Billing Code - PHMSA - Department of Transportation

and corresponding regulations to address the safe transport of such materials.
In this final rule, we are adopting entries in the HMT for various chemicals under
pressure and the corresponding packaging provisions. We are modifying § 173.313 to
include the packaging requirements for chemicals under pressure transported in portable
tanks. Specifically, we are revising the section title, introductory test, and table name to
reflect that chemicals under pressure are addressed in this section. We are also adding
table entries for identification numbers UN3500, UN3501, UN3502, UN3503, UN3504
and UN3505. Lastly, we are correcting the maximum filling density for UN3220.
The addition of packaging requirements specific to chemicals under pressure will
ensure that an appropriate level of safety is achieved for these unique materials. PHMSA
participated in, and concurs with, the discussions and decisions regarding the packagings
selected for these materials. The packagings adopted by the UN, ICAO and IMO provide
an appropriate level of safety for these materials and, thus, PHMSA is adopting similar
packagings in the HMR. Furthermore, aligning with international packaging standards
facilitates the movement of these materials both domestically and internationally.
Section 173.316
Section 173.316 provides the requirements for cryogenic liquids contained in
cylinders. Specifically, the HMR requires each cylinder containing cryogenic liquids be
equipped with one or more pressure relief devices.
PHMSA is revising § 173.316, “Cryogenic Liquids in Cylinders” to include a
requirement consistent with the UN Model Regulations that all pressure relief device inlets
must under maximum filling conditions be situated in the vapor space of the closed
cryogenic receptacle and the devices must be so arranged as to ensure that the escaping
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