Lumber Bridge, N.C. — The U.S. Chemical Safety Board doesn't have the resources to investigate a weekend ammonia leak at a Robeson County chicken processing plant that killed one worker.

Authorities said a high-pressure line appears to have ruptured Saturday morning at Mountaire Farms, 17269 N.C. Highway 71, in Lumber Bridge. As many as 40 workers evacuated the building as the rupture released anhydrous ammonia gas, which causes burning and swelling of the air passages in the nose, throat and lungs.

Mechanic Clifton Swain, 49, of Fayetteville, died in the accident, authorities said. Four other workers, whose identities haven't been released, were taken to hospitals.

One worker remained in critical condition Monday in the North Carolina Jaycee Burn Center at UNC Hospitals in Chapel Hill. Another victim was hospitalized at Southeast Regional Hospital in Lumberton, but a condition update wasn't available.

Daniel Horowitz, a spokesman for the Chemical Safety Board, said the agency, which investigates chemical accidents nationwide and develops recommendations to improve workplace safety, has 20 investigators to cover the entire country. The CSB already has 10 or 11 open investigations, including the June 9 explosion at the ConAgra Foods plant in Garner, he said.

Investigators have said a natural gas leak inside the ConAgra plant likely caused the explosion, which killed three and injured dozens. Four CSB investigators from the agency's Denver office have been assigned to the case and are expected to be in Garner for several weeks, which leaves nobody available to look into the Mountaire ammonia leak, Horowitz said.

Officials would like to investigate the Mountaire Farms incident, Horowitz said, but agents usually can't do so effectively if too much time elapses between the incident and the start of the investigation.

The CSB gets about 1,000 requests for investigations each year, and officials have to screen for the most serious ones to allocate their resources properly, he said.

Workers return to plant

Mountaire Farms reopened the plant Monday, saying authorities had inspected the plant and declared it safe. The plant employs about 2,500 people, and Millsboro, Del.-based Mountaire Farms said it planned to hold an internal employee meeting Monday and provide grief counselors for workers.

"Everybody's spirits are kind of down because they knew the guy that got killed," employee Reggie Richardson said.

"We have to (get back to work)," employee Dock Caldwell said. "Everybody's a little nervous, but we try to do the best we can."

Robeson County Sheriff Kenneth Sealey said a preliminary investigation showed the ammonia leak was accidental. Employees were replacing an inner sleeve on a machine used to process chicken when the ammonia line ruptured.

A spokesman for the state Department of Labor said determining what caused the leak could take three to six months. The State Bureau of Investigation, federal Bureau of Alcohol, Tobacco, Firearms and Explosives and the Occupational Safety and Health Administration are assisting in the investigation.

Since 2005, state and federal regulators have cited the plant for 19 workplace safety violations, including 15 in an inspection report dated April 21. Fines totaled $19,600.

Nine of those violations were labeled serious, and some involved standards for controlling hazardous energy and guarding floor and wall openings. Those areas could have something to do with ventilation. Other violations involved noise and sanitation standards.

"We take all OSHA regulations seriously, and our priority is to meet or exceed every workplace safety standard or guideline," Mountaire Farms spokesperson Chris Shigas said in a statement. "We have been working closely with OSHA to respond to the issues noted in the 2009 report. Our policy is to cooperate with regulators and work in conjunction with them to provide the safest workplace possible for our employees."

Workers said they had a hard time getting information from company officials about Saturday's incident.

"We have some employees that feel kind of upset about what happened and want to know more about it, but (managers are) not giving out information,” Caldwell said.

“It’s been hush-hush,” Richardson said. “They don’t want to make people feel uncomfortable.”