An employee had completed his lockout/tag-out procedure after cleaning the central cement batch mixer. He closed the central cement batch mixer, removed all locks and tags, and re-energized the central power source of the central cement batch mixer. He heard a strange noise coming from inside the mixer, so he shut down the mixer's power source, followed lockout/tag-out procedures, opened one of the hatches at the top of the batch mixer, and noticed a hammer inside of the central cement batch mixer. When he reached into the mixer to retrieve the hammer, the paddle struck the right side of his head, fracturing his face and partially amputating his right ear lobe. He was hospitalized.