At 11:00 a.m. on May 23, 2019, an employee removed a regulator from a chlorine gas cylinder to perform yearly maintenance and repacking. When the employee attempted the close the shutoff valve, the valve malfunctioned and stopped turning while still slightly open without the employee’s knowledge. When the employee removed the regulator, chlorine gas escaped. The employee removed himself from the area and donned a full-face respirator with total gas cartridges without inspecting the seals or valves. He proceeded to reenter the area to attempt to close the chlorine cylinder shutoff valve when he began fully, he became overwhelmed by the gas. The employee exited the area to catch his breath before reentry. He repeated this 2 to 3 times before successfully closing the shutoff valve. The employee then left the area, and a coworker called EMS. The employee suffered toxic exposure and chemical burns to the lungs and respiratory system and was hospitalized.