PG&E gas pipeline explodes near Fresno; at least 11 hurt

A fireball erupts after a large gas pipeline exploded in Fresno, Calif., Friday, April 17, 2015. The explosion and fire closed both directions of Highway 99, authorities said. (Kevin Ling via AP) MANDATORY CREDIT less A fireball erupts after a large gas pipeline exploded in Fresno, Calif., Friday, April 17, 2015. The explosion and fire closed both directions of Highway 99, authorities said. (Kevin Ling via AP) MANDATORY ... more Photo: Kevin Ling, Associated Press Photo: Kevin Ling, Associated Press Image 1 of / 1 Caption Close PG&E gas pipeline explodes near Fresno; at least 11 hurt 1 / 1 Back to Gallery

A Pacific Gas and Electric Co. natural gas pipeline near Fresno erupted in a fireball Friday afternoon — injuring at least 11 people and temporarily closing down Highway 99 — after a tractor operator accidentally punctured the 12-inch line, authorities said.

Eleven victims were transported to hospitals, where officials said four were in critical condition, two were in serious condition and the remainder suffered minor injuries.

The explosion, which sent flames surging past the tops of nearby trees, happened shortly before 2:30 p.m. on a shooting range close to busy Highway 99, one of the San Joaquin Valley’s two main freeways.

The tractor was being operated by a county public works employee who was using it to reinforce a berm behind the targets at the Fresno County Peace Officers' Range, according to spokesman Tony Botti of the Fresno County Sheriff’s Office. Three lanes and about 30 feet away, more than a dozen inmates were digging bullets out of the berm.

It was not immediately clear whether the tractor operator knew the gas transmission line was there. Anyone who digs with heavy equipment is supposed to check with local utilities in advance. PG&E spokeswoman Nicole Liebelt said the company had not received a call on its digging hotline from anyone working nearby.

A photo posted by Alan-Michael (@81vlvnmvc) on Apr 17, 2015 at 2:29pm PDT

But, according to Botti, the tractor operator was not engaged in digging at the time of the explosion. “All the indications are that he was driving and the explosion happened,” Botti said, perhaps because the front-end loader was scraping the ground.

Whatever the cause, the explosion was immense — flaring more than 100 feet into the air, according to onlookers, and spilling outward in heat and flames that injured at least 10 of the inmates. One was in such critical condition that he had to be airlifted to a nearby hospital.

“The driver of the tractor, amazingly, was able to walk over to the ambulance,” Botti said. He added a smaller example of the fireball’s intensity: plastic trash cans 200 feet away from the explosion, in an area where deputies clean their guns, melted. “They looked like trash-can lids,” Botti said.

Fortunately, most of the area around the explosion was grassland, the shooting range and an equestrian center.

Another factor that kept the toll from being more severe is that deputies were at the shooting range. “Hats off to them,” Botti said. “They jumped into action right away to get aid.”

According to Pete Martinez, a spokesman for the Fresno Fire Department, the response to the fireball included 15 fire engines, fire trucks and water trucks each containing roughly 2,000 gallons for the engines to draw on.

Highway 99 was closed in both directions until 4:30 p.m. A railroad line running alongside the shooting range sustained damage.

Last week, the California Public Utilities Commission slapped PG&E with a record $1.6 billion penalty for the September 2010 explosion of a natural gas pipeline beneath San Bruno, which killed eight people. The blast erupted from a 1950s-era pipeline that had been installed with substandard welds that failed, said federal investigators.

Since then, PG&E has spent or committed to spend $2.8 billion on repairing and upgrading its vast network of natural gas pipes, which spans most of Northern and Central California. The utility has replaced more than 800 miles of cast-iron pipe and installed 200 automatic or remotely controlled shut-off valves, as well as invested in new leak-detection technology.

Those investments, however, cannot prevent other people from digging into and puncturing gas lines — the most common cause of natural gas pipeline accidents nationwide.

But if the tractor in fact was not engaged in scooping dirt out of the ground, that raises the question of how close the 12-inch transmission line was to the surface.

Late Friday, the utilities commission reported that it had dispatched a team to Fresno and would conduct a full investigation of the explosion. The commission had already begun coordinating with the federal Pipeline and Hazardous Materials Safety Administration, said spokeswoman Terrie Prosper.

John King, David R. Baker and Kale Williams are San Francisco Chronicle staff writers. E-mail: jking@sfchronicle.com, dbaker@sfchronicle.com, kwilliams@sfchronicle.com Twitter: @JohnKingSFChron, @DavidBakerSF, @SFKale