How To Do Dive Tables
Recreational Dive Planners: Dive Tables explained
The most common dive table used by recreational diving companies and enthusiasts is the recreational dive planner. The recreational dive planner was the first dive table developed exclusively for recreational ‘no-stop’ dives and was developed as a result of data collected by the US Navy and later Doppler Ultrasound Research.
Why do we use dive tables?
Dives tables enable us to discover how long and how deep we can dive safely within the no-decompression limits for one or multiple scuba dives. They help us monitor the amount of nitrogen we have in our bodies during and after scuba diving activities. As human beings we are designed to breathe air under normal atmospheric pressure. This air consists primarily of oxygen and nitrogen. When we go scuba diving we are breathing air at increased pressures due to depth, and so our bodies are absorbing oxygen and nitrogen in higher quantities. Nitrogen is an inert gas and is not used by the body. When we scuba dive it is possible to put too much nitrogen in our bodies, and so we calculate our dive tables to help us monitor and ensure we don’t take in too much. It must be noted that dive tables can only give an educated estimate as to how much nitrogen is in our bodies. As every person is different, everyones bodies will take in and release nitrogen at different rates.
This website explains only the dive tables for use when breathing normal air. Different gas mixtures are not discussed here.
Important: No dive tables or dive computers can completely eliminate the risk of decompression sickness. All divers are advised to dive conservatively within their limits and adhere to all standards set by their dive supervisors and training agencies.
How do we take in nitrogen?
When we breathe in the nitrogen in our lungs is diffused into our blood stream and transported around the body. The amount of nitrogen we take in depends on two factors:
1) DEPTH: The deeper we are underwater the more nitrogen we breathe in and the more nitrogen can be diffused into our bodies 2) DURATION: The longer we breathe underwater the more time nitrogen has to saturate into different parts of our bodies
What are no-decompression limits?
Although every dive is a decompression dive (because we absorb nitrogen during the dive and then release nitrogen as we ascend), the term ‘no-decompression’ diving is just a shortened abbreviation of saying that we are always ‘no-decompression stop’ diving.
Recreational divers should always be ‘No-Decompression Stop’ diving. This means that recreational divers should always be able to ascend to the surface at the appropriate speed, WITHOUT having to do mandatory decompression stops on ascent. Our dive tables allow us to calculate how deep and how long we may dive before manditory decompression stops become necessary. (Note, ‘decompression stops’ are not the same as ‘safety stops’. Recreational divers should always practice safety stops at the end of every dive to add an extra level of safety to their dives).
Pop up link for ‘What does the term Decompression Diving refer to, and how is it different to the recreational diving discussed here?’
Decompression diving is when the amount of nitrogen taken into the body is considered too great to ascend directly to the surface, and so decompression stops must be made at different levels upon the ascent to ‘off-gas’ nitrogen. Decompression Stop Diving is considered technical diving and is outside the realm of what is discussed here.
Pop up Link To: ‘What are safety stops?’ Safety stops should be made at the end of every single scuba dive – at 5 meters (15 feet) for 3-5 minutes. Safety stops give the diver an added layer of safety and allow the body to get rid of excess nitrogen before ascending completely. They should be planned into the end of every dive. There are some exceptions when divers should not perform a safety stop however; such as in emergency out of air situations for example. (Safety stops are not the same as mandatory decompression stop diving, which is outside the realm of recreational diving and is not discussed here).
What if a diver exceeds the table limits? If you are using dive tables to calculate your nitrogen intake and you exceed the table limits, then there is no reliable way of estimating how much nitrogen is residual in your body. In this instance you should not dive for a minimum of 24 hours, and should seek advice from a dive professional. Divers should never exceed their depth and time limits. Good divers always plan their dives and execute their plan, staying conservatively within the limits.
Pop up link to ‘What is the Difference Between SSI and PADI’ At the recreation level there is not a great deal of difference between the training offered by PADI and the training offered by SSI. Both are reputable scuba training institutions and a qualification from either agency is recognized and accepted internationally. It is also possible to take scuba courses through different agencies – such as your Open Water Course with SSI and then your Advanced Course with PADI – in the same way you may do a degree at one university and get your masters at another. They are equally recognized and interchangeable.
Pop up link to ‘What is the difference between PADI Dive Tables and SSI Dive Tables?’ Where SSI use three dive tables, PADI uses just two tables by combining tables one and two together. Generally speaking SSI dive tables are much more conservative than PADI dive tables, although they both perform the same functions for the recreational diver and are used in much the same way.
Dive Tables Vs Dive Computers It should be noted that tables assume that the dive is spent at the maximum depth for the whole duration. This dive profile is known as a square dive. Dive computers monitor your estimated nitrogen absorption at different depths throughout a dive, and therefore have many benefits over using dive tables. See your local dive centre for further information or enrol upon a Scuba Diving Course.
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