Emergency workers clear the tractor trailer that rear ended a firetruck sending five victims to area hospitals and causing massive delays on the inner and outer loops of the beltway on Tuesday in Landover, Md. (Jonathan Newton/THE WASHINGTON POST)

A grisly crash early Wednesday involving a tractor-trailer and a Prince George’s County firetruck sent seven people, including four volunteer firefighters, to the hospital and backed up traffic on the Capital Beltway for hours, authorities said.

One of the firefighters, Lt. Ryan Emmons, suffered a severed arm and underwent surgery Wednesday at MedStar Union Memorial Hospital in Baltimore, said Chief John Alter of the West Lanham Hills fire station. His arm was reattached, fire station officials said. The other firefighters, all men in their late 20s with seven or eight years of experience, required “stitches and staples” and were released from the hospital by late Wednesday morning, Alter said.

“No broken bones, but they look like they’ve gone 10 rounds with Muhammad Ali,” Alter said.

Police and fire officials said the injuries of the firefighters and the three others were not life-threatening.

The crash left both vehicles overturned and the firetruck’s back end crushed.

On Wednesday afternoon, collision investigators with Prince George’s County police were still looking into the cause of the incident, which occurred about 3 a.m. near Route 50, in the Landover area. Their account of what happened varied slightly from Alter’s.

Lt. William Alexander, a police spokesman, said investigators believe that the firetruck was leaving the scene of a minor crash on the inner loop of the Beltway and was “intending to make a U-turn” through an emergency vehicle turnaround when the tractor-trailer hit it from behind. He said investigators initially believed that the tractor-trailer was the “favored vehicle,” although police had not yet assigned fault in the collision.

“It’s a very complex investigation,” Alexander said.

In legal cases in Maryland, “favored vehicle” typically refers to the one with the right-of-way.

Alter said he thought the firetruck was pulling up to the scene of the minor crash — slowing to about 10 or 15 mph with its emergency lights still on — when it was hit. He said the firetruck’s driver “saw the tractor-trailer coming and tried to put the fuel back on” but that his efforts were in vain.

The tractor-trailer pushed the firetruck nearly 100 feet along the Jersey barrier dividing the Beltway’s inner and outer loops, then crossed over the wall itself, Alter said. Alicia Francis, assistant chief of the Prince George’s County Fire/EMS Department, added that the wreckage collided with a sport-utility vehicle, which also overturned.

In total, officials said, seven people were taken to the hospital: the four firefighters aboard the truck, two people in the SUV and the driver of the tractor-trailer.

Alter and Francis said other volunteer and career firefighters were able to fill the staffing void left by those injured in the crash.

“We’re going to have to make some arrangements to have some other people fill in, but that, too, shall pass,” Alter said.

Police shut down several lanes in both directions of the Beltway while investigators worked at the scene and the wreckage was cleared.