A Limitations Checklist

Diving with a competent buddy or guide isn’t a substitute for self-accountability. You should dive only in conditions that you are confident lie within your limits. And remember, everybody has limits. The most skilled divers need to be just as aware of their limits as new divers.

Here’s follows a checklist of the limitations to which every diver should be attuned.

Your NDL

What: Remain within your no-decompression limit (NDL) — the time you can stay at a particular depth without performing mandatory decompression stops during your ascent.

Why: Heeding your NDL controls the amount of nitrogen dissolved in your tissues and thus keeps your risk of decompression sickness low. If the amount of dissolved nitrogen remains small and your ascent rate is reasonably slow (not exceeding 30 feet, or 9 metres, per minute), you can head right for the surface while keeping your risk of decompression sickness reasonably low. But if you exceed your NDL, you will have a “ceiling” — a depth where you will have to stop to allow time for off-gassing. This is known as a mandatory decompression stop and is essential to avoiding decompression sickness. Don’t confuse a mandatory decompression stop with a safety stop, which is an optional but highly recommended additional safety measure. The Divers Alert Network advises a 3- to 5-minute safety stop, about 10 to 20 feet (3 to 6 metres) below the surface, on every dive.

Step-by-Step: Staying within your NDL

  • Become familiar with your dive computer or dive tables on land, before you head into the water. Read the manual and ask for assistance if there’s any aspect of its operation you’re unclear about.
  • Consult your preferred tool before every dive to determine the NDL time for that dive.
  • Remember that electronics can break or malfunction, so be sure you have access to dive tables or a backup dive computer. A backup dive computer can only be used if it has been with you on all of your previous dives within 24 hours.
  • Never dive without a depth gauge and a timing device, either computer-based or analog.
  • Remember that every dive is a decompression dive. No-decompression limits assume a slow and safe ascent rate.

Dive professionals often say “Do not push the limits,” which means don’t remain at maximum depth throughout a dive. Instead, ascend and continue your dive while you still have some no-decompression time remaining. Cutting your time at depth shorter than your NDL adds safety to your dive.

Your Breathing Capacity

What: Account for the effects of breathing dense, compressed gas at depth.

Why: Underwater, your ability to increase your breathing rate is limited by the increased density of gas at depth and, consequently, the increased resistance to the movement of your breathing gas. But when you exert yourself, the frequency and volume of your breathing must increase to allow you to take in sufficient oxygen and wash out surplus carbon dioxide (CO2). So if you exert yourself too much during a dive, you won’t be able to get rid of enough CO2. This causes excess CO2 to accumulate in your body — a condition called hypercapnia. Symptoms include shortness of breath, headache, and confusion. It can occur without warning, and the only way to resolve it is to reduce your exertion level. Breathing deeply to flush out the excess CO2 also usually helps. This is why recreational divers should not exceed a depth of 100 feet (30 metres), where the density of gas is at least four times greater than at the surface — and why new divers and divers of modest fitness should stay even shallower.

Your Training

What: Do not dive beyond your training.

Why: Every new diving challenge comes with new risks. That is why it’s important to acquire sufficient training before you use different equipment or dive in an unfamiliar setting. Most entry-level dive certifications prepare you to dive in favorable conditions to a maximum depth of 60 feet (18 metres). If you wish to try something new — dive deeper, explore a wreck, or use a drysuit, for example — you should take additional training first. Never let anyone pressure you into a dive that you aren’t comfortable with or that’s beyond your training. And just because you are certified for a given depth doesn’t mean you should dive all the way to that depth. A depth limit is like a speed limit — a suggested maximum for the most ideal conditions. If conditions aren’t ideal, you should stay well above your certified depth — or avoid diving altogether. Even as your experience level increases, remember that continuing education courses are a great way to gain further experience, learn specific skills, and increase your competency while you’re under the direct supervision of a trained dive professional.

The Dive Site

What: Choose a dive site that lies within the limits of your training and experience, and seek proper orientation whenever you try a new dive site.

Why: Many entry-level courses are conducted at fairly calm and controlled dive sites that may not be reflective of more strenuous conditions at other dive sites. If you were certified on a protected, shallow and bright tropical reef, for example, then a quarry dive in 60 feet (18 metres) of cold, murky water will present new challenges. An ocean dive may involve other challenges, like boat traffic, tides, strong currents, or encounters with hazardous marine life. Always be sure you’re oriented to a new site — including factors such as wave height, visibility, the strength and direction of the current, and the water temperature. And consider seeking additional training or hiring a professional guide whenever you try a more challenging site than usual. In particular, a dive around a shipwreck, as enticing as it may sound, involves significant risk of injury. Before you undertake any dive involving penetration of an overhead environment, such as a shipwreck or cavern, you must receive training in the proper techniques for such settings. Remember, too, that conditions at the same site can change from day to day or even during your dive. So assess conditions before every dive.

Your Physical Condition

What: Consider your health status and physical fitness.

Why: Scuba diving has an impact on your entire body and all its systems. Within the limits of recreational diving, a healthy body can adapt physiologically to the stresses of the underwater environment. However, conditions such as heart disease, diabetes, obesity, asthma, or other disorders may limit your capacity to adapt and lead to injury and even death. Even healthy divers can use the Recreational Scuba Training Council (RSTC) medical form for self-evaluation. And if you’ve been diagnosed with a chronic medical condition, we recommend you get a checkup before a trip, preferably from a physician experienced in dive medicine. And remember, the most common example of ignoring a physical limitation is diving with a cold. Cold symptoms are often not benign in an underwater setting. Congestion prevents proper equalization, increasing your risk of barotrauma. In addition, cold medications may affect your performance. Divers also sometimes take drugs to prevent or reduce seasickness, and among their side effects is drowsiness — a potentially dangerous effect when you’re underwater. In fact, you should consult a physician experienced in dive medicine before you dive while taking any medication. (For a referral to an expert in dive medicine near you, call the Divers Alert Network Medical Information Line at +27 828 10 60 10.) Remember, there is no reason to ever force a dive if you aren’t feeling at your best.

The Physiological Effect

What: Don’t dive too deep.

Why: Certain physiological effects cannot be modified by training or experience but can be avoided by limiting your exposure at depth. These are the two most common conditions:

Nitrogen narcosis: The symptoms of this condition are drowsiness and mental impairment. It is caused by breathing air under high pressure and develops gradually as your time at depth increases, usually becoming evident as you approach 100 feet (30 metres). It eventually affects every diver; some divers may feel they’re not affected, but it is awareness that varies, not susceptibility. The degree of impairment induced by nitrogen narcosis can be aggravated by exertion and carbon-dioxide retention.

Oxygen toxicity: This condition is associated with breathing nitrox or a technical diving gas mix beyond your prescribed depth and/or time limit(s); it is not a concern if you are breathing air and stay within recreational diving limits. Symptoms include seizures — a loss of consciousness, with vigorous muscle contractions — which can result in drowning. Air contains about 21% oxygen, while oxygen-enriched air, known as nitrox, typically contains 32% to 36% oxygen. Tanks containing nitrox should be properly marked, though such markings can vary. The most common designation is a green and yellow “enriched air nitrox” sticker wrapped around the cylinder; other markings include a green valve cap and/or a green on-and-off tank knob. All tanks should also carry a sticker or tape noting the tank’s fill date, oxygen percentage, and maximum operating depth, plus the initials of the person verifying those facts. Unless you’ve been trained in the use of nitrox, never use tanks marked as containing enriched air. In addition, technical divers sometimes use pure oxygen to aid in decompression. Tanks containing pure oxygen should be clearly labeled so they cannot be confused with recreational scuba tanks. The markings signifying pure oxygen vary by country — green on the top and shoulder of a tank in the U.S., for example, but white in Canada — so you should be familiar with such markings wherever you dive.

Your Psychological State

What: Be attuned to your state of mind, especially your anxiety level.

Why: Psychological limits can present an even greater challenge underwater than physical limits. Even in the best diving conditions, the thought of being submersed and isolated from the natural breathable environment may cause anxiety and apprehension. New divers are more likely to become anxious, but even experienced divers aren’t immune to anxiety when facing new or challenging dive tasks. Buddies, crew members, and instructors routinely try to offer encouragement to fellow divers, but the line between encouragement and pressure can be a fine one for a diver who feels nervous. While a little anxiety is normal — even healthy, as it may nudge you to pay attention to safety considerations — anxiety can also build and worsen during the course of a dive. This can lead a diver to panic and can even cause an accident, due to a too-rapid ascent or some other ill-advised reaction. While anxiety may not be completely preventable, you can control it. Here are some tips:

Step-by-Step: Minimizing anxiety while you're underwater

  • Plan every dive thoroughly to minimize stress and unknowns.
  • If you ever feel nervous about the conditions that day, the depth of a planned dive, or any other aspect of a dive, it’s fine to decline to participate. Listen to your inner voice if you feel any hesitancy about taking the plunge.
  • Don’t tackle too many new things all at once. Build your confidence gradually.
  • If you start feeling the grip of anxiety while you’re underwater — rising fear, a racing heart, or rapid breathing — try to calm yourself down, rest, relax, and breathe slowly and deeply.
  • Always follow your training, not your impulses.

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