Paragraph 4
In determining the subcriticality of individual packages in isolation for the purposes of this Schedule, it shall be assumed that water can leak into or out of all void spaces of the package, including those within the containment system. However, if the design incorporates special features to prevent such leakage of water into or out of certain void spaces, even as a result of human error, absence of leakage may be assumed in respect of those void spaces. Special features shall include the following:
Multiple high standard water barriers, each of which would remain leaktight if the package were damaged; a high degree of quality control in the production and maintenance of packagings; and special tests to demonstrate the closure of each package before shipment; or
Other features given multilateral approval.