The crowd gathered at 6 a.m., some sleeping in their cars overnight, in the nearby parking lot of a Lowe's Home Improvement store in Bakersfield to watch the planned implosion of the steam power plant owned by the public utility Pacific Gas and Electric that had been decommissioned for decades.
After buildings came down in a fiery crash, a police officer heard a man screaming for help and saw that his leg had been blown off.
"It was a piece of shrapnel that came flying out of the explosion and came across and went through a couple of chain link fences," said police Lt. Scott Tunnicliffe.
The 44-year-old victim also had major injuries to the other leg, and may lose it also, Tunnicliffe said. Officials declined to release his name.
Four other spectators were treated for minor injuries, said Kern County Fire engineer Leland Davis. All of the injured spectators were standing beyond a perimeter set up to ensure public safety, Davis said.
Fred Garten, 49, was standing behind the perimeter when a piece of metal roughly the size of a household door came flying at him and grazed his right leg, leaving his socks and shorts splattered with blood.
"It's a good gouge, but it's just scratches," Garten told the Bakersfield Californian, which first reported on the incident. "I just feel bad for the other guy. They took him away on a gurney, and I'm walking."
Kelly Patt, 21, who arrived five hours early to get a good view of the blast, said his girlfriend got sprayed with shrapnel but wasn't badly hurt. Patt said he was far more disturbed at seeing the man with the severed leg.
"I saw that dude's leg and I had to walk away," he told the Californian. "There was a lot of blood, a lot of blood."
Several cars were also damaged by the shrapnel.
Residents of the city about 100 miles northwest of Los Angeles were eager to see the old plant torn down to make way for new development. The plant was decommissioned in 1986 and has been idle ever since.
Pacific Gas and Electric reached an agreement with the city to clean up the property and prepare it for sale. The company hired subcontractors to handle the demolition of the plant's boiler structures and worked with local authorities to set up a safe perimeter 1,000 feet from the site, said Denny Boyles, a company spokesman.
"We are deeply saddened that this happened," Boyles said. "We're looking for answers like everyone else."
Boyles said the boiler structure consisted of two towers measuring 140 feet high that supported four 200,000 gallon tanks.
Cleveland Wrecking Co. of Covina, Calif., the main contractor on the demolition, issued a statement expressing sympathy and vowing a thorough investigation but declined further comment.
"This was a terrible accident, and our hearts go out to the individuals who were injured," the statement said. "We will be conducting a full investigation and will cooperate with the authorities."
Several subcontractors also worked on the project.
A previous accident at the same demolition site in 2012 killed a 51-year-old Cleveland Wrecking worker who was suspended in a basket and cutting beams with a torch when one of the beams hit him and he fell 50 feet to his death.
In June of this year in Philadelphia, the wall of a building under demolition collapsed onto a thrift store and killed six people. That contractor was not among those hired for the Bakersfield plant.