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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Decompression theory | 9/17 | https://en.wikipedia.org/wiki/Decompression_theory | reference | science, encyclopedia | 2026-05-05T10:06:49.112339+00:00 | kb-cron |
A saturation exposure is where the time exposed to pressure is sufficient for all tissues to reach equilibrium with the inert gases in the breathing mixture. For practical purposes this is usually taken as 6 times the half time of the slowest tissue in the model.
=== No-stop limits === A no-stop limit, also called no decompression limit (NDL) is the theoretical maximum dissolved gas content of each tissue compartment of the whole body, which can be decompressed directly to surface pressure at the chosen ascent rate used by the model, without a need to stop to outgas at any depth, which has an acceptable risk of developing symptomatic decompression sickness. No decompression limit is a misnomer as the ascent at the specified ascent rate is decompression, but the term has historical inertia and continues to be used.
=== Decompression ceiling, floor and window === Once the gas loading of one or more tissue compartments exceeds the maximum level accepted for the no-stop limit, there is a minimum depth to which the diver can ascend at the appropriate ascent rate, at an acceptable risk for decompression sickness. This depth is known as the decompression ceiling. It may be considered a soft overhead, in that it is physically trivial to ascend above it, but that increases the risk of developing symptomatic decompression sickness according to the decompression model to a theoretically unacceptable level. The tissue that reaches its decompression ceiling first is called the limiting tissue. The depth (or pressure) at which the controlling tissue starts to offgas for a given breathing gas is known as the decompression floor. Above this floor and below the decompression ceiling is the depth range known as the decompression window, the depth range in which safe decompression can occur according to the decompression model. Decompression stress is lower towards the floor, and decompression efficiency is greater nearer the ceiling. The floor depth depends on the concentration gradient of the inert gas, and thereby partial pressure of the inert part of the breathing gas. Offgassing near the floor is relatively slow, and some slower tissues may still be ingassing. If the diver stays in this depth zone the decompression obligation may increase, and off-gassing will eventually stop as the floor rises. At the same time, as offgassing of the limiting tissue progresses, the ceiling will also rise, allowing the diver to ascend to follow it. However if ingassing of other tissues is sufficient, one of them may take over as the limiting tissue and bring the ceiling deeper. Off-gassing near he floor also minimises bubble growth, and near the ceiling maximises off-gassing of dissolved gas.
=== Decompression obligation === A decompression obligation is the presence in the tissues of sufficient dissolved gas that the risk of symptomatic decompression sickness is unacceptable if a direct ascent to surface pressure is made at the prescribed ascent rate for the decompression model in use. A diver with a decompression ceiling can be said to have a decompression obligation, meaning that time must be spent outgassing during the ascent additional to the time spent ascending at the appropriate ascent rate. This time is nominally and most efficiently spent at decompression stops, though outgassing will occur at any depth where the arterial blood and lung gas have a lower partial pressure of the inert gas than the limiting tissue. When a decompression obligation exists, there will be a theoretical safe minimum depth known as the decompression ceiling. Obligatory decompression stops will be indicated at a depth at or below the current ceiling.
=== Time to surface === Time to surface (TTS) is the estimated total time required for a diver to surface from a given point on a dive profile, using a given set of decompression gases, ascending at the nominal ascent rate, and doing all the stops at the specifies depths. This value may be an estimate calculated from a dive plan, and followed by the diver as the ascent schedule, or shown on the screen of a dive computer as updated in real time. It may be based on the current gas selected, or the optimum gas selection from all gases set as active gases on the computer.
=== Staged decompression === Staged decompression is done with stops as specified depths based on an easily followed series. For most tables this has historically been a convenient 3 metres (10 ft) interval, but any arbitrary spacing may be used provided the computation of decompression stops uses it. The diver must stay at the prescribed stop depth until the ceiling decreases to the next shallower stop depth, at which point the diver ascends to that depth for the next stop. The calculation of stop time can also be done to follow the decompression ceiling, which will give a maximised pressure gradient for inert gas washout, and reduces the overall decompression duration by about 4 to 12% This strategy can be approximately followed when using a dive computer with the option enabled. The effect on decompression risk with this strategy is unknown, as no testing has been done as of 2022.