In this Thursday, July 4, 2013, photo, a triage area is set up at Ranch Santa Susana Community Park in Simi Valley, Calif. (AP Photo/The Ventura County Star, Wendy Pierro)
SIMI VALLEY, Calif. (AP) — For many people gathered to watch July Fourth fireworks at a Southern California park, it took time to realize the wild chain of explosions weren't just part of the show.
But those up close Thursday night knew immediately that something was wrong. They included Paulina Mulkern, who had to shove her 4-year-old cousin under a lawn chair as shrapnel came flying then shielded a 7-year-old cousin with her body as scorching debris flew overhead.
"You feel the big old heat come right over your back," Mulkern said Friday, still shaking a day after the chain reaction of accidental explosions at an annual fireworks show that had been put on since 1970 in Simi Valley northwest of Los Angeles.
Thirty-nine people ranging in ages from 17 months to 78 years old were injured. Some had burns and shrapnel wounds, and some were trampled, authorities and hospital officials said. The injured included 12 children.
Only three remained hospitalized Friday night. One was being treated by specialists at a burn center in West Hills, and two more were in fair condition at a community medical center in Simi Valley, hospital officials said.
Mulkern said she went into shock after being hit by a flying piece of debris that left her with bruises and red marks on her back, trembling badly as she was carried to a road where rescuers stripped off most of her clothes and wrapped her in a blanket.
"I was really terrified," she said. "Every time someone launched a firework it got me into panic mode."
Cellphone videos captured a frantic scene among the crowd of 10,000. Fireworks exploded in big balls of sparks close to the ground, and smoke enveloped the park grounds. People screamed and ran. One mistaken man could be heard shouting someone was shooting.
Colleen Schmidt was watching the show with guests at her house across the street when it slowly became clear something went terribly wrong. After a few fireworks lofted perfectly in the sky, there was a big explosion on the ground and a volley of blasts.
Though a piece of shrapnel created a crater across the street then bounced and shot over nearby trees, Schmidt and her guests were lucky.
"We had 150 people here and not one single spark hit our house," she said.
Police said it appeared a firework exploded prematurely in its mortar, knocking over others and aiming them across the field. Fire investigators, however, said later they had not yet determined a cause.
Police based their initial statement on the accounts of witnesses, who said a rack of fireworks fell over, said Ventura County Fire Capt. Mike Lindberry.
Among other key questions investigators were trying to answer was whether the pyrotechnics display was set far enough away, and whether guidelines needed to be revised to protect spectators.
Regulations require crowds be kept 70 feet away for every inch of diameter of the largest shell.
By those standards, the crowd should have been at least 350 feet away from the show, said Ventura County Fire Department Deputy Chief Mike LaPlant.
Investigators were making sure that guideline was followed Thursday night, though all of the injuries were at a distance of 350 feet or more, LaPlant said.
Bethpage, N.Y.-based Bay Fireworks, the company that put on the show, said it regretted that spectators were injured and that it planned to make public the results of a thorough investigation.
Although fireworks accidents at professional shows are rare, they are not unheard of.
In 2008 in New York, fireworks shells exploded on the ground and another one launched into the crowd, injuring five people at an event that also involved Bay Fireworks, said Julie L. Heckman, executive director of the American Pyrotechnics Association, a fireworks trade group.
And last year a fireworks show in San Diego put on by a different company went off in its entirety about 20 seconds into what was supposed to be a nearly 20 minute show, sending multiple explosions over the bay because of an error in the pyrotechnic computer system. No one there was injured.
The new accident is likely to bring changes to the national codes such shows must follow.
"This incident is a dark cloud over the entire industry," Heckman said. "We don't take it lightly."
Bay Fireworks is licensed by the state and had no violations on its record, said Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection. The state could cite the company after reviewing the results of the investigation by Ventura County, which issued the permit for the event.
Heckman noted that the company has been in business for a long time and was "not a small player in the industry."
The company website says it has produced events for NASA, Walt Disney World and Legoland.
Associated Press writers Amy Taxin in Santa Ana, Calif., and Greg Risling and Shaya Mohajer in Los Angeles contributed to this report.