Closure Notification Requirements
Pipeline and Hazardous Materials Safety Administration · Oct 12, 2006 · Reference No. 06-0180
Interprets: 49 CFR § 173.22
Reggie’s quick take
A company that makes solid carbon dioxide asked whether its product, which has extra ozone added during manufacturing, can still ship as "Carbon dioxide, solid or Dry ice" (UN 1845) even though the ozone level is above normal and may not meet the definition of a Division 2.3 gas. PHMSA said the shipper must classify and describe the material under §173.22, and that the agency does not make that determination. PHMSA added that if the shipper finds the ozone does not meet any hazard class or division in the HMR, including Division 2.3, and the material is not a hazardous substance or hazardous waste, then UN 1845 is the proper name.
Written by AI (Claude) on Oct 22, 2026. Robots make mistakes and leave things out, so the letter below is what counts. Not legal advice.
This is in response to your August 1, 2006 letter regarding the proper classification, description, and associated transportation requirements for materials under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180). Specifically, you state your product, solid carbon dioxide, contains an ozone concentration which is above the typical naturally-occurring concentrations and has been added to your product during the manufacturing process. You ask whether, because the ozone concentration in your material does not meet the definition of a Division 2.3 gas, the proper shipping name, "Carbon dioxide, solid or Dry ice" (UN 1845) is the proper classification and description of your material.
Section 173.22 of the HMR requires a shipper to properly class and describe the hazardous material in accordance with Parts 172 and 173 of the HMR, and to determine that the packaging or container is an authorized packaging in accordance with Part 173. This Office does not perform that function. However, if you determine that the ozone concentration does not meet the definition of any hazard class or division in the HMR, including Division 2.3, and is not a hazardous substance or hazardous waste, "Carbon dioxide, solid or Dry ice" (UN 1845) would be the proper classification and description of your material.
A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.