Is my approach to diving with Nitrox logical?

[BlueTrin]

Also there are multiple levels of bent: if you get an undeserved hit but you were within your NDL, I think it’s unlikely to lead to the same damage that someone missing 30 minutes of decompression.

 

[Nitrox_DiverNY]

Well do not assume your DC runs a GF software algorithm. My Suunto used the RGBM algorithms and not GF's relate to Bulhmann.
My Perdix uses the Bulhmann and gradient factors. So with the Perdix I get longer NDL times over the Suunto when I am doing 40 dives in 12 days. The Suunto was quite conservative and you would need to dive a lot shallower even is using the least conservative setting.

Perhaps you may want to reconsider your changing PPO2 1.4 to other settings if you do not fully understand the reasons for doing so.

Conservative settings on Mares computers

Does anyone happen to know what the P0 (standard setting / least conservative), P1 & P2 (most conservative) settings actually influence or refer to in the range of Mares dive computers? It would be helpful to understand if anyone can relate that to comparative gradient factors - I KNOW the...

scubaboard.com

thanks for sharing!

 

[Nitrox_DiverNY]

Hi @Nitrox_DiverNY

Thanks for answering my questions

Mares RGBM is one of the most conservative decompression algorithms. When you are close to your NDL, other divers with a more liberal decompression algorithm will still have considerable NDL time. Keep in mind that all dive computers are very safe, this simply represents the range in NDL values available. Have you dived with someone using DSAT or Buhlmann with a GF high of 95? You would likely signal that you are getting low on NDL while they had considerable time left. You have probably realized this but, as your Mares computer does not run Buhlmann ZH-L16C, you do not have gradient factors to adjust your decompression algorithm

As others have pointed out, the rate of DCS is very low. I would not be overly concerned. Instead, you should follow all the diving guidelines you have been taught. Make your ascent at the correct rate, make your safety stop with a good controlled final ascent to the surface.

It appears that your diving in Florida has not yet exposed you to the common banked nitrox mixes of 32 and 36%

Best of luck in your diving

very interesting, I honestly am just being exposed to the idea of Algorithms its something that has not really come up in my limited time diving so far. I have no idea what other algorithms dive buddies have been using, probably since most have been pair ups on boats. So the RGBM and Buhlmann are two of the most "common" algorithms? the former being more conservative and Buhlmann being liberal. got it

thanks for the reassurance about DCS, I think I have been overblowing its prevalence in my mind.

thank you for the help! its very much appreciated!

 

[Nitrox_DiverNY]

You are overthinking this as a new diver. DCS is not as common as you believe. There are hundreds of thousands of dives made every year, maybe more. Most are on air or 32%. If there were a lot of DCS cases, every training agency, dive resort, and commercial dive boat would have to re-write their policies. I know divers who began diving in the early 60s and dived deep air for decades without getting bent. I got certified in 1989 and have avoided the bends by making slower ascents than recommended. I strongly suggest you get in a lot of dives before considering rebreathers and/or high O2 concentrations for relatively shallow recreational dives.

Maxbottomtime, thanks for helping to clear up some of this uncertainty I have about DCS. as a new diver its something you think its rather common, but in fact is not. I will have to try and accept in my own mind that its a rather small risk, but with proper technique can be highly mitigated. thanks for your feedback!

 

[Nitrox_DiverNY]

@Nitrox_DiverNY the gradient factors are just a % of distance you add for “conservatism” against the Buhlamn algorithm: there are two gradient factors GFLo and GFHi, if you set them to 100% you are diving the unmodified Bühlmann algorithm.

This picture below explains it, the ascent starts on the right. The M-value line is the ascent from using 100% Buhlman.

IMHO, although the question is interesting, you will probably be ok by just diving your computer algo for recreational depth. If you want to add some conservatism maybe try to not reach your NDL or do a longer safety stop?

View attachment 733466

thanks for sharing but I have to admit I am lost with the graph lol. Might need another cup of coffee to understand this. What is the difference between GFlo and GFHi? so if they are both set to 100% then its very liberal correct since its Bulhman?

RGBM does not have a GF factor correct?

and yes as others have said here to adding in longer stop, not pushing NDL, etc all adds and I agree

 

[Nitrox_DiverNY]

Also there are multiple levels of bent: if you get an undeserved hit but you were within your NDL, I think it’s unlikely to lead to the same damage that someone missing 30 minutes of decompression.

that is something I have not thought about, but it makes sense. I guess I was conflating getting bend to be all on the same level nomatter the profile

 

[Nemrod]

I have been an active diver since 1968. I have never been bent and this during a time when we did not do safety stops, used the then liberal Navy Tables and did 60 fpm ascents straight to the surface. Of course I know of reported cases of the bends and we all read of people who visit the chamber whether for real need or precautionary need. I think the OPs concern over being bent is a little exaggerated.

A recent dive of mine that did incur a little deco obligation. Not ideal, but heck, there was turtle after turtle after shark after shark and goliath after goliath, What, like am I supposed to leave all that down there unmolested?



My mix was 36% (aluminum 80 starting psi 3200), my GF was set to High, I was back standing on deck with 800 psi and that after a 10 minute wait for the boat to come get me (still on my regulator/tank) as it worked it's way from group to group to finally me, yes, I was solo. I had my slung pony with bottom mix but of course do not use that but for emergency. Fun dive. No bends.

N

 

[scubadada]

...So the RGBM and Buhlmann are two of the most "common" algorithms? the former being more conservative and Buhlmann being liberal. got it...

Sorry, it's just not that easy.

The RGBM algorithms are generally more conservative, Mares, Cressi, Suunto. They can be made more conservative through adjustment. However, Suunto has several versions of RGBM and one can be made to be quite liberal.

Buhlmann is adjusted with the GFs and can be anywhere between very liberal and very conservative. Only the GF high applies to no stop diving. A GF high of 95 would generally be considered liberal, 85 moderate or middle of the road, and 75 conservative.

There are several other common deco algorithms such as DSAT, liberal and PZ+, moderate. Both of these can be made more conservative with settings.

You seem very inquisitive, I would suggest you consider reading Deco for Divers by Mark Powell, it will address many of your questions.

 

[scubadada]

Hi @Nemrod

That looks a lot like a profile in Jupiter, is that where you were, or someplace else?

 

[Nemrod]

Hi @Nemrod

That looks a lot like a profile in Jupiter, is that where you were, or someplace else?

Yes, exactly, how astute of you! Indeed it was Jupiter. I am just back from a near month of diving Florida from one end to the other. And darn if I do not have to go back in a week or so to recover my Toyota Tacoma whose engine decided to explode on me. But ever true blue it got me to the Toyota dealer before expiring where the poor things sits awaiting a new engine. So yes, I plan to hit Jupiter again. Captain wants all divers up at 55 minutes, I over stayed 1 minute and 20 seconds because I did a 5 minute (adaptive setting) safety stop.

James