I am by no means a physiologist, and have only a basic understanding.
1. There are multiple decompression theories and models.
2. They are a mathematical model that attempts to explain how the body is believed to work in terms of saturated tissues.
Note the phrase theoretical and model and believed.
It is known that the body can with stand a supersaturated state of an absorbed gas within its tissues, beyond a particular percentage a bend is likely to occur, below a certain percentage, a bend is unlikely to occur. This is what is often known as the M value. An M value exist for each compartment.
Models use multiple 'compartments' to simulate how different tissue types are likely to behave. i.e. tissues that are likely to on gas and off gas quickly, to tissues that are likely to on gas and off gas slowly.
Compartments are arbitrary numbers [1], at some point some one picked a number, when the model didn't work well, they picked some more numbers, either adjust existing compartment times, or adding new compartments to the model.
As such a relatively standardised set of compartment times have been developed.
The calculation (mathematical model) tracks each compartment.
For a no-stop dive, each compartment is tracked to ensure it won't exceed its M value for a given depth (& time). Thus allowing a direct ascent to the surface (within the limits of the model - ascent rate).
For dives where any one or groups of compartments exceed the safe M value are exceeded, a decompression stop will be required. The off gasing is calculated by the model, once the offending compartment(s) falls back within the safe limit (M-value), ascent can proceed, stoping again, as the pressure drops if the M value is calculated to be exceeded.
Stop depths are another arbitrary number [2], Fixed depths are a practical issue. For the original divers, hardhat divers, winching a diver to a particular depth, then leaving them there for a specified period of time was practical and simple.
It is possible to calculate stops on the fly allowing the divert progress ever shallower as they degas. The VR3 [3] allowed the 'diver on a rope' function rather than fixed stop depths, or as it was known in the UK, dick on a rope.
There are a number of good books on decompression theory available. Mark Powells book (deco for divers) is an excellent start. Even the PADI DM book has a good section on explaining the basics around decompression theory.
Nothing I have said here should be taken as fact. I am sure others will attempt to correct any error I have made.
Please always remember, what we know about decompression science is all theoretical, we still don't really understand it. No decompression model is 100% safe, all have an element of risk. There are personal actions you take that are highly likely to increase the risk of a decompression hit - irrespective of the model you wish to use.
Haladyn is probably regarded as the grandfather of decompression theory.
Bhulmann models are probably the most well known. A lot of this is the fact that Professor Buhlmann made is model free to all (un-licenced). So manufacturers have implemented into there equipment, all be it with manufacturer designed 'improvements'(?).
[1] A lot of these initial numbers where established by Haldane
[2] another series of numbers initially determined by Haldane
[3] Early technical computer
1. There are multiple decompression theories and models.
2. They are a mathematical model that attempts to explain how the body is believed to work in terms of saturated tissues.
Note the phrase theoretical and model and believed.
It is known that the body can with stand a supersaturated state of an absorbed gas within its tissues, beyond a particular percentage a bend is likely to occur, below a certain percentage, a bend is unlikely to occur. This is what is often known as the M value. An M value exist for each compartment.
Models use multiple 'compartments' to simulate how different tissue types are likely to behave. i.e. tissues that are likely to on gas and off gas quickly, to tissues that are likely to on gas and off gas slowly.
Compartments are arbitrary numbers [1], at some point some one picked a number, when the model didn't work well, they picked some more numbers, either adjust existing compartment times, or adding new compartments to the model.
As such a relatively standardised set of compartment times have been developed.
The calculation (mathematical model) tracks each compartment.
For a no-stop dive, each compartment is tracked to ensure it won't exceed its M value for a given depth (& time). Thus allowing a direct ascent to the surface (within the limits of the model - ascent rate).
For dives where any one or groups of compartments exceed the safe M value are exceeded, a decompression stop will be required. The off gasing is calculated by the model, once the offending compartment(s) falls back within the safe limit (M-value), ascent can proceed, stoping again, as the pressure drops if the M value is calculated to be exceeded.
Stop depths are another arbitrary number [2], Fixed depths are a practical issue. For the original divers, hardhat divers, winching a diver to a particular depth, then leaving them there for a specified period of time was practical and simple.
It is possible to calculate stops on the fly allowing the divert progress ever shallower as they degas. The VR3 [3] allowed the 'diver on a rope' function rather than fixed stop depths, or as it was known in the UK, dick on a rope.
There are a number of good books on decompression theory available. Mark Powells book (deco for divers) is an excellent start. Even the PADI DM book has a good section on explaining the basics around decompression theory.
Nothing I have said here should be taken as fact. I am sure others will attempt to correct any error I have made.
Please always remember, what we know about decompression science is all theoretical, we still don't really understand it. No decompression model is 100% safe, all have an element of risk. There are personal actions you take that are highly likely to increase the risk of a decompression hit - irrespective of the model you wish to use.
Haladyn is probably regarded as the grandfather of decompression theory.
Bhulmann models are probably the most well known. A lot of this is the fact that Professor Buhlmann made is model free to all (un-licenced). So manufacturers have implemented into there equipment, all be it with manufacturer designed 'improvements'(?).
[1] A lot of these initial numbers where established by Haldane
[2] another series of numbers initially determined by Haldane
[3] Early technical computer