So far, in the previous courses, 10m Diver and 20m Diver, we simply talked about air. But it's time now to see the different components of the air: Mainly 21% oxygen and 79% nitrogen. So, more precisely, during the dive, we breathe pressurized oxygen and nitrogen. The effect of a gaz on our body depends on its partial pressure. At 30 meters depth (4 bars), the partial pressure of Nitrogen is 3,16 bars (79% of 4 bars). Such pressure of nitrogen may cause the nitrogen narcosis.
The nitrogen narcosis is similar to drunkenness. This depends on the sensitivity of each of us. Some people may have the nitrogen narcosis around 30 meters depth while some others will be perfectly fine. More we dive, the less sensitive we are. But this can vary from one day to another. Your instructor will give you some simple test at 30 meters depth. For example, calculating 150-97 is pretty obvious on land, but at depth, you may spend a lot more time to find the result. Because of the nitrogen narcosis, you may forget to check your air consumption or your diving computer and so on... In short, The nitrogen narcosis do not hurt you directly, but you should pay attention to its effects.
In general: Lack of attention, euphoria or anxiety, difficulties to concentrate or a foolish behavior...
Ascend to a less depth until the narcosis stop. This is pretty simple, but you may not be aware that you have the nitrogen narcosis... Here comes the importance of diving with a buddy who may spot that you have the nitrogen narcosis. Then, your buddy will ask you if you're OK, if you don't answer or if you make a hand sign which is not clear, your buddy will understand the situation and he will gently assist you to ascend to a less depth.
The air you breath is 4 times denser. You empty your scuba tank 4 times faster than at the surface. Remember to monitor more frequently your air consumption and to avoid any effort. At this depth, because the air is 4 times denser, it is very hard to recover from an exhausting situation without being assisted by your buddy in ascending to a shallower depth. Besides, you must monitor more frequently your diving computer because you are quickly limited in time. Roughly, most of diving computers give you a maximum of 16 to 20 minutes available at 30 meters depth without the need of mandatory decompression stop during the ascend before ending the dive. If you plan decompression stop, make sure to have sufficient air in order to be able to do your decompression stop.
Unless required by specific circumstances, IFDI recommends not to plan decompression dives. It's better to ascend a bit and you'll discover with pleasure that your diving computer allows you to stay longer. This is what we call: Multilevel dives. For example, you spend 10 minutes at 30 meters, 20 minutes at 20 meters, 20 minutes at 10 meters and a 10 minutes safety stop at 5 meters. By doing so, you manage to dive deeply and long time, safely , because all your dive is a kind of very slow ascend. Check with your instructor. He or she will certainly encourage you to do multilevel dives.
To dive deeper than 30m, the major difference is in the practice rather than in the knowledge. See 40m 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 30m Diver certification. This certification allows you to dive till 30m guided or not by an instructor.
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Edited in 2015. Updated in 2022.