Without treatment, even those who survive experience problems, Weaver said. About half have new depression and anxiety. And without hyperbaric oxygen treatment, he said, half develop difficulty with cognitive thinking, which shows up within about six weeks.

Even with treatment, some people suffer permanent damage, Weaver said, so prevention is the most important tool. And that makes common sense all the more important — don't run machinery indoors and use carbon-monoxide detectors, which are inexpensive and very portable.

Weaver noted that many of the hotels that were involved in carbon-monoxide incidents have not since installed the devices, which can be placed in individual guest rooms or near the appliances that could emit carbon monoxide.

The Utah Hotel and Lodging Association did not return a call Wednesday afternoon.

So far, six states have enacted laws requiring carbon-monoxide alarms on hotel, motel and resort properties, although no state requires the device in all guest rooms. Vermont requires carbon-monoxide alarms in the hallways outside all sleeping rooms.

The study said that the risk from a one-night stay is small, but the more someone travels, the greater the lifetime-accumulated risk. The risk would "approach zero," the study said, "with effective carbon-monoxide prevention measures."

"I don't think I'm going to get poisoned in a hotel," Weaver said. "But I carry my carbon-monoxide alarm with me and hope it never goes off."

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E-mail: lois@desnews.com