Abstract: There are three inspections associated with this investigation. They are numbers 1299111, 1294521, and 1293967. This report is based on the information in report number 1293967. At 4:30 p.m. on January 31, 2018, Employee #1 was working for a building finishing contractor. He was at a jobsite using a welding rig. He was repairing metal hog pens within a hog confinement. This rig was manufactured by Hobart. It consisted of a generator/welder with a 305 cc (18.6 cubic inch) 19.7 Newton-meter (14.50 pound-foot) gross torque Brigg and Stratton Series 1450 gasoline combustion engine. Earlier that day, at approximately 3:30 p.m., Coworker #1 was working at the same facility. He was working for another contracting company. He had completed his shift for the day and went to use the restroom located within the jobsite's breeding room. He did not notice anything unusual upon entering the restroom. Shortly after he sat down on the stool, his heart began racing and he began having a difficult time breathing. Coworker #1 quickly exited the restroom and went back out into the breeding room, where he collapsed onto the ground. He was taken by Coworker #2 to the hallway, where his symptoms subsided. Coworker #1 stated that he did not know what had happened and thought he might have had a heart condition. With the assistance of other coworkers, Coworker #1 exited the area. At approximately 4:00 p.m. Employee #1 went to use the same restroom. He was in the restroom for approximately 20 minutes before his coworkers noticed that he had not returned. His coworkers, at the direction of company, went looking for him. A short time later, they found him in the restroom. He was unresponsive. He was sitting on the stool and slumped over an adjacent sink. He was foaming at the mouth with labored breathing. He had been potentially overcome with hydrogen sulfide, in combination with carbon monoxide from his welding activities. He was hospitalized as a result of this exposure to those gases. On February 2, 2018, he was pronounced dead. He had been welding from 6:00 a.m. until the time he went to use the restroom at 4:00 p.m., with only a short lunch break. The exposure to carbon monoxide during this activity, along with the presence of high levels of hydrogen sulfide, was thought to be the probable cause of this fatality.