Scuba Diving: Underwater Swimming with Your Own Air Supply

The term scuba comes from the initial letters or Self-Contained Underwater Breathing Apparatus, and the sport has boomed in recent years.

The apparatus consists of one or more compressed air cylinders (usually referred to as 'air bottles' or 'air tanks'), and a mouthpiece connected to an automatic air supply regulator ('demand valve').

The regulator supplies air to the lungs at a pressure equivalent to that of the surrounding water. Exhaled air floats straight up to the surface as bubbles. The length of time you can stay underwater is governed by the depth at which you are diving and the capacity of your tank.

An air supply that will last an hour at the surface is enough only for a half hour dive at 6m, or 20 minutes at 18m. Except in warm shallow water you will need to wear a neoprene (synthetic rubber) wet suit to protect you from cold. Most water sport shops hire out the necessary breathing equipment - commonly called an aqualung - and wet suits. Most divers use an aqualung with two air tanks and wear a life jacket inflatable by means of a small cylinder of compressed air for emergency surfacing.

Before making your first dive, you must complete a training course with a qualified instructor. Many water sport shops will refuse to hire out aqualungs or fill air bottles if they suspect you are inexperienced or untrained. To enroll on a coarse you must be reasonable fit. You will also have to have a medical examination and chest x-ray, to check that you do not suffer from respiratory or heart trouble, and that your middle ear and sinuses are able to stand changes of pressure.

SAFETY UNDERWATER

Never dive alone; you and at least one other diver should be responsible for each other's safety and be trained in lifesaving techniques. Never go into the water until you have checked all your equipment thoroughly. Panic underwater can be fatal, so stay calm underwater, breathe always (SCUBA)

PRECAUTIONS (to take before diving)

Enquire at the harbor master's office or the place where you hire your tanks about tides, current, hazards and local regulations.

Avoid shipping lanes, fisherman's markers and nets, and areas where there are likely to be power boats and water skiing. Listen and look around you when surfacing.

Make sure your escort boat has a radio transmitter/receiver or a portable telephone with adequate range.

Stick to an agreed dive plan. If a diver fails to surface promptly, summon help without delay.

Keep clear of sharp rocks and sea weed. Carry a knife with a floating handle in a sheath attached to your belt, in case you need to free yourself from weed or netting.

If you go underwater fishing, never point or fire a spear gun directly below you or in the direction of other divers. On land never leave or store a spear gun loaded.