The DeBreather creates of a low oxygen (hypoxic), low carbon dioxide (hypocapnic) environment that can peacefully end the life of the user. The closed system contains several liters of air. This air has an initial oxygen O2 carbon dioxide CO2
level of 21%, Nitrogen at 79% and of ~0.04%. This air is inhaled. On expiration,
the exhaled gas has an oxygen level of ~ 17%. and ~4% carbon dioxide. As this exhaled air passes through the soda lime scrub- ber, the carbon dioxide is removed, and what remains in the sys- tem is a gas where the oxygen level drops with each breath, but with no associated rise in carbon dioxide.
Provided the system remains closed, with no additional oxygen entering the system (from, for example, a poorly-fitting face mask) the process will continue with little discomfort. Breathing will be easy. Once the oxygen level drops to around 5 -10%, loss of consciousness occurs and with a further inevitable drop, death.
The time taken for death to occur using the DeBreather depends predominantly on volume of gas in the closed system, and the rate at which the oxygen is used. This depends on DeBreather design, and the size, body weight and lung capacity of the individual.
Of importance is the total removal from the closed system of ex- haled carbon dioxide. This is a function of design. The original Smith-Hofsess system made use of a reciprocating system with exhaled air passing through the absorber (scrubber) into a reser- voir (the ‘counter lung/) and then inhaled back through the scrub- ber. Their scrubber used a solution of lithium hydroxide which combined with the carbon dioxide to form lithium carbonate.