You can use Co2 on almost anything but untrained it can be a very dangerous tool. One thing to remember is keep your head down! Always stay very low or you can be singed.
Most firedepartments over here have special instruction courses for companies. We folow an onstructionprogram there every year

Maybe Borax is just an ingredient in dutch powder extinguishers, or the firedepartment where I was instructed had it all wrong...