What is the immediate action if a diver loses O2 at a depth of 30' or 20'?

In the scenario where a diver loses O2 at a depth of 30 or 20 feet, the appropriate immediate action is to shift the diver back to air. This is crucial because maintaining a breathable gas mix is essential for the diver's safety and to prevent hypoxia, which can occur if a diver is deprived of oxygen. Switching to air allows the diver to safely continue their dive or ascend while avoiding the risks associated with a lack of proper oxygen supply.

At these depths, divers are typically operating under conditions that allow for a safe transition to air, assuming the diver is not experiencing an emergency that necessitates an immediate ascent. This action also helps ensure that the diver does not panic or become disoriented due to the lack of oxygen.

While activating an O2 supply system may seem like a viable option, it may not be feasible or immediate depending on the type of diving gear and setup being used. Initiating an emergency ascent could be dangerous without proper gas supply, as it can lead to decompression issues. Informing the support team is important, but it should follow the immediate need to stabilize the diver's breathing situation. Therefore, returning to air is the most effective and direct method to address the loss of O2 promptly.