Abstract: A process for safely preventing, controlling and/or extinguishing fires in confined spaces without damage to equipment, loss of habitability for personnel, loss of consciousness for personnel or a significant impact on the mental acuity of personnel in the confined space, which comprises introducing carbon dioxide and another inert gas, e.g. nitrogen or helium, to the confined space to lower the oxygen content to a concentration in the range between 8% and 15% by volume while increasing the carbon dioxide content of the confined space to an amount in the range of 2% to 5% by volume. The combination of reducing oxygen concentration and increasing carbon dioxide concentration in the gaseous environment of the confined space works together to sustain mammalian life, in particular, maintaining consciousness and mental acuity while not supporting, i.e. extinguishing, flame.