Four people were sent to the hospital after inhaling fumes from a poisoned dog’s vomit at a veterinary clinic in Edwards, Colo.

According to the Vail Daily, a sickened dog was admitted to Vail Valley Animal Hospital on Dec. 7. The dog vomited while in the care of hospital staff, releasing toxic fumes from the rat poison the local fire department suspects the dog ingested.

The dog passed away and four people were sent to the hospital - three as a result of respiratory distress, and one because of precautionary measures, according to the news site.

Fire department investigators told the media they believe that the dog ingested rat poison containing zinc phosphate, which forms a poisonous gas - phosphine gas - when combined with water.

Investigators are still unsure how the dog was initially exposed to the poison.

Phosphine gas poisoning not an isolated incident

The CDC published a 2012 report on phosphine gas poisoning incidents in veterinary settings citing four separate incidents between 2006 and 2011. According to the report, two of the incidents were in Michigan, one occurred in Iowa, and one took place in Washington state.

The CDC advised that veterinarians and pet owners dealing with animals possibly poisoned by phosphine gas adhere to precautions outlined by the AVMA, which include:

• Keep upwind and above the animal’s level to avoid fumes.
• Induce the animal to vomit outdoors if possible.
• If the animal vomits indoors, immediately evacuate the area and contact the fire department.
• Seek immediate medical attention for anyone who is exposed to phosphine gas and exhibits signs or symptoms of poisoning.