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Poseidon Dive Center

Better Buoyancy Tips

  • A good place to start is with the right BCD since different models provide different amounts of lift. The BCD need to be appropriate to the activity.
  • Wearing the right amount of weight is essential to achieving buoyancy superstar status. When weighted properly and holding a normal breath, you should float at eye level. Then you’ll be able to sink slowly below the surface feet first when you relax and fully exhale, making sure you’ve dumped all the air out of your BC as well as out of your lungs. If you’re using a full scuba tank when you do this check, then add 2.5kg/5lbs to offset the air you use up while diving.
  • Note the word ‘slowly.’ If you sink like a stone then you’re wearing too much weight! On the other hand if you and your BCD are fully exhaled and your head’s still above water, try adding a few pounds.     
  • Adjust your weight for what you’re wearing and where you’re scuba diving. The type of dry suit or wetsuit you have on will affect your buoyancy, and everyone’s more buoyant in saltwater versus fresh. 
  • Get horizontal as soon as you can. Once underwater, you’ll start descending faster as the water pressure compresses your wetsuit, reducing your buoyancy. To counteract this, move into a swimming position as soon as you’re completely underwater. Add small amounts of air to your BCD so you descend slower and arrive near the bottom neutrally buoyant.
  • Remember your scuba tank will become lighter during the dive so make sure your descents are easy. If you have to struggle to get down, chances are you’ll have to work hard to stay down at the end of the dive and making a safety stop will be difficult if you’re too buoyan

Ascent Rate Guidelines and Why You Should Follow Them

A safe rule of thumb, (and the most commonly published maximum ascent rate at this time) is:

Never exceed an ascent rate of 30 feet/ 9 meters per a minute.

The easiest way for a diver to monitor his ascent rate is to use a dive computer. Almost all dive computers have ascent rate alarms which will beep or vibrate when the diver exceeds the computer's programmed maximum ascent rate. The moment the computer alerts the diver that he is ascending too quickly, the diver should take steps to slow his ascent.

A diver without a computer may use a timing device (such as a dive watch) in combination with his depth gauge to monitor the time he takes to ascend a predetermined number of feet. For example, a diver may use his timing device to check that he doesn't ascend more than 15 feet in 30 seconds.

However, in a worst case scenario, a diver may gauge his ascent rate by watching bubbles around him rise towards the surface. He should ascend more slowly than the smallest bubbles he can see.

All About Decompression Sickness

Also known as The Bends and Caisson Disease, Decompression Sickness is an illness that can affect divers or other people (such as miners) who are in a situation that involves pressure rapidly decreasing around the body.

DCS, as it is commonly know, is caused by a build up of nitrogen bubbles in the body. When we breathe, approximately 79 of the air we're breathing is nitrogen. As we descend in water, the pressure around our bodies increases, causing nitrogen to be absorbed into our body tissues. This is not actually harmful and it's quite possible for the body to continue to absorb nitrogen until it reaches a point called saturation, which is the point at which the pressure in the tissues equals the surrounding pressure.

The problem arises when this pressure needs to be released. In order to release the nitrogen slowly from the body, a diver must ascend slowly and carry out decompression stops if necessary - this allows the nitrogen to slowly seep out of the body tissues and either immediately revert to being a gas or to become tiny harmless bubbles which will eventually become revert to gas. This process is called "Off-gassing" and is normally carried out through the lungs.

If a diver ascends too fast and the nitrogen escapes the body tissue too quickly it becomes bubbles in the body and this leads to Decompression Sickness. The bubbles must normally be on the arterial side of the circulatory system to be harmful - they are usually harmless on the venous side. There are several types of Decompression Sickness:

Type I Decompression Sickness

Type I Decompression Sickness is the least serious form of Decompression Sickness. It normally involves only pain in the body and is not immediately life threatening. It is important to note that symptoms of Type I Decompression Sickness may be warning signs of more serious problems.

  • Cutaneous Decompression Sickness

    This is when the nitrogen bubbles come out of solution in skin capillaries. This normally results in a red rash, often on the shoulders and chest.

  • Joint and Limb Pain Decompression Sickness

    This type is characterized by aching in the joints. It is not known exactly what causes the pain as bubbles in the joint would not have this effect. The common theory is that it is caused by the bubbles aggravating bone marrow, tendons, and joints. The pain can be in one place or it can move around the joint. It is unusual for bisymmetrical symptoms to occur.

Type II Decompression Sickness

Type II Decompression Sickness is the most serious and can be immediately life-threatening. The main effect is on the nervous system.

  • Neurological Decompression Sickness

    When nitrogen bubbles affect the nervous system they can cause problems throughout the body. This type of Decompression Sickness normally shows as tingling, numbness, respiratory problems, and unconsciousness. Symptoms can spread quickly and if left untreated can lead to paralysis or even death.

  • Pulmonary Decompression Sickness

    This is a rare form of Decompression Sickness that occurs when bubbles form in lung capillaries. Fortunately, the majority of the time bubbles dissolve naturally through the lungs. However, it is possible for them to interrupt blood flow to the lungs which can lead to serious and life-threatening respiratory and heart problems.

  • Cerebral Decompression Sickness

    It is possible for bubbles that make their way into the arterial blood stream to move to the brain and to cause an arterial gas embolism. This is extremely dangerous and can be identified by symptoms such as blurred vision, headaches, confusion, and unconsciousness.

Other Forms of Decompression Sickness

Extreme tiredness is very common in cases of Decompression Sickness and can sometimes be the only symptom of Decompression Sickness present. It is not know what causes this but you should be aware that extreme fatigue could be a sign of more serious problems. It is also possible for Decompression Sickness to occur in the inner-ear. This is caused by bubbles forming in the cochlea's perilymph during decompression. The result can be hearing loss, dizziness, ringing of the ears, and vertigo.

Symptoms

Decompression Sickness can manifest itself in many different ways and has many different symptoms, but the most common symptoms are:

  • Extreme Fatigue
  • Joint and Limb Pain
  • Tingling
  • Numbness
  • Red Rash on Skin
  • Respiratory Problems
  • Heart Problems
  • Dizziness
  • Blurred Vision
  • Headaches
  • Confusion
  • Unconsciousness
  • Ringing of the Ears
  • Vertigo
  • Stomach Sickness

Nitrogen Narcosis and Scuba Diving

Nitrogen narcosis is an altered state of mind caused by breathing nitrogen at a high partial pressure. The deeper a diver descends, the higher the partial pressure of nitrogen and other gasses in his air will be. For this reason, nitrogen narcosis is usually thought of as a function of depth. The deeper a diver goes, the greater the narcosis.

Although nitrogen is the principle component of air (79%), other gases in a diver's tank are also narcotic at great depths, such as oxygen and carbon dioxide. For this reason, many training agencies are now referring to the narcosis caused by breathing compressed air at depth as “inert gas narcosis” rather than “nitrogen narcosis”. Of course, oxygen and carbon dioxide are not inert gases, so perhaps the best term to use is simply “narcosis”. Whatever you call it, the point is that more than one gas may influence a diver's level of narcosis underwater.

Narcosis has been called the “rapture of the deep” and many divers compare narcosis to a feeling of pleasant drunkenness. In fact, divers sometimes use the “Martini Rule” to roughly estimate the effects of narcosis during a dive. Depending upon the source, the Martini Rule states that for every 30 or 60 feet of depth, a diver experiences the narcotic effect of drinking one martini.

At What Depths Do Divers Experience Narcosis?:

The average depth at which a diver experiences at least a mild narcosis is 100 feet of seawater. By 140 feet, most divers will experience significant narcosis. Diving beyond 140 feet (the recreational diving depth limit) while breathing air is strongly discouraged by most training organizations. Some divers will make dives up to 160 - 190 feet on air, but such dives require deep air training, and are generally frowned upon. If a diver exceeds a depth of 200 feet wile breathing air, he is likely to experience debilitating narcosis – even unconsciousness.

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