Residue of a Reportable Quantity
Pipeline and Hazardous Materials Safety Administration · Jun 7, 2002 · Reference No. 02-0100
Interprets: 49 CFR § 172.101
Reggie’s quick take
Someone asked whether an empty cargo tank truck that once carried Diuron, an environmentally hazardous substance shipped as UN3082 and regulated only because it met the reportable quantity (RQ), must still carry marks or placards. PHMSA said yes, that is correct: markings and placards may be removed once the tank no longer holds an RQ, provided the material was regulated only because of the RQ while the tank was full. The agency also said no rule has changed this. The RESIDUE placard was dropped for rail tank cars in 1996, and it never applied to cargo tank trucks.
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 further response to your request regarding the marking and placarding requirements under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) for an empty cargo tank motor vehicle that you previously stated was an empty tank car.
Specifically, you ask for confirmation of your understanding that an empty cargo tank motor vehicle that no longer contains a reportable quantity (RQ) of a hazardous substance is not required to be marked or placarded. You state that the material, transported as "Environmentally hazardous substances, liquid, n.o.s. (Diuron), 9, UN3082" was regulated when the cargo tank motor vehicle was full solely because it met the RQ of Diuron. You also ask whether any rulemakings were issued that changed this provision and whether the RESIDUE placard requirement still applies under the HMR.
You are correct in your understanding that markings or placards may be removed from an empty cargo tank motor vehicle that no longer contains an RQ of a hazardous substance, provided the material was regulated only because it met the RQ when the cargo tank was full. No rulemaking was issued to change this provision. With respect to the RESIDUE placard, the requirement for its use on tank cars (rail cars) was removed from the HMR in a final rule (Docket HM-216, 61 FR 28666) published on June 5, 1996 and effective October 1, 1996. The requirement to use the RESIDUE placard was not applicable to cargo tank motor vehicles.
I hope this information is helpful. Please contact this office if we can be of further assistance.
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.