BASICS FOR THE CORRECT PRACTICE OF RECREATIONAL DIVING
Before we move forward in the summary explanation of the dive tables, we must leave some clarifications and draw attention to some fundamental concepts for the correct practice of recreational diving:
- The CMAS One Star Diver will have the full advantage of diving accompanied by a top-level diver.
- In these conditions, you know that you have at your side a more qualified and more experienced companion who will transmit greater security to you and that can help you solve any abnormal situation.
- The CMAS One Star Diver cannot do dives that require decompression stops. This type of dive is of greater danger, requiring increased safety and greater knowledge.
- The “yo-yo” or “sawtooth” profile dives are strongly advised due to constant pressure variations.
- The “successive dives” although possible are advised for the diver, with more experience and knowledge.
However, it is of fundamental importance for a diver of any level to have the minimum knowledge related to the use of dive tables in order to be able, in any event, to know how to make the “point of the situation”.
There are a huge variety of diving tables all over the world. All are reliable, but none is 100% safe, for the simple reason that a table is the result of mathematical calculations, not contemplating all the physiological factors that contribute to decompression accidents. Therefore, the reality of the facts is that the correct use of the tables does not give the absolute guarantee that such accidents cannot occur.
EVOLUTION OF DIVE TABLES
The first diving table was created in the early twentieth century (1907) by Scott Haldane, based on the works of Dr. Paul Bert. This table was initially used by national navies from several countries, namely France, England and the USA.
In 1948, the Groupe d’Etudes et Recherches Subaquatiques (GERS) adapted the metric system to the table and introduced the successive divetable.
Since then, the different national navies have calculated new tables or adapted existing tables, based on variable criteria and values, which caused significant differences between them. At the same time, the evolution of scientific knowledge in universities and research institutes has allowed the improvement of tables to be increasing. In this way, since the tables have been continuously improved, we must be prepared for any changes that may arise in the tables we have adopted.
All tables are made from mathematical models that are tested more or less exhaustively in humans. The credibility of the Organization that created them, the mathematical model adopted, the type and quantity of tests performed and the tracking and control equipment used is what dictatethe degree of reliability of a table.
TABLE ADOPTED BY CMAS
After the analysis of several versions of dive tables, CMAS adopted table BÜHLMANN 86, prepared by the Bühlmann Institut de Zürich, one of the world’s most prestigious organizations dedicated to the study of the behavior of gases under pressure in the human body.
The Bühlmann table 86 was elaborated with recreational diving in mind. In addition to contemplating altitude dives, it is done in such a way as to make simple the calculations necessary to perform successive dives. This table is used by several diving organizations and its algorithm is used in diving computers of various brands, such as Uwatec, Spiro, Suunto, Mares, among others.
TABLE BÜHLMANN 86
All dive tables are based on three fundamental parameters:
- Maximum depth (P)
- Background Time (TF)
- Ascent speed
These values are related to the dissolution of nitrogen in the blood and in organic tissues. The deeper and longer the dive, the higher the pressure and the longer the period in which the body is subjected to this pressure, so the greater the amount of nitrogen dissolved in the body.
Thus, it is important to start by defining these values and others equally important, so that we know how tables work.
It is the maximum depth, in meters, reached during the dive. For example, in the case of a dive carried out almost entirely at 15 meters deep, with a very fast descent to 30 meters, it is this depth that counts to consult the table and not the 15 meters.
BACKGROUND TIME (TF)
It is the time interval, in minutes, from the beginning of the descent to the beginning of the ascent directly to the surface.
The diver’s last gesture when leaving the surface is to mark on his watch the beginning of the time count. Many digital watches and profundimeters start counting time automatically, as soon as immersion is given, which is ideal.
BACKGROUND TIME + ASCENT TIME + TIME AT SEGUANÇA LANDING = TOTAL DIVE TIME
This is the amount that will be recorded in the Immersion Booklet.
The ascent rate is conditioned by factors related to decompression. The Bühlmann table 86 was calculated for the ascent speed of 10 meters/minute , a speed that should always be respected .
EXAMPLES FOR ASCENT SPEED = 10m/min.
If a diver is -40m, the climb to the safety level (-3m) will last 4 minutes; if you are -27m, 1 minute after starting the climb you should be -17m, and 2 minutes later at -7m.
ALWAYS MEET THE ASCENT SPEED OF 10 METERS PER MINUTE
The descent speed is largely conditioned by the individual compensation capacity. However, it is recommended that this speed does not exceed 30 meters per minute.