Correction: San Clemente Island lies about 60 miles offshore.
The rocks that spontaneously caught fire inside a San Clemente woman’s shorts had high amounts of the flammable element phosphorous, the Orange County Public Health Care Agency announced Thursday.
"Confirmatory laboratory testing confirmed elevated levels of phosphate on the rocks," said Deanne Thompson, spokesperson for the health care agency, in an email.
Phosphate is a form of phosphorous, an element that is highly flammable, self-igniting and toxic if ingested. Phosphorous is used in the creation of a number of products including detergents, pesticides, matches and fertilizers.
San Clemente resident Lyn Hiner, 43, suffered third-degree burns when the stones in her pocket burst into flames at about 3:30 p.m. May 17.
OC Health Public Health tests on the rocks found high levels of phosphorous, and on Thursday an independent lab confirmed it, according to Thompson.
Two rocks with high levels of the element appear to have “cross-contaminated” the other rocks in Hiner’s pocket.
Thompson said the fire was unusual event for the agency.
“This is pretty far outside our normal scope,” Thompson said.
On May 17, Hiner’s children were collecting stones along the beach near Trestles, and they gave her the seemingly unremarkable rocks to hold.
The rocks were smooth; some the size of a hamburger patty, others small enough to fit in a coffee cup, according to news reports.
At about 3:30 p.m. the rocks caught fire.
Hiner was hospitalized in Santa Ana with burns to her right thigh and knee, Orange County Fire Authority Capt. Marc Stone said.
Stone said the victim "stopped, dropped and rolled'' in an effort to douse the flames, and her husband suffered second-degree burns to his hand as he tried to help.
Hiner, who suffered third-degree burns, has now undergone two painful skin-graft surgeries to her damaged leg.
"We know bad things happen to many people," Hiner told the Orange County Register. "I'm thankful God carried us through this. That Jason, the deputy, the firefighters and the doctors, the hospital staff and our friends and family have all been with us. I know there are patients here that are going through a lot more than I am. I'm grateful it wasn't the girls and that it didn't happen on the freeway on our drive home."
Orange County Public Health will be conducting no further tests on the incident.
The beach where the rocks were found is not far from the and the Camp Pendleton Marine base.
San Clemente Island, which lies about 60 miles off the coast, is owned by the U.S. Navy. The island is its only remaining live firing range, according to a Navy website. The island has also been the site of rocket tests.