A hash oil manufacturer in downtown Los Angeles exploded Saturday night, shooting balls of flame out of the building.br The explosion sent firefighters running for their lives.br A dozen firefighters were injured, including some who tore off their burning protective equipment, including melted helmets.br Newser reports police and fire investigators have now launched a criminal probe into the cause of the blast.br Detectives from the LAPD's major crimes division are working with the city Fire Department's arson investigators.