The Casper fire boat that struck a bridge piling last week hit the structure after it landed at an angle while maneuvering through a rapid, an investigator said Monday.

The aluminum craft became slightly airborne in the rapid, and when it landed, a swift current helped push the boat toward the bridge, said John Lund, the game warden who investigated the crash for the Wyoming Game and Fish. The right side of the vessel struck the piling, but the boat's operator avoided a head-on collision by steering to the left at the last second.

"That correction, in my opinion, probably saved those guys from getting hurt worse," Lund said.

Four firefighters in the boat suffered various injuries and were treated and released within hours of the Wednesday crash, which happened during a training exercise at Casper Whitewater Park. The boat itself was heavily damaged but did not sink.

Lund believes the firefighters' life jackets prevented serious injuries by padding the men as they were thrown around in the impact.

"They bounced around pretty hard in there," Lund said.

The crash happened after the boat passed through a set of rapids just west of a foot bridge that crosses the North Platte River at the whitewater park.

Lund called the impact severe. None of the men were thrown from the boat, which had been traveling at a "moderate" speed, he said.

The men were practicing life-saving exercises, and Lund stressed that pushing the envelope is necessary for emergency responders to get the most out of their training.

"That is the purpose of good training," he said. "Sometimes those things happen."

One firefighter was knocked out in the crash, but regained consciousness by the time ambulances arrived. A second firefighter hurt his head and leg, while two others suffered minor injuries.

Reach crime reporter Joshua Wolfson at (307) 266-0582 or at josh.wolfson@trib.com. Read his blog at tribtown.trib.com/JoshuaWolfson/blog.