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New divers will usually feel a mixture of excitement and fear at the thought of doing a deep dive. Deep diving can certainly be exciting and it’s definitely healthy to maintain a certain level of caution as well. Depth attracts a lot of divers as deep dives provide this certain kick.
Get the experience of diving on a wreck below 100 feet/30 meters!
To do these dives safely, you need the right skills and the right knowledge .
Without proper training this kind of diving is an uncontrollable safety risk. To plan your dives properly you must first know about all of the potential risks involved in DEEP DIVING.
How Deep is Deep?
Different divers have different ideas about when a dive is considered a deep dive.
In recreational diving, PADI define anything from 18 metres (60 ft) to 30 metres (100 ft) as a “deep dive” (Other diving organisations vary)
In technical diving, 60 metres (200 ft) may be a “deep dive”
In surface supplied diving, 100 metres (330 ft) may be a “deep dive”
To put it in perspective, an Open Water Diver is certified to dive to 60 feet / 18 meters and an Advanced Open Water diver is certified to dive to 100 feet / 30 meters.
The limit of recreational diving is considered to be 140 feet / 40 meters and this is the depth that a diver trained in deep diving is certified to descend to.
Usually, a deep dive is considered to be a dive between 100 feet / 30 meters and 140 feet / 40 meters.
The main reason to dive deep is to see things that you can’t see at shallower depths. It’s quite common for well preserved wrecks to be found in deeper water, as the greater depth means less exposure to surface surge.
You will also find that different marine life exists at different depths. On tropical reefs it’s common to find healthier coral at greater depths due to less exposure to the sun and to divers. Many fish and other marine creatures also prefer greater depths.
Of course a disadvantage of diving deeper is less visibility and color due to less sunlight. Many divers will carry a dive light to bring the color back to coral and it is necessary to use strobe lighting for photography at any depth greater than 15 feet / 5 meters and particularly on deep dives.
Deep Diving Concerns
Like most types of recreational diving, deep diving is very safe as long as the proper precautions are taken. The main concerns in deep diving are increased chances of decompression sickness, rapid air consumption, and nitrogen narcosis.
Due to increased pressure at greater depths the chances of decompression sickness are increased. This can be countered by properly planning the dive using dive tables or a dive computer and ensuring that you ascend slowly and complete all necessary safety or decompression stops. Some divers believe performing deep stops in addition to a normal 3 minute safety stop will decrease their chances of suffering from decompression sickness. Decompression sickness, or the “bends”, can happen if a diver ascends too fast, when excess inert gas leaves solution in the blood and tissues and forms bubbles. These bubbles produce mechanical and biochemical effects that lead to the condition. The effects tend to be delayed until reaching the surface. Bone degeneration (dysbaric osteonecrosis) is caused by the bubbles forming inside the bones; most commonly the upper arm and the thighs.
Air embolism causes loss of consciousness and speech and visual problems. This tends to be life threatening, and requires a recompression chamber for treatment.
Deep diving involves a much greater danger of all of these, and presents the additional risk of oxygen toxicity, which may lead to a convulsion underwater. Very deep diving using a helium–oxygen mixture (heliox) carries a risk of high pressure nervous syndrome.
Using normal scuba equipment, breathing gas consumption is proportional to ambient pressure – so at 50 metres (160 ft), where the pressure is 6 bar, a diver breathes 6 times as much as on the surface (1 bar).
Heavy physical exertion causes even more gas to be breathed, and gas becomes denser requiring increased effort to breathe with depth, leading to increasing risk of hypercapnia, an excess of carbon dioxide in the blood. The need to do decompression stops increases with depth. A diver at 6 metres (20 ft) may be able to dive for many hours without needing to do decompression stops. At depths greater than 40 metres (130 ft), a diver may have only a few minutes at the deepest part of the dive before decompression stops are needed. In the event of an emergency the diver cannot make an immediate ascent to the surface without risking decompression sickness. All of these considerations result in the amount of breathing gas required for deep diving being much greater than for shallow open water diving. The diver needs a disciplined approach to planning and conducting dives to minimise these additional risks.
Due to more rapid air consumption at greater depths it is important to closely monitor air gauges ad to allow a greater air reserve at the end of the dive. It is also recommended to make use of a redundant air source in case you become low on air. This means either carrying an additional small cylinder of air called a pony bottle or having a drop tank available. A drop tank is an additional cylinder with an attached regulator that is hung from a rope off the dive boat. It is normally hung at 15 feet / 5 meters, so that it is easily accessible during safety stops.
Nitrogen narcosis, the “narks” or “rapture of the deep”, starts with feelings of euphoria and over-confidence but then leads to numbness and memory impairment similar to alcohol intoxication.
The air we breathe is constituted of 79 nitrogen, an inert gas that has no effect on our bodies under normal surface pressure. However, as we descend into the water the increased pressure increases the partial pressure of the nitrogen, which means that it has the same effect as breathing greater concentrations of nitrogen. This increased nitrogen affects the synapses in our brain and brings on a feeling very similar to drunkenness. Nitrogen narcosis becomes noticeable to different people at different depths, but begins to affect most people at around 50 feet / 15 meters. The first effects are normally tingling of the fingers, followed by slow thinking, dizziness, disorientation, and impaired decision making. Most people report feeling the effects of nitrogen narcosis at depths greater than 100 feet / 30 meters. The deeper you go the greater the effects. Nitrogen narcosis poses no long term health risks and all symptoms are relieved as soon as the diver ascends. It is recommended that dive buddies monitor each other for symptoms of nitrogen narcosis and ascend to avoid severe narcosis.
Coping with the physical and physiological stresses of deep diving requires good physical conditioning
- USC Dornsife Scientific Diving: The Navy Dive Tables (blogs.scientificamerican.com)
- Going down with the extremely extreme sport of deep-breath diving (uwtreasures.wordpress.com)
- Down world’s deepest pool (uwtreasures.wordpress.com)