which gas helps to make the foam that firefighters use?

Answer 1

Compressed carbon dioxide is used as a gas in Fire Extinguisher. The idea is to deprive fire of oxygen and stop combution process. Though they do not foam.

For foam type of fire extingusiher, the principle is based on surfactant that can stay on water and foam. Fire Retardant Foam, or fire suppression foam, is a foam used for fire suppression. Its role is to cool down the fire and to coat the fuel, preventing its contact with oxygen, resulting in suppression of the combustion. The surfactants used have to produce foam in concentration of less than 1%.

Answer 2

There is no 'gas' in foam. It is usually detergent and water under pressure. The foam covers the burning material and takes away the oxygen.