49 CFR § 173.29 - Empty packagings.
(a) General. Except as otherwise provided in this section, an empty packaging containing only the residue of a hazardous material shall be offered for transportation and transported in the same manner as when it previously contained a greater quantity of that hazardous material.
(1) Any hazardous material shipping name and identification number markings, any hazard warning labels or placards, and any other markings indicating that the material is hazardous (e.g., RQ, INHALATION HAZARD) are removed, obliterated, or securely covered in transportation. This provision does not apply to transportation in a transport vehicle or a freight container if the packaging is not visible in transportation and the packaging is loaded by the shipper and unloaded by the shipper or consignee;
(2) The packaging—
(i) Is unused;
(ii) Is sufficiently cleaned of residue and purged of vapors to remove any potential hazard;
(iv) Contains only the residue of—
(A) A limited quantity material; or
(c) A non-bulk packaging containing only the residue of a hazardous material covered by Table 2 of § 172.504 of this subchapter that is not a material poisonous by inhalation or its residue shipped under the subsidiary placarding provisions of § 172.505—
(1) Does not have to be included in determining the applicability of the placarding requirements of subpart F of part 172 of this subchapter; and
(f) Smokeless powder residue when transported by motor vehicle or container/trailer in container-on-flatcar (COFC) or trailer-on-flatcar (TOFC) service is excepted from subpart C (shipping papers) and the subpart F (placarding) requirements of part 172 of this subchapter when transported in conformance with the following:
(1) The outer packaging must be:
(2) The amount of smokeless powder per outer packaging does not exceed 5 grams;
(g) A package which contains a residue of an elevated temperature material may remain marked in the same manner as when it contained a greater quantity of the material even though it no longer meets the definition in § 171.8 of this subchapter for an elevated temperature material.
(h) A package that contains a residue of a hazardous substance, Class 9, listed in the § 172.101 Table, Appendix A, Table I, that does not meet the definition of another hazard class and is not a hazardous waste or marine pollutant, may remain marked, labeled and, if applicable, placarded in the same manner as when it contained a greater quantity of the material even though it no longer meets the definition in § 171.8 of this subchapter for a hazardous substance.