Billing Code - PHMSA - Department of Transportation

transportation of shipments UN2211 and UN3314. To address the concerns presented by
off gassing of flammable vapors which lead to a rise in pressure that may damage cargo
transport units, the IMO instituted measures to ensure an adequate exchange of air within
the cargo transport unit is provided. PHMSA is harmonizing with the recent changes to
the IMDG and addressing safety concerns presented by the off gassing of flammable
vapors from shipments of UN2211 and UN3314 by requiring that when UN2211 or
UN3314 are transported by vessel, the cargo transport unit must provide an adequate
exchange of air. This adequate exchange of air may be accomplished by using a ventilated
container, an open-top container, or a container in one door off operation. As an
alternative to these methods of air exchange, shippers may transport these cargos under
temperature control in refrigerated cargo transport units. Exceptions to the cargo transport
unit providing an adequate exchange of air requirement are provided for shipments packed
in hermetically sealed packagings or IBCs which conform to the packing group II
performance level for liquid dangerous goods in which the total pressure in the package
(i.e., the vapor pressure of the liquid plus the partial pressure of air or other inert gasses
less 100 kPa (15 psia)) with a filling temperature of 55° C (131° F) does not exceed two-
thirds of the marked test pressure. Cargo transport units containing shipments of UN2211
or UN3314 must be marked with a warning mark including the words “CAUTION- MAY
CONTAIN FLAMMABLE VAPOR” or “CAUTION- MAY CONTAIN FLAMMABLE
VAPOUR” with lettering not less than 25 mm high. This mark must be affixed at each
access point in a location where it will be easily seen by persons prior to opening or
entering the cargo transport unit and must remain on the cargo transport unit until the cargo
transport unit has been completely ventilated to remove any hazardous concentration of
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