It happened as the Los Angeles Police Department bomb squad was transporting about 5,000 pounds of the confiscated items.
LAPD Chief Michael Moore said the explosion happened as officers intentionally detonated improvised explosives in the truck.
“Protocols were followed and pursued,” Moore said. “But something happened in that containment vehicle that should not have happened, and we don’t know why. But we intend to find out why.”
A man is charged with possessing the illegal fireworks that police had hauled away on pallets earlier Wednesday.
He also faces a child endangerment case because officers found two kids at the home.