LAYTON — A 4-year-old Layton girl died Saturday night from what officials believe may have been ingestion of a toxic gas emitted by rat poison pellets.

Firefighters were called to the family's home near 1500 North and 2400 West around 2:30 p.m. Friday when the family's carbon monoxide alarm went off. Although fire officials detected trace amounts of carbon monoxide, Questar Gas representatives were unable to find any concentrations of the gas.

The family was allowed to return to their home, but within 24 hours, the youngest two children began feeling ill. Neighbor Ashley Cornia said she saw an entry on the family's Facebook page that the parents thought some of the kids had food poisoning because they began vomiting.

The 4-year-old, whom neighbors identified as Rebecca Toone, began experiencing breathing problems and was taken to the Wee Care pediatric clinic in Layton. Layton police said the girl went into respiratory distress and then cardiac arrest and was rushed to the adjacent Davis Hospital and Medical Center where she died.

Initial reports from the State Medical Examiner's Office show the girl had no carbon monoxide in her system. However, Layton Fire Battalion Chief Lonnie Adams said a pest control company had placed rat pellets in the ground around the family's home on Friday.

When the family's home was closed off Sunday for hazmat teams to investigate, the National Guard's 85th Civil Support team, which tested the home, found measurable amounts of phosphine gas, a fumigant commonly used in rodent control, in the air. Rat pellets often have a compound called aluminum phosphide, which, when wet, becomes a toxic gaseous substance called phosphine, which has no antidote. When the aluminum phosphide gas is inhaled, it can react with moisture in the lungs to become phosphine, which can cause blistering and edema, which can be fatal, according to the National Institute for Occupational Safety and Health Web site.

Adams said a carbon monoxide detector could possibly mistake one fume for another.

"We don't know what happened, but one theory is that the (aluminum phosphide) gas got in the house somehow," he said.

The Davis County Board of Health has ordered the house vacated while the situation is investigated.

Neighbors said their prayers and hearts go out to the family and that they were horrified to learn of the tragedy.

"She always had that smile on her face that would melt you," said neighbor Jerri Lynn Smith, who has a 3-year-old daughter who occasionally played with Rebecca.

Smith said the young girl would often follow her older sister around the neighborhood and was very friendly.

"We've known the family for six years," Smith said. "It's really a tragedy."

e-mail: lgroves@desnews.com