49 CFR § 173.320 - Cryogenic liquids; exceptions.
(a) Atmospheric gases and helium, cryogenic liquids, in Dewar flasks, insulated cylinders, insulated portable tanks, insulated cargo tanks, and insulated tank cars, designed and constructed so that the pressure in such packagings will not exceed 25.3 psig under ambient temperature conditions during transportation are not subject to the requirements of this subchapter when transported by motor vehicle or railcar except as specified in paragraphs (a)(1), (a)(2), and (a)(3) of this section.
(1) Sections 171.15 and 171.16 of this subchapter pertaining to the reporting of incidents, not including a release that is the result of venting through a pressure control valve, or the neck of the Dewar flask.
(2) Subparts A, B, C, D, G and H of part 172, (§§ 174.24 for rail and 177.817 for highway) and in addition, part 172 in its entirety for oxygen.
(b) The requirements of this subchapter do not apply to atmospheric gases and helium:
(1) During loading and unloading operations (pressure rises may exceed 25.3 psig); or
(2) When used in operation of a process system; such as a refrigeration system (pressure may exceed 25.3 psig).