What terminates an exhaust duct system?

Termination of exhaust ducting can be of several choices, if vertical, vertical discharge damper allowing the damper to open with the force of extract air, this too relying on the exhaust air to stop rain entering, when system shuts down (no discharge of air) the damper relying on gravity closes to prevent rain or foreign matter birds, etc.. to enter, a China mans hat (not at all approved), a wind cowl that turns to favour the wind or a 135 degree bend complete with wire mesh grill, 135% selected to impede any rain that falls less than an angle of 45 degrees. Horizontal discharge can be terminated with either a fix bladed Louvre or an anti blow back bladed Louvre. On no account any discharge to emit to areas where people assemble or walk. Termination if vertical must exceed roof height and not to discharge onto roof. If offending odours to adjacent buildings or even noise of the system causes complaints you must consider installing attenuators (silencers) and carbon filters to eliminate the odours