Dangerous Goods by Road
independent safety valves capable of opening at the maximum working pressure indicated on the tank.
two of these safety valves shall be individually sized to allow the gases formed by evaporation during
normal operation to escape from the tank in such a way that the pressure does not at any time exceed
by more than 10% the working pressure indicated on the tank.
one of the safety valves may be replaced by a bursting disc which shall be such as to burst at the test
pressure.
in the event of loss of the vacuum in a double-walled tank, or of destruction of 20% of the insulation
of a single-walled tank, the combination of the pressure relief devices shall permit an outflow such
that the pressure in the shell cannot exceed the test pressure. the provisions of 6.8.2.1.7 shall not
apply to vacuum-insulated tanks.