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Ken Gould wrote: >Surely the decompression meter is *assuming* that you are >absorbing nitrogen from the air in your lungs which is at ambient >pressure? Which, on a free dive, it isn't. A breath of air taken >at the surface and held on a free dive to 30m doesn't result in your >lungs compressing to one quarter of their size! The musculature of >the body resists the thoracic squeeze. Think about what would >happen to Pippin free diving to over 100m? > According to my NOAA manual the average person's lung's residual volume is 1.5 liters. I recall that the average persons total lung capacity is about 6 liters. Hence a free diver may descend to 4 ATA or 99 fsw before his lungs are compressed to the residual volume (6/1.5 = 4). Until this depth is reached the lungs will be at ambient pressure. This can be demonstrated by a simple experiment. Fully exhale all the breath from your lungs. Now without breathing in, try to increase the volume of your lungs. However I will agree that the SOS decompression meter may not be an accurate instrument for measurement of DCI risk in free divers. I can think of many reasons why it might be in error. What other tools can we use? Anyone doing a doppler study? Barrie Kovish Vancouver, Canada bmk@ds*.bc*.ca*
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