Officials say the use of a heater in a Detroit-area hotel room raised carbon monoxide levels to a dangerous high, causing a couple and their dog to pass out and forcing the evacuation of the establishment.

Warren Mayor James Fouts says the couple visiting from Colorado were found unresponsive Monday at the Hawthorn Suites north of Detroit. WWJ-AM reports the couple is expected to be OK. The dog is expected to recover.

Consumers Energy spokesman Roger Morgenstern tells The Detroit News that initial carbon monoxide readings were about 400 parts per million, which could be fatal. The levels dropped by the time utility crews arrived.

The hotel's general manager Dean Jamoua told WJBK-TV it's not clear why the heat was on, since temperatures outside were in the 90s.