Additional testing has confirmed beach rocks that spontaneously combusted in a Southern California woman's pocket contained elevated levels of phosphorus, an official said Friday.
The source of the substance is still unclear, but an expert says it probably was manmade.
Results from an independent lab matched those obtained by the Orange County Public Health Care Agency, which examined the rocks immediately after the May 12 incident, agency spokeswoman Deanne Thompson said.
Lyn Hiner, 43, suffered second- and third-degree burns on her right leg from her thigh to her knee and on her right arm when the rocks set her shorts on fire several hours after her children collected them on a San Clemente beach. Hiner couldn't extinguish the flames, and her husband suffered second-degree burns when he tried to help her.
The phosphorus on the smooth, greenish-orange rocks is likely manmade, said Kenneth Shea, an organic chemistry professor at the University of California, Irvine.
Phosphorus is found in oxidized form in rocks, but in its pure elemental form can burn when exposed to air. Phosphorous compounds are used in everything from flares to munitions to fertilizer.
"You can't go digging on the beach and find it," Shea said. "It's manmade, and it's pretty common."
Trestles, the beach where the family gathered the rocks, is near the San Onofre Nuclear Generating Station and the Camp Pendleton Marine base.
San Clemente Island, 60 miles off the coast of Trestles Beach, is owned and operated by various naval commands. The island has at least a dozen ranges there.
Capt. Barry Edwards, a Camp Pendleton spokesman, said when the incident occurred that there was no evidence military training aids were involved.
He said Friday he had no new information.
The rocks kept burning after they fell out of Hiner's pocket, scorching the couple's wood floor and filling the house with smoke. They were still smoking when paramedics brought them to Western Medical Center in Santa Ana to show the doctors there, The Orange County Register reported.