Abstract: Breathing apparatus is provided for use under water which comprises a connection device such as a helmet, mask, or the like and a breathing circuit in communication with the connection device. The breathing circuit includes a carbon-dioxide absorber and an expansible gas chamber, and, in operation, provides a first operating period wherein the breathing circuit is closed and a breathing gas is caused to circulate in the breathing circuit until the oxygen concentration of the circulating breathing gas is reduced to a predetermined value and a second operating period, which alternates with the first, wherein the used breathing gas is released to ambient and a fresh gas, the quantity of which is substantially independent of the depth of the user under the water surface, is applied to the breathing circuit.

Abstract: Breathing apparatus is provided for use under water, in a noxious atmosphere or under like conditions, which provides pressure compensation during release of the consumed breathing gas. The apparatus includes a connection device such as a breathing mask for connecting the apparatus to the breathing organs of a user and a breathing circuit which communicates with the connection device and includes a carbon-dioxide absorber and an expansible gas chamber. The apparatus includes controls which, during the operation of the breathing circuit, provide (i) a first operating period wherein the breathing circuit is closed and a breathing gas is caused to circulate in the breathing circuit until the oxygen concentration of the circulating breathing gas is reduced to a predetermined value and (ii) a second operating period which alternates with the first period, wherein the used breathing gas is released to the ambient environment and fresh gas is supplied to the breathing circuit.