I wonder what is the function of a cold vent system within an oil and gas production system?

Cold vent is when relief flows are directed to an unignited flare (we are not going to burn it but discharge directly to atmosphere). Of course requirements of safety applied here: the flaretip must be at certain distance from the platform, the discharge flow will have to reach some minimum velocity to make sure that the hydrocarbon being discharged and the air being well mixed and have a ratio lower than the flammable limit. Those values must be verified by rigorous calculations.