Pressure-demand breathing apparatus with automatic air shut-off

In a pressure-demand breathing apparatus including a face mask providing a mask chamber when fitted against the face of a wearer and means including an air supply line for connecting said mask to a pressurized air supply, a pressure demand regulator positioned in said air supply line between said face mask and said air supply,

• said pressure-demand regulator including means responsive to pressure within said mask chamber for admitting said pressurized air to said mask chamber at flow rates required for normal breathing or abnormally deep breathing when said mask is worn and for maintaining a predetermined positive pressure in the mask chamber above the ambient pressure when said mask is worn, said regulator also admitting said pressurized air to said mask at a predetermined high air flow rate substantially greater than that required either for normal breathing or for abnormally deep breathing when said mask is removed, the improvement comprising shut-off means positioned between said pressure-demand regulator and said air supply, said shut-off means being responsive to said predetermined high air flow rate through said pressure demand regulator which exceeds that required even for abnormally deep breathing for automatically interrupting the supply of air to said mask under unrestricted flow conditions such as occurs when the mask is removed from the face of a wearer and is open to the ambient atmosphere, whereby said shut-off means is inoperative during normal breathing and during abnormally deep breathing when the mask is worn but only becomes operative when the flow therethrough exceeds the flow which occurs during abnormally deep breathing so that sufficient air is supplied to the wearer at all times when said mask is worn but the air supply is shut off when said mask is removed, to thereby prevent unwanted depletion of said air supply.