During the dive, your body absorbs pressurized air. More you dive long time, the more you absorb. More you're diving deeply, the more you absorb. This is called the saturation of a scuba diver. If you dive deeply and long time, you will saturate even more. That's why time and depth are two important parameters to monitor during the dive.
Long time ago, we were using some diving tables to estimate our saturation level. Nowadays, you use diving computers. Your instructor will show you how to use them. Even though the diving computers can calculate your saturation level in many circumstances, you should keep in mind the following safety rules:
Do first the deepest part of the dive.
Stay well within the limits of the diving computer.
If possible, it's good to spend about 5 minutes at 10 meters depth while ascending.
If suitable, do not hesitate to spend the last 10 minutes of diving at 5 meters depth.
Always do a 3 minutes safety stop at 5 meters depth before ending the dive.
You may add an extra marge to the desaturation time planned by the computer.
If you do many dives in a day, plan first the deepest dive.
The above rules allow a soft transition of pressure for your body cells. Also keep in mind that your saturation process can be modified by the following factors: Your age, fatness, physical and psychological fitness, dehydration, cold, stress, physical effort, the air consumption and eventual other unknown factors. All these factors may increase your saturation and disturb the desaturation process while ascending and after the dive... Yes indeed, after a dive, your body is a bit as an opened soda water bottle, you should not shake it... And it can take up to 24 hours for your body to totally desaturates. Here are two more rules:
Wait a minimum of 24 hours before flying by plane or going at altitude (more than 300 meters).
Wait a minimum of 6 hours before doing any activity which may affect your blood circulation.
You expose yourself to decompression sickness: The tiny micro bubbles of air in your body cells expand and these bubbles get jammed here and there. The most common signs and symptoms appear within 12 hours after the dive. Here is the list: Unusual fatigue, skin itch, skin rash, joints pain, muscles pain, muscles weakness, difficulty urinating, numbness, tingling, dizziness, vertigo, confusion, changes of personality, bizarre behavior, paralysis, amnesia, tremor, staggering, shortness of breath, collapse, loss of consciousness... In case you have one or more of the above signs and symptoms, you should breathe pure oxygen, call your insurer DAN or the nearest decompression chamber and follow their directives. In very rare cases, you might have the decompression sickness even though you respected your diving computer and all the basic rules.
At 20 meters depth, the pressure is 3 bars. Each breathing is three times denser. You empty your scuba tank three times faster. Do not forget to monitor your air consumption. In general, it's good to head to a depth of 10 meters around 80 bars and to be at 5 meters depth around 50 bars.
In the water, your body cools down 25 times faster than in the air. If you start shivering, you stop diving. You get out of the water. You dry yourself and you put some clothes on.
At 20 meters depth, the density of the air we breath is 3 times higher than at the surface. More you're diving deeply, the more lazy you must be. If you have too much swam and if you feel tired, you stop moving, you stand to your buddy or on something, you rest yourself and you exhale deeply. If you don't recover. Your buddy will assist you in going up to shallower waters.
As described in the above case, you would be very happy to have your buddy next to you. That's one of many reasons why we must never dive alone.
The underwater currents will always be stronger than you but they have no brain whereas you have a brain. So, before diving, you must always take some time to evaluate the diving conditions in order to adjust your plans. If the diving conditions are too bad, just do not dive today or change location. Remember that you are hosted by the sea and that you should dive only when the sea welcomes you. Your instructor will tell you more in natural conditions. Now, if ever you are surprised by a strong current while diving, never fight against, be smart and position yourself accordingly. If opportunity arises, your instructor will show you that a difference of few meters in your positioning can help a lot. Now, if you are caught in a strong current at the surface, make sure to float well and swim perpendicularly to the current in order to exit from the path of this current. If you dive in a small current and if you need to come back to your starting point, start the dive against the current. If ever you get tired, the way back will be easy.
Deeper than 20m, you may be more affected by the higher pressure and higher density of the breathed air and you need more knowledge about those effects. See 30m Diver. We invite you to test your knowledge and do a medical check. Once you'll finish the course, your instructor will give to you your IFDI 20m Diver certification. This certification allows you to dive till 20m guided or not by an instructor.
IFDI focuses on the minimum information, goes straight to the point and avoids you a long reading of a book.
Of course, if you want to read more, your instructor may propose you the right book for your level.
IFDI displays very few images to allow an easy loading even in remote islands.
Edited in 2015. Updated in 2018.