In even our earliest training, divers are taught procedures for emergency situations, such as running out of air. Unfortunately, many divers never practice these skills beyond their entry-level training. Being unfamiliar and out of practice with these basic life-saving procedures can lead to catastrophe. Take the case of Mary and Steven.
Mary was a certified divemaster, and Steven was a newly certified advanced open-water diver on his first ocean diving excursion. Both divers were reasonably fit and by most accounts had good water skills.
They were diving off the coast of North Carolina with a group that had traveled there to dive the spectacular wrecks offshore. The day started uneventfully with the group boarding the vessel for the two-hour journey to a popular wreck site at 115 feet. Steven experienced the anxiety typical on a diver's first ocean dive.
The boat arrived and anchored at the site on calm seas with a slight to moderate current running north. The captain gave a very thorough and detailed briefing of the wreck site. The briefing included entry and exit procedures for the boat, the lay of the wreck, the current conditions and, most importantly, procedures to be followed in case of an emergency. The group entered the water, where they found excellent visibility as they descended the anchor line to the wreck.
Fifteen minutes into the dive, Steven discovered that in the deep water, he depleted his air supply much sooner than anticipated. His buddy was too far away to be reached. Fortunately, Mary was hovering just above the group and immediately sensed the problem. She swam quickly to Steven with her octopus in hand and provided him air to breathe. Steven's anxiety was now dramatically elevated by his brush with death. Mary assessed the situation and discovered that they were in a moderate current at a part of the wreck that was a good distance from the ascent line. Other divers recalled seeing Mary check her gauges as she grabbed Steven and began swimming toward the anchor.
Mary and Steven reached the anchor line and began their ascent. Unfortunately, Mary underestimated the impact Steven's elevated breathing rate would have on her air supply. Best estimates indicate that around 50 feet, Mary also ran out of air, leaving both divers in dire straits. At this point, panic set in. Mary pushed away from Steven, who drowned and sank to the bottom. She made a panicked rush for the surface. Unfortunately, either holding her breath or ascending too fast for air to escape her lungs, she suffered an embolism. The crew of the dive boat saw Mary break surface a short distance astern and immediately pulled her from the water. She was given oxygen, but because of lung damage and excessive fluid buildup, she did not survive to be evacuated, despite the best efforts of the crew.
Mary was well-versed in procedures for sharing air. Her colleagues noted an almost excessive habit of practicing the skill. Unfortunately, her practice rarely included direct ascents to the surface or procedures for arriving safely at the boat.
The boat captain had cautioned the divers during his briefing to ascend immediately in the event of any trouble. He addressed the current by assuring the divers that if they were to surface behind the boat, either a mate would swim a line to them or the boat would come around and pick them up. He also cautioned that gas supplies would dwindle very quickly on a dive of this depth.
In diving, it's rare for a single mistake to lead to a fatality. In this case, Steven made two mistakes that were then compounded by a bad judgment call on the part of the divemaster. First, Steven failed to manage and monitor his air supply properly. Second, he was too far from his buddy when he ran out of gas. Mary's response at this point was exemplary. Unfortunately, after responding, she made the final tragic error of trying to swim several hundred feet to the anchor line against the current before ascending. Had they ascended immediately, the divers would have had an ample supply of air to ascend and possibly even to have completed a safety stop.
Lessons for Life
- Divers and dive leaders alike should practice emergency skills routinely. To be effective, these skills must take you all the way to the surface and beyond--back to the boat, beach, etc.
- Surface immediately in an out-of-air situation. It is far easier to breathe with an empty tank on the surface than it is under water. Although very inconvenient, surfacing down current from the boat is usually quite survivable, especially compared to the alternative.
- On deep dives especially, divers should consider the use of a completely redundant air source such as a pony bottle. Be certain that the volume of air available is adequate for the depth of the dive.
- Never underestimate the impact of depth on your air supply. On deep dives, divers should take particular care to monitor air supply constantly.
- When diving with a buddy, divers should maintain close proximity and the ability to communicate visually at all times.
Are You Really Out of Air?
What a diver senses as an out-of-air situation is usually a low-on-air situation. Indeed, in nearly all scuba accidents, the victim still has air and the regulator still functions. What usually happens is that divers breathe their air supply down so low that the regulator can no longer provide air at the effort level required by the diver. In theory, this occurs when ambient (surrounding) pressure equals tank pressure. At 100 feet, this would be about 60 psi. This is not what actually occurs, however. Regulator studies and diver experience have shown that because of the mechanics and maintenance of regulators, diver breathing habits and rates, and the inaccuracies of submersible pressure gauges, the diver will feel out of air at a tank pressure higher than ambient pressure and that this disparity increases with depth. These are among the reasons why the current practice is to surface with 500 to 800 psi remaining, rather than 300 psi.