LOS ANGELES (AP) -- An investigation by the state fire marshal found that a Fourth of July fireworks accident that injured nearly 30 people at a show in Southern California was caused by the malfunction of a shell inside its mortar tube, authorities said Thursday.
The blast occurred during an aerial display show in Simi Valley, northwest of Los Angeles, as debris from fireworks, mortar tubes and the racks holding them flew into the crowd.
The findings conclude a 5-inch diameter, two-part fireworks shell failed to function as designed and exploded inside a mortar tube, resulting in several chain-reaction explosions, the Ventura County Fire Department said. Twenty-eight people were hurt.
The report found the show had proper permits, and Ventura County Fire Chief Mark Lorenzen said the display was properly designed and set up.
"All of the information we have on this incident indicates that there was simply a tragic malfunction that resulted in the explosions," he said.
The findings support statements made shortly after the mishap by witnesses, police and Dennis Brady Jr., chief executive of Bethpage, N.Y.-based Bay Fireworks, which put on the display.
County officials pledged to review state fireworks policies to see if additional local measures might be warranted, beyond what the state requires. Cal Fire spokesman Dennis Mathisen said it was unlikely that the incident would prompt the state to review its fireworks policies.
"As far as our investigation was able to tell, this was pretty much an isolated incident," he said.
The company had planned to shoot nearly 2,500 shells that ranged from 2.5 inches to 5 inches in diameter, Brady said in July.
At the time, Brady blamed a bad batch of shells for the Simi Valley accident and problems at another of its July 4 events in Laguna Hills.
The Laguna Hills show was shut down almost as soon as it started by a fire marshal because one of the mortars exploded at or near the ground, damaging some of the wiring to the rest of the fireworks that had yet to go off, city officials have said. No one was hurt.
A call and an email by The Associated Press seeking comment from Bay Fireworks were not returned Thursday.