Abstract: Confinement houses such as those housing poultry or hogs are artificially ventilated. To provide fresh air, there are openings along the walls. To control the amount of effective opening, fabric curtains are provided to cover the openings to varying degrees, depending on the inside conditions. The curtain opening is manipulated by a linear actuator and a manual hand-crank. When the power grid is interrupted for more than a moment, ventilation fans stop and the livestock become in danger of asphyxiation. As a fallback strategy, the curtains are opened fully by releasing the manual hand-crank, permitting it to spin as the curtains fall open under their own weight. A tension device such as a cord, chain, cable, string or wire runs between the manual hand-crank and a safety ventilation curtain release device. The safety ventilation curtain release device will release the tension device when the power grid has been off for a predetermined time.