Scuba diving can be hazardous because of the pressure exerted on the body by the water, which becomes greater as you dive deeper. To balance this, air breathed from a scuba tank is at equivalent pressure.
If divers are careless, they can experience potentially fatal problems such as decompression sickness (‘the bends’). This can occur if a diver surfaces too quickly. If affected, the diver must be rushed to a recompression chamber for treatment. There are two such facilities in New Zealand: one at Auckland’s Devonport naval base and the other at Christchurch Hospital.
The nitrogen in the air supplied from a scuba tank dissolves in the diver’s tissues under pressure, just as high-pressure carbon dioxide gas dissolves in liquid to make fizzy drinks. When a diver comes to the surface too quickly, the effect is a bit like taking the cap off a bottle of lemonade – the gas is released, causing bubbles to rise. The nitrogen bubbles can block tiny blood vessels, sometimes with fatal results. To avoid this condition, called ‘the bends’, divers need to ascend slowly, gradually relieving pressure and allowing the excess nitrogen in the body to disperse.
Other problems caused by breathing the mix of high-pressure oxygen and nitrogen from a scuba tank include oxygen toxicity, which can trigger convulsions, and nitrogen narcosis, which impairs judgement.
Divers can drown if they are caught in currents and become trapped underwater.
Clubs have offered scuba training since the 1950s. The New Zealand Underwater Association (NZUA) introduced diver certification and standards for scuba equipment in 1963 and a licensed instructors system in 1964, the same year it joined the World Underwater Federation (also known as CMAS or Confédération Mondiale des Activités Subaquatiques).
Precautions became standard: planning dives, diving with a buddy, and using safety equipment such as depth gauges or dive computers, safety floats and signalling devices.
By 1984 a competing international system of certification endorsed by the Professional Association of Dive Instructors (PADI) was being offered through dive shops, and the NZUA adopted it in 1985. New Zealand Qualifications Authority-approved tertiary diving courses are now offered by private training institutions. They are based on a range of international scuba education systems, but global guidelines for diver instruction are set by the Recreational Scuba Training Council.