In the PADI Open Water Scuba Diver course, you learned several ways to handle running low on or out of air, including using an alternate air source. This usually means using your buddy's extra second stage, but consider using an independent alternate air source (pony bottle or self contained ascent bottle) for more self reli­ance, especially when diving in more challenging environments such as currents, limited visibility or depths below 18 metres/60 feet. Since pony bottles and self contained ascent bottles hold addi­tional air and function independently from your primary scuba, you can make a safe independent ascent in the event of unexpected air supply loss. Of course, you and your buddy should always plan your dives with an ample air reserve so you don't run out in the first place.

You probably recall that vertigo is the unpleasant experience of losing your orientation when ascend­ing or descending so that you can't tell whether you're going up or down. Dizziness often accompa­nies vertigo, with potential hazards if you become significantly disoriented. To reestablish orientation quickly, make contact with a stationary reference, such as an ascent/descent line or the bottom. If you're in midwater and lack a stationary reference, checking your depth gauge and watching your bubbles may reorient you. It often helps to make contact with your buddy.