- Messages
- 1,938
- Reaction score
- 168
- # of dives
- 500 - 999
The "it's just simple algebra" line of thought is right in terms of instant states. But the point being missed for that model to work is that this is not about instant states, this is about a time bound process.
The gasses dissolved in tissue will come to equillibrium with ambient gas pressure. No matter what the starting pressure of the gasses dissolved in the body are and no matter what the ambient pressure is, but that is something that will happen over some period of time.
One way of thinking about DCS is that DCS is the result of that time being so short that the gas has to move out of solution really fast.
Because the change of pressure happens over time, and because at each instance the relative difference between the pressures is changing due to the passage of time, what you're dealing with is not simple algebra, rates are changing. You're dealing with differential equations (Calc 101). But you're also dealing with different body tissues that take on and give off gas at different rates, so you're dealing with multiple differential functions.
You also are dealing with changing depths, and rates of change of depth, so you're dealing with multiple partial differential equations.
And you're dealing with wide variability between individuals, so you're dealing with a statistical component to those multiple partial differential equations.
Eventually, even if all the mechanisms were completely perfectly understood (which they aren't), the math gets to be too much.
And with many of the mechanisms in question, there are plenty of competing models to choose from.
Almost all of which, however, seem to be easily reducable to "ascend slowly and take a couple of minutes stop at a point where the pressure is likely to be low enough to allow off-gassing but high enough to prevent DCS if the N2 load is in the range predicted by NDL tables."
But the idea that it's just algebra really doesn't grasp the complexity of the system being modelled. And not getting that complexity misses the point of why we're using models that approximate rather than duplicate the physical reality.
The gasses dissolved in tissue will come to equillibrium with ambient gas pressure. No matter what the starting pressure of the gasses dissolved in the body are and no matter what the ambient pressure is, but that is something that will happen over some period of time.
One way of thinking about DCS is that DCS is the result of that time being so short that the gas has to move out of solution really fast.
Because the change of pressure happens over time, and because at each instance the relative difference between the pressures is changing due to the passage of time, what you're dealing with is not simple algebra, rates are changing. You're dealing with differential equations (Calc 101). But you're also dealing with different body tissues that take on and give off gas at different rates, so you're dealing with multiple differential functions.
You also are dealing with changing depths, and rates of change of depth, so you're dealing with multiple partial differential equations.
And you're dealing with wide variability between individuals, so you're dealing with a statistical component to those multiple partial differential equations.
Eventually, even if all the mechanisms were completely perfectly understood (which they aren't), the math gets to be too much.
And with many of the mechanisms in question, there are plenty of competing models to choose from.
Almost all of which, however, seem to be easily reducable to "ascend slowly and take a couple of minutes stop at a point where the pressure is likely to be low enough to allow off-gassing but high enough to prevent DCS if the N2 load is in the range predicted by NDL tables."
But the idea that it's just algebra really doesn't grasp the complexity of the system being modelled. And not getting that complexity misses the point of why we're using models that approximate rather than duplicate the physical reality.
