Aerosol fire extinguishers chemically and physically extinguish a fire by breaking the chain of chemical reactions that sustain the fire and by absorbing free radicals, such as hydrogen and hydroxyl molecules, which are important for the fire to continue. This is done by binding free radicals to the aerosol particles and removing them from the combustion reaction. Aerosol fire extinguishers do not significantly reduce the oxygen level in the environment and can therefore be safely used in areas where people or other living things are present without posing a risk to them.