A dive profile
is a two dimensional graphical representation of a dive showing depth and time. It is useful as an indication of the risks of decompression sickness
and oxygen toxicity
and the consumption of open-circuit gas for a planned dive as these depend in part upon depth and time. A dive profile diagram is often drawn with time running from left to right and depth increasing down the page.
Planning and monitoring decompression
For planning and monitoring of nitrogen adsorption, the data usually consists of the maximum depth reached during the dive and the length of time underwater. For repetitive dives it also includes the "surface interval", or the time spent above the water between the previous dive and the start of the current dive. This information is used to calculate the amount of residual nitrogen build-up in the diver's tissues after completing a dive.
Types of dive profile
Some types of dive profile have been named.
The diver descends directly to maximum depth, spends most of the dive at maximum depth and then ascends directly at a safe rate. The sides of the "square" are not truly vertical due to the need for a slow descent to avoid barotrauma
and a slow ascent rate to avoid decompression sickness.
This type of profile is common for dives at sites where there is a flat sea-bed. It is the most demanding profile for decompression for a given maximum depth and time because adsorption continues at maximum rate for most of the dive. Decompression tables assume the diver has done a square profile.
Where the dive site and underwater topography
permit, divers often prefer to do a more triangular than square dive profile; they descend to maximum depth and slowly ascend throughout the dive.
This slow ascent and pressure reduction is a good decompression practice and when using a dive computer often results in no need for decompression stops. Dive computers, unlike decompression tables, measure depth and time at short intervals and calculate the exact decompression stops required, which for a triangular profile will be less than the square profile with the same maximum depth and duration.
Repetitive diving occurs when one dive is followed by another dive. Multiple decompressions per day over multiple days can increase the risk of decompression sickness.
When no stop depth or time limits are exceeded the diver must do decompression stops
to reduce the risk of decompression sickness
. Stops when breathing gases
containing nitrogen tend to be in shallow water, often in 3 metre/10 feet steps near the surface. Stops when breathing helium mixes tend to be in deeper water. The duration of the shallower stops is more than the duration of deeper stops. Stops tend to make a dive profile triangular.
Reverse profiles occur when one dive is followed by another deeper dive. Many diver training agencies
discourage reverse profiles because they are not the best way to plan for safe decompression; it is better to do the deeper dive first when the body's tissues hold less adsorbed nitrogen. The American Academy of Underwater Sciences
workshop concluded there was no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw).
Saw tooth profile
In a saw tooth profile the diver ascends and re-descends a number of times during the dive. Each ascent and re-descent increases the risk of decompression sickness.
With a bounce dive the diver descends directly to the maximum depth, spends very little time at maximum depth and ascends directly at a safe rate to the surface. Bounce dives are often described in professional diving
as the opposite to saturation dives
where the diver lives at pressure for very long periods before ascending.
Ambient pressure on the surface
Sometimes changes in ambient pressure, while diver is on the surface, are drawn on a dive profile. The changes may be caused by flying, land travel involving changes in altitude or atmospheric pressure changes due to weather. Ambient pressure changes before and after diving can be significant in decompression planning. Starting dives at altitude
also has an impact on dive and decompression planning.