northcoast_diver
Contributor
- Messages
- 278
- Reaction score
- 3
[I put together the following outline for a dive club that I belong to, for an upcoming trip to scuba dive at high altitude. You may find it helpful in preparing for your next high altitude dive. One caveat is that my altitude measurements are from a topographical map, and as such are not exact, but the differences are insignificant.]
HIGH ALTITUDE SCUBA DIVING
LAKE TAHOE IS AT AN ALTITUDE OF 6225 FEET. ANY SCUBA DIVING IN THE RANGE OF 1000 TO 10,000 FEET IS DEFINED AS HIGH ALTITUDE DIVING.
ISSUES INVOLVED IN HIGH ALTITUDE DIVING CONSIST OF THE FOLLOWING:
1) ARRIVING AT ALTITUDE FROM LOWER ELEVATION, AND COMPENSATING FOR RESIDUAL NITROGEN;
2) DIVING AT HIGH ALTITUDE WITH DIVE TABLES OR A DIVE COMPUTER DESIGNED FOR SEA LEVEL ONLY, MAKING THE PROPER EQUIVALENT DEPTH ADJUSTMENTS FOR HIGHER ALTITUDE;
3) ADJUSTING WETSUIT AND DRYSUIT BUOYANCY FOR FRESH WATER DIVING, AND FURTHER ADJUSTING WETSUIT BUOYANCY FOR HIGH ALTITUDE DIVING;
4) WAITING AT HIGH ALTITUDE AFTER DIVING FOR A SUFFICIENT LENGTH OF TIME BEFORE ASCENDING ANY MOUNTAIN PASSES ON THE JOURNEY HOME; AND
5) SAFETY PRECAUTIONS AND EMERGENCY PROCEDURES DUE TO ISOLATION OF THE DIVE SITE.
1) ARRIVING AT ALTITUDE FROM LOWER ELEVATION, AND COMPENSATING FOR RESIDUAL NITROGEN
ACCORDING TO NOAA TABLE 4.2, PRESSURE VARIATIONS WITH ALTITUDE, WHEN YOU ARRIVE AT LAKE TAHOE FROM THE BAY AREA, YOUR RESIDUAL NITROGEN LEVEL IN YOUR BLOOD AND BODY TISSUES WILL BE THE SAME AS NAVY/NOAA/NAUI GROUP E.
ACCORDING TO NAVY/NOAA DIVE TABLES, YOU WOULD NEED TO WAIT 12 HOURS BEFORE THIS LEVEL OF RESIDUAL NITROGEN IS SHED COMPLETELY.
ACCORDING TO NAUI DIVE TABLES, YOU WOULD NEED TO WAIT 24 HOURS BEFORE THIS LEVEL IS SHED COMPLETELY. NAUI IS MORE CONSERVATIVE THAN THE NAVY TABLES.
IN REALITY, YOU WOULD PROBABLY NEED TO WAIT 5 DAYS BEFORE ALL OF THIS RESIDUAL NITROGEN IS SHED.
IF YOU ARE USING NAUI DIVE TABLES, AND YOU BEGIN YOUR DIVE BEFORE 24 HOURS OF ARRIVING AT THE HIGH ALTITUDE DIVE SITE, YOU NEED TO TREAT YOUR FIRST DIVE AS A REPETITIVE DIVE, AND COMPUTE YOUR BEGINNING RESIDUAL NITROGEN AS A NAVY/NOAA/NAUI GROUP-E DIVER WITH A SURFACE INTERVAL IN HOURS EQUAL TO THE TIME ELAPSED SINCE YOU ARRIVED AT LAKE TAHOE.
IF YOU GO DIVING AS SOON AS YOU ARRIVE AT LAKE TAHOE, THEN YOUR NDL TIME LIMITS WOULD BE AS FOLLOWS FOR AN AIR DIVE (NOT EANx):
30 FT 81 MINS
40 FT 42 MINS
50 FT 19 MINS
60 FT 12 MINS
70 FT 5 MINS
80 FT 4 MINS
90 FT OR DEEPER NONE !
THIS TELLS US THAT IF WE ARRIVE AT LAKE TAHOE AND IMMEDIATE DECIDE TO GO SCUBA DIVING, WE SHOULD PLAY IT SAFE BY NOT DIVING DEEPER THAN 40 FEET NOR FOR LONGER THAN 40 MINUTES.
IF YOU ARRIVE AT LAKE TAHOE AND THEN WAIT 9 TO 24 HOURS BEFORE YOU BEGIN YOUR FIRST DIVE, YOU STILL NEED TO COMPUTE YOUR RESIDUAL NITROGEN FOR THE BEGINNING OF YOUR FIRST DIVE. ACCORDING TO THE NAVY/NOAA/NAUI TABLES, YOU WOULD BEGIN YOUR FIRST DIVE AS A GROUP-A DIVER, AND YOU WILL HAVE THE FOLLOWING RESIDUAL NITROGEN, MEASURED IN MINUTES OF DIVE TIME ALREADY USED, FOR THE FOLLOWING MAX PLANNED DEPTHS OF YOUR DIVE:
30 FT 7 MINS
40 FT 6 MINS
50 FT 4 MINS
60 FT 4 MINS
70 FT 3 MINS
80 FT 3 MINS
90 FT 3 MINS
100 FT 3 MINS
AFTER SUBTRACTING THESE RESIDUAL NITROGEN TIMES FROM YOUR NDL LIMITS FOR YOUR FIRST DIVE, THESE WILL BE YOUR NEW NDL LIMITS FOR DIVING AT ALTITUDE AT LAKE TAHOE FOR YOUR FIRST DIVE, FOR AN AIR DIVE (NOT EANx):
30 FT 123 MINS
40 FT 74 MINS
50 FT 41 MINS
60 FT 31 MINS
70 FT 22 MINS
80 FT 19 MINS
90 FT 9 MINS
100 FT 5 MINS
THIS TELLS US THAT IF WE WANT TO PLAY IT SAFE DURING OUR FIRST DIVE ON THE DAY FOLLOWING OUR ARRIVAL AT LAKE TAHOE, WE SHOULD NOT DIVE DEEPER THAN 60 FEET NOR FOR LONGER THAN 30 MINUTES, WHEN DIVING WITH COMPRESSED AIR.
FOR ALL SUBSEQUENT DIVES, WE SHOULD BE CAREFUL TO COMPUTE OUR RESIDUAL NITROGEN FROM THE PREVIOUS DIVE, USING THE EQUIVALENT DEPTHS SHOWN ABOVE FOR AIR DIVES. EANx DIVES WOULD BE DIFFERENT.
KEEPING REPETITIVE DIVES SHALLOWER THAN PREVIOUS DIVES ALSO HELPS PREVENT DECOMPRESSION INJURY.
2) DIVING AT HIGH ALTITUDE WITH DIVE TABLES OR A DIVE COMPUTER DESIGNED FOR SEA LEVEL ONLY, MAKING THE PROPER EQUIVALENT DEPTH ADJUSTMENTS FOR HIGHER ALTITUDE
ACCORDING TO NOAA TABLE 4.1, SEA LEVEL EQUIVALENT DEPTHS, WHEN YOU ARE SCUBA DIVING AT LAKE TAHOE, YOUR EQUVALENT DEPTHS ARE DEEPER THAN YOUR ACTUAL DEPTHS COMPARED TO SEA LEVEL FOR NDL PURPOSES. HERE IS A COMPARISON TABLE
ACTUAL DEPTH / EQUIVALENT SEA LEVEL DEPTH
30 FT/ 40 FT
40 FT/ 50 FT
50 FT/ 70 FT
60 FT/ 80 FT
70 FT/ 90 FT
80 FT/ 100 FT
90 FT/ 120 FT
100 FT/ 130 FT
THIS MEANS THAT YOU HAVE A MUCH SHORTER NDL TIME LIMIT THAN YOU ARE ACCUSTOMED TO AT SEA LEVEL FOR ANY GIVEN DEPTH AT LAKE TAHOE.
IF YOU ARE DIVING WITH A DIVE COMPUTER, AND IT DOES NOT HAVE HIGH ALTITUDE CORRECTION FEATURES IN IT, THEN YOU HAVE TO KEEP THE EQUIVALENT DEPTH TIME LIMITS IN MIND ALWAYS. USING A COMPUTER LIKE THIS AT HIGH ALTITUDE CAN BE VERY DANGEROUS.
SOME DIVE COMPUTERS CAN BE ADJUSTED FOR HIGH ALTITUDE DIVING. THE SUUNTO COMPUTERS ALLOW YOU TO DIAL-IN 3 OPTIONS:
1) SEA LEVEL
2) 1000 FT TO 5000 FT
3) 5000 FT TO 10,000 FT
IF YOUR COMPUTER HAS THESE FEATURES, YOU SHOULD CAREFULLY SET THE COMPUTER, BUT ALSO REMEMBER THAT YOUR COMPUTER WILL NOT KNOW YOU HAVE RESIDUAL NITROGEN IN YOUR BODY FROM YOUR ARRIVAL ON YOUR FIRST DAY. UNLESS YOU WAIT 24 HOURS AFTER ARRIVING AT LAKE TAHOE BEFORE DIVING, YOU STILL NEED TO REDUCE THE COMPUTERS NDL TIMES BY YOUR RESIDUAL NITROGEN TIMES.
USING NITROX AT HIGH ALTITUDE CAN INCREASE YOUR NDL DIVE TIMES, IN THE SAME MANNER AS IT DOES WHEN DIVING AT SEA LEVEL. DIVING AT HIGH ALTITUDE WITH EAN32 IS ABOUT THE SAME AS DIVING AT SEA LEVEL WITH AIR (21% O2, 78% N2, 1% OTHER), ALTHOUGH NOT EXACTLY.
3) ADJUSTING WETSUIT AND DRYSUIT BUOYANCY FOR FRESH WATER DIVING, AND FURTHER ADJUSTING WETSUIT BUOYANCY FOR HIGH ALTITUDE DIVING
WHEN DIVING WITH A WETSUIT OR A DRYSUIT IN FRESH WATER, YOUR WEIGHTING WILL BE APPROXIMATELY 4 TO 6 LBS LIGHTER THAN COMPARED WITH OCEAN DIVING. FRESH WATER IS LESS DENSE THAN SEA WATER.
WHEN DIVING AT HIGH ALTITUDE WITH A WETSUIT, THE SUIT WILL BE SLIGHTLY MORE BUOYANT AT ALTITUDE IN FRESH WATER THAN AT SEA LEVEL IN FRESH WATER. ACCORDING TO NOAA TABLE 4.2, PRESSURE VARIATIONS WITH ALTITUDE, THE AMBIENT ATMOSPHERIC PRESSURE AT 6000 FT IS 11.78 PSI, COMPARED WITH 14.70 PSI AT SEA LEVEL. DIVIDING SEA LEVEL PRESSURE BY HIGH ALTITUDE PRESSURE GIVES 125%.
FOR AN APPROXIMATE CORRECTION TO YOUR WETSUIT WEIGHTING, YOU CAN TAKE YOUR TOTAL WEIGHTING AT SEA LEVEL FOR OCEAN DIVING, THEN SUBTRACT ABOUT 6 LBS FOR THE FRESH WATER CORRECTION FROM SEA WATER, THEN SUBTRACT ABOUT ANOTHER 4 LBS FOR YOUR PERSONAL CORRECTION, FOR A TOTAL SUBTRACTION OF ABOUT 10 LBS. TAKING WHAT IS LEFT, AND MULTIPLYING BY 125% MAY GIVE YOU A CLOSE APPROXIMATION TO YOUR WEIGHTING CORRECTION FOR YOUR WETSUIT AT ALTITUDE.
INTERESTINGLY, THE HIGH ALTITUDE CORRECTION MAY COMPLETELY OFFSET THE FRESH WATER CORRECTION, AND YOU MAY END UP DIVING WITH THE SAME WEIGHTING AT LAKE TAHOE AS YOU WOULD AT THE OCEAN, IN YOUR WETSUIT.
FOR THESE TWO REASONS, WETSUIT DIVERS MAY NEED TO ADJUST THEIR WEIGHTING WHEN DIVING AT HIGH ALTITUDE IN FRESH WATER. AND DRYSUIT DIVERS WILL NEED TO MAKE THE FRESHWATER FROM SEA WATER CORRECTION.
4) WAITING AT HIGH ALTITUDE AFTER DIVING FOR A SUFFICIENT LENGTH OF TIME BEFORE ASCENDING ANY MOUNTAIN PASSES ON THE JOURNEY HOME
ALONG INTERSTATE HWY 80, DONNER PASS NEAR KINGVALE IS AT AN ALTITUDE OF 7260 FEET, WHICH IS 1035 FEET HIGHER THAN LAKE TAHOE.
IN ADDITION, STATE HWY 267 BETWEEN THE NORTH SHORE AND INTERSTATE HWY 80 RISES TO AN ALTITUDE OF 7260 FEET AS WELL.
ALONG US HWY 50, ECHO PASS IS AT AN ALTITUDE OF 7425 FEET, WHICH IS 1200 FEET HIGHER THAN LAKE TAHOE.
THESE HEIGHTS ARE INCREASES IN ALTITUDE FROM LAKE TAHOE, AND LIKE FLYING AFTER DIVING, A PERSON MUST WAIT A SPECIFIED NUMBER OF HOURS BEFORE ASCENDING TO THESE ADDITIONAL HEIGHTS AFTER DIVING.
NOAA TABLE 4.3, REQUIRED SURFACE INTERVAL BEFORE ASCENT TO ALTITUDE AFTER DIVING, GIVES THE FOLLOWING REQUIRED SURFACE INTERVALS, BASED ON THE NAVY/NOAA OR NAUI REPETITIVE DIVE GROUP OF THE DIVER, FOR AN ASCENT OF 2000 FT:
A NONE
B NONE
C NONE
D NONE
E NONE
F NONE
G NONE
H NONE
I 1 HR 32 MINS
J 3 HRS 9 MINS
K 4 HRS 37 MINS
L 5 HRS 57 MINS
M 7 HRS 11 MINS
N 8 HRS 20 MINS
O 9 HRS 24 MINS
Z 9 HRS 54 MINS
FOR EXAMPLE, A DIVER ARRIVING AT LAKE TAHOE AT NIGHT FROM THE BAY AREA, DIVING TWO AIR DIVES THE FOLLOWING DAY, THE FIRST TO 60 FT FOR 30 MINS, FOLLOWED BY A 1 HOUR SURFACE INTERVAL, WITH THE SECOND DIVE TO 30 FEET FOR 30 MINS, WOULD BE CLASSIFIED AS A NAVY/NOAA/NAUI GROUP J DIVER.
A GROUP J DIVER MUST WAIT AT LEAST 3 HOURS AND 9 MINUTES BEFORE CROSSING ONE OF THE ABOVE DESCRIBED MOUNTAIN PASSES ON THE RETURN TRIP TO THE BAY AREA.
5) SAFETY PRECAUTIONS AND EMERGENCY PROCEDURES DUE TO ISOLATION OF THE DIVE SITE
DIVE TABLES AND DIVE COMPUTERS SHOULD ALWAYS BE UTILIZED CONSERVATIVELY, AND DIVE DEPTHS AND BOTTOM TIMES SHOULD NOT BE PLANNED TO THE MAXIMUM NDL LIMITS OF THESE TABLES AND COMPUTERS.
THE NEAREST RECOMPRESSION CHAMBER TO LAKE TAHOE IS AT THE UNIVERSITY OF CALIFORNIA CAMPUS IN DAVIS.
IN CASE OF A DECOMPRESSION INJURY (DCI), BREATHING PURE O2 AFTER THE DIVE IS THE MOST RAPID AND EFFECTIVE FIRST AID TREATMENT. CALLING 9-1-1 WILL PROVIDE EMS RESCUE THAT WILL HAVE OXYGEN AVAILABLE.
UPON TRANSPORT BY EMS TO THE HOSPITAL, OXYGEN WILL ALSO BE AVAILABLE THERE. FURTHER EVACUATION AFTER EXAMINATION BY A PHYSICIAN WOULD PROBABLY BE BY AMBULANCE AND ON OXYGEN TO THE U.C. DAVIS CHAMBER.
DIVING CONSERVATIVELY CAN AVOID PROBLEMS OF DCI AT HIGH ALTITUDE.
HIGH ALTITUDE SCUBA DIVING
LAKE TAHOE IS AT AN ALTITUDE OF 6225 FEET. ANY SCUBA DIVING IN THE RANGE OF 1000 TO 10,000 FEET IS DEFINED AS HIGH ALTITUDE DIVING.
ISSUES INVOLVED IN HIGH ALTITUDE DIVING CONSIST OF THE FOLLOWING:
1) ARRIVING AT ALTITUDE FROM LOWER ELEVATION, AND COMPENSATING FOR RESIDUAL NITROGEN;
2) DIVING AT HIGH ALTITUDE WITH DIVE TABLES OR A DIVE COMPUTER DESIGNED FOR SEA LEVEL ONLY, MAKING THE PROPER EQUIVALENT DEPTH ADJUSTMENTS FOR HIGHER ALTITUDE;
3) ADJUSTING WETSUIT AND DRYSUIT BUOYANCY FOR FRESH WATER DIVING, AND FURTHER ADJUSTING WETSUIT BUOYANCY FOR HIGH ALTITUDE DIVING;
4) WAITING AT HIGH ALTITUDE AFTER DIVING FOR A SUFFICIENT LENGTH OF TIME BEFORE ASCENDING ANY MOUNTAIN PASSES ON THE JOURNEY HOME; AND
5) SAFETY PRECAUTIONS AND EMERGENCY PROCEDURES DUE TO ISOLATION OF THE DIVE SITE.
1) ARRIVING AT ALTITUDE FROM LOWER ELEVATION, AND COMPENSATING FOR RESIDUAL NITROGEN
ACCORDING TO NOAA TABLE 4.2, PRESSURE VARIATIONS WITH ALTITUDE, WHEN YOU ARRIVE AT LAKE TAHOE FROM THE BAY AREA, YOUR RESIDUAL NITROGEN LEVEL IN YOUR BLOOD AND BODY TISSUES WILL BE THE SAME AS NAVY/NOAA/NAUI GROUP E.
ACCORDING TO NAVY/NOAA DIVE TABLES, YOU WOULD NEED TO WAIT 12 HOURS BEFORE THIS LEVEL OF RESIDUAL NITROGEN IS SHED COMPLETELY.
ACCORDING TO NAUI DIVE TABLES, YOU WOULD NEED TO WAIT 24 HOURS BEFORE THIS LEVEL IS SHED COMPLETELY. NAUI IS MORE CONSERVATIVE THAN THE NAVY TABLES.
IN REALITY, YOU WOULD PROBABLY NEED TO WAIT 5 DAYS BEFORE ALL OF THIS RESIDUAL NITROGEN IS SHED.
IF YOU ARE USING NAUI DIVE TABLES, AND YOU BEGIN YOUR DIVE BEFORE 24 HOURS OF ARRIVING AT THE HIGH ALTITUDE DIVE SITE, YOU NEED TO TREAT YOUR FIRST DIVE AS A REPETITIVE DIVE, AND COMPUTE YOUR BEGINNING RESIDUAL NITROGEN AS A NAVY/NOAA/NAUI GROUP-E DIVER WITH A SURFACE INTERVAL IN HOURS EQUAL TO THE TIME ELAPSED SINCE YOU ARRIVED AT LAKE TAHOE.
IF YOU GO DIVING AS SOON AS YOU ARRIVE AT LAKE TAHOE, THEN YOUR NDL TIME LIMITS WOULD BE AS FOLLOWS FOR AN AIR DIVE (NOT EANx):
30 FT 81 MINS
40 FT 42 MINS
50 FT 19 MINS
60 FT 12 MINS
70 FT 5 MINS
80 FT 4 MINS
90 FT OR DEEPER NONE !
THIS TELLS US THAT IF WE ARRIVE AT LAKE TAHOE AND IMMEDIATE DECIDE TO GO SCUBA DIVING, WE SHOULD PLAY IT SAFE BY NOT DIVING DEEPER THAN 40 FEET NOR FOR LONGER THAN 40 MINUTES.
IF YOU ARRIVE AT LAKE TAHOE AND THEN WAIT 9 TO 24 HOURS BEFORE YOU BEGIN YOUR FIRST DIVE, YOU STILL NEED TO COMPUTE YOUR RESIDUAL NITROGEN FOR THE BEGINNING OF YOUR FIRST DIVE. ACCORDING TO THE NAVY/NOAA/NAUI TABLES, YOU WOULD BEGIN YOUR FIRST DIVE AS A GROUP-A DIVER, AND YOU WILL HAVE THE FOLLOWING RESIDUAL NITROGEN, MEASURED IN MINUTES OF DIVE TIME ALREADY USED, FOR THE FOLLOWING MAX PLANNED DEPTHS OF YOUR DIVE:
30 FT 7 MINS
40 FT 6 MINS
50 FT 4 MINS
60 FT 4 MINS
70 FT 3 MINS
80 FT 3 MINS
90 FT 3 MINS
100 FT 3 MINS
AFTER SUBTRACTING THESE RESIDUAL NITROGEN TIMES FROM YOUR NDL LIMITS FOR YOUR FIRST DIVE, THESE WILL BE YOUR NEW NDL LIMITS FOR DIVING AT ALTITUDE AT LAKE TAHOE FOR YOUR FIRST DIVE, FOR AN AIR DIVE (NOT EANx):
30 FT 123 MINS
40 FT 74 MINS
50 FT 41 MINS
60 FT 31 MINS
70 FT 22 MINS
80 FT 19 MINS
90 FT 9 MINS
100 FT 5 MINS
THIS TELLS US THAT IF WE WANT TO PLAY IT SAFE DURING OUR FIRST DIVE ON THE DAY FOLLOWING OUR ARRIVAL AT LAKE TAHOE, WE SHOULD NOT DIVE DEEPER THAN 60 FEET NOR FOR LONGER THAN 30 MINUTES, WHEN DIVING WITH COMPRESSED AIR.
FOR ALL SUBSEQUENT DIVES, WE SHOULD BE CAREFUL TO COMPUTE OUR RESIDUAL NITROGEN FROM THE PREVIOUS DIVE, USING THE EQUIVALENT DEPTHS SHOWN ABOVE FOR AIR DIVES. EANx DIVES WOULD BE DIFFERENT.
KEEPING REPETITIVE DIVES SHALLOWER THAN PREVIOUS DIVES ALSO HELPS PREVENT DECOMPRESSION INJURY.
2) DIVING AT HIGH ALTITUDE WITH DIVE TABLES OR A DIVE COMPUTER DESIGNED FOR SEA LEVEL ONLY, MAKING THE PROPER EQUIVALENT DEPTH ADJUSTMENTS FOR HIGHER ALTITUDE
ACCORDING TO NOAA TABLE 4.1, SEA LEVEL EQUIVALENT DEPTHS, WHEN YOU ARE SCUBA DIVING AT LAKE TAHOE, YOUR EQUVALENT DEPTHS ARE DEEPER THAN YOUR ACTUAL DEPTHS COMPARED TO SEA LEVEL FOR NDL PURPOSES. HERE IS A COMPARISON TABLE
ACTUAL DEPTH / EQUIVALENT SEA LEVEL DEPTH
30 FT/ 40 FT
40 FT/ 50 FT
50 FT/ 70 FT
60 FT/ 80 FT
70 FT/ 90 FT
80 FT/ 100 FT
90 FT/ 120 FT
100 FT/ 130 FT
THIS MEANS THAT YOU HAVE A MUCH SHORTER NDL TIME LIMIT THAN YOU ARE ACCUSTOMED TO AT SEA LEVEL FOR ANY GIVEN DEPTH AT LAKE TAHOE.
IF YOU ARE DIVING WITH A DIVE COMPUTER, AND IT DOES NOT HAVE HIGH ALTITUDE CORRECTION FEATURES IN IT, THEN YOU HAVE TO KEEP THE EQUIVALENT DEPTH TIME LIMITS IN MIND ALWAYS. USING A COMPUTER LIKE THIS AT HIGH ALTITUDE CAN BE VERY DANGEROUS.
SOME DIVE COMPUTERS CAN BE ADJUSTED FOR HIGH ALTITUDE DIVING. THE SUUNTO COMPUTERS ALLOW YOU TO DIAL-IN 3 OPTIONS:
1) SEA LEVEL
2) 1000 FT TO 5000 FT
3) 5000 FT TO 10,000 FT
IF YOUR COMPUTER HAS THESE FEATURES, YOU SHOULD CAREFULLY SET THE COMPUTER, BUT ALSO REMEMBER THAT YOUR COMPUTER WILL NOT KNOW YOU HAVE RESIDUAL NITROGEN IN YOUR BODY FROM YOUR ARRIVAL ON YOUR FIRST DAY. UNLESS YOU WAIT 24 HOURS AFTER ARRIVING AT LAKE TAHOE BEFORE DIVING, YOU STILL NEED TO REDUCE THE COMPUTERS NDL TIMES BY YOUR RESIDUAL NITROGEN TIMES.
USING NITROX AT HIGH ALTITUDE CAN INCREASE YOUR NDL DIVE TIMES, IN THE SAME MANNER AS IT DOES WHEN DIVING AT SEA LEVEL. DIVING AT HIGH ALTITUDE WITH EAN32 IS ABOUT THE SAME AS DIVING AT SEA LEVEL WITH AIR (21% O2, 78% N2, 1% OTHER), ALTHOUGH NOT EXACTLY.
3) ADJUSTING WETSUIT AND DRYSUIT BUOYANCY FOR FRESH WATER DIVING, AND FURTHER ADJUSTING WETSUIT BUOYANCY FOR HIGH ALTITUDE DIVING
WHEN DIVING WITH A WETSUIT OR A DRYSUIT IN FRESH WATER, YOUR WEIGHTING WILL BE APPROXIMATELY 4 TO 6 LBS LIGHTER THAN COMPARED WITH OCEAN DIVING. FRESH WATER IS LESS DENSE THAN SEA WATER.
WHEN DIVING AT HIGH ALTITUDE WITH A WETSUIT, THE SUIT WILL BE SLIGHTLY MORE BUOYANT AT ALTITUDE IN FRESH WATER THAN AT SEA LEVEL IN FRESH WATER. ACCORDING TO NOAA TABLE 4.2, PRESSURE VARIATIONS WITH ALTITUDE, THE AMBIENT ATMOSPHERIC PRESSURE AT 6000 FT IS 11.78 PSI, COMPARED WITH 14.70 PSI AT SEA LEVEL. DIVIDING SEA LEVEL PRESSURE BY HIGH ALTITUDE PRESSURE GIVES 125%.
FOR AN APPROXIMATE CORRECTION TO YOUR WETSUIT WEIGHTING, YOU CAN TAKE YOUR TOTAL WEIGHTING AT SEA LEVEL FOR OCEAN DIVING, THEN SUBTRACT ABOUT 6 LBS FOR THE FRESH WATER CORRECTION FROM SEA WATER, THEN SUBTRACT ABOUT ANOTHER 4 LBS FOR YOUR PERSONAL CORRECTION, FOR A TOTAL SUBTRACTION OF ABOUT 10 LBS. TAKING WHAT IS LEFT, AND MULTIPLYING BY 125% MAY GIVE YOU A CLOSE APPROXIMATION TO YOUR WEIGHTING CORRECTION FOR YOUR WETSUIT AT ALTITUDE.
INTERESTINGLY, THE HIGH ALTITUDE CORRECTION MAY COMPLETELY OFFSET THE FRESH WATER CORRECTION, AND YOU MAY END UP DIVING WITH THE SAME WEIGHTING AT LAKE TAHOE AS YOU WOULD AT THE OCEAN, IN YOUR WETSUIT.
FOR THESE TWO REASONS, WETSUIT DIVERS MAY NEED TO ADJUST THEIR WEIGHTING WHEN DIVING AT HIGH ALTITUDE IN FRESH WATER. AND DRYSUIT DIVERS WILL NEED TO MAKE THE FRESHWATER FROM SEA WATER CORRECTION.
4) WAITING AT HIGH ALTITUDE AFTER DIVING FOR A SUFFICIENT LENGTH OF TIME BEFORE ASCENDING ANY MOUNTAIN PASSES ON THE JOURNEY HOME
ALONG INTERSTATE HWY 80, DONNER PASS NEAR KINGVALE IS AT AN ALTITUDE OF 7260 FEET, WHICH IS 1035 FEET HIGHER THAN LAKE TAHOE.
IN ADDITION, STATE HWY 267 BETWEEN THE NORTH SHORE AND INTERSTATE HWY 80 RISES TO AN ALTITUDE OF 7260 FEET AS WELL.
ALONG US HWY 50, ECHO PASS IS AT AN ALTITUDE OF 7425 FEET, WHICH IS 1200 FEET HIGHER THAN LAKE TAHOE.
THESE HEIGHTS ARE INCREASES IN ALTITUDE FROM LAKE TAHOE, AND LIKE FLYING AFTER DIVING, A PERSON MUST WAIT A SPECIFIED NUMBER OF HOURS BEFORE ASCENDING TO THESE ADDITIONAL HEIGHTS AFTER DIVING.
NOAA TABLE 4.3, REQUIRED SURFACE INTERVAL BEFORE ASCENT TO ALTITUDE AFTER DIVING, GIVES THE FOLLOWING REQUIRED SURFACE INTERVALS, BASED ON THE NAVY/NOAA OR NAUI REPETITIVE DIVE GROUP OF THE DIVER, FOR AN ASCENT OF 2000 FT:
A NONE
B NONE
C NONE
D NONE
E NONE
F NONE
G NONE
H NONE
I 1 HR 32 MINS
J 3 HRS 9 MINS
K 4 HRS 37 MINS
L 5 HRS 57 MINS
M 7 HRS 11 MINS
N 8 HRS 20 MINS
O 9 HRS 24 MINS
Z 9 HRS 54 MINS
FOR EXAMPLE, A DIVER ARRIVING AT LAKE TAHOE AT NIGHT FROM THE BAY AREA, DIVING TWO AIR DIVES THE FOLLOWING DAY, THE FIRST TO 60 FT FOR 30 MINS, FOLLOWED BY A 1 HOUR SURFACE INTERVAL, WITH THE SECOND DIVE TO 30 FEET FOR 30 MINS, WOULD BE CLASSIFIED AS A NAVY/NOAA/NAUI GROUP J DIVER.
A GROUP J DIVER MUST WAIT AT LEAST 3 HOURS AND 9 MINUTES BEFORE CROSSING ONE OF THE ABOVE DESCRIBED MOUNTAIN PASSES ON THE RETURN TRIP TO THE BAY AREA.
5) SAFETY PRECAUTIONS AND EMERGENCY PROCEDURES DUE TO ISOLATION OF THE DIVE SITE
DIVE TABLES AND DIVE COMPUTERS SHOULD ALWAYS BE UTILIZED CONSERVATIVELY, AND DIVE DEPTHS AND BOTTOM TIMES SHOULD NOT BE PLANNED TO THE MAXIMUM NDL LIMITS OF THESE TABLES AND COMPUTERS.
THE NEAREST RECOMPRESSION CHAMBER TO LAKE TAHOE IS AT THE UNIVERSITY OF CALIFORNIA CAMPUS IN DAVIS.
IN CASE OF A DECOMPRESSION INJURY (DCI), BREATHING PURE O2 AFTER THE DIVE IS THE MOST RAPID AND EFFECTIVE FIRST AID TREATMENT. CALLING 9-1-1 WILL PROVIDE EMS RESCUE THAT WILL HAVE OXYGEN AVAILABLE.
UPON TRANSPORT BY EMS TO THE HOSPITAL, OXYGEN WILL ALSO BE AVAILABLE THERE. FURTHER EVACUATION AFTER EXAMINATION BY A PHYSICIAN WOULD PROBABLY BE BY AMBULANCE AND ON OXYGEN TO THE U.C. DAVIS CHAMBER.
DIVING CONSERVATIVELY CAN AVOID PROBLEMS OF DCI AT HIGH ALTITUDE.
Don't forget to make safety stops shallower that in ocean and decrease ascent rates...just sayin...use an altitude equivalent table and ORCA makes great computers that compensate and adjust for altitude of dive...
