Gary Markowitz sent NBC4 this image of a fireworks explosion July 4, 2013 in Simi Valley.
An investigation into an explosion that sent debris into a crowd at a Southern California Fourth of July fireworks show determined that a malfunction involving a shell inside a mortar tube led to the blast.
Twenty-eight people were injured in the explosion when mortar tubes and the racks holding them were blasted into the crowd at the Simi Valley event. The report released Thursday that faults the fireworks shell was issued by the California fire marshal.
The agency concluded that a 5-inch diameter, two-part fireworks shell failed to function as designed. The shell exploded in the mortar tube, leading to more explosions.
The show had proper permits and the display was properly designed and set up, according to the report. Investigators determined the was not a pattern of problems with the type shell, known as a "double bubble."
"All of the information we have on this incident indicates that there was simply a tragic malfunction that resulted in the explosions," said Ventura County Fire Chief Mark Lorenzen. "The display was properly designed and set up. That being said, our responsibility is to do everything we can to ensure the safety of the people of Ventura County. As a result, we will be reviewing the state fireworks polices to see if additional local measures might be warranted."
A representative of Bay Fireworks said the company will no longer use the type of shell that malfunctioned and increase the minimum distance between specatators and the launch area.
Most of the victims injured in the blast at Rancho Santa Susana Community Park were treated at a hospital and released.
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