The future of a Montana animal shelter remains uncertain after a cloud of smoke from two pounds of methamphetamine seized by the FBI and incinerated filled up the building and sent workers to the hospital.

The smoke started to fill the building of the nonprofit Yellowstone Valley Animal Shelter in Billings on Wednesday while the FBI used an incinerator at the animal shelter to burn the drugs, city officials said.

Assistant City Administrator Kevin Iffland said Friday that the smoke was sucked in apparently because of negative pressure. A fan was supposed to be on hand in such situations to reverse the pressure so smoke would flow out of the building, but it wasn’t readily available.

The incinerator is used primarily to burn carcasses of animals euthanized or collected by the city’s animal control division. But every couple of months, local law enforcement or FBI agents use it to burn seized narcotics, Iffland said.

Fourteen animal shelter workers were evacuated and went to the hospital. The shelter’s 75 dogs and cats were relocated or put into foster homes, said Iffland and shelter director Triniti Halverson.

The shelter shares space with Billings’ animal control division. When smoke started filling parts of the building, Halverson assumed it was from burning carcasses because she said they had never known about the drug burns.

Halverson said she had a very intense headache and sore throat, and others had dizziness, sweating and coughing.

“Not a party,” she said.

The workers found out it was methamphetamine smoke through a call from a city official while they were in the hospital, Halverson said. Most of the staff spent several hours in an oxygen chamber for treatment.

Symptoms have lingered for some workers, Halverson said.

They were also closely monitoring four litters of kittens that got more heavily exposed because they were in a closed room with lots of smoke, she said.

The FBI routinely uses outside facilities to conduct controlled drug evidence burns, agency spokesperson Sandra Barker said. She referred further questions to Billings officials.

A city animal control supervisor who was present for Wednesday’s burn declined to go to the hospital, Iffland said. The FBI agents were told to go to the hospital by their supervisor.

The incinerator is meant to operate at a certain temperature, so it doesn’t emit toxins. Iffland said officials were trying to determine if it was at the appropriate temperature on Wednesday.

The shelter will remain closed until it can be tested for contamination. Shelter workers were tested for potential exposure, and Iffland said he did not know the results.

“We have no idea of how much we’ve lost,” shelter board member and attorney Frans Andersson told CBS affiliate KTVQ. “We don’t have inventory at the moment of what was in there.”

The company hired to assess and clean up the building told the station that they are doing air quality tests before any remediation can happen.

“This is a unique situation and project,” said Andrew Newman, owner and CEO of Newman Restoration. “Typically, what we’ll see is more on the residential side with, you know, kind of a meth lab that either caused a fire or triggered some type of needing remediation. With this being a larger commercial facility and what the intentions were, it makes it a unique situation and cleanup.”

Newman expects the lab results to come back by next week.

Billings resident Jay Ettlemen went to the shelter on Friday to donate dog food and said he was angry when he found out about the drug burns.

“Why the hell are they destroying drugs inside the city limits?” Ettlemen asked. “There’s so many other places in the middle of nowhere.”