A device comprising: an intake pump that draws in gas from outside the device to create a gas stream; a first sieve comprising an input, a separated output, and a residual output, wherein: the gas stream created by the intake pump enters the first sieve through the input; the first sieve separates the gas stream into a mixture including oxygen and a residual stream; and the mixture flows to the separated output of the first sieve and the residual stream flows to the residual output of the first sieve; a second sieve comprising an input, a separated output and a residual output, wherein: the input of the second sieve is coupled to the residual output of the first sieve such that the residual stream flows from the first sieve to the second sieve; the second sieve separates nitrogen from the residual stream, which is output through the separated output of the second sieve; and a remaining portion of the residual stream, which is stripped of nitrogen, vents to outside of the device through the residual output of the second sieve; a gas processor that couples to the separated output of the first sieve, wherein the gas processor separates the oxygen from the mixture, the device characterized by a primary oxygen storage canister that stores oxygen separated from the mixture until an oxygen-concentration threshold is met; a nitrogen storage canister coupled to the separated output of the second sieve that stores the separated nitrogen; and a breathing mask that receives a breathable air comprised of stored oxygen and nitrogen. an intake pump that draws in gas from outside the device to create a gas stream; a first sieve comprising an input, a separated output, and a residual output, wherein: the gas stream created by the intake pump enters the first sieve through the input; the first sieve separates the gas stream into a mixture including oxygen and a residual stream; and the mixture flows to the separated output of the first sieve and the residual stream flows to the residual output of the first sieve; the gas stream created by the intake pump enters the first sieve through the input; the first sieve separates the gas stream into a mixture including oxygen and a residual stream; and the mixture flows to the separated output of the first sieve and the residual stream flows to the residual output of the first sieve; a second sieve comprising an input, a separated output and a residual output, wherein: the input of the second sieve is coupled to the residual output of the first sieve such that the residual stream flows from the first sieve to the second sieve; the second sieve separates nitrogen from the residual stream, which is output through the separated output of the second sieve; and a remaining portion of the residual stream, which is stripped of nitrogen, vents to outside of the device through the residual output of the second sieve; the input of the second sieve is coupled to the residual output of the first sieve such that the residual stream flows from the first sieve to the second sieve; the second sieve separates nitrogen from the residual stream, which is output through the separated output of the second sieve; and a remaining portion of the residual stream, which is stripped of nitrogen, vents to outside of the device through the residual output of the second sieve; a gas processor that couples to the separated output of the first sieve, wherein the gas processor separates the oxygen from the mixture, a primary oxygen storage canister that stores oxygen separated from the mixture until an oxygen-concentration threshold is met; a nitrogen storage canister coupled to the separated output of the second sieve that stores the separated nitrogen; and a breathing mask that receives a breathable air comprised of stored oxygen and nitrogen.