ASME Div 1 vessel, so PSV is unavoidable - mount the PSV on some liquid nozzle since this has a diaphragm which makes it impossible for an air side PSV to work. Liquid relief rate must be the same as volumetric rate of steam generated during a fire. But also check if there are any tube rupture relief scenarios at chilled water HXs' that must be catered for at this PSV.
The diaphragm helps with reducing air consumption, so if you've got plenty of compressed air available, get rid of the diaphragm (or poke a hole in it), install a feedforward PCV to charge the tank, a backpressure PCV to normally relieve the tank, and then you can mount the firecase PSV on the vapor side to cater for the mass rate of steam generated.