Exceeding the NDL during recreation diving

[Miyaru]

Looks like the software forgot to recalculate density from metric grams per liter into imperial pounds per gallon

 

[MarkA]

Deleted

 

[scubadada]

What RMV are you using? Setting aside deep air questions, I get a bigger obligation and need 78cf.

I have to reduce RMV to 0.30cfm to get your numbers, and that's... impressive. I'm jealous of that.

(Edit: on Nx32 with a plan RMV of 0.5cfm I get more reasonable stops and only 65cf needed... but that's still an ugly plan and pushing ppO2 and way under mingas.)...

My post figure was straight off MultiDeco. I used my average RMV of 0.36 cu ft/min from 1,917 dives over the last 14 years under all kinds of conditions. The variation around this average is not very great, with a std dev of 0.04 cu ft/min. My avg RMV over the last several years is a bit lower than the overall average.

I was using @crofrog example of a planned rec deco dive of 15 min at 130 ft using air, GFs of 40/85, that ended up going over by 5 min. I would do this dive on 28% and do not use 40/85.

Deep air, oh, come on now.

.75cuft/min

Which is a reasonable default to use to take into account the effects of stress. I'd recommend using at least a 1.5 multiplier or .75cuft/min whichever is more to build in a safety factor.

I'm not sure why this planned dive, that ended up going over by 5 min, would result in an overall dive RMV of 1.5 times average gas consumption. If that were the case, I would probably just squeeze by with an AL80 with a gas requirement of just over 70 cu ft. Of course, I would still have my pony.

I encourage divers to know their gas consumption rate and to plan for the gas requirements for their dives. There has been a thread going on SB for over 8 years now discussing average gas consumption

Average Gas Consumption

There has been extensive discussion lately regarding average gas consumption. A poll may help give us a better idea of what the normal distribution of RMVs is. 1 cu ft = 28.32 liters 1 liter = 0.035 cu ft 28.3 l/min

scubaboard.com

 

[crofrog]

I'm not sure why this planned dive, that ended up going over by 5 min, would result in an overall dive RMV of 1.5 times average gas consumption. If that were the case, I would probably just squeeze by with an AL80 with a gas requirement of just over 70 cu ft. Of course, I would still have my pony.

You shouldn't plan on things going perfectly, you should plan on them going very poorly.

Then when they go well, like they do 99% of the time you've had a bit of extra conservatism and you can lament from the safety of the surface the fact you could have spent a few extra minutes down there, and when they go very poorly you get to still go home.

 

[scubadada]

You shouldn't plan on things going perfectly, you should plan on them going very poorly.

Then when they go well, like they do 99% of the time you've had a bit of extra conservatism and you can lament from the safety of the surface the fact you could have spent a few extra minutes down there, and when they go very poorly you get to still go home.

I did not say that I do not plan for contingencies, only that I did not understand why your example dive would require 1.5 times the average gas requirement.

In fact, I use 2 times my average gas consumption rate when planning my required pony volume (very close to your 0.75 cu ft/min).

 

[lairdb]

My post figure was straight off MultiDeco. I used my average RMV of 0.36 cu ft/min from 1,917 dives over the last 14 years under all kinds of conditions. The variation around this average is not very great, with a std dev of 0.04 cu ft/min. My avg RMV over the last several years is a bit lower than the overall average.

I was using @crofrog example of a planned rec deco dive of 15 min at 130 ft using air, GFs of 40/85, that ended up going over by 5 min. I would do this dive on 28% and do not use 40/85.

Oh, not disputing -- just jealous of your SAC. I average 0.44 and use 0.5 for rough planning, and the 20min@130fsw on air came out needing more than the AL80 even without contingencies, so I was curious. Agreed across the board on the rest.

 

[scubadada]

Oh, not disputing -- just jealous of your SAC. I average 0.44 and use 0.5 for rough planning, and the 20min@130fsw on air came out needing more than the AL80 even without contingencies, so I was curious. Agreed across the board on the rest.

Your gas consumption is considerably below the average. I hope you voted in the poll.

 

[johndiver999]

No obviously not. It'd be 21/35 and 50%. In fact I mentioned that in the post, but you can't get over your trigger words and actually read.

The point is if you want to do decompression dives, you need to bring equipment, skills and knowledge appropriate for technical diving, to effectively manage the risk of decompression diving, and that technical diving equipment and procedures greatly reduce the risk. I can only speak to the GUE ones because I don't know what gas planning the other technical agencies do, but I'm pretty sure it's not sling a pony and hope.

No you are mistaken. I have done many decompression dives without all that gear, training or gas. In fact 2 of 3 dives I did today were short deco dives with a pony bottle while solo and one was to about 130 ft.

You don’t need all that stuff to do a little deco

 

[crofrog]

No you are mistaken. I have done many decompression dives without are that gear, training or gas. In fact 2 of 3 dives I did today were short deck dives with a pony bottle while solo and one was to about 130 ft.

You don’t need all that stuff to do a little deco

You do "to effectively manage the risk of decompression diving"

 

[Scared Silly]

No you are mistaken. I have done many decompression dives without are that gear, training or gas. In fact 2 of 3 dives I did today were short deck dives with a pony bottle while solo and one was to about 130 ft.

You don’t need all that stuff to do a little deco

No you are mistaken, you are doing deco with some knowledge, albeit poor knowledge.

'Good judgment comes from experience; experience comes from bad judgment' - Dr Kerr L White.

There is a great quote when diving in Chuuk in Truk Lagoon, "if your computer screen shows a view you have never seen, you are likely in deco." During the surface interval, one then sees said diver pouring over the computer manual.