A technical rescue in Collin County turned into a recovery effort early Thursday afternoon.
Two men who dropped into a 60-inch sewer pipe Thursday morning to remove a 12-inch plug never surfaced.
Supervisor Jeronimo Cruz, 44, of Arlington, died in the pipe and was recovered late Thursday morning.
Firefighters and rescuers were still searching Thursday night for a second man whose name has not yet been released. Fairview fire Chief Dick Price said crews will continue to search through the night.
Price said search crews are using a sonar device to search the pipeline.
The men worked for S.J. Louis Construction of Texas and were in the final stages of a yearlong project for the North Texas Municipal Water District. Cruz was the first to go into the pipe to remove the plug. When he didn't surface, the second man on the crew went in after him.
At 8:04 a.m., when the second man didn't surface, the third man, who is Cruz's brother, grabbed a rope and called 911.
Rescuers arrived and quickly found and recovered Cruz's body. Unable to find the second man, officials worried that he had suffered the same fate as Cruz and was swept downstream by a mixture of fast-moving sewage and storm water.
At noon, officials shut off the flow of water in the pipe and continued their search for the man using cameras along the mile-long stretch of pipe stretching between the Thompson Springs subdivision to the nearby North Texas Municipal Water District facility.
Price said searchers do not believe the man was swept to the water treatment plant.
Officials said neither of the men were wearing respiratory devices and that it's likely they were either overcome by fumes or a lack of oxygen. Fairview Fire Chief Dick Price said it's standard procedure for those working in sewer lines to check the air quality before going in, but it wasn't clear if those checks were done.
"Our initial indications are that the oxygen level was probably insufficient to support their operation," Price said.
Cruz's brother told NBC 5 that he had also worked for S.J. Louis, but left because of what he described as unsafe working conditions. He said his brother was married and had five children.
There are 15 records of OSHA contact with the construction company in Texas, and 46 nationwide, over the past 10 years. Ten of the Texas incidents resulted in fines being assessed including a $51,000 fine for a 2010 investigation in Leander where a trench was not properly shielded to protect against a cave-in.
Cruz's 18-year-old son, Jeronimo Cruz Jr., said his father was a good man.
"He always wanted to work," he said. "He never had an excuse not to go to work."
He said his father was a hard worker who wanted to give his five children the best life possible.
"[He was] always telling me the right thing to do -- 'Finish school. Don't do this. Don't do that' -- you know, from right and wrong," he said.
It was originally believed the men went into a septic tank, but that was an error. The neighborhood uses septic systems, but the men were servicing a sewer line that runs back to a North Texas Municipal Water District facility, officials said.
NBC 5's Julie Tam, Ken Kalthoff, Randy McIlwain and Amanda Guerra contributed to this report.