SCUBA Gas Laws

Earth's atmosphere is composed of a mixture of gasses that obey the famous chemistry "Gas Laws." Some of these laws become matters of life and death when using a Self Contained Underwater Breathing Apparatus (SCUBA) device. Understanding just four of these laws will help you stay alive and out of trouble while SCUBA diving.

Boyle's Law

For SCUBA divers, the most important of the gas laws--and the most deadly one to ignore--is Boyle's law. Boyle's law says that as long as temperature is constant, pressure and volume are inversely proportional--when one goes up the other goes down and vice versa. If you have an inflatable container--such as your lungs-- decreasing the pressure increases the volume. So if you take a deep breath and then move toward the surface while holding your breath, your lungs expand. If you hold it too long your lungs will explode. This is why you should never hold your breath while SCUBA diving--not even briefly. If you breathe consistently the volume of air in your lungs will constantly adjust to the changing pressure.

Amonton's Law

Amonton's law says that if the volume of a gas is constant--as it is in a SCUBA tank--the pressure and temperature are directly proportional. If one increases so does the other, and vice versa. If you fill up your tank on a summer day and then jump in water that's 40 degrees cooler, you are going to have less pressure than you might think. Therefore, the tank will not last as long. If you fill up a tank and then put it in the trunk of the car where it is 60 degrees hotter, the pressure might rise to dangerous levels and damage your equipment.

Henry's Law

Henry's law describes how pressure determines a liquid's ability to absorb gasses. As pressure increases, more of a gas will dissolve in a liquid. When a diver dives, the pressure increases and more gasses dissolve in the diver's tissues. Most of Earth's atmosphere is nitrogen, which is relatively inert so it does no real harm. If the diver ascends slowly the nitrogen comes out of the tissues as the pressure decreases. If the diver with nitrogen-saturated tissues (too deep, too long) ascends too quickly, the nitrogen comes out too fast--in bubbles. This causes a very dangerous condition known as the "bends," which can cause permanent damage or even death.

Dalton's Law

Dalton's law says that if a gas is a mixture, the pressure of each component depends on the percentage of that component in the mixture. Earth's atmosphere is about 78% nitrogen, 21% oxygen, and one or two percent other gasses--depending on where you live. If your tank is filled using faulty equipment, you might be getting a lethal dose of something that is relatively safe at low pressures. Even oxygen can be toxic at high pressures. Nitrogen at high pressures can have a narcotic effect (known as "rapture of the deep") that can cause a deadly loss of judgement.

By Carlos Mano, eHow Contributor

Kathy Dowsett
www.kirkscubagear.com

The PADI Story

Reprinted from PADI

The PADI story: How frustration and scotch helped create the world’s biggest scuba organization

Frustration over the state of the diving industry in the 60s paired with long conversations over a bottle of Johnny Walker served as the springboard for what is today the Professional Association of Dive Instructors – or PADI as most of us call it.

Founders John Cronin and Ralph Erickson – a scuba equipment salesman and swimming instructor, respectively – both had major concerns about the industry. Basically, they thought it was unprofessional and made it unnecessarily difficult for new people to join the sport.

Over shared libations, a partnership formed and with $30 the pair started PADI. The goal was simple: provide people the chance to learn important scuba skills and enjoy the underwater world through modern scuba diving training. They wanted to reach people around the world, helping to create confident scuba divers who dive regularly and support the growth of the sport.

For how big PADI is today, it’s hard to imagine the days when the organization was a small community of passionate divers. In fact, the first couple years the organization struggled. By the late 1960s, PADI only had 400 members.

It was soon after that a few key milestones took place. First, Cronin went to a huge tradeshow in New York City and met with Paul Tzimoulis, who later became the editor of Skin Diver Magazine. Tzimoulis suggested divers’ pictures be placed on all PADI certification cards. The change was implemented and helped propel PADI’s global reach.

Starting in the late 1970s, PADI created its own multi-media student and instructor educational materials for each course, positioning themselves as the industry experts. This change parlayed significant growth, and differentiated it from other scuba organizations.

By the late 1980s, PADI was the industry leader, offering scuba diving training around the world. With the realization that so many new people were embracing the sport, the organization was compelled to embrace additional activities to promote protection of the underwater environments. Today there are numerous PADI initiatives to help protect endangered species, reduce pollution and increase understanding of humanity’s impact on our oceans and waterways.

Today there are more than 6,000 PADI Dive Shops and Resorts, and 400 employees in PADI corporate offices around the globe. The vision in the 60s remains the vision for the organization today: “PADI intends to be the world leader in the educational development of scuba diving professionals and enthusiasts.”

Kathy Dowsett
www.kirkscubagear.com

Key Largo dive spawned young girl’s passion for scuba

It was during a cruise on the family boat from Hamilton, Ontario, to the Bahamas that Tess Miller came to appreciate her parents’ passion for scuba diving.

Just eight years old at the time, Tess, from London, Ontario, had taken some scuba lessons before the journey began. But she first experienced the beauty and serenity of diving in Key Largo. They were waiting there to rendezvous with two other families who also had their own boats, before going on together to their Bahamas destination.

“We dove every other day. It was amazing. I found it so peaceful,” says Tess. “It is my favourite thing to do. Any problem you have is wiped away under water. Everything is so quiet and beautiful. The water is crystal clear and the fish are stunning. I was very comfortable.”

Charlie Miller, Tess’s father, says Pennykamp, a protected coral reef off the Florida Keys, was their prime diving site in that area. It has great coral and aquatic life. “We were two months in that area.”
One of the things Tess saw underwater near Key Largo was the Christ statue, 30 or 40 feet down. “It is life size or bigger. I couldn’t really tell.”

Later, near Staniel Cay in the Exumas, a district of the Bahamas with almost 400 islands, she dove with her family in the Thunderball Grotto, a rock formation with a huge opening. Popular with both scuba divers and snorkelers, it was featured in two James Bond Movies, Thunderball and Never Say Never Again.

“That is my most vivid dive,” says Tess. “There is a hole in the ceiling and the light that shines through made it surreal. The whole cave was filled with fish. It was amazing.”

Her other favourite dive is the shark dive off Paradise Island in the Bahamas. “It’s a planned event. You sit in a circle called a ring and there is a person feeding the sharks. They don’t bite the hand that feeds them.”

The boat trip itself was an experience. Originating in Hamilton, Ontario in mid-August of 2004, the first part of the trip involved navigating the Erie Barge Canal, which connects the Great Lakes to the Atlantic Ocean at New York. When they got to Baltimore they left their 53-foot vessel there for repairs, before continuing on. There were several other repair stops along the way. The southbound trip was made in segments of a week at a time. They arrived in Fort Lauderdale, Florida a few days after Christmas in 2004, before moving on to Key Largo.

From there they headed to the Bahamas, with their first stop there being Cat Cay to clear customs. Then it was on to Chubb Cay, 35 miles west of Nassau. Some good diving followed.

“We started to anchor out and felt we were remote. We were out for days just living on the boat,” says Charlie.
Nassau was the next stop to get provisions before heading south for the Exumas islands. “It (the Exumas) was magnificent. The beaches are unbelievable. They are like the postcards,” says Charlie.

There is an island there inhabited by pigs that swim out to meet boaters, who have been feeding them for years. “The pigs will come up to the boat and you can feed them,” adds Charlie.

The Exumas has a “land and sea protected park.” Fishing is not allowed.

Underwater, the Millers found an old shipwreck that was “crawling with lobsters.”

The family started to work their way home in May, beginning with restocking in Nassau. “Then we went out to Eleuthera, a really exclusive series of islands northeast of Nassau, where we dove some wrecks, Charlie says.

They reached Freeport by mid-May of 2005 before heading on to Fort Lauderdale. From there it took them just 21 days to get back to Port Stanley, Ontario, on Lake Erie’s northern shore. They accomplished that by running 10 to 12 hours a day, as well as some “all nighters.”

It was the end of June by the time they got home, but on July 15 they decided to take the boat north to Killarney, Ontario, in the North Channel.

“When we got back to London we were still prepared to go for another trip.”

Diving has been a long-time passion for the Miller family, beginning with Charlie’s diving certification about 30 years ago in the British Virgin Islands. He was the first to dive the 250-foot, steel-hulled freighter SS Wexford, which sank in a storm in November of 1913 eight miles off the Lake Huron shoreline from Grand Bend, Ontario. That discovery was made on Aug. 25, 2000.

Tess, now 17 and on schedule to finish high school soon, has now logged about 75 dives, of which 40 to 50 were on the boat trip to the Bahamas.

There will be many more dives for Tess. As well as easy access to summer diving in Lake Huron, she has passage to warmer waters much farther south.

“I have a 55-foot Sea Ray, full of dive gear in Nassau,” says Charlie. “It’s a great dive boat. We go down once a month from October to March. We have 10 special dive sites around Nassau.”

Access to great diving with her family has whetted Tess’s appetite for diving much farther away: “I would like to do some of the big dives, like the Great Barrier Reef in Australia, things that most people that dive would love to see.”

Kathy Dowsett
www.kirkscubagear.com

Cookie Cutter Sharks

Thanks to e-How

The cookie cutter shark is a relatively small deepwater shark known for its rather unusual feeding habits and the round wounds it leaves on its prey items. There is still relatively little known about this elusive species, but better deep sea exploration and improved dissection techniques in recovered specimens have helped shed light on it. While the species is not considered threatened, they are difficult to find and observe due to their deep water habitat.

Appearance

The cookie cutter shark was once called the cigar shark due to the fish's dark brown color and long, rounded shape. Most cookie cutters average 12 to 15 inches long, though specimens as large as 20 inches have been recorded. The shark has a distinctive, rounded jaw opening with somewhat fleshy lips and protruding lower teeth.

Habits

Cookie cutters have been observed at depths of over 11,000 feet, though it is highly possible that they travel deeper still. Like many deep sea species, cookie cutters generally rise to much shallower depths in search of prey during the night, and return to deeper water by daylight. Their range is vast, and specimens have been recovered in virtually every sea in the world. Like many other deep sea fish, they do not do well in captivity. Little is known about their reprodiction habits, except that females give birth to live young. Litters may average five to seven sharks, but that data was insufficient as of 2010.

Feeding

Considered a parasitic species, the shark attaches itself to large prey items such as squid, whales, and even other sharks by suctioning on with its fleshy lips. The shark then sinks its lower teeth into the flesh of its victim, and through a combination of swiveling its teeth and thrashing its body, removes an almost perfect circle of flesh from the prey animal---just like a cookie cutter. This process is normally over in a few quick movements, and most prey animals will recover with just a scar as evidence of the attack.

Other Adaptations

Large eyes help the cookie cutter see at extremely low light levels, which makes it very much at home in dark waters. The cookie cutter's enlarged liver is filled with low-density oils that help the shark remain floating in its high-pressure deep sea environment. It also has a small bioluminescent patch on its abdomen, which glows to attract prey.

Interesting Facts

Cookie cutters shed their entire lower row of teeth all at once, rather than singularly like other sharks. This ensures that the shark has a razor sharp cutting edge at all times, and acts to prevent individual teeth from becoming dull and snagging in the flesh of prey items. Another point of interest is that the bioluminescent patch on the shark's abdomen may continue to glow for up to three hours after its death.

Kathy Dowsett
www.kirkscubagear.com

Compressed Gas Tears Skin, Penetrates Body

Reprinted From Divers Alert Network for the Diving Community

A scuba diving high-pressure hose ruptures, causing air under pressure to inject into arm.

Reported Story

The boat driver was helping one of the divers. He held the first-stage regulator with his left hand and opened the tank valve with right hand. At that moment the high-pressure hose ruptured, and a jet of gas under pressure made a hole in the boat driver's left hand.

His hand started to bleed and appeared to be full of air. We stopped the bleeding by applying pressure, and we stopped the air from spreading further by applying a bandage at armpit area. We massaged his arm, pushing the trapped air to his hand. This helped a bit; we saw some bubbles coming out of his hand.

We called for an ambulance and administered oxygen during the time it took us to return to the harbor, approximately 20 minutes. The ambulance were there when we arrived.

I recommended that his boss to take him to the recompression chamber, but he told me the doctors would take care of him. I later asked about his state of health, and his boss told me he is OK and ready to go back to work.

Expert Comments

The injury described above is rare, especially outside of an industrial setting. Certain terms do need to be clarified for discussion purposes. In the diving vernacular any reference to high pressure (HP) is related to the compressed gas in the cylinder at 3,000 psi. Any reference to low pressure (LP) relates to the intermediate pressure that results from reduction of high pressure in the first stage. Typically this can range from 120 psi to 140 psi. Clinical references designate any pressure at and above 100 psi as HP. It has been established that pressure at a minimum of 100 psi can penetrate unbroken skin.1 These wounds require immediate medical treatment no matter how benign they might appear.

In the industrial setting the possible materials that can be injected at HP include but are not limited to compressed gas, oil, grease, solvents, paints and diesel fuel. There are, of course, greater concerns with the petroleum products and other chemicals due to their toxicity and potential tissue damage. The risk of an inflammatory reaction from surrounding tissues and infection is quite high.

In the diving environment compressed gas is obviously the most likely injectible. Industrial workers who sustain these injuries are generally inexperienced or unfamiliar with the devices they are using or servicing. With divers, familiarity may lead to a certain level of complacency. Despite fewer potential complications there is still a risk of secondary injuries that can result from any HP injection injury.

Common injection injury sites are the palm or fingers of the nondominant hand. Injection into a finger(s) can be particularly problematic. The fingers cannot accommodate a large volume of any material due to limited tissue compartment space. The immediate insufflation and swelling can cause vascular compression, which can severely compromise circulation. The palm of the hand or other similar sites can accommodate the same volume with less risk of circulatory issues. However, a larger volume can produce the same risk of vascular compromise.

While compressed gas poses less risk from toxicity or surrounding tissue damage compared with other possible injected substances, it is not benign. Along with the compressed gas, fragments of hose, brass fittings and bacteria from the skin or environment will be injected into the wound simultaneously. This is part of the mechanism for a high infection risk.

It is unknown if there was any previous problems or concerns with the HP hose on this regulator. It is also unknown if a visual inspection would have offered any suggestion of hose failure. It is still worthwhile to remember to inspect all hoses and consider periodic replacement. Please discuss these issues with a local certified repair technician.

Proper first aid should include bleeding control and urgent transport to the nearest medical facility. For a compressed-gas injection, surface oxygen is of little benefit as it would not expedite the absorption or elimination of the injected gas. Treatment in a hyperbaric chamber is not an appropriate first choice for treatment for this type of injury. The bystanders made an effort to express the gas through the injection site by massaging the arm. This is not recommended. They may have inadvertently forced the gas into other areas or into the fingers. Forcing the gas into the fingers could further complicate the injury, as explained previously. Some HP injection injuries may require surgical intervention to reduce pressure and to clean the wound. Thorough cleaning and disinfection is best left to the medical professionals.

This is a very rare injury, but diligence and forethought will likely reduce the occurrence. Do not underestimate the energy released with the rapid expansion of compressed gas. Cases like the above should not increase fear but rather remind us to be respectful of the potential consequences of inattention.

Thanks again to Divers Alert Network

Kathy Dowsett

www.kirkscubagear.com

How to Determine the Diopter for a Scuba Mask

Thanks to e-how and Pamela Stephens

Obtain a current eye glass prescription. Using an out-of-date prescription can result in an inaccurate diopter choice for your scuba mask lenses.

Refer to the eye glass prescription. Decoding the prescription is not as difficult as it might first appear. "Oculus dexter" (OD), "oculus sinister" (OS) and "oculus utrique" (OU) are Latin terms that mean right eye, left eye and both eyes. Sphere is the amount of correction needed in each eye. Cylinder is the amount of astigmatism.

Locate the sphere number and the cylinder number for the OD and OS. These numbers will likely be different for each eye.

Choose the numbers for one eye and calculate the diopter. Add the sphere number and half of the cylinder number to determine the diopter. For example, if the prescription indicates a sphere of 2.0 and a cylinder of -.50 this would be calculated as 2.0 - .25 = 1.75.

Round down when possible, because water is a natural magnifier. Diopters are in increments of .25. In the example, a diopter of 1.5 would be chosen.

Repeat the same formula to calculate the diopter for the other eye.

Purchase specific diopters for each lens in the scuba mask. Most full-service dive shops have step diopter lenses in stock and can easily replace regular lenses with them. You will not need to show your prescription to purchase step diopter lenses; however, dive shop professionals can double check your prescription to make sure that you purchase the correction that is best for your sight.

Kathy Dowsett
www.kirkscubagear.com

Secrets to Saving Air

Do you consistently run through your gas supply faster than other divers on the boat? Do you frequently have to end the dive before the rest of the group? What's going on? And what can you do about it?

First, you can stop beating yourself up over it. People are different. Those with slower metabolisms will--other factors being equal--use less oxygen. Small divers have to use less energy than big ones to swim forward, so they also use less oxygen. Nature doesn't distribute her gifts equally, and you may never be the stingiest sipper of gas on the boat.

On the other hand, most of us can reduce our gas consumption and thereby extend our dives. We can be better, even if we can't be the best. Typically, divers waste air in one or more of these three ways:

By leaking it before it gets to their lungs, thanks to free-flowing octos and worn out O-rings.

By using more energy than necessary. Using energy means using air, because oxygen is necessary to burn the calories that make energy. Every bit of unnecessary exertion costs you psi.

By getting less than maximum benefit from each breath. When divers breathe inefficiently, they exchange less oxygen for carbon dioxide with each breath, so they need to take another breath sooner.

Here are 18 tank-stretchers to try, starting with the obvious first step.

Fix the Small Leaks

Even a tiny stream of bubbles from an O-ring or an inflator swivel adds up over 40 minutes, and may be a sign of more serious trouble ahead anyway. You don't think you have leaks? Do you have eyes in the back of your head? Ask your buddy to look behind you to be sure. A mask that doesn't seal is another kind of leak in that you have to constantly blow air into it to clear out the water. It's also a source of stress, which needlessly elevates your breathing rate and thereby reduces your breathing efficiency. Does your octo free-flow easily? That can dump a lot of air quickly. Detune it or mount it carefully so the mouthpiece points downward.

Dive More

Inexperienced divers are famous for burning through their air supply at a furious rate. The reason is anxiety. A new diver is understandably nervous, and his body's automatic response to danger is to raise his metabolism, his heart rate and his breathing rate. It's hard-wired, the body revving its engine to be ready for fight or flight, though the result is a lot of air cycled through his lungs but never used, just dumped into the ocean.

You may not be a new diver, but unless you dive almost every week it's still an unnatural activity, and your body isn't as happy as you are about putting its head under water. Dive more--your body will get used to the idea, and you'll breathe less.

Take a Class

Any class, almost, will reduce your gas consumption just by making you feel more accomplished and therefore more comfortable. But the best bet is probably a class to improve your weighting and buoyancy control. When you get that dialed in, you can control your altitude mostly with your lungs, so you're not squirting that valuable gas into your BC and then venting it to the ocean. Most important, you can now forget (nearly) about the mechanics of diving, drift like a fish, and relax.

Sleep More, Party Less

Be well rested on dive day. Fatigue is stress. If you start the dive already tired, your body has to work harder to overcome the extra burden, so you breathe harder. A hangover is stress too. You may think you're sober in the morning, but in fact alcohol and other drugs affect your physiology the next day. As SSI instructor Jim Bruning puts it, "Your body does what your mind tells it to. If you had a good night of sleep, your body and mind are going to be much more relaxed, much calmer."

Be Early

If you're late to the boat, running to get your gear on board, worried about the hard looks of divers who were on time, stuck with the least-convenient gear station and generally playing catch-up all day, you're giving yourself unnecessary fatigue and mental stress. You start the day breathing hard and never have a chance to calm down. On the other hand, if you're early to the boat, early to gear up and early to the dive briefing, you'll conserve your energy, feel confident and relaxed, and your breathing will remain slower.

Swim Slowly

The energy cost of speed is even more than you might think because it's an exponential function proportional to the square of the speed. So swimming twice as fast requires four times as much energy and air. But the reverse is true, too: Swim half as fast as you do now, and you'll use only one-fourth as much air.

Stay Shallow

It's physics again. Because your regulator has to deliver air at the same pressure as the water, a lungful at 33 feet (two atmospheres) takes twice as much out of your tank as does the same breath at the surface. At 99 feet (four atmospheres) it takes twice as much as at 33 feet.

There's absolutely nothing you can do about that except to avoid being deeper than you have to be. If you're making a transit over an uninteresting sand flat to get to the edge of the drop-off, do it at 15 feet instead of at 40 feet, and you'll save air.

Minimize the Lead

If you're overweighted, you have to put more air into your BC to float it and be neutral. The inflated BC is larger and requires more energy and oxygen to push it through the water.

An extra eight pounds of lead means your BC is one gallon bigger when inflated enough to make you neutral. Imagine the extra effort of having to push a gallon-sized water jug through the water.

Adjust Your Trim

If your body is horizontal in the water, when you swim forward, your legs and fins will pass through the "hole" in the water made by your head and shoulders. You'll disturb less water and expend less energy and air.

Many divers, however, swim with their feet lower than their torso and their head higher. Adjust your trim by moving some lead from your hips to your back--to trim pockets on your BC or to your tank.

Seek Neutral Buoyancy

Always being exactly neutral is the key. If you're not, if you're slightly heavy or light, you're constantly using fin power (and air) to maintain a constant depth. If you're not neutral, you can't glide between fin strokes and you can't hang effortlessly.

Streamline Your Gear

All fast-swimming fish have smooth skins with few or no protuberances. That minimizes drag so they can swim with the least energy and oxygen consumption. Divers, by contrast, have rough, convoluted surfaces with all sorts of attachments from scuba tanks to whistles. Anything disturbing the flow of water past your body creates drag and wastes air.

Do your best to imitate the fish. If you don't need a light on this dive, for example, don't take it. If you do need something, try to hide it in a pocket instead of dangling it from a D-ring. Take the snorkel off your mask and strap it to your leg or tuck it under your BC or get a folding snorkel that fits into a pocket. Shorten hoses that are too long. Clip your console close to your body. Suit your gear to conditions: You don't need the bulk of a BC with 40 pounds of lift in the tropics.

Streamline Your Movements

Keep your arms close to your body. Straighten your legs and keep them as close together as your fins will allow. Kick with short strokes so your fins stay within the slipstream of your body. Some fins do require a wider stroke so you have to compromise between efficient propulsion and streamlining. But usually you're better off finning faster instead of wider.

Breathe Deeply

Any oxygen taken from your tank but not absorbed into your bloodstream is wasted. That's the case when you take short, shallow breaths. A large part of the air you take in fills your throat and bronchia, but doesn't reach your lungs before it is expelled again. You have to take another shallow breath sooner because you didn't get much benefit from the first one, and a lot of air is wasted.

Instead, try to inhale deeply, filling your lungs completely with each breath. A deeper breath brings air to more of your lungs' tiny "air sacs" (the alveoli) where gas exchange takes place. It also adds more fresh air to the volume of "dead air" that remains in your lungs, throat and mouth from the previous breath, so the mix is richer. When more alveoli are more fully inflated with fresher air, gas exchange is more efficient: More oxygen is extracted from the incoming air and more carbon dioxide is released. Although each breath uses more air, you will take fewer breaths, and the net effect will be that less air is used. Short, shallow breaths are more frequent and less efficient.

Exhale fully too, so you expel as much carbon dioxide as possible. Anything not exhaled is carbon-dioxide-heavy "dead" air. On your next inhale, that dead air — instead of fresh air--partially fills your lungs. The urge to take the next breath is triggered not by lack of oxygen but by excess of carbon dioxide, so you find yourself inhaling again sooner. On the other hand, a deep exhale extends the time before you feel the need for another breath.

Breathe Slowly

You consume considerable energy just by breathing, by sucking the air in and pushing it out again. To inhale, you have to suck open a demand valve in your second stage and pull gas down your throat and into your lungs. Each inch along the way and each corner the gas stream turns mean friction and turbulence. Both increase the effort you put out in just breathing and decrease the amount of gas that actually gets to your lungs. Friction and turbulence are unavoidable, but the amount goes up dramatically when you try to breathe quickly--just as a faster-moving boat creates a bigger wake. The problem gets worse as you go deeper because the gas is thicker--it's like trying to suck a milkshake instead of water through a straw.

So don't force it. Try for a long, slow inhale until your lungs are full, then a long, slow exhale until they are empty. More air will get to your lungs, it will spend more time there exchanging "good" for "bad," and you will use less energy pushing the air back and forth.

Upgrade Your Gear

Overhaul your regulator on schedule and consider one with lower work of breathing, especially if you often dive deep. Scuba Lab tests have shown that the work of breathing demanded by some regs can be three times as much as others, even more. A "hard-breathing" reg not only demands more energy and therefore oxygen just to operate it, your difficulty breathing through it increases your anxiety level and elevates your breathing rate. So it wastes gas two ways.

Get in Shape

Two people climb a flight of stairs. At the top, one is huffing and puffing and the other is breathing normally. The heavy breather is getting more oxygen, but he's wasting a lot of what he inhales because he's breathing so rapidly there isn't much time for gas exchange. It's an adaptation that makes sense only on land where the air supply is unlimited.

Diving can be surprisingly strenuous because water is so much denser than air. Swimming into a current, it's not difficult to elevate your breathing to the very wasteful rate of huffing and puffing. But even much lower levels of exertion will cause your breathing rate to rise. How much it rises and how soon depend mostly on your aerobic conditioning. A diver in better condition will have less increase when the workload goes up, so he will use less air. The other part of getting in shape is to lose fat and achieve a more streamlined shape.

Stay Warm

Even warm water is cold when you're immersed in it, because if it's cooler than about 95 degrees, it takes heat out of your body at a surprising rate. Heat is energy that has to be replaced by metabolism, using oxygen to make it. Getting cold also creates mental stress which, often without your noticing it, increases your breathing rate.

And Just Chill Out

The competition over who uses less air can itself be a problem when divers associate low gas consumption with diving skill, virtue and the right to take up space on the boat. It's one of those self-fulfilling prophecies: You worry about using more air than your buddy, which causes stress, which elevates your breathing so you do, in fact, use more air.

In fact, a higher rate of air consumption can be caused by many things, some of them fixable and some not. In itself it means little or nothing and is nobody's business but yours and arguably your buddy's--who, we hope, is not out to ruin your day. So if you'd like to reduce your gas consumption, work gradually on reducing your lead, controlling your buoyancy, improving your shape and posture in the water, going slowly, breathing slowly and relaxing. Then forget about it. That alone will help.

Thanks to Sport Diver

Kathy Dowsett
www.kirkscubagear.com