An explosion sounded at the Salt Lake City Intermodal Hub. A SWAT team ran through the parking lot. Some 100 victims staggered out of a FrontRunner train, bloody and moaning in pain.

The scene looked like a terrorist attack, but the chaos was oddly subdued -- it was just a test. The mock disaster held Sunday morning was the largest police training event since the 2002 Olympic Games came to the city, said Salt Lake City Police Chief Chris Burbank.

"It's an opportunity to test how we respond," to a mass casualty situation, he said. "It really tests all of the police and fire departments in the valley."

The training started about 8 a.m. and continued until about 11:30 a.m. Sunday, and closed the area around 300 South and 600 West to traffic. TRAX service also ended at the EnergySolutions Arena until about noon.

In the scenario, civilians were attacked with a bomb and guns, starting on a TRAX train near the arena, then moving to the hub, where the shooters took hostages and barricaded themselves on a FrontRunner train. While the scenario involved movement from the arena to the hub, the training event took place only at the hub.

In a large disaster, Salt Lake City police would call on officers and resources from around the Salt Lake Valley. Nineteen agencies, from the U.S. Department of Homeland Security to the South Jordan Fire Department, "responded" to the mock disaster Sunday morning. Training helps make sure all the officers, paramedics, SWAT teams and bomb squads are working together, rather than "self-deploying," Burbank said.

The importance of good coordination and communication was one of the lessons emergency leaders took from the real-life response to the shooting at Trolley Square mall in 2007, Burbank said.

Using trains in the scenario also helped the Utah Transit Authority practice their disaster response, said Salt Lake City police Lt. Rich Brede.

Preparations for the mock disaster took almost a year. "Victim" volunteers came from American Fork Junior High School, Granite and Alpine high schools and elsewhere, said Helen Langan, a Salt Lake City spokeswoman. The victims were loaded onto a UTA bus for transport to area hospitals.

The bus station at the Intermodal Hub continued to operate during the mock disaster, and a few people wandered through the disaster scene, including some who yelled at officers and were escorted out.

Overall, though, the training went, "very well," Brede said.