CHATTANOOGA (WRCB) - Fire investigators say they now know how a gas station fire started that severely burned a woman last week.

Captain Anthony Moore with the Fire Investigation Division said that while 20-year-old Samantha Lawrence was putting gas into her Jeep Cherokee, her boyfriend, Derek Seretean, went inside the store to buy some cigarettes.

Captain Moore says Seretean told investigators that he then returned to Lawrence at the pump and lit up a cigarette. As he flicked the lighter next to Ms. Lawrence, there was a flash fire that caught her clothes on fire.

Investigators say Lawrence screamed for help and a bystander reportedly told her to drop to the ground and roll around to extinguish the flames.

Meantime, a store cashier saw the fire and hit the cut-off switch to keep more gas from getting to the flames. The cashier and another employee then brought out a fire extinguisher and put out the flames. There was very little damage to the gas pump.

Lawrence suffered second and third degree burns to approximately 30% of her body. Since the fire, investigators say her condition has improved and she is being treated for her injuries at the Joseph M. Still Burn Center in Augusta, Georgia. The cause of the fire will be listed as accidental.