The invention relates to an on-site medical gas production plant (100) comprising a unit (50) for purifying gas, such as air, a first compartment (A) for storing purified gas, and a main gas line (10) fluidically connecting the gas purification unit (50) to the said first storage compartment (A). It furthermore comprises a three-way actuated valve (VA) arranged on the main gas line (10) upstream of the first storage compartment (A), and furthermore connected to the atmosphere (at 12) via a vent line (11), as well as an operating device (4) which controls at least the three-way actuated valve (VA), and at least a first gas analysis device (D1) of which a first measurement line (29) is fluidically connected (at 28) to the main line (10), upstream of the three-way actuated valve (VA), and which is electrically connected to the said operating device (4).