Scuba Diving FAQ - An Ongoing Work
This page contains frequently and not so frequently asked questions about scuba diving. The answers are my answers, based on my personal experience. As they are my answers, it does not necessarily follow that they are the right answers. This holds especially true at the more technical end of diving, where debates run for years concerning the tiniest details of equipment configuration.
If you feel something is missing, is incorrect or misleading please contact me with your suggestion.
- Did you see sharks?
- How long can a diver stay underwater with one tank of oxygen?
- Don't you get scared
Questions from the Beach.
These are some of the questions often asked at the end of a beach night dive by well intentioned tourists with absolutely no kowledge of diving beyond seeing a couple of Jaques Cousteau documentries. They are usually asked as divers walk out of the surf onto the beach after a night dive.
- You need nitrox to go deep. Is that right?
- If you can't dive deeper with Nitrox, why use it?
- Is it true that cave diving is the world's most dangerous sport?
A Little Knowledge is Dangerous
These are some of the questions that come from people with a basic idea of diving, perhaps gleaned from television or from family and friends that dive. They often involve a misconception, which makes them very interesting and useful to discuss here.
- What is Nitrogen Narcosis?
- Does a recreational diver require dive insurance.
General
General questions concerning the sport of scuba diving.
Questions from the Beach
These are some of the questions often asked at the end of a beach night dive by well intentioned tourists with absolutely no kowledge of diving beyond seeing a couple of Jaques Cousteau documentries. They are usually asked as divers walk out of the surf onto the beach after a night dive.
Did you see sharks?
It's really amazing how often a diver is asked this question or a variation of it, and so I will rephrase the question to, "Do you often see sharks while diving?" The answer is no not that often, but I am quite sure they see me a lot more than I see them. Diving in Florida we would often see generally harmless nurse sharks and once in a while bull sharks when first arriving on a wreck.
How long can a diver stay underwater with one tank of oxygen?
Divers shudder everytime they hear their breathing gas referred to as "Oxygen", there are in fact uses for oxygen in staged decompression diving, but the vast majority of divers will never touch oxygen and will only ever use plain old compressed air or a mix of air with an increased level of oxygen commonly known as Nitrox. So now that I have removed the oxygen niggle, I can answer the question that is actually being asked which is, "How long can a diver stay underwater with just a single Al80 tank (The most common tank used by recreational divers.)
Unfortunately there is no simple answer as the time that a tank lasts is entirely dependent upon the depth of the dive and the workload of the diver. The deeper the dive the larger the volume of gas used in every breath. However to give an idea, on a normal easy going dive to 60 feet (20m) with an Al80 cylinder filled to 3000 psi (200 bar) the dive should last aproximately 35 - 40 mins including a reserve. An equivalant dive at 30 ft would be a little bit over an hour.
Don't you get scared?
This question is very common at the end of a night dive, when suprised vistors gather on the beach to watch the strange underwater lights advance UFO like towards them through breaking surface bubbles. As the divers climb out someone usualy asks "Did you see sharks?" followed by don't you get scared out there?
The answer is no, pretty much never, though I must admit odd moments of fear when followed to closely by Baracuda, but more about that some other time. I believe that fear eminates from the unkown and uncontrollable. Before I started cave diving I would not have believed that I would do the dives that I do now simply because I didn't believe it possible to overcome the fear factor of being so far from a natural air source. Training and practice are everything, never stepping outside the personal comfort zone until absolutely ready. Diving in the ocean does have one uncontrollable factor though which is the unkown response of marine life to divers. Education, observation and a healthy helping of respect for the undersea environment go a long way to minimising this particular factor from the fear equation.
A Little Knowledge is Dangerous
These are some of the questions that come from people with a basic idea of diving, perhaps gleaned from television or from family and friends that dive. They often involve a misconception, which makes them very interesting and useful to discuss here.
You need nitrox to go deep? Is that right?
Actually no, its actually quite the opposite. Oxygen becomes increasingly more toxic the deeper it is breathed. In fact 100% oxygen when used as a decompression gas by technical divers is considered seriously unsafe to breath deeper than 20ft (6m). It follows then that Nitrox having a greater percentage of oxygen than the 20.9% of oxygen found in air is also increasingly more toxic than air when breathed at depth.
If you can't dive deeper with Nitrox, why use it?
While you can't dive deeper with nitrox than air, you can stay longer at the same depth within the depth limits of nitrox. During a dive a diver absorbs dissolved nitrogen from the gas being breathed into the bloodstream and bodies tissues. This nitrogen can cause serious problems if not allowed to escape from the divers body on ascent. Dive tables (and dive computers) give a diver an indication of what is generally considered safe exposures to nitrogen at various depths. If there is less nitrogen in the breathing gas, then those limits are longer as there is less nitrogen exposure.
Is it true that cave diving is the world's most dangerous sport?
No, the sport worldwide with the most fatalaties while being played is in fact crown green bowling! Suprising? Not so suprising really when you consider the average age of the proponents!
Of course, it is ridiculous to make one sport appear safe just because another has a higher statistical risk of death or injury. So the question is really, "Just how dangerous is cave diving?"
The answer is that there are certainly occasional fatalaties, but the reputation of cavediving as being the pastime of the suicidal is very much based on the statistics from the early days of cave diving from the 1970's through to the mid 1990's. Modern equipment and more importantly advances in training and procedures through detailed accident analysis have contributed almost entirely to a massive drop of incidents in relation to the number of individuals enjoying the sport.
General
General questions concerning the sport of scuba diving.
What is nitrogen narcosis?
Nitrogen narcosis or inert gas narcosis is the often pleasant but very dangerous feeling that arises from the absorbion of nitrogen at depth. The effect as the name implies is narcotic. Also known as 'rapture of the deep' or the narcs, nitrogen narcosis can lead to a false sense of security and the feeling of being superhuman. The abilty to complete simple tasks and the divers ability to stay focused are lessened increasingly with depth until a point where the diver is pretty much diving drunk, A condition that can be extremely dangerous to both the diver and the buddies that are relying upon him. The pleasant effects of Nitrogen Narcososis can quickly turn to anxiety and paranoia when faced with a the smallest of problems.
The only way to treat nitrogen narcosois is to ascend until the effects diminish.
Does a recreational diver require dive insurance.
I can't think of a technical or cave diver that I know that does not have insurance against accidents caused directly by diving, basically hyperbaric chamber insurance. I would advise strongly that a diver owes it to themselves and their families to be properly insured. I say this from witnessing first hand the denial that an uninsured, but clearly injured diver goes through while being persuaded to go to a chamber. While denial, is a common symptom of DCS it is far easier to coax an insured diver to the chamber who has only to worry about the inconvenience of the chamber ride as opposed to the significant financial burden it can bring to bear. Extensive dive insurance covering all levels of diving can be bought for around 60 USD per year. Both DAN and PADI offer respected insurance.
Some people are mistakingly under the impression that they are covered by household or credit card insurance. Be sure to check the fine print and particularly the depth limits. An elderly British diver in 2005 faced a bill of 20,000 GBP from a DCS incident in Egypt, because his houshold insurance had a depth limit of 40m.
