Underwater diving

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Signal flag A(lpha) - "I have a diver down - Keep clear"

This article refers to underwater diving done by humans. For other uses of the term diving, see dive

Underwater diving refers to the practice of going underwater with or without breathing apparatus. When done for sport, this is sometimes called subaquatics. There are several types of underwater diving.

Snorkelling and free-diving: swimming underwater without breathing apparatus.
Scuba diving and surface supplied diving: swimming or walking underwater with breathing apparatus.

Humans are not the only ones to dive (in the first sense of the term). Some species of amphibious animals such as marine mammals and some seabirds dive to catch their prey underwater. When dealing with equipment such as submarines and underwater remotely operated vehicles, the act of descending into the water is called diving and the command for the descent, especially in battle, is "dive."

Scuba divers sometimes jump into water feet first from some height above the water (e.g. from a large boat or from a pier. Jumping into the water headfirst is unsafe for those wearing any sort of scuba or snorkelling equipment. In particular, an open-circuit scuba banging about on the back is big and hard and heavy and during a headfirst dive (in sense 1) may sprain or break the back or neck. In addition, one hand should be used to hold the mask on when jumping from distance; as the force of entering the water at speed may otherwise cause it to come off.

[edit] Swimming underwater and diving

The ability to dive and swim underwater can be a useful emergency skill, and is an important part of watersport and navy safety training. More generally, entering water from a height is an enjoyable leisure activity, as is underwater swimming with or without breathing apparatus.

[edit] Learning to swim underwater/ basic freediving

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Assuming that you can swim on the surface, the main obstacle to diving is likely to be the barrier of immersing your head. To overcome this, try hard to keep your eyes open while under the water. A good exercise is to lie face down in the water with a snorkel in your mouth and no mask. Breathe slowly and deeply without using your nose - this will get you used to breathing with mask and snorkel. Don't be afraid of water getting into your eyes; although chlorinated water can sting, it is not harmful. (Salt water is less irritating.) Your eyes and nose will become accustomed to immersion. Earplugs should NEVER be worn while diving as the increase in pressure can force them into the ear canal. Prevention of ear infections is better achieved by simply washing your ears properly afterwards, but do not use cotton buds as the removal of ear wax allows infections to set in more easily. Also 'goggles' (which cover only the eyes) are dangerous at depth causing facial barotrauma such as burst capillaries. Instead a mask which includes the nose should always be worn so that air can be blown into the mask as the diver descends in order to equalize the air space. In breath-hold diving - even at shallow depths - it is crucial to equalize your ears by blowing gently against the roof of your mouth with your mouth and nose closed, allowing air to move up in to your middle ear and equalize the pressure created by immersion. Note: If you practice in your local pool, make sure they allow glass-lensed masks in beforehand; if not, polycarbonate lenses are available.

The crucial step in gaining underwater mobility is adopting a suitable posture. To do this, first try to reach an object on the floor of the pool (or other body of water) that is within your depth. It will be difficult to reach from an upright posture. To get your hands to the object, jump up, bend your body well forward, throw your feet in the air, and try to reach the object, head foremost. Before you descend, take no more than 3 to 4 deep, rapid breaths. Excessive hyperventilation is dangerous as it can cause shallow water blackouts leading to drowning.

The next exercise might be to swim a few metres towards the object on the surface, and then dive for it. It is difficult at first to get the chest below the surface, but if your legs are thrown well up in the air, their weight will force your body downwards. This is surface diving (also known as a jackknife); some snorkellers and scuba divers call it duck diving.

After that you can practice to swim large lengths and then dive down in deeper waters.

Swimming underwater should follow quite naturally given some practice. It is largely a matter of maintaining a slightly inverted posture so as to counteract the natural buoyancy of the lungs (although this will diminish with depth as the lungs compress), and to conserve your energy as much as possible. This is best achieved by moving slowly and calmly. Most important of all: RELAX. Strokes used in surface swimming must be adapted somewhat, and some arm movements (such as the crawl) cannot be used. However for the greatest efficiency good quality fins should be used, with a dolphin kick being preferred by experienced free divers. Especially in the sea it is vital not to skin dive alone as problems that are easily solved with assistance can become life threatening without it.