An oxygen mask for pilots and crew of an airplane, the oxygen mask having an oronasal face seal defining an oronasal cavity, an oxygen supply regulator, and an auxiliary breathing flow channel apparatus, the auxiliary breathing flow channel apparatus comprising: an auxiliary breathing flow channel defined through a portion of the oxygen mask; a flow regulating valve mechanism for regulating flow through the auxiliary breathing flow channel, the flow regulating valve mechanism being movable between at least one closed position in which flow through the auxiliary breathing airflow channel is blocked and an open position in which flow through the auxiliary breathing flow channel is enabled; biasing means for applying a biasing force to the flow regulating valve mechanism to maintain the flow regulating valve mechanism in the at least one closed position, such that the auxiliary breathing flow channel is blocked; means (116, 120) for moving the flow regulating valve mechanism into the open position; latching means (82, 90, 92, 94, 96) for releasably retaining the flow regulating valve mechanism in the open position; and means (116, 120, 128) for releasing the latching means (82, 90, 92, 94, 96) to allow the flow regulating valve mechanism to revert to the closed position, the oxygen mask being characterised in that: said auxiliary breathing flow channel is an additional flow channel defined through a portion of the oxygen mask, said auxiliary breathing flow channel being connected to ambient air and configured to deliver ambient air through said auxiliary breathing flow channel to the oxygen mask. an auxiliary breathing flow channel defined through a portion of the oxygen mask; a flow regulating valve mechanism for regulating flow through the auxiliary breathing flow channel, the flow regulating valve mechanism being movable between at least one closed position in which flow through the auxiliary breathing airflow channel is blocked and an open position in which flow through the auxiliary breathing flow channel is enabled; biasing means for applying a biasing force to the flow regulating valve mechanism to maintain the flow regulating valve mechanism in the at least one closed position, such that the auxiliary breathing flow channel is blocked; means (116, 120) for moving the flow regulating valve mechanism into the open position; latching means (82, 90, 92, 94, 96) for releasably retaining the flow regulating valve mechanism in the open position; and means (116, 120, 128) for releasing the latching means (82, 90, 92, 94, 96) to allow the flow regulating valve mechanism to revert to the closed position, the oxygen mask being characterised in that: said auxiliary breathing flow channel is an additional flow channel defined through a portion of the oxygen mask, said auxiliary breathing flow channel being connected to ambient air and configured to deliver ambient air through said auxiliary breathing flow channel to the oxygen mask. said auxiliary breathing flow channel is an additional flow channel defined through a portion of the oxygen mask, said auxiliary breathing flow channel being connected to ambient air and configured to deliver ambient air through said auxiliary breathing flow channel to the oxygen mask.