49 CFR 174.201
Class 2 (gases) material cylinders.
(a)Except as provided in paragraphs (b) and (c) of this section, cylinders containing Class 2 (gases) materials being transported in a rail car must be:#
(1)Securely lashed in an upright position so as to prevent their overturning;#
(2)Loaded into racks securely attached to the car;#
(3)Packed in boxes or crates of such dimensions as to prevent their overturning; or#
(4)Loaded in a horizontal position.#
(b)Specification DOT-4L (§ 178.57 of this subchapter) cylinders being transported in a rail car must be loaded in an upright position and be securely braced.#
(c)Cylinders containing Class 2 (gases) materials may be transported in stock cars, gondola cars and flat cars. However, they may not be transported in hopper bottom cars.#