Minimum N2 flow in relief header to prevent reverse flow

[DJK2]

I'm looking at a 24" relief header which goes to a knock out pot before entering a scrubber. The knock out pot contain a corrosive medium and we would like to prevent the acidic gases diffusing back into the relief header.

At the moment I'm thinking 2 to 3 cm/s should be enough but I was wondering if there are any design guides or references out there that deal with this issue?