Abstract: An emergency ventilation system especially adapted for use with an electrically-powered fan driven ventilation system in an enclosed livestock confinement structure includes solenoid actuated, hydraulically driven ventilation door control apparatus which is responsive to the presence or absence of the delivery of commercial electrical power service to the main ventilation system for automatically opening or closing one or more spring biased access doors in lower regions of the structure in order to assure ventilation of the structure at all times, even in the event of electrical power failures. A hydraulic cylinder assembly for shifting the position of each of the doors is operated by a hydraulic control system provided with a normally closed, solenoid operated valve which is electrically connected with the commercial power lines delivering power to the main ventilation system.