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Deep Diving: How Deep is Deep?

Deep Diving: How Deep is Deep?

Written by Noreen
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Published on November 30, 2009
two scuba divers in dive wreck

There’s always a fascination and illusion that Scuba diving means to dive deep. The belief doing rounds is that there’s better stuff to see, but this in fact is one of the most common mistakes of many new divers, as we’ve seen in Myth Buster: More Scuba Diving Misconceptions Dispelled.

Recreational Scuba divers breath compressed air and are limited by physical laws to a certain amount of time underwater at a certain depth. The standard rule of thumb however is the deeper you dive, the less time you can spend underwater. That leads us to one of the most common questions asked about diving: “How deep can you scuba dive?”.  While there’s no fixed answer to the question as you can potentially dive as deep as you like, there are consequences and risks of diving beyond certain depths with standard scuba diving equipment.

To put it in perspective, when you get your first certification to dive (Open Water Diver) the dept limit to dive is 60 feet (18 meters) whereas an Advanced Open Water diver is certified to dive to 100 feet (30 meters). Different Scuba certification agencies permit different depth after the various training levels are complete. However, PADI recommends that the absolute maximum depth for any recreational diver is 40m (130ft), while BSAC says a maximum depth of 50m (165ft) is ok with proper training.

Just because you can go a certain depth does certainly not mean it is safe to dive at to that depth. At depths between 30-60m, while not dangerous in itself, divers are likely to experience the intoxicating condition of nitrogen narcosis which can have a severe impact on a diver’s decision making, leading to stupid and sometimes dangerous actions. After a certain depth, at partial pressures greater than 1.44bar, the oxygen in a divers air supply becomes toxic, so going further or experiencing this toxicity for too long could prove fatal.

Due to increased pressure at greater depths the chances of decompression sickness are also increased. Diver’s are required to take longer decompression stops, to avoid the formation of gas bubbles in the body. By releasing the water pressure on the body slowly at the end of the dive and allowing gases trapped in the bloodstream to gradually break solution and leave the body, a diver minimizes their chances of getting ‘the bends’. Another concern when diving deep is air consumption. Under  water pressure the air in a diver’s tank too gets compressed further, providing fewer “breaths” which in turn runs out a lot quicker than if you were diving at a shallower depth. This means either carrying an additional small cylinder of air called a pony bottle or having a drop tank available is advisable.

In technical diving, 60 metres / 200 feet may be a “deep dive”. These divers use specialized pieces of scuba diving equipment or special gas mixtures other than normal atmospheric air to overcome depth issues like nitrogen narcosis, oxygen toxicity and the tremendous pressure. It is possible to technical divers to go deeper than 200m (700ft) with closed circuit rebreathers. This sort of ultra-deep diving requires extraordinarily high levels of training, experience, fitness and surface support in the form of decompression chambers.

FUN FACT: The Holy Grail of deep SCUBA diving was the 1,000 ft (300 m) mark, first achieved by John Bennett in 2001 and has only been achieved twice since. Only eight (or possibly nine) persons are known to have ever dived below a depth of 800 feet (240 m) on self contained breathing apparatus recreationally. That is fewer than the number of people who have walked on the surface of the moon!