Post by knotical on Feb 4, 2005 16:38:37 GMT -5
I posted something similar to this on another board, and would like to hear what the pros on this board think.
What are DCS risks when driving through mountain passes after diving? We do this a lot in the Rockies, but I’ve found nothing available from the recreational agencies. We have a lot of information on altitude diving and rules for flying after diving, but not what happens with small ascents after diving. The 12 and 18 hour rules for flying after diving are impractical for many of us, and don’t really apply anyway. One silly example, if we dive at 10,000 feet and then board an airplane pressurized to the classic 8000 feet, we are essentially descending. What we frequently experience is something like diving at 8000 feet then driving over an 11,000 foot mountain pass.
NOAA has a relevant table.
Ascent to Altitude Table : www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf
Note that this table is based on NOAA pressure groups, not your recreational table’s groups.
And NOAA’s basic dive tables are here:
No deco Air Dive table:http://www.ndc.noaa.gov/pdfs/NoDecoAirDiveTable.pdf
Residual Nitrogen Table: www.ndc.noaa.gov/pdfs/ResidNitroTable.pdf
Or combined, but truncated here: www.ndc.noaa.gov/pdfs/NoDecoAirTable.pdf
caveat: These are NOAA tables, not recreational tables. Use them (or not) at your own risk. At best they should be considered only a guide.
What follows is my opinion as a diver, not representing my certifying agency or LDS.
There are two ways to use the NOAA Ascent to Altitude table.
One way would be to run all your dives on the NOAA tables (that’s why I also provided those links).
Or, you could convert your recreational pressure groups to NOAA’s.
THIS IS NOT TESTED, but if you compare PADI’s single dive table (Table 1) to NOAA’s at all depths and round “up” (conservative), you should get a conversion chart like this:
A-B
B-C
C-D
D-D
E-D
F-D
G-E
H-E
I-E
J-F
K-F
L-G
M-G
N-G
O-G
P-G
Q-H
R-H
S-I
T-I
U-J
V-J
W-K
X-L
Y-L
Z-M
Determine your highest PADI pressure group in the last 24 hours. Find that letter on the left and use the letter next to it to enter the NOAA Ascent to Altitude table to see how long you should wait. Other agencies’ tables would require a different conversion.
Example, if I was in PADI’s “T as in tango” pressure group late yesterday afternoon, and I’m driving from 5000 to 8000 feet this afternoon, I will pretend I’m a NOAA “I as in india” diver and wait 3 hours and 20 minutes. I can use part of that time to drive toward the mountains, but I don’t want to climb more than a few hundred feet for quite some time.
On the encouraging side, you’re almost certainly going to do a gradual ascent during your drive.
Also encouraging is that NOAA has you use your highest pressure group in the last 24 hours, but if you did your more aggressive diving yesterday (as in the example), you’re better off than if you just became a NOAA India diver.
On the discouraging side, you’ve probably just loaded a bunch of stuff into your car and we all know that exercise increases DCS risk.
Also on the discouraging side, NOAA and PADI algorithms are not the same and use different assumptions. The only counter argument I have is that anybody’s pressure group supposedly represents some state with a certain amount of residual nitrogen in your body. Thus, I’m not entirely uncomfortable correlating pressure groups from table to table.
Any thoughts from this august board appreciated.
What are DCS risks when driving through mountain passes after diving? We do this a lot in the Rockies, but I’ve found nothing available from the recreational agencies. We have a lot of information on altitude diving and rules for flying after diving, but not what happens with small ascents after diving. The 12 and 18 hour rules for flying after diving are impractical for many of us, and don’t really apply anyway. One silly example, if we dive at 10,000 feet and then board an airplane pressurized to the classic 8000 feet, we are essentially descending. What we frequently experience is something like diving at 8000 feet then driving over an 11,000 foot mountain pass.
NOAA has a relevant table.
Ascent to Altitude Table : www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf
Note that this table is based on NOAA pressure groups, not your recreational table’s groups.
And NOAA’s basic dive tables are here:
No deco Air Dive table:http://www.ndc.noaa.gov/pdfs/NoDecoAirDiveTable.pdf
Residual Nitrogen Table: www.ndc.noaa.gov/pdfs/ResidNitroTable.pdf
Or combined, but truncated here: www.ndc.noaa.gov/pdfs/NoDecoAirTable.pdf
caveat: These are NOAA tables, not recreational tables. Use them (or not) at your own risk. At best they should be considered only a guide.
What follows is my opinion as a diver, not representing my certifying agency or LDS.
There are two ways to use the NOAA Ascent to Altitude table.
One way would be to run all your dives on the NOAA tables (that’s why I also provided those links).
Or, you could convert your recreational pressure groups to NOAA’s.
THIS IS NOT TESTED, but if you compare PADI’s single dive table (Table 1) to NOAA’s at all depths and round “up” (conservative), you should get a conversion chart like this:
A-B
B-C
C-D
D-D
E-D
F-D
G-E
H-E
I-E
J-F
K-F
L-G
M-G
N-G
O-G
P-G
Q-H
R-H
S-I
T-I
U-J
V-J
W-K
X-L
Y-L
Z-M
Determine your highest PADI pressure group in the last 24 hours. Find that letter on the left and use the letter next to it to enter the NOAA Ascent to Altitude table to see how long you should wait. Other agencies’ tables would require a different conversion.
Example, if I was in PADI’s “T as in tango” pressure group late yesterday afternoon, and I’m driving from 5000 to 8000 feet this afternoon, I will pretend I’m a NOAA “I as in india” diver and wait 3 hours and 20 minutes. I can use part of that time to drive toward the mountains, but I don’t want to climb more than a few hundred feet for quite some time.
On the encouraging side, you’re almost certainly going to do a gradual ascent during your drive.
Also encouraging is that NOAA has you use your highest pressure group in the last 24 hours, but if you did your more aggressive diving yesterday (as in the example), you’re better off than if you just became a NOAA India diver.
On the discouraging side, you’ve probably just loaded a bunch of stuff into your car and we all know that exercise increases DCS risk.
Also on the discouraging side, NOAA and PADI algorithms are not the same and use different assumptions. The only counter argument I have is that anybody’s pressure group supposedly represents some state with a certain amount of residual nitrogen in your body. Thus, I’m not entirely uncomfortable correlating pressure groups from table to table.
Any thoughts from this august board appreciated.