The Dive Computer, an Essential Item You Should Own

The recreational dive computer has allowed divers to extend their diving as well as giving a better means to prevent DCI. The development and publishing of the recreational dive tables was one of the first steps that increased the safety of divers. These tables were a modification of the tables that the U.S. Navy had developed for their divers. For the recreational diver, the Navy tables had some fundamental even fatal flaws. Navy divers normally worked at one depth, they descend, do the job and return to the surface. The No-Decompression Limits (NDL) were easy to follow for them. Recreational diver are more likely to spend time at different depths while diving. So following the NDL left the potential of unused diving time. On the other side of the coin, the Navy tables accepted a higher degree of risk than a recreational diver could be expected to accept. Navy divers would follow the same tables in times of war, were mission requirements were higher. The Navy divers also has rapid access to doctors knowledgeable in dive medicine and a better network of decompression chambers. The recreational tables used the same science, however, they assume a smaller number of acceptable DCS cases.

The Navy developed the dive tables primarily because their first attempts to make a mechanical device were too unreliable. Devices were designed in the early 1950s, but it was not until 1984, that the Navy had a device that was somewhat dependable. Still, they used the tables for planning. The concept of multiple level diving and the advancement of electronics brought in the early dive computers. As technology advanced and prices stabilized they became an acceptable tool for the recreational diver. We now teach you on your open water course how to us a dive computer on all of your training dives.

Why you should use a Dive Computer

The recreation dive tables, now in use, took decades of study to develop and they have been a great tool to reduce the incidents of decompression sickness (DCS). However, they are based on a concept of a steady descent, diving at one depth and a steady consistent return to the surface. Divers seldom dive that way. We might drop down to a wreck, explore it at the bottom, then come up five meters and explore the bridge. Maybe we will follow the contours of a reef, sometime going shallower than others. The point is we are not stationary and our depths changes. A dive computer is measuring our depths and times, then it calculates our remaining NDL times. If we go slightly deeper than the depth we planned with our dive tables, the dive computer will tell you how much NDL time you have. No guess work. It is also a constant reminder, every time we look at our gauges, it is right there reminding us how much time we have left with our dive. There is also a visual display that shows how close you are to the maximum safe level of nitrogen in your system. Another item not mention as much is the calculation of the surface interval. The dive computer will still be operating in the background keeping track of your off gassing. So when you start your next dive, the nitrogen in your system is already account for.

Many dive computer allow different user profiles. A diver that has one or more risk factors for DCS, can select a more conservative evaluation of his dive. This takes some the guesswork out of the planning.

Technical boring stuff

The science behind the functioning of a dive computer and the algorithms they use are very complicated. This explanation will give you some insight into how a dive computer works, however, it is oversimplified. The body absorbs nitrogen while under pressure, however, the rate of that absorption varies greatly between the different types of muscles and other tissues. Certain tissue will absorb the nitrogen much faster than others and will reach a saturation point where no other nitrogen can be absorbed in a faster time. The amount of nitrogen that can be absorbed is a factor of the pressure. This ability to absorb or release nitrogen is expressed in a half life in minutes. In your chemistry classes you learned that radioactive isotopes lose 50% of their radioactivity each half life. A similar concept is used in dive computers were each tissue will lose ½ of its nitrogen load over a certain period. The algorithms group the body structures into groups with the same half life. Many of the dive computer manufacturers use 10 groups that can be called tissues or compartments. Mares a leading manufacture has the following half times in minutes: 2.5, 5, 10, 20, 30, 40, 60, 80, 120 and 240.

As we start our dive, the computer calculated the time and pressure of the dive and applies that information to the compartments. This means that the dive computer has calculated the percent of saturation for each of the compartments. The algorithms are programmed with a maximum ascent rate and a percent of saturation, expressed in partial pressure of nitrogen, that is considered safe. To calculate a NDL time, the computer looks at all compartments, determines the amount of off gassing done while returning to the surface. It then tells the diver the remaining time for the compartment that will have the highest saturation upon returning to the surface. The same process of using algorithms were done to create the current recreational dive tables.

Why should own your dive computer and not rent?

The proper use of a dive computer can lead to safer diving. While dive computers are easy to use, each model has different features and may present the data in a different manner. You need to fully understand the operating manual for such a critical safety device. Getting a rental is better than none, but unless you have used it before, you are not getting its full benefits. Most liveaboard dive vessels require the use of a dive computer on all dives. Some dive centers have also adopted that requirement, as has a number of locations. Training agencies are reducing the reliance on dive tables and are focusing on computers. It may not be long before they will be mandatory. The price of a recreational dive computer that will also allow you to dive with nitrox is reasonable. The purchase price verses renting one can be recovered within a few rentals. If you are taking a dive vacation, you will likely be able to purchase one for less than the rentals.

Dive computers will store the dive information and recent computers will allow you to export the data and integrate it with your dive logs. You can have a visual representation of your dive depth and times for later reference. This is a feature not frequently available to you will a rental.

The dive computer has proven itself for many years. You will see few experienced divers, diving without one. While technology advances, the dive computer available for purchase will not be obsolete anytime soon. The core functions, the calculations that make you safe, are proven solid. An investment today, means you will recover that investment sooner.

Decompression Illness

Knowledge is your Best Protection

hey say that for every Ying there is a Yang, For every good there is a bad. For scuba diving the bad is Decompression illness, or DCI. To quote the Diver Alert Network (DAN), the largest organization focused on dive medicine,

“DCI encompasses two diseases, decompression sickness (DCS) and arterial gas embolism (AGE). DCS is thought to result from bubbles growing in tissue and causing local damage. While AGE results from bubbles entering the lung circulation, traveling through the arteries and causing tissue damage at a distance by blocking blood flow at the small vessel level.”

While there are similarities between the two, it best to remember DCS relates to tissue and AGE to blood supply.

In the early day of diving, before we learned about the effects of gases under pressure on a divers body, DCI caused many deaths and gave scuba diving the notoriety of being a deadly thrill. It is not really an accurate statement saying the effects were unknown, it is more accurate to say they were not understood, not by medical personnel and clearly not by divers.

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Decompression Sickness, What is it and how to avoid it

In your open water training, you review the basic principles of three laws of chemistry, they are Boyle’s, Charles’s and Henry’s laws. Elements of these laws will help to explain how gases under pressure react within our bodies. In 1662, a physicist and chemist named Robert Boyle proved a theory that volume and pressure were inversely proportional. We learned Boyle’s law in science whereas when pressure increases volume decreases. This principal is not only important for us to understand for DCS avoidance but also impacts how long a tank of air will last. Boyle also believed that nitrogen under pressure would be introduced into our blood stream in larger amounts and forced into tissue. Henry’s Law in 1803 proved that Boyle was right. It also showed two important concepts. Increased pressure also increased the solubility of blood to carry nitrogen, and the tissue would try to balance the present of nitrogen in the lungs. Boyle also stated that if the nitrogen was not able to escape the tissue, it could cause physical damage. As we descend the partial pressure of nitrogen we breath goes up, as well at the blood’s ability to carry it. So the tissues start loading nitrogen. When we ascend, the partial pressure is now higher in the tissue, so it will start exciting the tissue. However, the blood solubility for nitrogen has been reduced so there is a delay leaving the tissue. Think of it as a three lane highway going in but just a one lane coming out. If you give it enough time, it will get out. DCS is medically classified into two types, type I which is pain only, and type II which covers the rest.

In the late 1800’s, workers building the Eads Bridge (St. Louis) and the Brooklyn Bridge (New York City) were becoming ill and many of them died from the illness. The bridges were being built using caissons. These are metal devices with an air lock at the top and open at the bottom. They were placed on the river bed and filled with compresses air to pump the water out. The pressure was maintained to keep the water out. Workers would enter the device’s airlock, travel to the bottom to work digging and placing the foundations and anchors for the bridges. When they returned to the surface, many of them became ill within minutes. The illness became known as Caissons Disease, which we now know as Decompression Sickness. DCS can be slow in its appearance. Most cases appear between 5 minutes and six hours after a dive, a small percentage up to 12 hours and even smaller percentage as long as 48 hours. Flying or going to a higher elevation can also bring on DCS if excessive nitrogen remain in your tissue. Divers are advised to wait 24 hours before flying. Symptoms of DCS which the workers also endure are (these are things you feel):

• Unusual fatigue
• Skin itch
• Pain in joints and / or muscles of the arms, legs or torso
• Dizziness, vertigo, ringing in the ears
• Numbness, tingling and paralysis
• Shortness of breath

Signs of DCS (Item that are noticeable):

• Skin may show a blotchy rash
• Paralysis, muscle weakness
• Difficulty urinating
• Confusion, personality changes, bizarre behavior
• Amnesia,
• tremors
• Staggering
• Coughing up bloody, frothy sputum
• Collapse or unconsciousness

It did not take long before all workers suffer to some degree from DCS. It was noticed that the symptoms became milder or disappeared entirely while the worker was deep in the caissons. In the medical studies it was found that if they brought workers up slowly, fewer became ill, even less if they stopped for a few minutes on the way up. These doctors for the bridge building company’s were the first to bring light to the concept that we use for maximum assent rate and the principals of decompression diving. On a light note, the situation with the workers lead to the development of the term bends. In scuba slang we will hear someone say, “they got bent” or “be careful of the bends”. Technically this applies to type I DCS. For the caisson workers, within a few minutes most were bent over in some degree of pain after their work shift ending. At the time there was an upper class fashion called the Grecian Bends. The body position of the men in pain from their work was very similar to the body position of women wearing the Grecian Bends style. So the term was also applied to the workers.

These early studies were expanded upon by the US Navy and the U.S. Navy dive tables were developed. Using a maximum rate of assent as a part of the calculations, the dive tables gave some guidance how long a diver could stay down and avoid DCS. This is the science behind all the dive tables, dive computers and warnings you receive.

In your open water training, you will learn or did learn the principals of avoiding DCS. They include how to read the dive tables and use them to plan your dives. Also, included will be the safe rate of ascent and the practice of a 3 minute stop at 5 meters for extra safety. Currently, the use of the dive tables is not as frequent as it once was after training. Dive tables are based on diving to a specified depth and the calculations are based on that. Technology in the form of dive computers can read current depth and time then use formulas to give a real time evaluation based on your dive. Still, having a good understanding of dive tables are a good foundation to manage your risk.

Unexplained DCS

DCS does have another dark side, even if you follow all the rules, you still can get DCS. It is known that certain factors can increase the risk of DCS. Certain drugs, a hangover, being overweight and dehydration are just some the known factors that might make someone more likely to become a victim. Even setting those factors aside, some people get it anyway. The percentage is small but still there.

Treatment

If you have any concern that you or a fellow diver is being effected by DCI you need to seek medical attention. As an immediate first aid, administer 100% oxygen. This may be enough to slow the progression and maybe even stop it. Then get evaluated by a medical professional knowledgeable of dive medicine. A decompression chamber is used to treat DCI, it brings a patient to a condition under pressure and slowly brings them back to surface conditions. Prompt treatment may result in no lasting complications.

Arterial Gas Embolism (AGE)

The second member of the Decompression illness classification is the Arterial Gas Embolism. AGE happens when bubble in the blood stream blocks the flow of blood, a bubble larger than the capillary vessel. The lack of blood can cause tissue damage. As the brain is one of the largest users of blood, it is the one organ most at risk. AGE can cause strokes and create brain damage. The percent of AGE cases only make up about 7% of the DCI cases. As bad as that sounds there is one thing to remember, AGE is almost 100% preventable. When you breathe, the lungs diffuses gas into the blood stream. Large molecules are blocked. AGE is caused by a Pulmonary Expansion barotrauma. This happens when you hold your breath during ascent. The air in your lungs expand as the gas does. However, when it reaches its limit it will burst, just like adding air to a balloon eventually it will burst. This rupture in the lung will allow air to pass directly into the blood stream without the larger molecules being blocked. In some rare cases AGE has occurred on seemly normal ascents. These cases have mostly been linked to preexisting heart or lung conditions.

Symptoms of AGE

• Dizziness
• Visual blurring
• Areas of decreased sensation
• Chest pain
• Disorientation

Signs of AGE

• Bloody froth from mouth or nose
• Paralysis or weakness
• Convulsions
• Unconsciousness
• Cessation of breathing
• Death

Many of the signs and Symptoms of AGE are similar to DCS type II, and the first aid for them are the same. Administer 100% oxygen, make comfortable and seek medical attention immediately. AGE symptoms appear rapidly and escalate fast. Unlike DCS which seldom has symptoms underwater, death due to AGE can happen before the diver can reach the surface.

Insurance

There is an old joke against the medical field, it says the leading cause of heart attacks after surgery is seeing the hospital bill. The best means to avoid this is to have good medical insurance. Even if you have medical insurance, consider getting dive medical insurance. Dive insurance companies generally have agreements in place with decompression chambers where the chambers will accept the insurance. Most insurance companies do not and if not, you will need to made a deposit before treatment is started. Deposits can range from $5,000 to 25,000 cash. Best to think ahead.

Diving’s Worst Case

When you take your Open Water Diver training, most of the knowledge section and many of the skills relate to DCI and how to avoid it. It is these skills that you will practice and master that makes DCI a managed risk. Forty years ago if you became a certified scuba diver your life insurance company would cancel your policy. Some policies would have a higher premium for divers and exclude any benefits for deaths that happened elated to diving. Times have changed, today diving is considered safer than horseback riding, and you have a greater chance of being injured on a golf course than getting a DCI. This is due to the training and you understanding of the risk.

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How to Improve Your Style and Dive Longer

 Your Style and Dive Longer

 Have you every watched a shark as it moves along the reef? You see its smooth almost majestic movements, the   stream line body, and the relaxed manner it moves into a school of fish. You know that it has power and great   speed, however, the shark only calls on it when needed. The shark has evolved to be efficient under the water,   scuba divers have not. We have to work at it. The way we move through the water greatly impacts the energy we   spend and the air we consume. It is a skill that takes time and conscious effort to learn and sadly many divers do   not even try. Often, it is a case that we do not know how bad we really are, it takes someone to tell us or show us.

What is a proper form

The proper form will keep you moving in a stream line manner, much like your favorite shark. Your body from the head to your knees should form a straight line. Your head should be forward facing and you knee bent to a 90° angle. This may sound easy but it does take a little work. When you first start working on your form, do not concern yourself too much that you are not horizontal. The position of your weights will affect the horizontal position. Once you have the form proper or at least close, you can adjust the weight trim.

Most people have poor posture, no matter how many times our mother told us to stand up straight. We will find that our muscles have remembered those positions we normally use. When we float, the body will relax but may not necessarily form the position we need. Many will find their natural position is with the rump up higher than the spine. This forces the legs down, now when we kick we are forcing our selves up as well as forward. The best way to correct this is to arch your back slightly, square your shoulders and stretch your chest. This is the form you will see parachutist take in free fall.

Your knees should be bent so that your calves are slightly above your back and the ankle relaxed allowing the blade of the fins to be parallel with your body. Your hands are not a part of your propulsion underwater. They should be held in a stream line position if they are not in use such as holding a gauge or a light. Many divers will hold the arms in front of them, one hand lightly grasping the other wrist. Arms at your side or folded across your chest are also popular means to stay stream line.

I became certified at a local dive center near where I was living for a year. After becoming certified, many of my dives were with my instructor as the dive master. We would spend our 5 meter safety stop working on my and my dive buddies form. The instructor gently controlling our body positions to help create a muscle memory. That is something you and your buddy can do.

Using weights to adjust your trim

The article on buoyancy control briefly mentioned trim. Your body has a center of gravity (COG), a pivot point if you will. Like a seesaw you want to keep the weight on ether side in balance. The further away from the center of gravity the greater the impact weight will have. While the location of your dive weights are important, it has to be used in conjunction with other items. The cylinder is often overlooked as an element of trim. It’s position can matter a great deal as it is on both sides of your COG. If you find your trim changes between your first and second dive, the location of your tank may be the cause. Most BCD’s have an adjustable loop that fits over the neck of a dive cylinder. You can use that strap as a guide to position your tank each time. When you find the proper position for your tank, tighten the loop. Each time you place your BCD on a cylinder slide the BCD down until the loop is tight before securing the dive band. Many times divers will let the boat crew change over the equipment and they may not be as detail orientated as you should be.

The balance of the cylinder impacts your trim, however, as you start working on your trim its balance is less important than it being consistent. Some BCD’s have shoulder pockets for trim weights, weights added here will reduce a positive trim, one where your chest is higher than the COG. If your BCD does not have a shoulder pocket, you can purchase weights that will clip to your d-rings. Divers can place some weight on the tank or tank band. Weight added near the neck of a tank will bring the chest down and legs up. Weights near the tank boot will have the opposite effect. As you move weights to different locations, remember that you must maintain enough weight on your weight belt or other quick release to gain positive buoyancy in an emergency. You should also account for heavy gear. If you have a large dive light clipped to your BCD, not bringing it on a dive might affect your trim.

Streamlining your equipment is an important point. Like the streamlining you do with your hands, anything outside your body profile will cause drag, that will affect your profile. Keep hoses and gauges close to the body.

Do a five meter equipment check

As a part of each of my dive plans, I add a stop at five meters both on descent and ascent. Before you start your descent, you should make a check on your equipment. During decent, pause at five meters, become horizontal, check your trim and adjust your equipment if needed. On boat dives, the entry may have slightly moved your weights, and you might not notice it on the surface. After some practice, this stop will likely only take a few seconds. Check with your dive buddy and continue your decent.

Screen test

Thanks to the wide spread use of sports cameras, underwater video is not as expensive as it once was. The quality will not be the best, still it is good enough to share your passion. Instead of taking selfies underwater, occasional ask your dive buddy to take some video including you when you are not aware they are recording you. Examine the video and evaluate your form. Visualize doing it better next time.

 My most memorable dive was my 30th dive, about 18 years ago. It was my first dive in the Bahamas, and the first   dive where we were told to expect a number of sharks. It was also the first time where there was someone   recording   the dive. Back then video cameras were very large and very expensive. I spent a good portion of the   dive watching   the sharks, watching how smooth they were. After the dive, the dive master complimented me on   my form. When I   watched the video that was taken, I was pleasantly surprised, even proud, how good I looked   underwater. It also   showed me how most of the divers, even the experienced ones, took no care of their form.

Bad habits are hard to break

 It is best to start applying these skills, when you are first learning to dive. This gets you on the right path to having   great form before bad habits create a muscle memory. When that happens, it becomes more difficult to get the   proper form. When you were in school, your gym coach was always preaching about form and basic skills. The b   same principles apply in this sport as well. A bit of a conscious effort as a new diver and periodically checking   yourself as your diving continues will keep you in good form. A good form means less work, which results in   longer dive times and less fatigue after a dive. The knowledge you gain controlling your buoyancy also reduces   your risk of an uncontrolled ascent.

A little early work for a long time benefit.

 Learning what it takes for you to have a proper trim, excellent buoyancy and a good form will take a little effort at   first. A few minutes a dive working on it, will go along way to mastering it. Once it is mastered, everyone watching   the underwater videos will see you as the role model. The diver to follow.

 Improve you style with the Peak Performance Buoyancy course