A system and method controls a flow of vent gases to a combustion engine. The system includes an inlet for receiving the vent gases, a pressure relief device that enables the vent gases to escape to atmosphere when a pressure in the inlet exceeds a predetermined relief pressure, a flow-restricting orifice, and a back pressure regulator disposed downstream of the orifice. A shut-off valve disposed between the back pressure regulator and the air intake is set to only open when an intake pressure falls below a predetermined negative intake pressure.