decompression
When decompression is called when diving the controlled reduction of pressure on the prevention of decompression sickness . The decompression is carried out using empirical tables ( decompression tables ) or with the help of dive computers that are based on a decompression model. Diving time , diving depth and other factors determine the accumulation of inert gas (mainly nitrogen ) in the body and thus the required decompression time. Decompression usually takes place in stages ( decompression stops ) of decreasing depth and of varying duration.
Decompression time
The decompression time (short decompression time ) is the minimum period of time that is required to bring an organism from a high to a lower pressure level without damage.
Theoretically, when diving, the decompression time begins after the point of greatest depth has been reached during the dive and one only ascends. In practice, the decompression time is divided up so that there are decompression stops of decreasing depth and usually increasing length. The depths and lengths of the individual stops depend on the profile of the dive carried out, the breathing gas used and the ambient conditions. The sum of the duration of all necessary stops and the time for changing from one depth level to the next add up to the total decompression time, which should be observed at least in order to avoid decompression sickness or diving sickness.
While modern dive computers carry out their calculations in real time and take a slow ascent into account, when diving according to the decompression table, only the greatest depth reached and bottom time are important. As a rule, the decompression time according to the dive computer is therefore shorter than according to the table.
Decompression stop
The decompression stop ( decompression stop for short ) is a deliberate stay in a certain water depth during decompression. The gas bound in the tissue is slowly exhaled due to the reduced pressure in the shallower water, so that it is safe to descend until the next deco stop or to the surface. If the ascent is too rapid, gas bubbles form in the body tissue and in the body fluids, which can trigger life-threatening decompression sickness ("diving sickness ").
In a very simplified way, the formation of bubbles when surfacing can be compared to opening a bottle of carbonated mineral water: if the pressure can escape very slowly (slow surfacing / deco stop), then there is little pearling. However, if the bottle is torn open abruptly (rapid emergence), large gas bubbles form and the water gushes out of the bottle.
Practical implementation
In simple recreational diving , diving is only done within the no-stop time , so that apart from a safety stop (e.g. 3 minutes at a depth of 5 m), no decompression stops are necessary. However, a maximum depth of 40 m must not be exceeded. As a rule, stops below this are carried out at 12 m, 9 m, 6 m and 3 m. The duration of such stops depends on the breathing gases used, the diving depth and the diving time ( bottom time = duration of the dive until the start of the ascent phase).
Interestingly, the practice of these stops is constantly changing as they are only partially based on medical studies. As is so often the case, physical models and phenomena discovered by chance play an important role.
See also
- No deco
- Decompression models (e.g. Varying Permeability Model )
- Saturation diving
- Deep intoxication
- decompression chamber
- Reverse blocking
- Spacewalk
