Otherwise unexplained blackouts underwater have been associated with the practice of hyperventilation. Survivors of shallow water blackouts often report using hyperventilation as a technique to increase the time they can spend underwater. Hyperventilation, or over-breathing, involves breathing faster and/or deeper than the body naturally demands and is often used by divers in the mistaken belief that this will increase oxygen saturation. Although this appears true intuitively, under normal circumstances the breathing rate dictated by the body alone already leads to 98–99% oxygen saturation of the arterial blood and the effect of over-breathing on the oxygen intake is minor. What is really happening differs from divers' understanding; these divers are extending their dive by postponing the body's natural breathing mechanism, not by increasing oxygen load. The mechanism is as follows: