Ground traffic was crawling and commercial airline traffic was stalled at the Salt Lake International Airport Friday because of dense fog that shrouded most of the western half of the state.

Without fog seeding operations, which continued throughout the night, it is doubtful that any aircraft could have landed or taken off from runways, airport officials said.Frank Ratliff, airport operations manager, said commercial aircraft were taking off and landing with no apparent problems until about 10 a.m. Friday, when a 45-minute gate hold was established. That means aircraft, mainly those departing, were being delayed because of the fog and inbound traffic.

William J. Alder, meteorologist in charge of the Salt Lake office of the National Weather Service, said visibility was down to about one-eighth of a mile at 10:20 a.m.

Many commercial and other aircraft were diverted to the Ogden-Hinckley Airport and other airports Thursday.

An employee at the Ogden airport tower said visibility was about two miles at that airport at 10:45 a.m. Friday.

Tower manager Dan Piper said earlier Friday that the airport picked up several aircraft diverted from Salt Lake or other airports Thursday night.

The foggy conditions, which are expected to improve by Sunday, prompted state health officials to warn Utahns of the possible health problems associated with the fog.

"The fogs brings typically high levels of fine dirt, which gets into the lungs. It can impair lung function and can cause disease," said Kenneth L. Alkema, director of Department of Environmental Health, Utah Department of Health.

Alkema said people at high risk are those with asthma, emphysema, and any other lung diseases. It is especially hard on the very young and the very elderly.