Abstract: Employee #1, a machine operator, arrived at the beginning of his shift and began using an inner-layer etching machine. He did not check the machine's chlorine flow valve since it normally did not need adjusting. During the previous shift, janitorial workers had inadvertently bumped the valve to a higher-than-normal setting. As Employee #1's shift progressed, the etching machine became overchlorinated and began to release copper chloride fumes. Employee #1's lungs became irritated from inhaling the fumes and he was sent to the industrial clinic. He was transferred to Holy Cross Hospital for evaluation, then returned to work.