Fourteen staff members at a US animal shelter were hospitalised on Wednesday after the FBI used an incinerator at the facility to burn two pounds of seized methamphetamine.

Staff and some 75 cats and dogs were evacuated from the Yellowstone Valley Animal Shelter in Billings, Montana, when the building filled with smoke.

The incinerator is usually used by animal control officers to dispose of euthanised animals, but local authorities said it can also be used by law enforcement to burn seized narcotics.

The cats and dogs have been relocated, and the animals which experienced the most smoke exposure are now under supervision.

The incident was caused when smoke was pushed in the wrong direction because of negative pressure, according to Assistant City Administrator Kevin Iffland.

Shelter executive director Triniti Halverson said she was unaware that a drug burn was happening.

“I can firmly and confidently say that, as the Executive Director, I did not know that they were disposing of extremely dangerous narcotics onsite,” she wrote in a statement.

“My team and my animals had been confirmed to have been exposed to meth,” she said.

Before evacuating themselves, many employees put on masks and helped get the animals out.

Some staff were exposed to the smoke for more than an hour, and several began to feel sick. All 14 went to the emergency room, where they spent about three hours in a hyperbaric oxygen chamber to combat the effects of smoke inhalation.

FBI spokesperson Sandra Barker told CBS News that the agency routinely uses outside facilities for controlled drug evidence burns.

The impacted animals were given veterinary care and placed in temporary housing, including four litters of kittens who are being closely monitored because they were closed in a room with the smoke, Ms Halverson told the BBC’s US partner, CBS News.

A restoration team has also begun decontaminating the building, she said, but the process will take at least two weeks to a month.

Calling the incident “heartbreaking”, Halverson is asking the public for donations to source supplies like dog and cat food, blankets and bottles.

“We are displaced, lost, and homeless. For many of us — staff, volunteers, and fosters — YVAS is our safe space,” she said.