DevonDiver
N/A
Stopping on ascent permits your body to equalize saturated gasses at the ambient (surrounding) pressure. Thus, a stop at ~5m allows the nitrogen you absorbed during the dive (at deeper depths) to leave the tissues in your body, flow through your blood and leave your body each time you exhale.
Different parts of your body absorb and release nitrogen at different rates. Given the limited depth/duration of recreational scuba dives - restricted by 'no-deco' limits - most divers only tend to saturate the quicker absorbing/releasing parts of their body. Technically, that means most of your body would be releasing nitrogen at ~5m, but some (slower) parts of your body might still be absorbing nitrogen. You are equalizing saturated gas to ambient pressure at 5m.
If you did not stop on ascent, or ascended very quickly, that absorbed nitrogen would form bubbles in your body quicker than it could be exhaled. Those bubbles cause pain and injury - known as Decompression Illness. The common analogy used to describe decompression is of a carbonated soft drink. If you open a bottle of coke quickly, it causes more bubbles. If you open it slowly, there will be less bubbles. The speed of opening the bottle relates to how quickly the ambient pressure is reduced. That speed of pressure reduction equates to the speed of ascent from a dive.
Stopping at ~5m is optimum because you will de-saturate to a point very close to surface pressure (1ata), whilst retaining sufficient ambient pressure to help prevent bubble formation (it keeps the nitrogen saturated, whilst it is processed through your blood and out of your lungs). It is like pausing when you half-open a bottle of carbonated soft drink - allowing the pressure to hiss out, without causing too many bubbles.
The longer you stay at ~5m, the more nitrogen will leave your body. However, if your stay is excessive, then nitrogen will also have more opportunity to spread into your slower body tissues. That generally won't cause a problem unless your stay is very, very long. It is worth remembering that it is technically incorrect to say that you can stay there 'forever' or that 'longer is better'. That said, the duration of stay is limited by the air in your cylinder - and that amount of air is not sufficient to allow you to stay for long enough to saturate the slowest parts of your body.
However, it is important to remember that whilst you are primarily off-gassing, it is only to ambient pressure at ~5m. You still contain surplus nitrogen in your body. That means when you leave 5m and ascend to the surface, you should do so very slowly. Experienced divers will generally take about 1 minute to ascend from 5m to the surface.
If your purpose is to guard against risk of DCI - then you can also consider graduating your stops. Perhaps spend 1 min at 12m, 2 min at 9m, then your safety stop at 5m...before a very slow ascent to the surface. This ensures your 'bottle is opened slowly'... keeping you more safe from bubble formation.
Different parts of your body absorb and release nitrogen at different rates. Given the limited depth/duration of recreational scuba dives - restricted by 'no-deco' limits - most divers only tend to saturate the quicker absorbing/releasing parts of their body. Technically, that means most of your body would be releasing nitrogen at ~5m, but some (slower) parts of your body might still be absorbing nitrogen. You are equalizing saturated gas to ambient pressure at 5m.
If you did not stop on ascent, or ascended very quickly, that absorbed nitrogen would form bubbles in your body quicker than it could be exhaled. Those bubbles cause pain and injury - known as Decompression Illness. The common analogy used to describe decompression is of a carbonated soft drink. If you open a bottle of coke quickly, it causes more bubbles. If you open it slowly, there will be less bubbles. The speed of opening the bottle relates to how quickly the ambient pressure is reduced. That speed of pressure reduction equates to the speed of ascent from a dive.
Stopping at ~5m is optimum because you will de-saturate to a point very close to surface pressure (1ata), whilst retaining sufficient ambient pressure to help prevent bubble formation (it keeps the nitrogen saturated, whilst it is processed through your blood and out of your lungs). It is like pausing when you half-open a bottle of carbonated soft drink - allowing the pressure to hiss out, without causing too many bubbles.
The longer you stay at ~5m, the more nitrogen will leave your body. However, if your stay is excessive, then nitrogen will also have more opportunity to spread into your slower body tissues. That generally won't cause a problem unless your stay is very, very long. It is worth remembering that it is technically incorrect to say that you can stay there 'forever' or that 'longer is better'. That said, the duration of stay is limited by the air in your cylinder - and that amount of air is not sufficient to allow you to stay for long enough to saturate the slowest parts of your body.
However, it is important to remember that whilst you are primarily off-gassing, it is only to ambient pressure at ~5m. You still contain surplus nitrogen in your body. That means when you leave 5m and ascend to the surface, you should do so very slowly. Experienced divers will generally take about 1 minute to ascend from 5m to the surface.
If your purpose is to guard against risk of DCI - then you can also consider graduating your stops. Perhaps spend 1 min at 12m, 2 min at 9m, then your safety stop at 5m...before a very slow ascent to the surface. This ensures your 'bottle is opened slowly'... keeping you more safe from bubble formation.
