Dive Course (1) PDF

Section 1 The Ultimate Dive Experience You’ve just taken your first step toward becoming a diver for life! You’re on your way to explore a magical, mysterious and captivating world that has gone untouched and unchanged for centuries or even millennia. The knowledge and skills you build now will sta...

Section 1 The Ultimate Dive Experience You’ve just taken your first step toward becoming a diver for life! You’re on your way to explore a magical, mysterious and captivating world that has gone untouched and unchanged for centuries or even millennia. The knowledge and skills you build now will stay with you as you jump in for your first "Ultimate Dive Experience" — as well as many more after that. Before you dip your fins in the water, you’ll need to prepare yourself to embark on your journey toward becoming a diver for life with some important information about diving. Combined with the pool sessions that are part of your SSI Open Water Diver course, the knowledge you build studying this information will help you explore the planet’s last great frontier for the rest of your life! SSI offers the best diving education programs in the industry, which means that by completing the Open Water Diver course, you’ll be ready to have the ultimate dive experience every time you jump in. As leaders in dive training, we take our responsibility seriously to ensure that the beautiful underwater landscape stays pristine for generations to come. SSI, your training center, and your SSI Professionals all support the ongoing efforts to protect our oceans, coral reefs and all aquatic environments for future generations. In the early days of sport diving, the oceans were seen by many as an indestructible, self-renewing resource. We know now that it can be fragile at the hands of humans and exploration. We also know that it has an impressive capacity for regeneration when given the chance. Always dive as the guest that you are in this new environment. As long as you do, you will be welcomed and have many opportunities to return. As an SSI diver, we encourage and invite you to share responsibility for protecting these valuable resources. One simple way you can participate is to embrace a personal ethic of leaving nature the way you find it. Many dive boats and dive resorts already have this policy, so we hope you will adopt this model and support it. Your behavior can help ensure that divers of the future will still be able to experience and enjoy the beauty of our aquatic world. Now, let’s get started! A Brief History of Human's Attempts to Enter the Aquatic Realm Our fascination with the underwater world goes back to the beginning of recorded history. Humans have long felt a deep-seated desire to explore the unknown, and the oceans are some of the last largely unexplored parts of our planet. Let’s look back at how diving has evolved so you can see how scuba diving has grown into the exciting, challenging and mind-expanding activity that it is today. Ancient Divers Early divers used breath-hold techniques to accomplish their tasks. No matter how capable these early divers were, they were limited by their lung capacity to the duration and depth of their dives. Stories from ancient Greece are awash in evidence of people holding their breath to dive underwater, from Spartan divers sneaking past Athenian warriors in the sea to Greeks diving for moss, sponges and oysters. The need for food, the need to work, the need to conquer, but most of all, the need to explore the unknown provided motivation to continue the quest to go — and stay — beneath the sea. The Beginning of Snorkeling In an attempt to remain underwater longer, man began using hollow reeds to breathe while submerged. These makeshift breathing tubes allowed the diver to stay beneath the surface indefinitely — but not very far beneath the surface. At more than 30 cm of depth, the water pressure made it difficult for the diver to breathe, even if the reed was open. The straight breathing tubes also forced divers to swim on their backs where they could not see the ocean floor. Swimming on your back just under the surface has a very limited range of uses, so this wasn’t a great solution for the problem of exploring the world under the sea. Along with breathing tubes, ancient art shows divers using large sheep or goatskin breathing bags. The volume of the bags would have required the diver to carry considerable weight to descend, and then water pressure compressed the bag, rendering it almost useless. The Diving Bell One of the major diving advances was the diving bell. Around 330 B.C., Alexander the Great watched his divers destroy the Phoenicians’ underwater defenses from a diving bell designed by Aristotle. Shaped like an upside-down bucket with the bottom open to the water, the diving bell, weighted to sink, was secured to the surface by cables. As the bell sank, the air within compressed. Divers swam down to the bell and used it as a base of operations, returning whenever they needed another breath. But after being used for a relatively short amount of time, the bell’s air supply became fouled by carbon dioxide, and little oxygen remained inside the bell. At this point, the divers were in grave danger, and the bell had to be brought to the surface to replenish the air supply. Image ©: Borut Furlan / WaterFrame Image © Mk V Centuries later, the first wearable diving suits were devised. These rudimentary suits and helmets were literally enclosed diving bells with watertight openings for arms. Major technological advancement came in the late 18th and early 19th centuries. Pumps were developed that were capable of delivering air at depth under pressure. Diving suits and bells could now be effective when supplied with air from the surface. The first diving helmet was introduced around 1800. It was designed like a miniature diving bell, with the wide opening at the bottom resting on the diver’s shoulders. Still, this was not a perfect solution to the problem of getting humans underwater. Sufficient air had to be pumped from the surface to keep water from entering the helmet, and divers had to be careful not to fall and tip over while wearing the heavy device. Consequences of Diving Emerge In the mid-1800s, the first fully enclosed, waterproof diving rig was developed and a new industry in Great Britain called salvage diving was born. As these salvage divers extended their bottom times, more and more cases of what was erroneously called "rheumatism" were reported. Since this type of diving was relatively new, divers’ physiological problems could only be related to surface maladies. Medical science had no understanding of the effects of water pressure on the human body. The problem became greater when pumps were designed to maintain air pressure underwater in relatively large spaces. Large, dry chambers called caissons allowed divers to build bridge footings and tunnels underwater. Workers entered caissons from the surface through air locks, but after extended periods at depth, they showed severe physiological disorders upon surfacing, and many died. This pressure malady was called caissons disease, or "the bends" due to the contorted posture the disorder causes in its victims. In the late 1870s, French physiologist Paul Bert studied the effects of gradual decompression and his findings led to the development of the decompression chamber. The new industry of "underwater work" with greater times at greater depths had its share of other new maladies never before described by scientists. In response to the Royal Navy’s Deep Diving Committee request to investigate the possible causes of the bends, British physiologist J.S. Haldane composed a set of diving tables based on stage decompression. The tables were based on the amount of time a diver spent at a certain depth. The greater the depth and the longer the bottom time, the more slowly the diver would have to ascend to remain free of the bends. Haldane discovered that if the divers controlled their rate of ascent in accord with the tables, the problems associated with caissons disease would be alleviated. Diving technology made great leaps and bounds in the 19th and 20th centuries, but other maladies still affect divers, such as nitrogen narcosis. This condition, caused by the buildup of nitrogen in the body at deeper depths, causes a narcotic-like state. Nitrogen narcosis impairs good judgment and hinders the ability to make rational decisions at depth. Jacques Cousteau and the SCUBA It wasn’t until 1943 that Jacques Cousteau, a young French naval officer, and his partner, Emile Gagnan, developed the demand regulator. The demand regulator enabled a diver to breathe air at the proper pressure for his depth and in the amount that he needed. For the first time a diver could descend into the undersea world with a complete, independent life support system, self-contained and free. This innovation, along with high-pressure compressors and cylinders, gave birth to the name Self-Contained Underwater Breathing Apparatus along with its better known acronym SCUBA. After millennia of working underwater with the constraints of a single breath or heavy hoses and lines, humans could, for the first time, enter the sea untethered. The foundation was set for the exciting sport of scuba diving and the world renewed its romance with the ever mysterious, but now accessible sea. In the mid-1900s, primitive, consumer-targeted SCUBA systems appeared on the market, but diving instruction for the recreational diver was non-existent. This was SCUBA’s "Wild West" period, when most sport divers were very fit individuals whose strength and sheer determination made up for their SCUBA systems’ lack of safety. The risk of physical injury and even death was viewed as part of the challenge and excitement of SCUBA diving. Thankfully, this naive perspective has been replaced by proper knowledge, skills and safe diving equipment. Around 1955, the lack of an air gauge was the most significant hazard to SCUBA divers. When their air supply was depleted, divers were forced to ascend rapidly to the surface. Also, the regulators of this era developed greater breathing resistance as depth increased or as cylinder pressure decreased. Diving in Context Now, you may be wondering why we are telling you about the horse-and-buggy era of diving when you’re here to learn to dive. Scuba diving as we know it today is a relatively young sport. The major breakthroughs in modern technology and instruction have only occurred within the last 25 years. Our successful attempts to dive to depth have been dependent on the refinements of reliable diving equipment. Why? In the underwater environment, we are totally dependent on our training and equipment. As you learn to be an SSI scuba diver, the Diver’s Diamond of knowledge, skills, equipment and experience will show you how these four ingredients work together to create the best possible diving experience each and every time you enter the water. To get started with your new adventure, you will first learn how pressure affects your body in air and water. Right now, you may not be aware of the air pressure surrounding your body on land because it is evenly applied in all directions. However, most individuals have felt the effects of pressure changing while flying or traveling to the mountains. You would recognize this feeling by your ears "popping." This phenomenon represents your body’s adjustment to a relatively mild pressure change. You might also have some experience with your body adjusting to water pressure changes. Have you ever experienced discomfort in your ears while descending to the bottom of a swimming pool? That discomfort is caused by the building pressure of the water against your eardrums as you descend. Now, imagine how it would feel to dive even deeper, 10 or even 20 meters below the surface — the discomfort would quickly give rise to pain and possible injury. To avoid injury, divers must be aware of immediate pressure changes upon descent and understand the effects of pressure on the human body. The Weight of Air and Water We know that air weighs approximately 1.29 grams per liter. One atmosphere—which represents the weight of a column of air that extends from sea level to the outer edge of the Earth's atmosphere—equals about 1.0 bar of pressure. We are not usually aware of this air pressure because it is evenly applied on our bodies. Pressure is defined as force per unit area and is commonly expressed in bar in the metric system and pounds per square inch (psi) and atmospheres in the Imperial system. It is common to think of pressure in terms of the number of bars and atmospheres. However, we do become aware of pressure changes when we enter the water environment. Both freshwater and salt water weigh considerably more than air. Freshwater weighs 1.0 kg per liter, and salt water weighs 1.025 kg per liter. That means that a liter of water is about 800 times heavier than a liter of air — a pretty significant difference! An increase of 1 bar of pressure underwater takes place in a relatively short distance: only 10 meters sea water (msw) or 10.2 meters fresh water (mfw). For each additional 10 meters of descent in saltwater or 10.2 meters in fresh water, another bar is added to the pressure on our bodies. Absolute and Gauge Pressure Absolute pressure — also called ambient pressure — refers to the total pressure exerted on an object. Absolute pressure includes 1 bar exerted by the air that is above the surface plus whatever additional pressure is exerted by the water at depth. Absolute pressure is expressed in bar. Gauge pressure refers to the pressure readings on gauges. Since the gauge reads zero at one bar, gauge pressure may be found by subtracting one bar from absolute pressure. Gauge pressure is expressed in bar. The absolute pressure at sea level would be 1 bar. Gauge pressure would be zero. This graphic above illustrates the pressure changes in even bar in salt water and in fresh water. As you can see, due to the density of salt water and fresh water, pressure changes vary slightly. For ease of understanding, we will focus on salt water only throughout this manual. The pressure increase per meter of descent in salt water is 0.1 bar (1 bar / 10 m). Pressure-Related Diving Injuries Pressure-related diving injuries occur when a sufficient pressure differential exists between ambient pressure and the pressure in the air spaces in our body, or gas spaces that are in contact with our body. Our bodies are almost three-quarters liquid, and the liquid portions of our bodies have no difficulty with pressure changes. At the depths that sport divers dive, the liquid areas of the body are incompressible. This means that they will not change as pressure increases or decreases. Gases, however, are compressible. Pressure on air-filled spaces in the body — from lungs to microscopic spaces in dental fillings — will compress and expand as the ambient pressure changes. Boyle’s Law Boyle’s Law says that if the temperature remains constant, the volume of a gas in a flexible container will vary inversely as the absolute pressure changes and the density will vary directly. More simply stated for diving: as water pressure increases, the volume of air spaces in your body decreases — and as water pressure decreases, the volume of air spaces in your body increases. In other words, as pressure increases, air volume decreases, and as pressure decreases, air volume increases. Boyle’s Law is: P1 × V1 = P2 × V2 P1 = Starting Pressure V1 = Starting Volume P2 = Ending Pressure V2 = Ending Volume Using this formula, it is possible to compute the volume of a flexible air-filled container as it is subjected to increasing pressure at depth. Depth in bar Ambient Volume of a Density of Meters Pressure in Sealed Gas bar Container 0 1 1 1 1x 10 2 2 0.5 2x 20 3 3 0.333 3x 03 4 4 0.25 4x Notice on the chart that the greatest relative volume change takes place between 0 and 10 meters. This means that you’ll need to react immediately to pressure changes as soon as you start descending below the surface. Your body’s air spaces experience compression (diminished volume) upon descent (pressure increase) unless you introduce more air into them to equalize the internal pressure with the ambient pressure. Now that you understand the science behind water pressure changes and their effect on your body, let’s talk about the different types of compression you might experience when you dive, as well as how to counteract them. Pressure equalization protects against a condition known as "squeeze," the uneven application of pressure. Squeeze is always uncomfortable and, unless dealt with promptly, can lead to tissue damage. You will learn the proper equalization techniques for each body air space that can be subjected to squeeze — your ears, sinuses, lungs, teeth and intestines. The Ear Your ear is made up of the outer ear, the outer ear canal, the tympanic membrane, the middle ear and the Eustachian tube. The tympanic membrane, or eardrum, is a relatively thin membrane that seals off the middle ear from the external environment (air or, in our case, water). This membrane and its connective tissue are the most sensitive areas for squeeze. The middle ear and the inner ear contain the body's balancing and hearing mechanisms. Separating the middle ear from the inner ear are two of the thinnest membranes in the human body, the round and oval windows. These membranes embody one of the reasons you are taught to gently blow to equalize your middle ears — damage to the round or oval windows may cause a leakage of fluid from the inner to the middle ear. This can cause a ringing or roaring in the ears, and even hearing loss. Window rupture can also cause severe vertigo and vomiting, a dangerous combination when underwater. The Eustachian tube connects the middle ear with the back of the throat and allows air to pass from the throat into the middle ear. The Eustachian tube is very important to the equalization process. Image ©: Peter LECKO 1. Outer Ear 2. Ear Canal 3. Ear Drum 4. Eustachian Tube Image © iStock As a diver descends, external pressure (water) on the tympanic membrane increases and pushes the eardrum inward. If the diver fails to introduce additional air into the middle ear through the Eustachian tube, ear squeeze can occur. Ear squeeze (aerotitis or barotitus media) is easy to recognize and prevent. It is the same discomfort felt when you dive underwater even in a shallow swimming pool. This discomfort or pain is the primary symptom that indicates that the eardrum and its connective tissue are under stress. Pain generally occurs before the eardrum ruptures, and it is an indication that some tissue damage may already be taking place. Therefore, you should never wait for pain to begin to start equalizing — a technique you will learn. Injury can occur with a pressure differential of as little as 0.1 bar at a depth of only 1 meter. Even the added pressure of just 30 cm more of depth can lead to a perforated tympanic membrane. The most immediate result of a perforated tympanic membrane is loss of hearing, and with water rushing into the middle ear, the diver could experience vertigo. Ear Squeeze usually occurs during descent and is extremely rare upon ascent. If you feel pain on the ascent, immediately stop and then slowly continue your ascent. If ear pain persists after a dive, or if there is blood in the ear canal (indicating a perforated eardrum), do not put anything in your ear and contact a physician. Image ©: Peter LECKO Image © iStock The Sinuses We have four pairs of sinuses: the frontals, the maxillaries, the ethmoidals and the sphenoidals. Sinuses are hollow spaces in the bones of the skull. They lighten the skull, warm and moisten the air we breathe, and cause our voices to resonate. Sinuses are lined with mucous membranes and are connected to the nasal passage by narrow tubes which can become blocked by congestion or irritation. Sinus squeeze (aero sinusitis) occurs when congestion traps air in a diver’s sinuses. As the diver descends, increasing pressure can cause the sinus membranes to rupture. If this happens, the result is that air in the sinuses is replaced by blood and tissue in a process of pressure equalization. The first sign of sinus squeeze is usually a sharp pain or wedging sensation directly above the eyes. If you ignore the pain and pressure and continue descending, minor tissue damage occurs, resulting in a slightly bloody nose when you’re done diving. Most divers have experienced sinus squeeze and it does not require medical treatment. However, if pain or congestion persists, consult your physician. Sinus squeeze can easily be prevented by not diving with a cold or congestion. Do not use decongestants unless you have consulted your physician and explained that you will be taking medication while diving. Image © iStock The Lungs Lung squeeze (thoracic squeeze) does not occur while scuba diving, but it can occur when snorkeling or freediving. If you descend even 1 – 2 meters below the surface without filling your lungs with air, the water pressure can compress the small residual volume of air in your lungs. This can cause your lung walls to collapse or, at greater depths, the lining of your lungs to rupture and release blood and fluid into your lungs in the process of equalization. When you freedive, you can easily prevent lung squeeze by completely filling your lungs with atmospheric air prior to descending, staying above 20 meters and not releasing any of this air until you reach the surface. Lung squeeze is easily prevented by taking a normal breath before descending while freediving. Equipment-Related Squeeze There are two equipment related squeezes: mask squeeze and suit squeeze. Mask Squeeze Your mask forms an almost rigid pocket of air around your nose and eyes. Just like all squeezes, pressure increases, volume decreases and this pocket of air compresses against your face. Since your eyes and surrounding tissues are supplied with blood at ambient pressure, the difference between the pressure in your bloodstream and the air in your mask can cause surface capillaries in and around your eyes to rupture. This doesn’t cause much pain, but you might not look very pretty. In severe cases the optic nerve can be damaged and blindness may occur. If you have any visual distortion after a mask squeeze consult a physician immediately. Mask squeeze is easy to prevent! Ask your SSI Dive Professional to properly fit you for a mask and exhale into your mask every meter while descending. Suit Squeeze Suit squeeze is a potential problem only for drysuit wearers or when wearing a loosely-fitted wetsuit. If you wear a drysuit, some air will always be trapped between your body and the suit. As you descend, the drysuit compresses (since as pressure increases, volume decreases), and bunches up. The wrinkles and folds in the suit pinch your skin leaving red marks or bruises where this occurs. If this happens to you while diving in a drysuit, there is no reason for concern — the marks will clear up in just a few days with no further treatment. Equalization Techniques Prevention of ear squeeze is easy. The following equalization techniques relax the muscles that control the opening of the Eustachian tube and allow air to enter the middle ear at ambient pressure: Swallowing Rotating the jaw Valsalva technique To perform the Valsalva technique, simply pinch your nostrils closed and blow gently until the pressure is equalized. DO NOT BLOW TOO HARD or try to force air into the middle ear. The Valsalva technique should be used very carefully with practice only after swallowing and jaw rotating do not work. Rules for Equalization: Breathe Continuously and Never Hold Your Breath! This ensures proper equalization of your lungs on descents and ascents. Never Wait for Pain to Begin Before Equalizing! On descent, immediately begin to equalize, relax and equalize often throughout your descent. If possible, descend feet first in an upright position or by using a descent line. Never Dive With a Cold or Congestion. Mucus blocks the Eustachian tube, making equalization very difficult. Never Dive With Earplugs! If pain develops, stop your descent using your fins or line; ascend until the pain stops. Try equalizing again. If the pain persists do not dive. If you feel pain on the ascent, immediately stop and then slowly continue your ascent. Reverse Squeezes Unlike other squeezes, reverse squeezes can only happen on ascent — as the ambient pressure decreases, the volume of the air-filled spaces in your body increases. Reverse squeezes happen rarely and can usually be dealt with by ascending extremely slowly or even stopping occasionally to allow the trapped gas to escape. One example of reverse squeeze is congestion trapping air in the sinuses. As the diver ascends and ambient pressure decreases, the volume of the trapped air expands. The result is a sharp pain or wedging sensation above the eyes. If this occurs, simply ascend slowly or stop and allow the trapped air to escape. Another example of reverse squeeze is tooth squeeze (barodontalgia), previously known as aerodontalgia. This is pain in a tooth caused by a change in atmospheric pressure. No one knows for sure why tooth squeeze happens but certain explanations have been proposed. Very rarely when a cavity is filled, there is a possibility that a small air pocket is left between the filling and the tooth’s nerve endings. Since the tooth is hard and tissue is soft, as you descend, pressure increases and volume decreases. The air pocket would decrease in size or completely diminish causing a vacuum against the nerve endings thereby producing pain. If this happens, simply ascend slowly and return to the boat or shore. Consult your dentist as soon as possible. Most likely your tooth will just require some additional care. Tooth squeeze is more likely to occur in divers with tooth decay, dental infections, or recent tooth extraction or fillings. One other form of reverse squeeze is intestinal squeeze, which is caused by eating gas-producing foods prior to diving and takes place in the stomach. While diving, these gas-producing foods start producing gas, which becomes pressurized at depth. As you ascend, the ambient pressure decreases and the volume of the gas in your belly increases causing stomach pain and discomfort. If this happens to you, simply ascend slowly and let the gases escape. As we have already discussed, there is a definite link between owning your own equipment and your comfort in the water. This is because the equipment is personally fitted to you. This is your Total Diving System. Your Total Diving System is made up of six sub-systems. In this section, we are only going to talk about the Snorkeling System. Your Mask Your dive mask is the first component of the Snorkeling System and gives you clear vision underwater, protects your face and eyes from irritants in the water, keeps water out of your nose and gives you some protection from cold water. Unlike our amphibious ancestors, our eyes are adapted to see through air, not water. That’s why, when you open your eyes underwater, your vision is blurred. The diving mask places a layer of air between your eyes and the water to allow clear vision underwater. You should never wear goggles when diving below the surface of the water. Since goggles do not cover the nose, there is no way to equalize the air pressure around your eyes when you descend — causing eye damage. 1. Positive Locking Device 2. Frame 3. Lens 4. Nose Pocket 5. Mask Strap Image © Cressi Selecting the right mask requires the assistance of your SSI Dive Professional. The mask will be fitted to the contours of your face. A double seal along the mask edge is very effective in keeping water out. Flexible mask straps or comfort straps comfortably secure the mask to your face and locking devices keep your mask strap from slipping. The lenses of your mask should be tempered glass to resist scratching and breaking. Most high quality masks today are also made with non-allergenic silicone. These materials are the softest and most durable. Some masks utilize two types of silicone: a harder compound near the frame for structure and stability and a softer compound close to your face for comfort and a perfect seal. Just as important, your mask should give you a good range of peripheral vision. To test the fit of your mask, simply place the mask on your face without the help of the mask strap and inhale gently. If the mask stays, it fits. It’s that easy! Image © Mares If you wear glasses, a high-quality mask gives you the option of putting your prescription in the mask lenses. Diving with a prescription mask can provide improved vision for many divers than diving with contact lenses due in part to pressure changes underwater. Consult your SSI Dive Professional for more information concerning prescription lenses or contacts. To prepare your mask for diving, clean it with an approved mask cleaning compound. Before each dive, simply apply a special anti-fog solution that you can get from your SSI Training Center to maintain clear vision throughout the dive. Clean again to remove oils and contaminants whenever the anti-fog alone does not work. Clearing water from your mask is a relatively simple skill you will learn and practice over and over. While diving, if water happens to enter your mask, merely tilt your head back and apply pressure to the top rim of your mask and start exhaling gently through your nose. It’s really that easy. Image © Aqualung Your Snorkel Snorkels let us swim on the surface and watch the world beneath, and they let us maneuver on the surface easily and breathe without lifting our heads out of the water. As part of the Total Diving System, the snorkel can help you conserve the air in your cylinder by using your snorkel to surface-swim to a dive site. For unrestricted breathing and easy clearing, a snorkel should have a smooth internal construction with a large bore and self-draining vent, be made of relatively flexible material and have a comfortable mouthpiece. Your SSI Dive Professional will help you select the most comfortable snorkel for you. Before you dive down, simply take a good deep breath from the snorkel. As you descend, the snorkel fills with water. Once back on the surface, most of the water will drain out through the built-in purge valve. To clear the rest of the water from your snorkel, exhale sharply and the remaining water will be displaced through the same valve. Your SSI Dive Professional will train you on proper breathing patterns and how to properly empty the water from your snorkel. 1. Mouthpiece 2. Self-Draining Purge Valve 3. Flexible Tube 4. Dry or Semi-Dry Vent Image © Scubapro Your Fins 1. Blade 2. Vent 3. Foot Well 4. Buckle 5. Heel Strap Image © Mares Unlike swimmers, snorkelers and scuba divers do not use their arms for propulsion. Fins provide 100% of our propulsion. Fins are not built for speed — they are designed to propel the scuba diver effortlessly at a moderate rate of speed to cover great distances with low energy output. The right fins make the difference between an easy, fun-filled dive and a difficult, tiring one. During class, you will learn that for the best performance, you should kick your fins with your legs stretched out, kicking from the hips rather than the knees. Today’s fins are lightweight and sleek compared to fins of the past. You also have a few material types and combinations to choose from, including technopolymer and rubber. Technopolymer fins are usually thinner and lighter than rubber fins, offer more thrust and can help your buddy keep you in sight when made of high-visibility colors. There are two types of fins: full-foot fins designed to be worn without dive boots, and open-heel fins designed to be worn with dive boots. Fin straps should have an adjustable heel strap with locking device unless they are of a stretchable type, such as bungee straps or stainless spring straps. The heel straps should be replaceable in case of wear or breakage (and it’s always a good idea to carry an extra set of straps!). The fins should have a wide, fairly rigid blade to give more thrust and greater kicking ease. To be properly balanced, fins should be nearly neutrally buoyant in both fresh and salt water. Your Dive Boots Dive boots are worn with open-heel scuba fins. They protect the foot from chafing in the foot pockets, from cold temperatures and from abrasion while walking to and from the dive site. Check with your SSI Dive Professional to find the right type and fit of boots and fins for you. Your Gloves and Mitts When you dive, it’s important to protect your hands. In cold water, gloves and mitts ensure that your hands are warm and flexible enough to operate your diving equipment. They also protect your hands from abrasion and irritants in the water. There are different types and thicknesses designed for a variety of diving conditions. Gloves and mitts, however, are not an invitation to touch marine and plant life underwater and some dive sites even forbid wearing gloves. Your SSI Dive Professional will explain when and where you can and cannot wear gloves in the underwater environment. Your Exposure Suit When you dive, you need thermal protection to keep you warm and comfortable. Just as you need appropriate clothing for different temperatures and activities on land, you also need appropriate protection for different diving situations. Exposure suits (also known as wetsuits, drysuits, dive skins, and others) are made from a variety of materials and are designed to protect you in different water environments. Your SSI Dive Professional will work with you on selecting the type of exposure suit for your type of diving. We’ll talk more about exposure suits in Section 2. Image ©: Stephen Frink Image © Aqualung Your Mesh Bag Your mesh bag holds all of your equipment and makes it easy to rinse in fresh water after a salt water dive. Maintenance is important to ensure your dive equipment’s long life of good service. Maintaining Your Equipment Here are some valuable tips for keeping your snorkeling equipment in top condition: Mark your dive equipment with your name or initials. Record all equipment in your MySSI Logbook. After any dive, thoroughly rinse your equipment with fresh water and allow it to dry in a cool, well-ventilated area. Take special care of your mask. Particles in the water (turbidity) can also limit vision. Light rays break up in fantastic patterns as the water moves and diffuses the light. Variables affecting visibility underwater — refraction, illumination, absorption, diffusion and turbidity — can make the same diving spot look very different throughout the day. Water Temperatures Depending on where you dive, water temperatures can range from around 0 degrees C to over 26 degrees C. You may even encounter a temperature difference of 10 to 20 degrees C between the surface and depth. Because cold water is dense, it sinks below warm water. This causes layers of various temperatures as you descend. The difference in temperature can be harsh. These layers of different temperatures are called thermoclines. Thermoclines occur in all bodies of water. Some are more dramatic than others, which is why you need to wear thermal protection on every dive. Theoretically you can lose body heat underwater about 25 to 30 times faster than in air through direct contact with the water (conduction) and through the movement of the water across your skin (convection). Adequate exposure protection increases your enjoyment in the water. Since we cannot talk underwater, we need to communicate by using hand signals. Pictured here are the most commonly used hand signals. Review these hand signals before heading to the pool. You can review them again before diving on the MySSI app. Sound behaves very differently underwater than it does in air. Sound travels four times faster underwater and seems to come from all directions. This is because our ears have not adjusted to the increased speed. Sound is very poorly transmitted from air to water or from water to air, but sounds made underwater travel great distances. If you cannot get your message across with hand signals, there are other underwater devices that can be used for communication, such as writing slates or wet notes. Image © Subgear There are also other signaling devices you can use for getting your buddy’s attention, or the whole group’s attention, such as your diver’s tool or shakers. You can use your diver’s tool by banging on your cylinder and a shaker for creating a loud sound. Both can be heard from a distance. Clear communication is a key element. Therefore communication techniques should be discussed with your buddy prior to any dive Adaptation to the Aquatic Environment During your Dive Sessions you will learn basic snorkeling and freediving skills. While it may not seem necessary to learn these skills if your goal is to become a diver, these skills can come in handy. If, for example, you ever find yourself on the surface away from the security of land or your dive boat, simply inflate your Buoyancy Compensator (BC), put your snorkel in your mouth, and swim - it's that simple! The aquatic environment is a beautiful, exciting place — but you might feel challenged by the many new sensations the water offers. Let’s preview some of the things you might notice when you first begin to freedive, snorkel or dive. Constant Waves When you snorkel or freedive in the ocean, one of the first things you become aware of is the constant movement of the water. You might feel the urge to struggle against this movement, but when you learn to relax and use the water to your advantage you will make every outing a pleasurable one. Vision Underwater Underwater, vision changes in unique ways and you will experience an interesting optical illusion called refraction. Light rays bend as they pass from water into the airspace in your mask. This makes objects look 33% larger and 25% closer. This means that when you see a 1-meter long fish from a distance of one meter, it will appear to be about 1.33 meters long and about 0.75 meters away from you. The illumination, or amount of light in the water, will vary according to the position of the sun, clouds, and surface wave conditions. Heavy water movement diminishes light penetration. In addition, light spreads when it encounters water molecules, it becomes softer, less harsh, and the intensity is decreased. This is called diffusion. The deeper we dive, the more warm colors — such as red, orange, yellow — diminish in intensity and virtually disappear until we see only blues and purples. This is called absorption. Particles in the water (turbidity) can also limit vision. Light rays break up in fantastic patterns as the water moves and diffuses the light. Variables affecting visibility underwater — refraction, illumination, absorption, diffusion and turbidity — can make the same diving spot look very different throughout the day. Water Temperatures Depending on where you dive, water temperatures can range from around 0 degrees C to over 26 degrees C. You may even encounter a temperature difference of 10 to 20 degrees C between the surface and depth. Because cold water is dense, it sinks below warm water. This causes layers of various temperatures as you descend. The difference in temperature can be harsh. These layers of different temperatures are called thermoclines. Thermoclines occur in all bodies of water. Some are more dramatic than others, which is why you need to wear thermal protection on every dive. Theoretically you can lose body heat underwater about 25 to 30 times faster than in air through direct contact with the water (conduction) and through the movement of the water across your skin (convection). Adequate exposure protection increases your enjoyment in the water. Summary We’ve covered many topics in this section that will help you dive safely and confidently. Your commitment to your personal well-being will motivate you to read the manual, watch the video or study online until your knowledge becomes second nature. Remember, knowledge replaces fears and fantasies with correct information. Get ready for some fun in the pool! Objectives At the end of Section 1, you will be able to: 1. Describe the historical event that led to the use of the acronym SCUBA to describe diving. 2. Explain why pressure on an object increases as it descends underwater and give examples of the effects of this increasing pressure. 3. Explain why the air volume in a flexible container decreases as it descends underwater and give examples of the effects of this change in volume. 4. Contrast the differences between salt and fresh water as it relates to weight and pressure. 5. Calculate the total pressure exerted on a diver’s body at a given depth in terms of bar. 6. List five air spaces in the body that can be affected by increasing pressure and describe its effects on these air spaces. 7. State the procedure used to equalize pressure in the ear during descent. 8. List the individual components of the Snorkeling System. 9. Describe the effects of depth on light penetration and body heat loss.