49 CFR § 172.302 - General marking requirements for bulk packagings.
(a) Identification numbers. Except as otherwise provided in this subpart, no person may offer for transportation or transport a hazardous material in a bulk packaging unless the packaging is marked as required by § 172.332 with the identification number specified for the material in the § 172.101 table -
(1) On each side and each end, if the packaging has a capacity of 3,785 L (1,000 gallons) or more;
(2) On two opposing sides, if the packaging has a capacity of less than 3,785 L (1,000 gallons); or
(b) Size of markings. Except as otherwise provided, markings required by this subpart on bulk packagings must -
(1) Have a width of at least 6.0 mm (0.24 inch) and a height of at least 100 mm (3.9 inches) for rail cars;
(2) Have a width of at least 4.0 mm (0.16 inch) and a height of at least 25 mm (one inch) for portable tanks with capacities of less than 3,785 L (1,000 gallons) and IBCs; and
(3) Have a width of at least 6.0 mm (0.24 inch) and a height of at least 50 mm (2.0 inches) for cargo tanks and other bulk packagings.
(c) Special permit packagings. Except as provided in § 173.23 of this subchapter, the outside of each package used under the terms of a special permit must be plainly and durably marked “DOT-SP” followed by the special permit number assigned. Packages authorized by an exemption issued prior to October 1, 2007 may be plainly and durably marked “DOT-E” in lieu of “DOT-SP” followed by the number assigned as specified in the most recent version of that exemption.
(1) Sufficiently cleaned of residue and purged of vapors to remove any potential hazard; or
(e) Additional requirements for marking portable tanks, cargo tanks, tank cars, multi-unit tank car tanks, and other bulk packagings are prescribed in §§ 172.326, 172.328, 172.330, and 172.331, respectively, of this subpart.
(f) A bulk packaging marked prior to October 1, 1991, in conformance to the regulations of this subchapter in effect on September 30, 1991, need not be remarked if the key words of the proper shipping name are identical to those currently specified in the § 172.101 table. For example, a tank car marked “NITRIC OXIDE” need not be remarked “NITRIC OXIDE, COMPRESSED”.
(g) A rail car, freight container, truck body or trailer in which the lading has been fumigated with any hazardous material, or is undergoing fumigation, must be marked as specified in § 173.9 of this subchapter.