Updated: Jul 14, 2020
“How deep have you been underwater?”. This is a tricky question, which many of my students ask, one that I don't like to answer because I fear that my students may aspire to my maximum depth, or worse, attempt to beat it. A more appropriate question is, “How deep can scuba divers dive?” Unfortunately, the answer is not straightforward – it depends on a variety of factors such as breathing gas, experience level, and personal tolerance for high partial pressures of inert gasses and oxygen.
Different divers have different ideas about when a dive is considered a deep dive. To put it in perspective, an Open Water Diver is certified to dive to 18 meters and an Advanced Open Water diver is certified to dive to 30 meters. As part of the Advanced Open Water course a student will complete a Deep Dive to 30 meters, so for an Advanced Open Water Diver any depth greater than 18 meters could be called deep. The limit of recreational diving is considered to be 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 30 meters and 40 meters.
Photo courtesy of PADI©
The main reason we divers have to dive deep is to see things that you can't see at shallow waters. 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.
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.
The absolute limits for Recreational Diving is 40m , Depths greater than this are the realm of technical diving!
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 an emergency 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 5 meters, so that it is easily accessible during safety stops.
The third concern when deep diving is nitrogen narcosis. 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 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 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.
The Advanced Open Water course includes a deep dive to 30 meters. Afterwards divers are able to complete a course in Deep Diving. This specialty course involved four dives of between 18 meters and 40 meters. The course covers theory including deep dive planning and nitrogen narcosis, as well as practice using pony bottles and/or drop tanks and performing deep stops. You'll normally carry out some experiments with your instructor to test for the effects of nitrogen narcosis and are almost certain to feel it during the course. After certification, divers will be certified to dive to 40 meters. Depths greater than this are the realm of technical diving.
Author : Ahmed Fouad