Mystery fumes that cause nausea and headaches continued to plague Salt Lake County's emergency phone center Sunday night.

The fumes forced evacuation of the center Thursday night and affected workers on a smaller scale Friday as crews tried to pinpoint the source of the noxious odors.Salt Lake Sheriff's Lt. Dave Bishop said officials determined that the odors are not toxic but have been unable to determine their source. He said Sunday's problem was apparently solved by shutting down a fan.