Abstract: On April 2, 2002, Employee #1 and a coworker, employees of a water treatment plant as waste water treatment operators, were changing out five 1-Ton cylinders, located in a chlorine cylinder room. Employee #1 attempted to disconnect the yoke number two of the five 1-Ton cylinders, but a high pressure leak of chlorine gas escaped from the cylinder into his breathing zone. Employee #1 was able to immediately tighten the yoke connection, stopping the leak, but required the coworker to finish the task. With Employee #1 sitting to the side, the coworker, after a couple of attempts, was able to disconnect the yoke connection without any further chlorine gas escaping. After notifying management of the incident, the coworker drove Employee #1 to Antelope Valley Hospital Emergency Room. Once admitted, Employee #1 was treated for chlorine gas exposure and diagnosed with bilateral lower lobe pneumonia.