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MUSCATINE, Iowa — Daniel Nitzel, a teacher at West Middle School in Muscatine, Iowa, came up with an idea from the school’s active shooter training.

He has invented “The Sleeve,” a 12-gauge carbon steel case that fits around the door’s closer arm, securing it from the inside. It can withstand more than 550 foot-pounds of force.

“We were instructed to tie a belt or a cord around the closer arm,” Nitzel said. “It seemed like a logical way to secure a door without having to go into the hallway, (but) it took us a long time to get a cord, stand on a chair and tie a knot, which could potentially be the most important tie of your life.

“I can tell you in our training, all five rooms that the teachers were trained in, the doors were breached, the cords were ripped and the officer who was portraying the active shooter came in and killed all of us.”

Read more at WQAD.