How to determine the cold vent volume at the water injection station

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There is an existing water injection project in an oil field. The flow sequence at the water injection station is as follows: oil removal tank – IGF feed pump – IGF (air flotation unit) – filter feed pump – walnut shell filter – buffer tank – water injection pump. To ensure water quality, the oil removal tank, IGF unit, and buffer tank are all sealed using the associated gas produced in the oil field (the natural gas separated from the fluid). In addition to inlet pipelines, these devices are also equipped with PVSV valves connected to cold vent pipelines. How can the maximum discharge capacity of these cold vent pipelines be determined? This is how I think about it: the maximum discharge volume from the cold vent line should occur when the downstream feed pump stops operating suddenly (with liquid flowing in but no liquid flowing out). Is it incorrect to consider the sum of the breathing capacity of the buffer tank and the discharge volume of the pump? In this process, does it still necessary to consider the breathing volume of the degreasing tank and IGF? If considered in this way, the amount of leakage would be very large, because there are several oil removal tanks and buffer tanks, all of which have large capacities, resulting in a very high thermal venting capacity. I would be extremely grateful if experts and colleagues could provide some guidance!