Before any type of dangerous gas (Halon, CO2) is released there should be some type of warning emmitted. (CO2 will sufficate people)
Halon is a type of gas that used to be commonly used, it is no longer used do to CFCs. (it is also dangerous to people). It was banned by the “Montreal protocol”* in 1987. effective replacement is FM-200 or others on top of pg 444*