To limit the probability that internal stress or mechanical damage will lead to failure of the valves, which could lead to the escape of liquid, which could lead to the ignition of vapour from a nearby ignition source, which could lead to harm to persons, including emergency responders.
To limit the probability that exposure of the valves to fire will lead to failure of the valves, which could lead to the escape of liquid, which could lead to the ignition of vapour from a nearby ignition source, which could lead to harm to persons, including emergency responders.