Diving basics

Seven tenths of the surface of our planet is made up of water, yet we know more about the surface of the moon than we do about our oceans. While advances in technology have enabled us to explore many wonders of the deep, we are still very far from discovering all that lies hidden beneath the surface.

One of the easiest ways to see what's down there is by scuba diving. Diving offers a whole new world of weightlessness, space and freedom of movement. Many describe it as space travel without the inconvenience of leaving Earth's orbit. The contrasts of colour, scenery and marine life truly change the way we see things when back on land.

It requires only a basic level of training to unlock the opportunity to explore and appreciate our oceans, from tropical coral reefs to the icy seas of the north. Thanks to the pioneering work of Jacques Cousteau, divers are able to spend a significant amount of time underwater without ever having to hold their breath. Cousteau and a team of other divers were responsible for introducing millions to the ocean with the development of the scuba system.

However, the physical demands of being in water at depth mean that proper training is essential. Diving is not a self-taught sport and should never be embarked upon without the assistance of a properly qualified instructor.

Learning to scuba dive

Most people begin their diving experience in a pool or in very sheltered conditions elsewhere. Training is progressive so that you can learn important skills and become familiar with your equipment step-by-step, until you are ready to bring it all together for the early dives in the sea. In shallow protected areas you can get familiar with the equipment and the essential safety procedures, all of which will allow you to move on and enjoy your diving. As experience grows, divers can enjoy more and more of what the ocean has to offer, whether it's shark-spotting or wreck-hunting.

An entry-level scuba diving course takes either a few days of intensive training or is spread out over a number of weeks. Whichever option you take, the course should provide you with the necessary skills and knowledge to safely enjoy diving to a maximum of 20 metres in water conditions matching those where the course was held.

Equipment

There are lots of bits of kit you need to learn to use. First and foremost is the scuba (self-contained underwater breathing apparatus) system, which consists of a large cylinder of air designed to be strapped to the diver's back. It supplies air to the diver's lungs by way of a hose and mouthpiece. A small valve in the mouthpiece opens and allows air through as the diver breathes in, and then expels unwanted air through openings in its sides as they breathe out.

You'll also need a mask to allow you to see underwater, fins to help propel you, and a snorkel so you can swim at the surface without a cylinder. Air from the cylinder is also used to feed a device for buoyancy control, called a BC (buoyancy compensator). This is a jacket that enables divers to maintain a constant depth without sinking down or floating up. Wetsuits and drysuits are buoyant at the surface, so divers must wear weights around their waist to help them sink, but at depth, the buoyancy they had at the surface disappears. At this point, air pumped into the BC can compensate for both the loss in buoyancy and the weights that were necessary at the surface.

A dive instructor will prepare you for every eventuality, including a flooded mask, an out-of-air situation, and what to do if your 'dive buddy' needs to share your air. All divers dive as a 'buddy pair' for safety reasons and will practice skills together in a pool before trying them out in open water.

Your body

As well as knowledge of equipment, divers also need a basic understanding of the physiological effects of being underwater at these depths.

The air in the cylinders simulates what we breathe on land, which is made up of approximately 79% nitrogen and 21% oxygen. It is compressed so that it lasts longer. The apparatus supplies air at the same pressure as the surrounding water (ambient pressure), and the lungs automatically fill to their normal surface volume with the same effort of inhalation.

When learning to dive, any instructor will tell you, you must never hold your breath because you could run the risk of bursting a lung. This is especially true when you are returning to the surface because air expands as the water pressure drops (water pressure drops off near the surface and increases with depth).

Another golden rule is never to surface too quickly. During a scuba dive, the pressure of the air that you breathe increases with increasing depth. This is because the air you breathe from the tanks is at the same pressure as the water. The higher the pressure, the more gas is forced out of your lungs and dissolves in your body fluids. So at depths you have more air dissolved in your body than normal. As you surface, and the pressure on your body decreases, nitrogen that is dissolved in your blood will come out of solution. If you come up too fast, the gas can form bubbles and block vital blood vessels. This condition, which can be fatal, is known as decompression sickness, though is more commonly referred to as 'the bends'. If you come up slowly enough though, the nitrogen released from the bloodstream can be expelled through the lung.

If all this sounds a little like living dangerously, remember that diving is one of the safest sports to take part in as long as you have good training and knowledge.

UK scuba diving

Many people will get their first taste of scuba diving while on holiday and will never wander into UK waters, either because they think there is nothing to be found or it's just too dark and cold. It's true that the diving in Britain can be dark and cold and the range of visibility will never match that of the Red Sea or Caribbean. However, the UK hides some real treats in its waters, from amazing marine life encounters to countless shipwrecks. That's why there are more than 250,000 people who dive this coastline on a regular basis.

A good way to get into British diving is to a join a club. The largest network of diving clubs in the UK is headed by the British Sub-Aqua Club (BSAC), which is recognised around the world as one of the foremost diver-training associations. Many BSAC clubs have been involved in major marine archaeological finds, most notably the finding and recovery of the Mary Rose in Portsmouth.

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