A device for providing buoyancy comprising; —a bladder capable of being inflated; —a vessel containing fluid for inflating the bladder; and —one or more valves for controlling the passage of fluid between the bladder and the vessel; wherein one or more of the valves are capable of being opened to permit the passage of fluid from the vessel to the bladder in response to at least one of exposure of the device to a pre-determined pressure level and detection of blood oxygen concentration below a pre-determine threshold in an individual using the device.