Lumber Bridge, N.C.-A high-pressure line that ruptured during maintenance is being blamed for the ammonia release June 20 at the Mountaire Farms poultry processing plant here that killed one person and injured at least four. The victim was identified as a company mechanic who may have been working on the system at the time. One worker was in critical condition last week at a burn center in Chapel Hill, and another was still hospitalized in nearby Lumberton. Two were treated and released from the same hospital. As many as 40 people were evacuated because of concerns about the gas causing burning and swelling of the air passages in the nose, throat, and lungs. No one was available to speak for the company, but reports were that the plant, which employs about 2,500, reopened early last week after undergoing an inspection.