Scrubbers The fluid from reliefs, sometimes two-phase flow, must first go to a knockout system, where the liquids and vapors are separated. Liquids are subsequently collected and the vapors may or may not be vented. If the vapors are nontoxic and nonflammable, they may be vented unless some regulation prohibits this type of discharge. If the vapors are toxic, a flare (described previously) or a scrubber system may be required. Scrubber systems can be packed columns, plate columns, or venturi-type systems. Details of scrubber designs are covered by Treybal.ll C