49 CFR § 172.313 - Poisonous hazardous materials.
In addition to any other markings required by this subpart:
(a) A material poisonous by inhalation (see § 171.8 of this subchapter) shall be marked “Inhalation Hazard” in association with the required labels or placards, as appropriate, and shipping name when required. The marking must be on two opposing sides of a bulk packaging. (See § 172.302(b) of this subpart for size of markings on bulk packages.) When the words “Inhalation Hazard” appear on the label, as prescribed in §§ 172.416 and 172.429, or placard, as prescribed in §§ 172.540 and 172.555, the “Inhalation Hazard” marking is not required on the package.
(b) Each non-bulk plastic outer packaging used as a single or composite packaging for materials meeting the definition of Division 6.1 (in § 173.132 of this subchapter) shall be permanently marked, by embossment or other durable means, with the word “POISON” in letters at least 6.3 mm (0.25 inch) in height. Additional text or symbols related to hazard warning may be included in the marking. The marking shall be located within 150 mm (6 inches) of the closure of the packaging.
(c) A transport vehicle or freight container containing a material poisonous by inhalation in non-bulk packages shall be marked, on each side and each end as specified in § 172.332 or § 172.336, with the identification number specified for the hazardous material in the § 172.101 table, subject to the following provisions and limitations:
(1) The material is in Hazard Zone A or B;
(2) The transport vehicle or freight container is loaded at one facility with 1,000 kg (2,205 pounds) or more aggregate gross weight of the material in non-bulk packages marked with the same proper shipping name and identification number; and
(3) If the transport vehicle or freight container contains more than one material meeting the provisions of this paragraph (c), it shall be marked with the identification number for one material, determined as follows:
(i) For different materials in the same hazard zone, with the identification number of the material having the greatest aggregate gross weight; and