Mountain Fuel and fire investigators Friday were trying to determine the cause of a foul smell in Salt Lake County's emergency phone center that sent eight people to the hospital.

Dispatchers in the Emergency Operation Center, which handles calls made to the 911 emergency number, reported a nasty smell Thursday night. The smell caused dispatchers in the center and the Salt Lake County sheriff's office to suffer nausea, shortness of breath and headaches, said City Fire Department Battalion Chief Jim Kleine."The specific cause of why people are nauseated at this time is unknown to us," Kleine said.

Emergency calls go through the switchboard in the center, located in the basement of the Metropolitan Hall of Justice on Third East and Fourth South. Dispatchers then route the calls to the appropriate agencies.

"Anybody who calls 911 in Salt Lake County calls here," said Kleine. "It's impossible to abandon this system."

Firefighters and Mountain Fuel workers used sophisticated measuring instruments to determine what caused the foul smell, first noticed about 7:30 p.m. Thursday. Five sheriff's dispatchers and three emergency dispatchers were treated and released from Holy Cross Hospital.

Mountain Fuel was called in to assist in the monitoring, since the natural gas supply company has sophisticated equipment to detect leaks.

"Nothing absolutely certain was ever determined," said Mountain Fuel spokeswoman Louise Jacobsen. "But Mountain Fuel did pick up some carbon monoxide," which coupled with the odor may have contributed to making the employees ill.

Crews investigated the air-handling system in the basement phone offices. "And they found that the way it is set up, the portion that serves the dispatch area is capable of pulling in air from the underground garage. And there were some cars idling in that," Jacobsen said.

"Nobody really knows. They just weren't able to determine for sure that anything else was there. But the symptoms they were complaining of could be attributed to carbon monoxide," she said.

The parking area and jail are near the county dispatch center. No problems were reported in the jail.

"We are going to send someone in there about 3:30, about the time they have a shift change when there are more vehicles running in the garage just to see if we can pick up if that was the probable cause," Jacobsen said.

One dispatcher in the 911 section refused to leave, and bottled oxygen was brought down as she showed members of the Fire Department's Hazardous Materials team how to operate the switchboard.

"All the emergency numbers come in here," Kleine said. "If she walks away, no one's there to answer the phones."

Kleine said city fire personnel had received no additional reports of anyone becoming ill during the night. No emergency units were dispatched after 10 p.m. Thursday, he said.

Efforts made to correct the problem included forcing air from the outside into the building. Also, personnel from a hazardous-materials unit took samples of air inside the building, and city building maintenance personnel changed all air conditioning system filters before starting up the system. No toxic materials were found. After that and other efforts were made, city personnel retired for the night, Kleine said.

Kleine said attempts made to find the source of odor may have corrected the problem. It may have just been a freak occurrence that has gone away, he said. Any further efforts are the responsibility of the County Fire and City-County Health Departments, Kleine added.