Why CO2 system not used in places where there are many people ?

CO2 is not recommended for places with population because in any case there is fire the gas will be released and with this system the area will become cloased like the doors and all air in let out ler areas for some time so if there is any person inside it will be harmful for him and may cause some incident. Because it is necessay to make CO2 occupy whole area so it can putoff fire.

Hope this will work

answer in these percentages:

CO2 in the air is  0.03 % by volume

if it's concerate arrive to20% the human death

and we need at min34 % of CO2 to fight the fire