An article of faith on ScubaBoard seem to be that using Buhlmann GF High = 95 gives very similar NDLs to what DSAT gives on Oceanic/AquaLung computers.
Let's look at that statement, especially in the context of new divers with new computers, wondering how to set them to be "safe?"
The caveats: this is for air, first dive of the day (no residual nitrogen).
Many computers by several manufacturers allow one to set the "conservatism" of the computers. For example, the setting is sometimes called High, Medium, or Low, where High means very conservative, i.e. shorter bottom times so less nitrogen accumulation.
Shown from left to right are: Depth in feet from 60 to 110, NDLs for some old and the newest US NAvy tables, the PADI RDP (Recreational Dive Planner), NAUI tables (based on the old Navy table with 5 minutes subtracted for conservatism), Canadian DCIEM tables, IANTD tables, two older DiveRite computers, a Zeagle computer similar to the DiveRite Duo (both Dive Rites and the Zeagle were made by Seiko), A Suunto Zoop runnig a very different algorithm, And Oceanic OC1 running two different algorithms DSAT is like the PADI RDP, PZ+ is based on Buhlmann), The OC1 with altitude-based conservatism), and several diffent Shearwater calculations for various Gradient Factors.
The PADI RDP (shown in Blue) is a standard of comparison. It has existed for four decades and used for (guessing) millions of dives. It does include mandatory safety stops (3-5 minutes at 15 ft) if your dive is close to an NDL or at 100 feet or deeper. The ocean OC1 DSAT column (shown in Red-Beige) is based on the same basic algorithm as the RDP.
But many people today are using computers with Buhlmann algorithms and Gradient Factors; how should they set those to "match" or "be safer" than the PADI RDP or DSAT? The Green column shows NDLs for a GF-High - 99, and the Yellow column for GF-High = 95.
On examination, it is pretty easy to argue that GFHi=99 is pretty similar to RDP/DSAT, and GFHi=95 is "safer" (i.e., smaller NDL) that RDP/DSAT. Pleae remember, however, that safety stops are mandatory if using RDP/DSAT near the NDL or at 100 ft or deeper.
So my answer to the question posed in the title to this thread is "No, GFHi=95 is slight better than RDP/DSAT, but don't forget your safety stop.
In case you are curious, i use GF-Hi=85, and try and NOT get close to the NDLs it recommends, AND I do safety stops, AND I go the surface very slowly from the safety stop. Almost 60 years of diving, and no DCS yet. Works for me.
Let's look at that statement, especially in the context of new divers with new computers, wondering how to set them to be "safe?"
The caveats: this is for air, first dive of the day (no residual nitrogen).
Many computers by several manufacturers allow one to set the "conservatism" of the computers. For example, the setting is sometimes called High, Medium, or Low, where High means very conservative, i.e. shorter bottom times so less nitrogen accumulation.
- The older computers achieved this kind of setting by artificially setting your altitude to be above sea level; for example you told it you wanted some conservatism so it calculated your dive parameters as if you were at (say) 2000 ft above sea level, which gives you sharter bottom times or NDLs (NDL = No Decompression Limits, sometimes called No Stop Times, meaning how long can you stay on the bottom before you need to use mandatory decompression stops).
- Many modern computers use a Buhlmann algorithm, which provides a conservatism setting using "gradient factors," which effectively lets you set a percentage of the maximum allowed gas pressure (determined by experiment) in your tissues. There are two gradient factors -- Low and High. The Low GF is only applicable to mandatory decompression dives, which are not relevant in this thread. The High GF might be (say) 95, which means you are allowing for 95% of your maximum allowable tissue pressure. Many manufacturers now use Low Conservatism to mean GF-High = 95 (i.e., not much conservatism); 85 means Medium conservatism; and 70 meams High conservatism (because you ae allowing only 70% of the maximum tissue pressure...so you ascend sooner).
Shown from left to right are: Depth in feet from 60 to 110, NDLs for some old and the newest US NAvy tables, the PADI RDP (Recreational Dive Planner), NAUI tables (based on the old Navy table with 5 minutes subtracted for conservatism), Canadian DCIEM tables, IANTD tables, two older DiveRite computers, a Zeagle computer similar to the DiveRite Duo (both Dive Rites and the Zeagle were made by Seiko), A Suunto Zoop runnig a very different algorithm, And Oceanic OC1 running two different algorithms DSAT is like the PADI RDP, PZ+ is based on Buhlmann), The OC1 with altitude-based conservatism), and several diffent Shearwater calculations for various Gradient Factors.
The PADI RDP (shown in Blue) is a standard of comparison. It has existed for four decades and used for (guessing) millions of dives. It does include mandatory safety stops (3-5 minutes at 15 ft) if your dive is close to an NDL or at 100 feet or deeper. The ocean OC1 DSAT column (shown in Red-Beige) is based on the same basic algorithm as the RDP.
But many people today are using computers with Buhlmann algorithms and Gradient Factors; how should they set those to "match" or "be safer" than the PADI RDP or DSAT? The Green column shows NDLs for a GF-High - 99, and the Yellow column for GF-High = 95.
On examination, it is pretty easy to argue that GFHi=99 is pretty similar to RDP/DSAT, and GFHi=95 is "safer" (i.e., smaller NDL) that RDP/DSAT. Pleae remember, however, that safety stops are mandatory if using RDP/DSAT near the NDL or at 100 ft or deeper.
So my answer to the question posed in the title to this thread is "No, GFHi=95 is slight better than RDP/DSAT, but don't forget your safety stop.
In case you are curious, i use GF-Hi=85, and try and NOT get close to the NDLs it recommends, AND I do safety stops, AND I go the surface very slowly from the safety stop. Almost 60 years of diving, and no DCS yet. Works for me.
