Indianapolis ? A truck traveling down a busy freeway with a crew of painters was engulfed in flames in a blaze that may have been started by a cigarette igniting fumes from paint thinner or lacquer. One man was killed and 12 others riding with him in the back of the truck were critically burned.

Witnesses said the workers piled out of the truck screaming, their clothing on fire and their lungs seared by toxic fumes. Passers-by poured bottled water on the men to soothe their burns until ambulances arrived after Tuesday’s fire.

The burned men, ages 18 to 32, lay hospitalized Wednesday with burns covering as much as 90 percent of their bodies.

“It’s going to be a long-term recovery in the burn ward. And depending on how many skin grafts are needed, we’re looking at a considerable amount of time at the hospital and potentially some fatalities,” said Michael Olinger, medical director of Wishard Ambulance Service.

Efforts to piece together the chain of events was complicated by the fact that eight survivors were placed on ventilators to help them breathe, and most were unconscious and under sedation to limit their pain, doctors said Wednesday.

“You can’t talk to somebody that is incoherent,” said Sgt. Ray Poole, an Indiana State Police spokesman. “That’s why the investigation has hit a little bit of a wall. Once they come out of that condition, hopefully they’ll be interested in talking.”

Temperatures inside the truck were believed to have reached as high as 1,000 degrees as paints and thinners in plastic containers caught fire in the enclosed space.

Several men were so severely burned that family members were allowed to see them only if they wore protective clothing to guard against the possibility that they might infect the men, whose burned skin is unable to protect them from germs.

A cargo truck that burned, killing one worker riding in the back, is shown on Interstate 465 near Indianapolis International Airport. Fire roared through the truck Tuesday, injuring more than a dozen members of the painting crew inside, some of them critically.

Most of the men faced multiple surgeries, including skin grafts, and long hospital stays.

“We’re not talking about hours or days here,” said Chuck Schufflebarger, emergency services director at Methodist Hospital, one of four hospitals treating victims.

John W. Webster died overnight after suffering third-degree burns over 90 percent of his body.

The men were all employees of the RPT Painting, which is based in Franklin, about 30 miles south of Indianapolis. The driver and three others in the cab were not injured.

Phone calls rang unanswered Wednesday at RPT Painting. A phone message was left for an Indianapolis attorney for the company, Craig Helmreich.

The workers were packed into the enclosed cargo area of the truck because another company vehicle had broken down, said Trooper Andy Shank. Police said it did not appear to be a violation for the men to be riding in the back.

The fire initially was blamed on a cigarette. Lead investigator Rick Batza said Wednesday it was too early to determine the exact cause, but authorities were not ruling out a cigarette.