Preloading a containment vessel with Low Vapor Pressure (LVP) liquid; partially evacuating the containment vessel to generate a vacuum in a headspace above the LVP liquid; and relieving material from a process vessel into the containment vessel during a process relief event in the process vessel. The containment vessel pressure may be equalized with ambient conditions prior to preloading the LVP liquid. The containment vessel size and quantity of LVP liquid may be determined to absorb the energy and mass of relieving fluids from the maximum anticipated relief scenario, permitting the gases to condense to liquid form to be recovered in liquid state instead of atmospherically venting or combusting the gases. The containment vessel headspace may be partially occupied with High Vapor Pressure (HVP) liquid comprising C5-C10 hydrocarbons configured to flash during the evacuation step to create and occupy a headspace, providing additional head space volume and heat rejection capacity.