating or refrigerating apparatus may not be loaded on a flatcar except as provided in paragraph (c) of this section.
3. (c)Heating or refrigeration apparatus on a motor vehicle loaded with Class 3 (flammable liquid) materials may be operated while the motor vehicle is loaded on a flatcar only if:
   1. (1)The lading space is not equipped with any electrical apparatus that is not non-sparking or explosion-proof;
   2. (2)There is no combustion apparatus in the lading space;
   3. (3)There is no connection for the return of air from the lading space to any combustion apparatus; and
   4. (4)The heating system conforms to § 393.77 of this title and does not heat any part of the lading over 54 °C (129 °F).
4. (d)Metal barrels or drums containing Class 3 (flammable liquid) materials may be transported in a steel gondola or flatcar or in a stock car. However, they may not be transported in a hopper bottom car.