A second worker in Wichita Falls, Texas, has died from exposure to concentrated hydrogen sulfide at the River Road Wastewater Treatment Plant. David Sheppard, a maintenance mechanic, died on Friday, July 22. His assistant, mechanic Daniel Arredondo, died on July 10 from the same incident.

On July 2, the two men were sent to work on a pipe valve that was leaking sludge into the plant’s basement. According to a timeline released by the city, a sensor alarm notified operators of a leak at 2:42 p.m. The mechanics were informed by operators that it smelled “gassy” in the area, and operators stated they observed Sheppard and Arredondo putting on protective gear. At 4 p.m., an operator checked with the mechanics, who were wearing protective gear at that time. The two men said they were going to pick up oxygen tanks from a storage area because their air was running low. The operator left to make plant rounds and returned at 5 p.m. when he found both men unconscious and not wearing protective gear. The air tanks were located in boxes at the top of the stairs. First responders were on site by 5:06 p.m.

Relief maintenance crews were called in to finished the repair. At that time, hydrogen sulfide levels registered 509 ppm.