By Marty Graham
SAN DIEGO (Reuters) - A California mother suffered severe burns from a handful of beach rocks that burst into flames in her pocket, and authorities on Friday said they are trying to determine why the stones appear to have been coated with flammable phosphorus.
The woman was identified on Friday as Lyn Hiner, 43, when she appeared on ABC program "Good Morning America" from her hospital bed at a burn center. She is from San Clemente, which is midway between Los Angeles and San Diego.
It is also near Camp Pendleton, the biggest U.S. Marine Corps base on the West Coast and a major training area where various types of munitions are used.
"All of a sudden something hot on my leg just sort of started to bug me and so I started to think it was a bug bite, and I started slapping it, and next thing I know my shorts are on fire," Hiner said on the show.
Orange County Fire Authority Captain Marc Stone, whose agency responded to the incident, said it was "not a hoax."
"The victim is undergoing skin grafts for third degree burns from these rocks which appear to contain phosphorus," he said.
The woman went with her family on Thursday morning to a spot at San Onofre State Beach, where her children gathered up seven small rocks they brought home, Stone said.
Hiner picked up the rocks at some point and put them in her shorts pocket where they burst into flames hours after the beach excursion, authorities said.
"We field-tested them for phosphorus and they tested positive," said Deanne Thompson, a spokeswoman for the Orange County Department of Environmental Health. "We've sent them to a state-certified laboratory for further tests and confirmation that it is phosphorus."
Phosphorus is a mineral that has to be stored in water or another medium that keeps it from being exposed to air, Thompson said. Once exposed to air, it burns very quickly and very hot, she said. It has been used in flares and hand grenades for precisely those destructive characteristics.
"I'm theorizing that the rocks must have dried out through the day and finally dried enough to react while they were in the woman's pockets," Stone said. "When we arrived, the husband was hosing her down - both of them had ... burns from trying to get the rocks out of her pockets. The rocks even burned the wood floors in the family's home."
Stone said he had searched the Internet for similar cases and found one in Europe that was traced back to phosphorus-laden flares from World War Two that washed up on a beach.
"It's a very unique situation," Stone said. "We're not saying rocks or shorts spontaneously combust."
(Editing by Alex Dobuzinskis and Eric Walsh)