PHMSA provides written clarifications of the Hazardous Materials Regulations (HMR; 49 CFR Parts 100-185) in the form of interpretation letters. These letters reflect the agency's current application of the HMR to the specific facts presented by the person requesting the clarification. While interpretations are one form of guidance provided by PHMSA, they do not create legally-enforceable rights or obligations and are provided to help the public understand how to comply with the HMR. PHMSA regularly reviews interpretations on this site for accuracy and applicability. Letters of interpretation which are found to be inaccurate or no longer applicable are removed and may be revised and reissued if warranted. Letters which do not appear on this website may no longer be valid. We welcome feedback from the hazmat safety community to ensure the most recent and accurate letters of interpretation are provided here. Questions or concerns about a specific letter or topic should be directed to the Hazardous Materials Information Center (HMIC).
The HMIC is available Monday through Friday, 9:00 am to 5:00 pm (ET), except Federal holidays. After hours, you can leave a recorded message and your call will be returned during the next business day. Furthermore, if you would like to submit an interpretation letter request, please email it to: firstname.lastname@example.org or mail it to:
PHMSA Office of Hazardous Materials Standards
1200 New Jersey Avenue, SE.
Washington, DC 20590-0001