By Frits Wybenga, Senior Technical Advisor

Inner Packaging Pressure Differential Requirements – WP/67.  As has been noted in several previous editions, DOT has for some time been concerned about the apparent failure of many shippers to comply with the pressure differential requirement applicable to inner packagings for liquids (see IATA 5.0.2.9).   In DOT’s experience, based on incident data and the Michigan State packaging analysis discussed in previous editions, leaks in air transport may be attributable in some instances to failure of the inner package to withstand pressure differentials encountered in air transport.  This occurs even though ICAO requires inner packagings for liquids to be capable of withstanding specified pressure differentials.  In spite of earlier efforts clarifying that a package’s ability to withstand pressure differentials must be verified by testing, DOT finds that incidents persist.

In WP/67, the US panel member – Bob Richard – provided a discussion paper on possible ways of simplifying and strengthening the requirements.  Noting that many shippers have difficulty in obtaining vapor pressure data for their products at 50C or 55C, the paper suggested dispensing with the vapor pressure considerations currently required to be taken into account in determining the appropriate pressure retention capability.  DOT also raised the question of whether the 95 kPa pressure differential limit was appropriate. DOT noted that the ICAO introductory text predicts a maximum pressure differential of 68 kPa at the higher altitudes flown by commercial aircraft.  (A separate proposal by the pilots recommended that this level be changed to 75 kPa.)

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