[media-credit name=’MATTHEW KUTZ/Herald photo’ align=’alignnone’ width=’648′][/media-credit]An unidentified chemical agent sweeping through the 5400 block of Elizabeth Waters inflicted uncontrollable coughs and distress for residents there Monday night, prompting hall directors to temporarily evacuate the building at approximately 7:30 p.m.

University of Wisconsin police suspect the chemical may have been pepper spray accidentally discharged by a resident, but hundreds of female students sat curbside across the street waiting for police and firefighters to determine the source of the irritable gas.

More than an hour after arriving on the scene, responders cleared the area for reentry, stating the chemical had "self-dissipated."

While responders took precautions for the worst possible situation, UW Police Sgt. Anita Kichefski said it was "probably more likely a prank, under the circumstances." She said it also could have resulted from a resident "accidentally discharging their own personal can of pepper spray."

Kichefski noted the department cannot determine for sure if the gas emission was a prank and said it is unknown if they will seek out anyone for possible charges.

"There was just one located area in one floor in Liz," she said. "There was an irritant causing slight coughing for a few people there."

But Liz Waters resident Allie Hayes, who lives in the 5400 block of the building, described more serious symptoms and said once the gas affected one resident, others poured into the hallway only to experience the same agony.

"We were just in the dorm [and] they come in coughing and say 'you won't believe what's in the hallway,'" she said. "So I go in the hallway and you just inhale it and it doesn't have a smell, but your eyes start watering, your nose and throat burn and you start coughing."

"It was scary, you couldn't smell it — it just burned," she said. "One breath, that's all you had to take and you were coughing. It was unbearable."

Allie Hayes' floor mate Andrea Hayes (no relation) described the same anguish.

"It hit me and we both just started coughing," Andrea Hayes said. "It was scary. Everyone just ran into the hallway."

Allie and Andrea Hayes said the gas was limited to the hallway and amid the confusion they and others notified house fellows, who in turn contacted emergency responders.

After performing sensing and monitoring tests Madison Fire Department Lt. Robert Hansbro said the cause and nature of the gas was still unknown.

"There was an irritant in the air but we couldn't tell what it was," he said. "It just self-dissipated."

Hansbro added the department walked around the dormitory with the air off to isolate the gas and make absolutely sure it was gone.

While authorities and dormitory officials cleared residents to reenter for the night, Allie Hayes, who said she had eight hours of homework and a quiz to prepare for, was a little apprehensive about sleeping there.

"I hope it's not going to come back again," she said. "Especially since they don't know what caused it or why it went away — I wish they vented some clean air in there."