BILLINGS, Mont. (AP) — A cloud of smoke from two pounds of methamphetamine seized by the FBI and incinerated inside a Montana animal shelter prompted its evacuation and sent workers to the hospital, city officials in Billings said.

The smoke started to fill the building during a drug burn on Wednesday, apparently because of negative pressure that sucked it back inside, Billings Assistant City Administrator Kevin Iffland said Friday. A fan was supposed to be on hand in such situations to reverse the pressure so smoke would flow out of the building, but Iffland said it wasn’t readily available.

The incinerator is used primarily to burn the 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 workers from the Yellowstone Valley Animal Shelter went to the hospital as a precaution, he said. The dogs and cats at the shelter were relocated or put into foster homes. Some workers had symptoms such as not feeling well. “I don’t know if it was from the smoke inhalation or exactly what it was,” Iffland said.

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.”

The FBI routinely uses outside facilities to conduct controlled drug evidence burns, agency spokesperson Sandra Barker said.