Method for producing a first pressurised gas and a second gas on a one-off basis by cryogenic distillation of air in a dual column including a first column and a second column, the second column operating at a lower pressure than the first column, wherein: i) according to a first step, the air cools down at a first pressure, which is substantially the operating pressure of the first column, in a first heat exchanger and is sent to the first column, two nitrogen-rich gas flows (21, 23) originating from the first and second columns heat up in the first exchanger, at least one air flow (11, 13) at a second pressure that is greater than the first pressure cools down in a third heat exchanger, a pressurised liquid vaporises in the third exchanger and a nitrogen-rich gas flow originating from the second column heats up in the third exchanger, and ii) according to a second step, air cools down at the first pressure in the first exchanger and is sent to the first column, a nitrogen-rich gas flow originating from the second column heats up in the first exchanger, a pressurised liquid flow originating from the dual column heats up and vaporises in a second exchanger to form a gas required on a one-off basis, an air flow at the second pressure cools down and potentially condenses in the second exchanger, whereby this air flow and the pressurised liquid flow are the only fluids exchanging heat in the second exchanger, an air flow (11, 13) at the second pressure cools down in the third exchanger, another air flow at a pressure that is greater than the first pressure, or even the second pressure, potentially cools down in the third exchanger, a pressurised liquid vaporises in the third exchanger and a nitrogen-rich gas flow originating from the second column heats up in the third exchanger, characterised in that according to the first step, no fluid heats up or cools down in the second heat exchanger. i) according to a first step, the air cools down at a first pressure, which is substantially the operating pressure of the first column, in a first heat exchanger and is sent to the first column, two nitrogen-rich gas flows (21, 23) originating from the first and second columns heat up in the first exchanger, at least one air flow (11, 13) at a second pressure that is greater than the first pressure cools down in a third heat exchanger, a pressurised liquid vaporises in the third exchanger and a nitrogen-rich gas flow originating from the second column heats up in the third exchanger, and ii) according to a second step, air cools down at the first pressure in the first exchanger and is sent to the first column, a nitrogen-rich gas flow originating from the second column heats up in the first exchanger, a pressurised liquid flow originating from the dual column heats up and vaporises in a second exchanger to form a gas required on a one-off basis, an air flow at the second pressure cools down and potentially condenses in the second exchanger, whereby this air flow and the pressurised liquid flow are the only fluids exchanging heat in the second exchanger, an air flow (11, 13) at the second pressure cools down in the third exchanger, another air flow at a pressure that is greater than the first pressure, or even the second pressure, potentially cools down in the third exchanger, a pressurised liquid vaporises in the third exchanger and a nitrogen-rich gas flow originating from the second column heats up in the third exchanger,