BLOOMINGTON - U.S. Cellular Coliseum was the site of a practice session Wednesday, but the professionals weren't using hockey sticks or footballs and wore very different kinds of protective gear. | Photo gallery

Twenty-two members of the Bartonville-based Illinois National Guard 5th Civil Support Team were being evaluated during a formal training exercise simulating a hazardous event at the Coliseum. Guardsmen were clad in hazardous materials suits, and an array of emergency trucks and trailers filled a lot northwest of the building.

In Wednesday's scenario, a "dissident group" attacked people attending a volleyball match the night before, said Lt. Col. Larry Ritter, from U.S. Army North in Fort Sam Houston, Texas.

Maj. Norman Brooks said that, when looking at venues for the exercise, organizers looked for a realistic and relevant, potential target.

"This facility could be packed for an event," Brooks said. "Someone could smuggle something in."

Capt. Lance Wilson, the commander of the team, said that in the scenario, nobody noticed a problem during the event, but hundreds of people started showing up at hospitals about six hours afterward with skin and eye irritation and sore joints. About 260 people became sick in the scenario, Wilson said.

Wilson's team didn't get advance notice and was called about the scenario at 3 a.m., he said. The first advance attachment arrived at 4:45 a.m., and the main body of the unit arrived at 5:30 a.m., he said.

And Brooks said that, because the Coliseum is relatively new, the event can be used to help build action plans and show response team members the inside in case something did happen.

Second Lt. Stacey Rieger said the Illinois civil support team has extensive experience and received perfect or nearly perfect scores on its last evaluation. She said it was one of the first 10 such teams in the nation, and some current members were part of the original team that formed in 1999.

"They really do a bang-up job because they have such seasoned members," Rieger said, later adding, "If something did happen at the Coliseum, we're prepared."

The team is trained to handle and determine the cause of chemical, biological, radiological, nuclear or explosive material incidents.

By 5 p.m., the team had finished its second entry and figured out the perpetrator in the scenario had released nitrogen mustard, a chemical warfare agent, Ritter said. The team also received radiological readings that they hadn't yet figured out was from a small amount of Cesium 137, a radioactive isotope, Ritter said.

The exercise concluded later that evening.

The 5th Civil Support Team is composed of Illinois Army National Guard and Air National Guard, and it is one of 55 such teams in the U.S. and its territories, Ritter said. The Army makes the scenarios as stressful as possible in order to make sure the teams have the flexibility and rapid response ability needed in an emergency, he said.

The team members work with police, fire and emergency management agencies, and they are supposed to be able to rapidly report to the governor what has happened, Ritter said. Unlike regular Guard members who may work other full-time jobs and attend training on weekends, the CST members are full time.

The event was closed to the media, the Guard release said.

Ryan Denham contributed to this report.