A total of 19 workers at the Tri-State Generation & Transmission power plant were taken to The Memorial Hospital early Saturday morning after complaining of flu-like symptoms.
TMH Emergency Medical Service responded to calls a little after midnight Saturday and took seven welders to the hospital, Tri-State Communications Manager Jim Van Someren said.
The welders, who work for a subcontractor hired by Tri-State, were coughing and said they felt nauseous.
A short time later, 12 other welders said they were experiencing the same symptoms and were taken to the hospital in private vehicles, Van Someren said.
None of the 19 people suffered symptoms serious enough to be admitted to TMH, and all were treated and released by noon Saturday, Van Someren said.
The cause of the illnesses remains a mystery, he added.
Officials attempted to recreate the welders' work conditions and tested the space for any gases or chemicals, but all tests came back negative, Van Someren said.
Tri-State hired two Denver-area industrial hygiene firms to look into the incident, he added, but they had not uncovered any leads into what caused the welders' sickness as of Sunday night.
Fire Chief Bill Johnston said he also investigated the area but could not find anything that would have led to the workers' conditions.
Van Someren said the welders were helping with an ongoing $39 million environmental renovation to the plant's third power unit.
The project will allow Tri-State to generate an additional 30 megawatts of electricity from the unit without increasing emissions.
The welders' situation did cause a temporary work stoppage, but there won't be a lengthy project delay, Van Someren said.
The immediate area where the welders started to feel ill will be closed until late today or Tuesday, and officials installed additional ventilators as a precaution, Van Someren added. Industrial hygienists and Tri-State staff will continue to monitor the area for any signs of what may have caused the incident.
Van Someren said some of the workers had returned to the job by Sunday afternoon, and he expected the rest to return by Sunday night.
Tri-State plans to continue investigating the cause of the welders' illness, Van Someren said, adding he was unaware of anything like this ever happening before.
Collin Smith can be reached at 875-1794 or firstname.lastname@example.org.