The self-contained breathing apparatus is a device for breathing and protecting the respiratory tract, which completely insulates the operator from atmospheric air; it is used for rescue, emergency or work operations in contaminated environments. It is a type of respiratory mask that does not filter harmful substances from the air, but supplies air in sufficient quantity; SCBAs can use two technologies.
Closed cycle breathing apparatus Also known as rebreathers, they have no gas exchange with the outside: the exhaled air passes through a purifying cartridge, loaded with alkaline substances, which fix carbon dioxide and water vapour. Then it passes from another device which automatically doses the oxygen, taken from a high pressure cylinder, thus restoring the correct proportion and then to another stage which cools it with dry ice and then returns usable to the operator. These self-contained breathing apparatus have a great useful autonomy, which can even reach 4 hours, for example for operations in mines.
Open cycle breathing apparatus They are fed by an air reserve contained in a high pressure cylinder. Compared to a considerable operating economy, they have a more limited autonomy than closed-cycle breathing apparatus.