02/12/2013 08:27 am ET

Ronnie And Deborah Pratt Killed After Cigarette Ignites Medical Oxygen Tank In Car

A cigarette and a medical oxygen tank are to blame for a car's explosion and fire that killed an Indianapolis couple on Sunday, authorities say.

Ronnie Joe Pratt, 62, and Deborah Pratt, 62, died in the blaze after their vehicle caught fire on Interstate 70 near Richmond, according to the Palladium-Item. A cigarette lit inside the vehicle ignited an oxygen tank that another occupant was using for medical reasons, police say.

Two other adults in the car -- driver Thomas Barham and Tina Brooks -- escaped. Brooks was listed in critical condition at a nearby hospital on Monday. Barham was treated for minor injuries.

Witnesses told WISH-TV that the car drove into a median after the fire took over.

"The car was completely engulfed in flames," Lee Gastineau said. "There was a young woman laying in the median and there were a few people that had stopped to try to put the car out and help the man that was driving the car calm down the woman."

Investigators found two oxygen cylinders in the car, one in the passenger seat and one in the trunk, according to the Indianapolis Star. One of the victims reportedly told police that another passenger was lighting a cigarette when the car caught fire.

"The vehicle was burned so badly we could not get the (vehicle identification number) off it, nor could we even read the license plates," Wayne County Sheriff Jeff Cappa told the paper.