Abstract: A hood comprising a flexible envelope and a reservoir of oxygen comprising a calibrated outlet orifice that leads into the internal volume of the envelope, the outlet orifice being closed off by a removable stopper, characterized in that the reservoir of pressurized oxygen comprises two independent storage compartments, a first compartment of which communicates with the outlet orifice and a second compartment of which is isolated from the outlet orifice via a sealed partition provided with a member for opening the partition, the opening member being switchable between a first configuration which prevents fluidic communication between the second compartment and the outlet orifice and a second configuration that allows fluidic communication between the second compartment and the outlet orifice, the opening member being sensitive to the pressure difference between the second compartment and the first compartment and being configured to automatically switch from the first to the second configuration when the pres