With a rebreather, ascents can be one the most dangerous part of the dive. As a rebreather diver ascends, the PO2’s drop & if PO2’s are already low, these levels can drop to dangerous & life threatening levels. The rebreather, even if automatic, can be too slow to catch up. An uncontrolled ascent can cause the PO2’s to drop to non- life sustaining levels. It is believed that this is what happened to cave diving explorer & videographer, Wes Skiles while filming footage in the Keys. He had signaled that he was going back up to the boat to get more film & was found unresponsive back on the bottom. Rebreathers take a constant diligence & one can not let their guard down, even for a moment.