Humans may have originated from the primordial oceans over millions of years, evolving on land to have lungs instead of gills, but in the process we have lost the ability of our very distant ancestors to breathe underwater. We thus have to take special equipment with us when we plan to swim below the surface of the sea, lakes or ponds, for any length of time.

 

To begin try taking a big gulp of air and duck down underwater. See how long you can stay under, before returning to the surface gasping for air. Not very long. About a couple of minutes at best.

 

Then came the snorkel, a curved tube so you can swim at the surface and keep you head submerged to view the fishes. There are free divers who can swim for a lot longer, such as pearl divers. The best being women, because they can withstand the cold for longer.

 

Some boats have onboard compressors, to feed tethered divers air through long tubes. This is cumbersome and restrictive, and not really used a lot today.

 

 

SCUBA DIVING

 

Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an acronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.

Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver at ambient pressure through a diving regulator. They may include additional cylinders for range extension, decompression gas or emergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption; they produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.

Scuba diving may be done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmen, combat divers or attack swimmers.

A scuba diver primarily moves underwater using fins worn on the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface. Other equipment needed for scuba diving includes a mask to improve underwater vision, exposure protection by means of a diving suit, ballast weights to overcome excess buoyancy, equipment to control buoyancy, and equipment related to the specific circumstances and purpose of the dive, which may include a snorkel when swimming on the surface, a cutting tool to manage entanglement, lights, a dive computer to monitor decompression status, and signaling devices. Scuba divers are trained in the procedures and skills appropriate to their level of certification by diving instructors affiliated to the diver certification organizations which issue these certifications. These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment, and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications.

 

 

BSAC

 

Learn to dive with BSAC and get started with either our Ocean Diver or Discovery Diver course today! Each course consists of both theory and practical modules, with the Discovery Diver offered for our youngest divers.

Q. Can I try scuba diving before starting a membership?

A. Every club offers try dive sessions to see if scuba diving is for you. Contact your nearest club to arrange a try dive session. 

Q. How much does/did it cost in 2024?

A. The cost comes in two parts - Your e-learning and qualification part (includes eLearning, training materials, qualification upon completion and 12 months BSAC membership). Then your practical training.

BSAC Ocean Diver: £128* or BSAC Discovery Diver: £101*

 

Practical Training: Roughly £400-500 with training providers or club prices vary. (Your chosen Training Centre or Club will charge for this). 

Please note: * There is an additional cost in the practical training. Your chosen Training Centre or club will charge for this. 

 

Q. How long does it take to qualify?

A. The beginner courses are designed to allow students to progress at their own pace. Independent learning using the BSAC eLearning platform takes about 8-10 hours. Pool training and open water dives can be completed in just a few days.
Only once you and your instructor feel confident that you've mastered a skill, will you move on to the next one.

Q. Is scuba diving safe?

A. Scuba diving has a really good safety record and this is mainly due to the training we do before participating in our adventurous sport. BSAC training is world-renowned for being extremely thorough and what's different about BSAC is we build in safety skills and training from the start.

 

Scuba diving's good safety record is justified by good training, sound equipment and safe practices. BSAC will teach you everything you need to know to be a competent safe diver.

Q. Does a BSAC scuba qualification expire?

A. Your BSAC qualification will not expire. However, if you haven’t been diving in a while and wish to refresh your diving knowledge skills, you may wish to do a BSAC Scuba Refresher Course.

 

 

 

 

 

 

 

PADI

 

Q. How long does a PADI course take?

A. PADI certification courses are flexible and performance based. Knowledge development or e-Learning can be completed at your own pace. PADI dive shops offer a variety of dive training schedules depending on how fast you progress. For new divers, the average time frame for Open Water Diver scuba certification is 3-5 days.

Q. How much does a PADI course cost?

A. Interested in learning to dive or advancing your dive skills? The average cost to obtain your PADI certification will vary by dive course and location. Learn about your PADI dive certification options in this step-by-step breakdown:

All dive certifications require knowledge development and in-water training. After completing your PADI eLearning, you will begin your in-water training with your chosen Dive Shop. Please contact your Dive Shop directly for pricing as costs may vary by location. Notify your Dive Shop if you have already purchased your e-Learning.

New Diver: You will want to begin with Open Water Diver. The knowledge portion of your dive training or e-Learning costs around $230 USD. After you complete your e-Learning, you will begin your in-water training with your chosen Dive Shop.

Continuing Education: After achieving your Open Water Diver certification, you can continue your dive journey with specialty courses to expand your underwater exploration skills and increase your bottom time, learn dive rescue and safety skills, ocean stewardship, underwater photography, or even how to become a dive equipment specialist. Pricing varies by course. Contact your chosen dive shop for in-water training costs. Learn more about continuing education courses.

Professional: Travel the world and get paid to do what you love or share your dive knowledge locally. As a PADI Divemaster or PADI Instructor, you’ll learn how to lead dives and help others with their dive education. Learn more about becoming a PADI Pro.

Q. Do PADI licenses expire?

A. No, your scuba diving certification is for life! However, diving regularly is highly recommended to maintain your dive skills and knowledge. Try to avoid long periods without diving (6 months or longer). If you haven’t been scuba diving recently, you should take the PADI Reactivate Scuba Refresher.

 

 

 

 

 Safiya Sabuka and Musa Bomani are both seasoned scuba divers.

 

 

 

 

BREATHING APPARATUS

The defining equipment used by a scuba diver is the eponymous scuba, the self-contained underwater breathing apparatus which allows the diver to breathe while diving, and is transported by the diver. It is also commonly referred to as the scuba set.

As one descends, in addition to the normal atmospheric pressure at the surface, the water exerts increasing hydrostatic pressure of approximately 1 bar (14.7 pounds per square inch) for every 10 m (33 feet) of depth. The pressure of the inhaled breath must balance the surrounding or ambient pressure to allow controlled inflation of the lungs. It becomes virtually impossible to breathe air at normal atmospheric pressure through a tube below 3 feet (0.9 m) under the water.

Most recreational scuba diving is done using a half mask which covers the diver's eyes and nose, and a mouthpiece to supply the breathing gas from the demand valve or rebreather. Inhaling from a mouthpiece becomes second nature very quickly. The other common arrangement is a full-face mask which covers the eyes, nose and mouth, and often allows the diver to breathe through the nose. Professional scuba divers are more likely to use full-face masks, which protect the diver's airway if the diver loses consciousness.

OPEN CIRCUIT DIVING REGULATOR

Open-circuit scuba has no provision for using the breathing gas more than once for respiration. The gas inhaled from the scuba equipment is exhaled to the environment, or occasionally into another item of equipment for a special purpose, usually to increase the buoyancy of a lifting device such as a buoyancy compensator, inflatable surface marker buoy or small lifting bag. The breathing gas is generally provided from a high-pressure diving cylinder through a scuba regulator. By always providing the appropriate breathing gas at ambient pressure, demand valve regulators ensure the diver can inhale and exhale naturally and without excessive effort, regardless of depth, as and when needed.

The most commonly used scuba set uses a "single-hose" open-circuit 2-stage demand regulator, connected to a single back-mounted high-pressure gas cylinder, with the first stage connected to the cylinder valve and the second stage at the mouthpiece. This arrangement differs from Émile Gagnan's and Jacques Cousteau's original 1942 "twin-hose" design, known as the Aqualung, in which the cylinder pressure was reduced to ambient pressure in one or two stages which were all in the housing mounted to the cylinder valve or manifold. The "single-hose" system has significant advantages over the original system for most applications.

In the "single-hose" two-stage design, the first stage regulator reduces the cylinder pressure of up to about 300 bars (4,400 psi) to an intermediate pressure (IP) of about 8 to 10 bars (120 to 150 psi) above ambient pressure. The second stage demand valve regulator, supplied by a low-pressure hose from the first stage, delivers the breathing gas at ambient pressure to the diver's mouth. The exhaled gases are exhausted directly to the environment as waste through a non-return valve on the second stage housing. The first stage typically has at least one outlet port delivering gas at full tank pressure which is connected to the diver's submersible pressure gauge or dive computer, to show how much breathing gas remains in the cylinder.

MIXED GAS

For some diving, gas mixtures other than normal atmospheric air (21% oxygen, 78% nitrogen, 1% trace gases) can be used, so long as the diver is competent in their use. The most commonly used mixture is nitrox, also referred to as Enriched Air Nitrox (EAN or EANx), which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the risk of decompression sickness or allowing longer exposure to the same pressure for equal risk. The reduced nitrogen may also allow for no stops or shorter decompression stop times or a shorter surface interval between dives.

The increased partial pressure of oxygen due to the higher oxygen content of nitrox increases the risk of oxygen toxicity, which becomes unacceptable below the maximum operating depth of the mixture. To displace nitrogen without the increased oxygen concentration, other diluent gases can be used, usually helium, when the resultant three gas mixture is called trimix, and when the nitrogen is fully substituted by helium, heliox.

For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as travel, bottom, and decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times. Back gas refers to any gas carried on the diver's back, usually bottom gas.

BUOYANCY CONTROL - SINK OR SWIM

To dive safely, divers must control their rate of descent and ascent in the water and be able to maintain a constant depth in midwater. Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether they ascend or descend. Equipment such as diving weighting systems, diving suits (wet, dry or semi-dry suits are used depending on the water temperature) and buoyancy compensators (BC) or buoyancy control device (BCD) can be used to adjust the overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes the effort of swimming to maintain depth and therefore reduces gas consumption.

The buoyancy force on the diver is the weight of the volume of the liquid that they and their equipment displace minus the weight of the diver and their equipment; if the result is positive, that force is upwards. The buoyancy of any object immersed in water is also affected by the density of the water. The density of fresh water is about 3% less than that of ocean water. Therefore, divers who are neutrally buoyant at one dive destination (e.g. a freshwater lake) will predictably be positively or negatively buoyant when using the same equipment at destinations with different water densities (e.g. a tropical coral reef). The removal ("ditching" or "shedding") of diver weighting systems can be used to reduce the diver's weight and cause a buoyant ascent in an emergency.

Diving suits made of compressible materials decrease in volume as the diver descends, and expand again as the diver ascends, causing buoyancy changes. Diving in different environments also necessitates adjustments in the amount of weight carried to achieve neutral buoyancy. The diver can inject air into dry suits to counteract the compression effect and squeeze. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy.

Neutral buoyancy in a diver is an unstable state. It is changed by small differences in ambient pressure caused by a change in depth, and the change has a positive feedback effect. A small descent will increase the pressure, which will compress the gas-filled spaces and reduce the total volume of diver and equipment. This will further reduce the buoyancy, and unless counteracted, will result in sinking more rapidly. The equivalent effect applies to a small ascent, which will trigger an increased buoyancy and will result in an accelerated ascent unless counteracted. The diver must continuously adjust buoyancy or depth in order to remain neutral. Fine control of buoyancy can be achieved by controlling the average lung volume in open-circuit scuba, but this feature is not available to the closed circuit re-breather diver, as exhaled gas remains in the breathing loop. This is a skill that improves with practice until it becomes second nature.

Buoyancy changes with depth variation are proportional to the compressible part of the volume of the diver and equipment, and to the proportional change in pressure, which is greater per unit of depth near the surface. Minimizing the volume of gas required in the buoyancy compensator will minimize the buoyancy fluctuations with changes in depth. This can be achieved by accurate selection of ballast weight, which should be the minimum to allow neutral buoyancy with depleted gas supplies at the end of the dive unless there is an operational requirement for greater negative buoyancy during the dive. Buoyancy and trim can significantly affect drag of a diver. The effect of swimming with a head up angle of about 15°, as is quite common in poorly trimmed divers, can be an increase in drag in the order of 50%.

The ability to ascend at a controlled rate and remain at a constant depth is important for correct decompression. Recreational divers who do not incur decompression obligations can get away with imperfect buoyancy control, but when long decompression stops at specific depths are required, the risk of decompression sickness is increased by depth variations while at a stop. Decompression stops are typically done when the breathing gas in the cylinders has been largely used up, and the reduction in weight of the cylinders increases the buoyancy of the diver. Enough weight must be carried to allow the diver to decompress at the end of the dive with nearly empty cylinders.

Depth control during ascent is facilitated by ascending on a line with a buoy at the top. The diver can remain marginally negative and easily maintain depth by holding onto the line. A shotline or decompression buoy are commonly used for this purpose. Precise and reliable depth control are particularly valuable when the diver has a large decompression obligation, as it allows the theoretically most efficient decompression at the lowest reasonably practicable risk. Ideally the diver should practice precise buoyancy control when the risk of decompression sickness due to depth variation violating the decompression ceiling is low. 

SEEING UNDERWATER

Water has a higher refractive index than air – similar to that of the cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye's crystalline lens to focus light. This leads to very severe hypermetropia. People with severe myopia, therefore, can see better underwater without a mask than normal-sighted people. Diving masks and helmets solve this problem by providing an air space in front of the diver's eyes. The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34% bigger and 25% closer in water than they actually are. The faceplate of the mask is supported by a frame and skirt, which are opaque or translucent, therefore the total field-of-view is significantly reduced and eye-hand coordination must be adjusted.

Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic corrective lenses are available off the shelf for some two-window masks, and custom lenses can be bonded onto masks that have a single front window or two windows.

As a diver descends, they must periodically exhale through their nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles are not suitable for diving because they only cover the eyes and thus do not allow for equalization. Failure to equalize the pressure inside the mask may lead to a form of barotrauma known as mask squeeze.

Masks tend to fog when warm humid exhaled air condenses on the cold inside of the faceplate. To prevent fogging many divers spit into the dry mask before use, spread the saliva over the inside of the glass and rinse it out with a little water. The saliva residue allows condensation to wet the glass and form a continuous wet film, rather than tiny droplets. There are several commercial products that can be used as an alternative to saliva, some of which are more effective and last longer, but there is a risk of getting the anti-fog agent in the eyes.

DIVING SUITS

Protection from heat loss in cold water is usually provided by wetsuits or dry suits. These also provide protection from sunburn, abrasion and stings from some marine organisms. Where thermal insulation is not important, lycra suits/diving skins may be sufficient.

A wetsuit is a garment, usually made of foamed neoprene, which provides thermal insulation, abrasion resistance and buoyancy. The insulation properties depend on bubbles of gas enclosed within the material, which reduce its ability to conduct heat. The bubbles also give the wetsuit a low density, providing buoyancy in water. Suits range from a thin (2 mm or less) "shortie", covering just the torso, to a full 8 mm semi-dry, usually complemented by neoprene boots, gloves and hood. A good close fit and few zips help the suit to remain waterproof and reduce flushing – the replacement of water trapped between suit and body by cold water from the outside. Improved seals at the neck, wrists and ankles and baffles under the entry zip produce a suit known as "semi-dry".

A dry suit also provides thermal insulation to the wearer while immersed in water, and normally protects the whole body except the head, hands, and sometimes the feet. In some configurations, these are also covered. Dry suits are usually used where the water temperature is below 15 °C (60 °F) or for extended immersion in water above 15 °C (60 °F), where a wetsuit user would get cold, and with an integral helmet, boots, and gloves for personal protection when diving in contaminated water. Dry suits are designed to prevent water from entering. This generally allows better insulation making them more suitable for use in cold water. They can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. For divers, they add some degree of complexity as the suit must be inflated and deflated with changes in depth in order to avoid "squeeze" on descent or uncontrolled rapid ascent due to over-buoyancy. Dry suit divers may also use the gas argon to inflate their suits via low pressure inflator hose. This is because the gas is inert and has a low thermal conductivity.

SAFETY EQUIPMENT

Any scuba diver who will be diving below a depth from which they are competent to do a safe emergency swimming ascent should ensure that they have an alternative breathing gas supply available at all times in case of a failure of the equipment they are breathing from at the time. Several systems are in common use depending on the planned dive profile. Most common, but least reliable, is relying on the dive buddy for gas sharing using a secondary second stage, commonly called an octopus regulator connected to the primary first stage. This system relies entirely on the dive buddy being immediately available to provide emergency gas. More reliable systems require the diver to carry an alternative gas supply sufficient to allow the diver to safely reach a place where more breathing gas is available. For open water recreational divers this is the surface. A bailout cylinder provides emergency breathing gas sufficient for a safe emergency ascent. For technical divers on a penetration dive, it may be a stage cylinder positioned at a point on the exit path. An emergency gas supply must be sufficiently safe to breathe at any point on the planned dive profile at which it may be needed. This equipment may be a bailout cylinder, a bailout re-breather, a travel gas cylinder, or a decompression gas cylinder. When using a travel gas or decompression gas, the back gas (main gas supply) may be the designated emergency gas supply.

Cutting tools such as knives, line cutters or shears are often carried by divers to cut loose from entanglement in nets or lines. A surface marker buoy (SMB) on a line held by the diver indicates the position of the diver to the surface personnel. This may be an inflatable marker deployed by the diver at the end of the dive, or a sealed float, towed for the whole dive. A surface marker also allows easy and accurate control of ascent rate and stop depth for safer decompression.

Various surface detection aids may be carried to help surface personnel spot the diver after ascent. In addition to the surface marker buoy, divers may carry mirrors, lights, strobes, whistles, flares or emergency locator beacons.

NAVIGATION INSTRUMENTS

Unless the maximum depth of the water is known, and is quite shallow, a diver must monitor the depth and duration of a dive to avoid decompression sickness. Traditionally this was done by using a depth gauge and a diving watch, but electronic dive computers are now in general use, as they are programmed to do real-time modelling of decompression requirements for the dive, and automatically allow for surface interval. Many can be set for the gas mixture to be used on the dive, and some can accept changes in the gas mix during the dive. Most dive computers provide a fairly conservative decompression model, and the level of conservatism may be selected by the user within limits. Most decompression computers can also be set for altitude compensation to some degree, and some will automatically take altitude into account by measuring actual atmospheric pressure and using it in the calculations.

If the dive site and dive plan require the diver to navigate, a compass may be carried, and where retracing a route is critical, as in cave or wreck penetrations, a guide line is laid from a dive reel. In less critical conditions, many divers simply navigate by landmarks and memory, a procedure also known as pilotage or natural navigation. A scuba diver should always be aware of the remaining breathing gas supply, and the duration of diving time that this will safely support, taking into account the time required to surface safely and an allowance for foreseeable contingencies. This is usually monitored by using a submersible pressure gauge on each cylinder.

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REFERENCES

 

https://www.bsac.com
https://www.padi.com

https://www.bsac.com
https://www.padi.com