Dr Deco
Contributor
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- # of dives
- I just don't log dives
Hello HJefferyM:
Dive Tables
Tables are designed or developed using actual dive data, and are collected from thousands of divers. What are most valuable are those dives in which DCS actually developed. Thousands of safe dives are of less value after a point.
The general starting point is the US Navy dive tables and modifications are made to these. [ USN tables are actually for decompression diving and only the no decompression limits [NDL] are utilized.] For recreational diving, the NDLs are reduced to yield lower tissue nitrogen loads because of the reduced bottom time allowed.
Table Physiology
Dive tables are not actually based on solid physiological principles. While they all have a model in mind, this is based more upon the ease of calculation [i.e., a simple algorithm] that exact anatomy and physiology.
Since the tables are derived from dive data, they cover a wide range of divers with respect to age, gender, body mass index, physical conditioning, etc. The safe dives are selected from the data [i.e., maximum depth and bottom time] and tables are derived from this. From the bottom time and depth, a set of NDLs are made.
It is purely a statistical process that requires a large database and a computer. The physiology and anatomy of divers is incorporated because actual divers are used. Since the majority of divers are below the age of fifty, they will weight the database to younger individuals. Older divers might consider being more cautious. The same is true for overweight divers.
What is always important to remember is those dive tables are constructed with considerable safety margins. This is not to imply that sloppiness should be considered acceptable in decompression.
Table Testing
Many and varied individuals were used by me when I tested the PADI Recreational Dive Planner. We did not see any evidence of more bubble formation [from the Doppler ultrasound bubble detector] in the older or heavier test subjects. The degree of conservatism [= safety] in the tables would not allow us to fine tune an analysis for these factors.
In decompression to altitude, considerable greater gas loads can be examined, and , even here, age and fitness effects do not show up with the sample size used.
What Should You Know?
1. Gas uptake and elimination is considered symmetrical in tissues. You should experience moderate exertion during the dive and some activity back on the boat. Do not swim below and then lie down during the surface interval. The heart rates will be so different that nitrogen exchange will not be symmetrical.
2. Know that decompression bubbles actually grow from seeds [microbubbles] in tissues. These are constantly present in your body. Do not add more nuclei [or enlarge those already present] by lifting, straining, or performing other heavy musculoskeletal tasks.
3. Neurological DCS can develop for bubbles entering the arterial circulation for the venous side. Prevent this from occurring by not performing Valsalva-like maneuvers topside. This are such things as momentary breath hold actions such as coughing, straining while lifting, etc.
Dr Deco :doctor:
Dive Tables
Tables are designed or developed using actual dive data, and are collected from thousands of divers. What are most valuable are those dives in which DCS actually developed. Thousands of safe dives are of less value after a point.
The general starting point is the US Navy dive tables and modifications are made to these. [ USN tables are actually for decompression diving and only the no decompression limits [NDL] are utilized.] For recreational diving, the NDLs are reduced to yield lower tissue nitrogen loads because of the reduced bottom time allowed.
Table Physiology
Dive tables are not actually based on solid physiological principles. While they all have a model in mind, this is based more upon the ease of calculation [i.e., a simple algorithm] that exact anatomy and physiology.
Since the tables are derived from dive data, they cover a wide range of divers with respect to age, gender, body mass index, physical conditioning, etc. The safe dives are selected from the data [i.e., maximum depth and bottom time] and tables are derived from this. From the bottom time and depth, a set of NDLs are made.
It is purely a statistical process that requires a large database and a computer. The physiology and anatomy of divers is incorporated because actual divers are used. Since the majority of divers are below the age of fifty, they will weight the database to younger individuals. Older divers might consider being more cautious. The same is true for overweight divers.
What is always important to remember is those dive tables are constructed with considerable safety margins. This is not to imply that sloppiness should be considered acceptable in decompression.
Table Testing
Many and varied individuals were used by me when I tested the PADI Recreational Dive Planner. We did not see any evidence of more bubble formation [from the Doppler ultrasound bubble detector] in the older or heavier test subjects. The degree of conservatism [= safety] in the tables would not allow us to fine tune an analysis for these factors.
In decompression to altitude, considerable greater gas loads can be examined, and , even here, age and fitness effects do not show up with the sample size used.
What Should You Know?
1. Gas uptake and elimination is considered symmetrical in tissues. You should experience moderate exertion during the dive and some activity back on the boat. Do not swim below and then lie down during the surface interval. The heart rates will be so different that nitrogen exchange will not be symmetrical.
2. Know that decompression bubbles actually grow from seeds [microbubbles] in tissues. These are constantly present in your body. Do not add more nuclei [or enlarge those already present] by lifting, straining, or performing other heavy musculoskeletal tasks.
3. Neurological DCS can develop for bubbles entering the arterial circulation for the venous side. Prevent this from occurring by not performing Valsalva-like maneuvers topside. This are such things as momentary breath hold actions such as coughing, straining while lifting, etc.
Dr Deco :doctor:
My home bud didn't realize why his did a few days ago. He's such a vacation diver, happy to just follow the DM. I talk, he listens, and I hope - but sometimes I have to grab his console and check. I explained later that he went into deco. :silly: He also kept giving me a 100# signal on dives for 1,000#.
