SAN FRANCISCO — Hundreds of pounds of bomb-making materials and handbooks on how to build a bomb were found in a Pacific Gas & Electric Co. storage facility Thursday, and a field worker for the utility was arrested. The 44-year-old employee, Paul Madronich, was very cooperative and led investigators to more such materials at a second PG & E facility, said San Francisco police spokesman Sherman Ackerson. Additional evidence was found at Madronich's San Francisco home, said a special agent of the Bureau of Alcohol, Tobacco and Firearms.
Police speculated that the material might have been meant for fireworks rather than bombs.
"We have no information to suggest that this is domestic terrorism. It may turn out to be something pretty silly," Ackerson said.
But, he said, "There's significant information, significant material to show there's a bomb-making operation going on, and so we're being very cautious."
The incident began when a PG & E building inspector was called to investigate a puddle of water on the ground floor of the utility's Potrero Hill warehouses about 7 a.m. Thursday. He found a locker filled with 50-pound bags of ammonium nitrate that had been frozen and were melting, PG & E spokesman Scott Blakey said.
The utility company does not use ammonium nitrate for any purpose, Blakey said, and would have no reason to store it.
Convicted killer Timothy McVeigh mixed ammonium nitrate with fuel oil to build the 4,800-pound bomb that destroyed the Oklahoma City federal building in 1995 and killed 168 people.
Teams of investigators from the FBI, ATF, the city's police bomb squad and the Fire Department descended on the block-long, three-story storage facility.
They cordoned off several blocks in the mixed-use industrial and residential neighborhood and searched the plant with bomb-sniffing dogs. Dozens of PG & E workers were evacuated from there and a second PG & E facility next door.
More than 250 pounds of ammonium nitrate was found in several lockers, Blakey said.
Investigators also found a 33-gallon drum of another volatile substance, calcium nitrate, along with broken flares, electronic devices and a small quantity of blasting caps, gunpowder and fuses, police said.
Madronich led officials to another PG & E warehouse, a block away on Harrison Street, where investigators found boxes containing "extensive bomb-making materials," Ackerson said.
Madronich was arrested on suspicion of possession of a destructive device. He will be formally charged Tuesday in San Francisco Municipal Court.
Blakey and other officials stressed Thursday that even if the storage facility had been damaged or destroyed by a bomb, it would not have disrupted gas or electric services in the city.
Times staff researcher Norma Kaufman contributed to this story.