To remove the requirement in Sentences 4.3.7.3.(1) and (2) to add a 10% safety factor in calculating the capacity of secondary containment if the containment is designed to prevent the entry of precipitation and water used for firefighting into the contained space.
This is to limit the probability of liquid overflow and escape, which could lead to the ignition of vapour from a nearby ignition source, which could lead to damage to the building or facility.