Your vacation in paradise offers a deep dive to the signature attraction, a wreck at 110 feet and beyond. You've never been that deep before. Should you attempt the dive?
The risks of DCS, running low on air and nitrogen narcosis increase as you go deeper, but these risks are manageable with training, the right equipment, experience and this five-step plan.
1. Decide If You're Ready
|Photo by Chris Jaffe|
To decide if you're ready for the dive, consider:
- Your diving experience. How many dives have you made since your open-water certification? Beginning divers are advised to stay above 60 feet, in large part to give them time to internalize skills and procedures at a comfortable depth. Become totally comfortable with shallow diving before you go deeper.
- Your deepest previous dive. How deep have you already been, how often have you been deep and how recently? It's best to increase your depths gradually. Get in a few dives to 80 feet or below before you try 110. They should be dives within the last year, since learning degrades over time.
And how did you feel the last time you went deep? Getting back on the horse that threw you may or may not be the way to learn to ride, but if you were scared witless at 80 feet don't expect to cure yourself by going to 110.
- Your equipment. Obviously, you need to be properly equipped and your gear has to be in good condition. Not so obviously, none of your equipment should be brand-new on that deep dive. In order to stay calm and able to handle the unexpected, you need to keep your "task loading" to a minimum. At depth on a 110-foot dive is no place to forget which is the inflate button on your new BC. Or to discover that your new mask fogs. You should feel confident with your gear before you go deep.
- Your buddy's experience and equipment. The least-prepared buddy should determine the limits of the dive. Resist the temptation to exceed your buddy's comfort level ("Relax. You'll be fine!") or your own ("I guess he knows what we're doing"). When you're nervous about a dive, pride and the fear of admitting fear can make it hard to face the truth.
- The conditions of the dive. In many ways, "deep" is relative. A 110-foot dive in warm, clear, calm Caribbean water is probably not as challenging as a 70-foot dive on a cold, current-swept New Jersey wreck. What counts is the total stress level. Depth is one stress—others are cold, current, low visibility, surge, equipment load, anxiety, fatigue and more.
- Surface support. Is someone staying with the boat to make sure it stays anchored, and to render help if it's needed? Is there oxygen on board? A radio? Will an ascent/descent line be deployed? A hang bar? Is a recompression chamber reachable within a few hours? Do the divemaster, the boat captain and the diving operation inspire confidence?
- Your motivation. Finally, ask yourself why you are considering this dive at all. Because you want to see the wreck is a valid reason. Because you want to make a moderate and prudent expansion of your deep diving experience to help prepare you for that dream trip to Truk is valid too. "Because everybody else is doing it and I don't want to look like a wimp" is not.
2. Prepare Yourself
If you and your buddy decide to make the deep dive, use the dives between now and then to prepare:
- Fine-tune your weighting. You want the minimum weight that lets you hang at 15 feet on a nearly empty tank. Any excess weight requires more air in your BC. The excess air compresses, so your buoyancy fluctuates more with depth and will be more difficult to control.
- Compare air consumption. Who ends a dive with more air, you or your buddy? Plan the deep dive according to the needs of the "air hog."
- Sort out gear problems. The shallower dives are a chance to make sure your equipment is working right and is adjusted properly.
3. The Dive Day
- Be rested. Plan on an early night before the morning of your dive. Fatigue predisposes you to DCS, nitrogen narcosis and—probably more important—carelessness.
- Be hydrated. Dehydration also increases the DCS risk, and leads to fatigue sooner. Limit your intake of alcohol and caffeine starting the night before, because both cause dehydration for many hours afterward. And drink lots of water—about two extra quarts per day.
- Be "green." That is, be well into the green zone of your computer. It's best to make the deep dive the first of the day, so you have the benefit of a full night of off-gassing. "Deepest dive first" is no longer considered an absolute rule because a dive computer can track your nitrogen loading fairly accurately, but it's still a wise practice. Any of the green zone you use up in an earlier dive reduces your available time on the deep dive.
- Plan the dive. This is the time for a more complete, more formal dive plan than seemed necessary on shallower dives. Remember to plan for the limits of the least-capable buddy.
As important as time, depth and route decisions is the opportunity dive planning gives you and your buddy to consider how you both feel. If either has any doubts, both of you should abandon the deep dive.
- Make a buddy check. If you'll ever trap a hose under a BC strap it will be now, when you're a bit nervous. And make sure each of you locates, and knows how to use, the other's alternate air source, BC inflator and weight release.
- Make a final go/no go decision. Look each other in the eye: does this still feel good? Actually, this is not a final decision. Either buddy can abort the dive for both at any point, and shouldn't hesitate to do so for any reason.
4. In the Water
- Watch your buoyancy. Your buoyancy will fluctuate more with greater depth as the air in your BC and the bubbles in your wetsuit compress. Your descent rate can accelerate so much that it can be hard to stop at your planned depth. You can then waste considerable air inflating and venting your BC as you search for neutral buoyancy.
- Watch your breathing rate. Slow, deep, relaxed breathing is especially important during a deep dive because the air you're breathing is much denser. As the air stream turns corners and passes restrictions in its journey from your tank to your lungs, friction causes turbulence, which restricts the air flow and increases your breathing effort. Denser air and fast-moving air both increase the amount of turbulence. So as the air becomes denser with depth, it's important to keep the speed of the air stream down—to breathe slowly. Likewise, you can easily lose control of your ascent rate from depth unless you watch your rate carefully and vent your BC constantly.
- Watch your gauges. All the readouts for depth, air pressure and bottom time change more quickly at depth. At the same time, the margin for error is smaller and the consequences are more serious. Check your gauges more often than you're used to on shallower dives.
- Watch your buddy. Check your buddy more frequently than you normally do. Some buddies agree to make eye contact every three to five breaths, for example. Look for signs of anxiety, like rapid breathing, jerky movements and a "wide-eyed" look. Is your OK sign returned quickly and calmly? Check your buddy's gauges from time to time, and expect your buddy to check yours.
- Dive the plan. Follow the dive plan you've agreed to, especially the maximum depth and bottom time, and the time or air pressure for beginning your ascent.
- Ascend early and slowly. The greatest danger in a deep dive is probably in the ascent. Because your buoyancy changes more than you're used to, it's easy to lose control of your ascent rate and blow through your safety stop. Because you use air so rapidly at depth, if you don't watch your gauges closely it's easy to run low and have to make a dangerously rapid ascent.
Denser air also means more molecules of the stuff that your regulator has to process with each breath. Rapid breathing can exceed the flow rate of even a good, well-maintained regulator, increasing your work of breathing.
Shallow breaths, which tend to be rapid ones, lead to a build-up of carbon dioxide in your system. That's because the CO2-rich "dead air" space in your throat, mouth and second stage is diluted less by incoming fresh air. High carbon dioxide concentrations, which can also be caused by high work of breathing, trigger the impulse to breathe quicker and shallower. Now you're in a "vicious cycle": breathing harder because you're breathing harder, and getting less and less air.
Finally, shallow, quick breathing is an early sign of anxiety. When breathing also becomes harder, anxiety can become panic.
What to do? Stop finning and hold on to something like a mooring line if you can. Take a slow, deep breath, trying to completely fill your lungs. Then exhale slowly trying to completely empty your lungs. Do it again, until you relax.
One exception: never be reluctant to begin your ascent earlier than you had planned, whether because you've used air faster than you expected or because either of you feels uneasy.
To control your ascent rate, make a serious effort to locate and use the ascent line, or an anchor or mooring line, or a stand of kelp. Begin venting your BC early. Don't use the lift of your BC to ascend; instead, stay neutral or even slightly negative and fin to ascend.
Beginning your ascent with enough air means planning very conservatively. Some divers follow the rule of thirds, using the first third of their air supply for the descent and bottom exploration and the second third for the ascent, retaining the final third for reserve. That would mean beginning your ascent when a 3,000 psi tank reaches 2,000 psi.
Another rule of thumb is to plan on 100 psi for each 10 feet of ascent. Adding a 500 psi reserve, that would mean beginning your ascent from 110 feet at 1,600 psi (100 x 11 + 500 = 1,600).
How conservatively you plan will depend on your (and your buddy's) experience and breathing rate.
If you have some doubt whether you have enough air to maintain a 30-foot-per-minute ascent rate from the bottom, make a faster ascent at first (say, 60 feet per minute), then slow down to 30 feet per minute at 60 feet. Even if you reach 15 feet with less than the normal 500 psi reserve, use it there for a safety stop.
Remember that all dives, and especially those to below 60 feet, are in fact decompression dives. A slow ascent rate and a safety stop at 15 feet serve the same purpose as planned decompression stops. Don't omit them.
5. After the Dive
- Rest. Though you have not violated no-decompression limits, you have taken on a large nitrogen load, and DCS is possible. Avoid exertion for at least an hour and drink plenty of water. Moist tissues exchange gas more quickly, and a well-hydrated blood supply is thinner so it circulates more quickly.
- Don't fly immediately. The current Divers Alert Network advice is to wait 12 hours after a single no-decompression dive and "more than 12" after a planned decompression dive, or multiple dives, or multiple days of diving. Better put a deep dive in the latter category.
How much "more than 12?" Because a deep dive may be pushing the no-decompression limits, it's safest to wait at least 24 hours. And it probably helps to make your deep dive near mid-week, when you're recovered from jet-lag, up to speed with your equipment and still have several days to off-gas nitrogen.
Planning a Deep Dive
Formal dive planning is more important when the stresses are higher and the margin for error is smaller. The planning process is also a time to gauge your buddy's anxiety level—and your own. The elements:
- Objective and route.
- Time, depth, air limits. Especially important when no-decompression bottom time may be only a few minutes. And decide on a time or air pressure for starting your ascent.
- Conditions. Are you both comfortable with the planned depth, the vis, the current, the cold?
- Equipment. Where is your buddy's BC inflator, alternate air, weight release, etc.? Are you both rigged correctly?
- Communications. Have you agreed on the same hand signals?
- Lost buddy procedure. What will you do if you are separated?
- Emergency skills. Review what to do in the event of low air, entanglement, etc.
Gearing Up for Going Down
- Equipping yourself for deeper diving means having the proper gear and maintaining it.
1. High-performance regulator. Delivering enough air to two divers at depth from a low tank requires a high-performance reg. Consult Rodale's ScubaLab tests for the latest performance reviews. Regular maintenance of your regulator may be as important as its initial design. Regulator flow characteristics degrade over time, even when just sitting in your gear bag. Have your reg overhauled regularly.
2. Alternate air source. If you run out of air at depth you'll be glad your buddy's octopus is a high-performance regulator. It is, isn't it? In reality, your buddy is probably low on air too, and his octopus won't do you much good. That's why many deep divers use a completely redundant air source—a pony bottle and regulator or Spare Air.
3. Compass. Navigation is more important at depth because you can't realistically pop to the surface to orient yourself. And finding the ascent line will make it much easier to control your ascent rate.
4. Dive computer. If you don't have one yet, now's the time. A dive computer is far more capable than a table at predicting your nitrogen loading over several multilevel dives, and this is especially important when you may be pushing the no-decompression limits.
5. Submersible pressure gauge. Of course you have one, but how accurate is it? Better have it checked.
6. Surface signaling devices. If you have to make a free-swimming ascent from depth when current is running, you may surface far from the dive boat. An auditory signal (like a Dive Alert horn) and a visual one (like a safety sausage) will make your day.
7. Exposure protection. You'll probably need more at greater depths. One reason is that you may pass through a thermocline and enter much colder water. Another is that neoprene compresses as you go deeper. At 110 feet, your wetsuit loses more than three-fourths of its insulating value.
Q: What is it?
A: An impairment of your thinking processes caused by breathing nitrogen under pressure. The likelihood increases with depth. U.S. Navy tests showed all subjects had some narcosis at 100 feet.
Q: What are the signs?
A: Most often, a false sense of security and inappropriate euphoria. Though if you start the dive anxious, narcosis may take the form of paranoia. It seems to magnify your current emotional state, whatever that is. The tricky part is recognizing when your sense of security is false or when your fear is justified.
Q: What can you do about it?
A: Stay focused. At recreational depths narcosis is normally mild. You can usually overcome it by concentrating on your dive plan, your instrument checks, your buddy checks, etc.
Ascend. Often, going up only 10 feet will alleviate the symptoms almost immediately. Then, you can often return to the original depth without symptoms.
Be warm and rested. Breathe slowly. Fatigue, cold and high carbon dioxide levels promote nitrogen narcosis.
Be clean. Many drugs, including favorites like Sudafed, Dramamine and Scopolamine, interact with nitrogen and accelerate its effect.
Get used to it. Divers seem to be able to develop a tolerance for nitrogen narcosis with deep diving experience. Working up to your planned depth will reduce narcosis problems, though the adaptation fades in a week or so.