OTHER JULY FOURTH ACCIDENTS

• An 8-year-old boy riding on a martial arts group’s float at LibertyFest in Edmond, Okla., died Thursday after his father accidentally ran him over. The boy either got down or fell from the vehicle at the end of the parade, and part of the float — a truck and flatbed trailer with red, white and blue decorations that was loaded with hay bales — struck the child and knocked him to the ground.

•A 32-year-old working at a fireworks show in Ojai, Calif., was struck by fireworks that apparently exploded on the ground. The worker’s face and left leg and arm were injured. The worker was taken to a local hospital and transferred to a burn center.

•One person was killed and others injured after a pickup plowed into pedestrians after the fireworks show in Grand Lake, Colo. The 33-year-old driver was arrested and is being held on suspicion of driving under the influence as investigators piece together what happened.

•A barge being used to set off the annual Fourth of July fireworks on Whitefish Lake in Montana caught fire just as the grand finale began. The local fire chief said a spark from a low-bursting firework started the blaze. The two pyrotechnicians on board dove into the water. No one was injured.

•A worker at a fireworks show in North Myrtle Beach, S.C., was injured when a shell exploded prematurely. The explosion at the Cherry Grove Pier caused the show to end after just six minutes and left a hole in the pier.

•In Seattle, fire investigators blamed illegal fireworks for a blaze that damaged 14 boats at a storage facility, causing an estimated $1.5 million in damages. One firefighter received minor injuries fighting the fire.

•A pyrotechnician suffered severe head trauma and burns after fireworks malfunctioned during a display in northwestern Arizona.

As many as 10,000 Fourth of July revelers were just settling into their seats for the fireworks show at a Simi Valley park when a bright plume of red and white bursts spread across the ground, injuring more than 30 people and sending others fleeing for safety.

Police in the city northwest of Los Angeles were still investigating what caused Thursday night’s explosion. They said the cause was still unknown, although they had earlier indicated it appeared a firework detonated prematurely in its mortar, knocking over a row of others.

The victims ranged in age from 8 to 78, Sgt. Tom Meyer said. Twenty people were taken by ambulance to area hospitals; four suffered serious, but not life-threatening, injuries.

One police officer who ran into the crowd when the blasts occurred had shrapnel tear through his leather belt and his clothing, Shannon said. He had minor injuries to his back.

On Friday morning, blackened debris from the explosion littered the ground. Huge chunks of black shrapnel were still scattered across the park, and the stand the fireworks had been on was sitting, charred, in the middle of a green lawn. Investigators planned to fly over the scene to photograph it and examine the debris, Meyer said.

The fireworks company, Bay Fireworks, said in a statement that it regrets the injuries, and planned a thorough investigation, with results to be made public.

The company also said that injured spectators should contact the Simi Valley Rotary Club to reach the company’s insurer. The annual July Fourth celebration has been sponsored by the city and the local Rotary Club for the past 43 years.

The company, based in Bethpage, N.Y., has produced events for NASA, Walt Disney World, Legoland and the Republican National Convention, according to the company’s website.

A video clip of the Simi Valley accident that aired on KCAL-TV shows a pair of firework blasts at or near the ground. Another clip, posted on YouTube and shot from a distance, shows three ground-level bursts. The fireworks continue for almost another minute before stopping.

Colette Schmidt, who lives across the street from the park and had about 150 guests over to watch the fireworks from her front lawn, said they could tell almost immediately that something went wrong.

Two regular fireworks went off, she said, and then others started exploding at ground level and shooting off horizontally toward the crowd “like a fan.”

One hit the ground across from their home, leaving a crater, and bounced twice before shooting up over nearby trees and exploding in a puff of reddish-purple smoke, Schmidt’s daughter, Alessi Smith, said.

The family herded their guests inside and drew the blinds as sparks and embers rained down. Sparks set a dry field next door on fire, but the flames were quickly put out.

“It was terrible, but we were so blessed because we had 150 people here and not one single spark hit our house,” she said. “It was all around us, but nothing here.”

Shannon said most people responded admirably and left in an orderly fashion. A bomb squad was sent to the park to deactivate the remainder of the fireworks.

Shannon said the fireworks primarily shot in one direction.

“They are going to travel the same distance across the park as they would in the air,” she said. “The ones that had actually ignited that had to run their fuse were going directly into the crowd.”

Simi Valley, home to the Ronald Reagan Presidential Library, is about 40 miles northwest of Los Angeles.