Frank, and all,
I ran the same numbers through my spreadsheet, based solely upon the PADI RDP modified for altitude.
I used the following assumptions, similar to what Frank used, to see what I would get the old fashioned way (i.e., using the RDP with the application of altitude).
All altitudes are rounded up to the next 1000 foot, and depths are round down to what the RDP requires.
Started at 6,000 ft and ascended to 10,000 ft. Diving mix was air (21% O2). If this assumption is correct, that puts you in PG H upon arrival at the lake.
It takes about 45 minutes to park, unload, kit up, before entering the water. If this is correct, then the surface interval at 10,000 ft is 45 minutes, reducing the original PG H to PG C upon entry into the water. This means we have a RNT of 17 minutes for our 50 ft dive (see next step) before we even enter the water.
Assuming a square profile at 43 ft yields and EAD of 49.665 ft which rounds to 50 feet. At that depth, the Max. Bottom Time (NDL) is 80 minutes. Tom only spent 37 minutes (ABT) plus the 17 min RNT from above yields 54 min TBT, so NDLs werent violated on this dive. The O2 Partial Pressure =0.53 and the % of allowable O2=10%. The PG upon exiting this dive is PG R.
Using Franks assumption of a 1 hour (60 minutes) SI, the PG for entering the next dive is PG G.
Again assuming a square profile for the next dive, the 52 ft yields an EAD of 60.06ft which rounds to 70 ft. Yeah, the way the math works, 52 ft at 10,000 ft altitude rounds to 70 feet for use on the RDP. Using this 70 ft along with the PG G gives us an RNT of 18 min. The Max NDL (from Table 3) for 70 ft is 40 minutes. Since we have an RNT of 18 minutes, we only have a remaining ABT of 22 minutes. This is where the analysis blows up. In the example dive, Tom spent 35 minutes at this depth (assuming square profile). This exceeds the Table limits as my OW instructor would say you just killed yourself.
Ok, to try to get this to work, I decreased the reported 52 ft to 51 ft. Remember, that due to rounding, the 52 ft went to 60.06 at altitude, which then rounded to 70 ft for use with the RDP. If we use 51 ft, that yields and EAD = 58.9 ft, which rounds to 60 ft for the RDP. This gives us a Max NDL of 55 min (vice 40 min). Subtracting the 21 min (at 60 ft) RNT, we still bust the NDL by 1 minute. So, lets decrease the dive time of the second dive by 1 min to see what happens. (Of course, we could also increase either SI to lower the dive #2 beginning PG also). Using 34 min dive time, we come in right at the NDL (TBT =55 min). The O2 Partial Pressure =0.59. This yields a % of allowable O2=5% and the cumulative O2% = 15% The PG upon exiting this dive is PG W.
Based upon the above, this dive could have been accomplished if the depth of dive #2 was 1 foot less, and the time of dive #2 was one minute less.
All this assumes that the depth measured is true depth. That is, the instrument measuring the depth is calibrated to read correctly at 10,000 (most analog gauges are calibrated at sea level) and that it is measuring in feet fresh water (FWF),not salt-water (again, most analog gauges measure SWF). Computers may compensate for either or both, but my manual doesnt say how it does it. I can only set my computer in ranges (0-2300ft, 2300-4900ft, 4900-7900ft, and above 7900 ft). I included the O2 data for comparison to VPM. Using air (21% O2) we really dont have to worry about it.
I dont know how VPM works and I have no training in decompression diving (to include decompression stops and different decompression gases). It would be interesting if Frank were to make the slight changes to the input to VPM, and see if would allow a non decompression dive.
Regarding Jefferson Lake, it doesnt look like we will need to take any passes or higher altitude adjustments into consideration on the return trip, since all our diving will have been at the highest altitude. Does this make sense? Do my calculations make sense?
