Example - for a 3-bedroom, 2,000-sq.ft. home, with an exhaust-only ventilation strategy, and a target ventilation rate of 50 CFM you would need to install a 50 CFM fan with an adjustable-speed DC motor for continuous operation.
Quick Answer. Trenches were built during World War I to protect stalemated troops on both sides from artillery and rifle fire. Although the war began with rapid movement of the German army, when the Allied forces stopped the Germans, both sides dug trenches to help avoid losing territory they had gained.
Excavation â self dug hole. Trenches in World War I 1. Used to protect soldiers from enemy fire in the fields 2. Used extensively during World War I 3. Came out of necessity because of improved weapons, particularly: better rifles, machine guns, and tanks. Impact of technology during World War I 1. Allowed for weapons to fire from greater distances 2.