A faulty pyrotechnic shell caused that Fourth of July fireworks explosion in Simi Valley. That's according to the findings of an investigation by the California fire marshal.
The findings released Thursday conclude that a 5-inch diameter, two-part fireworks shell failed to function as designed and exploded inside a mortar tube, resulting in several subsequent sympathetic explosions.
"Consequently the explosions after that were basically due to the force of that initial explosion in the mortar spreading to other mortar, and that caused the main failure of the system," said Ventura County Fire spokesman Mike Lindbery.
That accident sent fireworks and debris into a crowd of spectators, injuring 28 people. Video footage showed people screaming and running for cover.
The report also found that the show had proper permits and that the display was properly designed and set up.
"We make sure that the pyrotechnic agency has all of their licenses and permits to do the show. The city of Simi Valley also does conditional use permits and the Fire Prevention signs off to make sure the display is safe and permitted," explained Lindbery about the process required to put these fireworks displays together.
It's still not clear how this incident may affect future fireworks shows in Simi Valley, said Lindbery.
"[The Ventura County Fire Department] will be looking at the state regulations regarding this type of display and see if we need to do any additional things here on the local level."