Estimate vent line dia & PSV Pr. setting adjustment reqd to route 3 PSVs to 1 vent line going to atmosphere.?

The set pressure of the 3 PSV s is 3.5, 5.2 and 1.7 kg/cm2 respectively. The flash towers and stripper where these PSVs are located operates at 2.2, 3.6 and 0.34 kg/cm2. We have to connect discharge lines of the 3 PSV's to a common stack. What all constraints to be considered & how to overcome that in terms of HAZOP study?