This is the first in a series of comparisons between SAUL and other dive planners. For obvious reasons, I can’t do a direct NDL to NDL comparison. (SAUL, being a probability-based model, doesn’t actually have NDLs.) Instead, single NDL profiles from the PADI tables will be paired with their expected probability of DCS according to SAUL.

#### Dives with air, including 3 min safety stop at 15 fsw

PADI NDL SAUL SAUL at 75% PADI NDL BT

Depth(fsw) BT(min) Prob. of DCS (as a %) Prob. of DCS (as a %)

35 205 0.1750 0.0637

40 140 0.1560 0.0645

50 80 0.2090 0.1020

60 55 0.3210 0.1510

70 40 0.4030 0.1720

80 30 0.4140 0.1490

90 25 0.4740 0.1670

100 20 0.4080 0.1130

110 16 0.3000 0.0640

120 13 0.2020 0.0300

130 10 0.0796 0.0014

140 8 0.0250 0.0000

To put it another way, your likelihood of getting bent, if you dive profiles right at the PADI no-decompression limits, averages out at just over 1 in 400. But your likelihood of getting bent on any particular NDL profile ranges from a low of about 1 in 4000 (140 fsw, 8 min) to a high of almost 1 in 200 (90 fsw, 25 min). Of course, most of us don’t usually dive right at the limits. If you limit your bottom time to three-quarters of the PADI no-decompression limits, your likelihood of getting bent (shown in the right-hand column) averages out at just over 1 in 700 and ranges between a low of pretty near zero (less than 1 in 1,000,000 for 140 fsw, 6 min) to a high of about 1 in 550 (70 fsw, 30 min). If you were diving with SAUL, your own personal “NDL” would depend on what you chose as an acceptable level of risk. If, for example, you input 0.5000 (1 in 200) as your risk level – not really advisable – you could dive any of the profiles in the PADI NDLs and even increase your bottom times on many of them. If you input a more sensible 0.2500 (1 in 400), you could dive the PADI NDLs at 35, 40, 50, 120, 130, or 140 fsw but would be held to varying shorter bottom times between 60 and 120 fsw.

##### Dives with “32 NITROX” (32% O_{2}), including 3 min safety stop at 15 fsw

PADI NDL SAUL

Depth(fsw) BT(min) Prob. of DCS (as a %)

45 220 0.0219

50 155 0.0122

55 110 0.0073

60 90 0.0194

70 60 0.0444

80 45 0.0845

90 35 0.1100

100 30 0.1690

110 25 0.1730

120 20 0.1060

130 18 0.1260

##### Dives with “36 NITROX” (36% O_{2}), including 3 min safety stop at 15 fsw

PADI NDL SAUL

Depth(fsw) BT(min) Prob. of DCS (as a %)

50 220 0.0004

55 155 0.0000

60 115 0.0000

65 90 0.0000

70 75 0.000008

80 55 0.0150

90 40 0.0198

100 35 0.0688

110 29 0.0822

SAUL indicates that diving with either form of Nitrox is safer than PADI NDL tables would suggest. The “riskiest” dive in the lot – 32 NITROX at 110 fsw , 25 min – has just slightly more than a 1 in 600 chance of resulting in DCS. The safest for 32 NITROX – 55 fsw, 110 min – runs a DCS risk of less than 1 in 14,000. The 36 NITROX in the PADI NDL tables, as a group, are safer still, with almost half of them bearing DCS risks of less than 1 in 1,000,000. The “riskiest” 36 NITROX dive – 110 fsw, 29 min – still has a DCS risk of less than 1 in 1,200. While I did calculate the probabilities of DCS for dives at 75% of the PADI NDL bottom times for both forms of Nitrox, it’s not really worth printing them out – they’re all pretty close to zero, the highest probability there being just over 1 in 10,000 (32 NITROX, 110 fsw, 18 ^{3}/_{4 }min)._{ }

Looking in a more general way at comparisons between SAUL and PADI, their respective conclusions on safe versus unsafe dives are not too far apart. Nitrox is, indeed, significantly safer than air. For air, SAUL sees the PADI NDLs as being, for the most part, of roughly equal risk and at a level of risk that is reasonable (considering that they are NDLs – i.e, limits, not necessarily preferred profiles). SAUL diverges from PADI in finding its NDLs in the mid-depth range to be a little riskier than some divers may expect, while dives at more shallow or deeper depths are safe enough that divers who tolerate greater (but still reasonable) risks could be allowed a little more leeway. Of course, being “allowed” to increase times at the shallowest depths means nothing on a single tank of air. Very few, if any, divers can stretch their air to accommodate the 205 minutes PADI permits at 35 fsw or even the 140 minutes permitted at 40 fsw.

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