Authorities estimate people were about 900 feet away from where the fireworks were being launched. 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.
Shannon said most people responded admirably and left in an orderly fashion. A bomb squad was at the park to deactivate the remainder of the fireworks.
She added the fireworks primarily shot in one direction.
"They are going to travel the same distance across the park as they would in the air," Shannon said. "The ones that had actually ignited that had to run their fuse were going directly into the crowd."
The annual July Fourth celebration has been sponsored by the city and the local Rotary Club for the past 43 years. Shannon said she had no information about the company hired for the fireworks show.
Simi Valley, home to the Ronald Reagan Presidential Library, is about 40 miles northwest of Los Angeles.