Next time get an Ordnance Disposal Tech from the Army. A pile of fireworks will contain the gunpowder burn and give you a much larger explosion than you might expect. In Vietnam I saw “mere” concussion grenades (”only” 1/4lb C4) throw wood splinters (very dangerous) a hundred yards. It can definitely ruin your day. It’s nothing like in the movies.
Ping. Follow up story.
Tl;dr - “Our people screwed up.”