Authorities in suburban Chicago said a release of chlorine gas that sickened 19 people at a hotel hosting a 'furries' convention early Sunday was "intentional."

The source of the gas was apparently chlorine powder left in a ninth-floor stairwell at the Hyatt Regency O'Hare hotel, according to the Rosemont Public Safety Department. Investigators are treating the evacuation as a criminal matter.

The sickened people reported nausea or dizziness.They were treated at local hospitals and at least 18 were released shortly thereafter. The convention-goers, dressed in cartoonish animal costumes, were ushered across the street to a convention center hosting a dog show.

Within hours, emergency workers decontaminated the Hyatt Regency O'Hare and allowed people back inside. Six-foot-tall rabbits, foxes and dragons poured into the lobby, chatting and giving each other high paws.

"I think we'll recover from this," said Kit McCreedy, a 28-year-old from Madison, Wisconsin, his fox tail swinging behind him as he headed back inside for the last day of the Midwest FurFest. "People are tired but they're still full of energy."

While authorities conducted their investigation, organizers tried to assure the participants that the evacuation would not overshadow the convention. But attendees seemed to think the evacuation was part of the fun — particularly those who recalled being herded into the Donald E. Stephens Convention Center as it was hosting a dog show.

"In walk all these people dressed like dogs and foxes," said Pieter Van Hiel, a 40-year-old technical writer from Hamilton, Canada, chuckling as he thought back to the scene.

Others said they did not have a clue as to why anyone would intentionally disrupt the convention that includes dance contests and panel discussions on making the costumes, with some quick to point out that the brightly colored outfits are made from fake fur and foam and not real fur.

"Nobody uses real fur," said Frederic Cesbron, a 35-year-old forklift operator who rode a plane to Chicago from his home in France. He attended the convention dressed head-to-toe in a fox outfit that he said cost him about $2,000 four years ago but would go for $3,000 today.

Attendees said they came for fun, but also for the spiritual and artistic aspects of the convention that have them celebrating animal characters from movies, TV shows, comic books and video games. Some also create their own characters and appreciate being in an atmosphere where nobody seems surprised or shocked by an elaborate, bright purple dragon.

"Everyone is from a different background," said Michael Lynch, a 25-year-old from Madison, Wisconsin, who, like his buddy, McCreedy, dressed as a fox. "Nobody judges anybody. It's nice to come to a place like that."

Or, as Van Hiel put it, "It's kind of weird, but it's not weird here."

The Associated Press contributed to this report.