Dangerous Goods by Road
measures shall be taken to protect shells against the risk of deformation as a result of a negative
internal pressure. shells, other than shells according to 6.8.2.2.6, designed to be equipped with
vacuum valves shall be able to withstand, without permanent deformation, an external pressure of not
less than 21 kpa (0.21 bar) above the internal pressure. shells used for the carriage of solid substances
(powdery or granular) of packing groups ii or iii only, which do not liquefy during carriage, may be
designed for a lower external pressure but not less than 5 kpa (0.05 bar). the vacuum valves shall be
set to relieve at a vacuum setting not greater than the tank's design vacuum pressure. shells, which are
not designed to be equipped with a vacuum valve shall be able to withstand, without permanent
deformation an external pressure of not less than 40 kpa (0.4 bar) above the internal pressure.