Do recreational dive computers factor in air consumption rate when calculating nitrogen loading?

[fuzzybabybunny]

My initial assumption is that a computer tracks air consumption at different depths to help calculate nitrogen loading in your body, which means it needs to know how your tank pressure is changing over time and depth (and gas mix). Or maybe it just calculates nitrogen loading based on depth and time spent, regardless of tank pressure changes? So what happens when you switch off of your main tank with the attached computer and breathe off of a second tank that's not attached to that computer? The computer would see the tank pressure not changing over a period of time, so it would determine nitrogen loading based only on time and depth?

I'm just in the exploratory stage of reading up on sidemount diving, and since you've got two tanks with fully independent regulators and no manifold connecting the two, how does the computer situation work? Is there a wireless transmitter on each tank with a single computer receiving input from both? Or can you just have a single computer attached to one tank, with the second having a simple pressure gauge? If the latter, the computer wouldn't be able to track your air consumption on the second tank, and so would it fail to accurately calculate nitrogen loading?

 

[Lorenzoid]

This thread may be of interest: Does SAC rate have any impact on NDL?

 

[lv2dive]

“it just calculates nitrogen loading based on gas mixture, depth and time spent, regardless of tank pressure changes” - bold was added by me: gas mixture, meaning air vs any Nitrox mix such as 32% EAN or even trimix. How much you breath has no impact.

My initial assumption is that a computer tracks air consumption at different depths to help calculate nitrogen loading in your body, which means it needs to know how your tank pressure is changing over time and depth (and gas mix). Or maybe it just calculates nitrogen loading based on depth and time spent, regardless of tank pressure changes? So what happens when you switch off of your main tank with the attached computer and breathe off of a second tank that's not attached to that computer? The computer would see the tank pressure not changing over a period of time, so it would determine nitrogen loading based only on time and depth?

I'm just in the exploratory stage of reading up on sidemount diving, and since you've got two tanks with fully independent regulators and no manifold connecting the two, how does the computer situation work? Is there a wireless transmitter on each tank with a single computer receiving input from both? Or can you just have a single computer attached to one tank, with the second having a simple pressure gauge? If the latter, the computer wouldn't be able to track your air consumption on the second tank, and so would it fail to accurately calculate nitrogen loading?

 

[JohnnyC]

Short answer, no.

Independent tanks requires having the ability to monitor the amount of gas in both tanks. If you go with wireless AI like a Perdix, the computer will show pressure remaining in each tank if you have two transmitters. Most people just use SPG's. I don't know anyone that has one transmitter and one SPG. Defeats the purpose of having wireless AI.

Really, nobody is going to have a wired AI computer on a sidemount tank.

 

[fuzzybabybunny]

Ok, so what I'm getting is that computers don't factor in air consumption. You can be a huge air hog or a sipper and the nitrogen loading it calculates will be the same for each case if the dives and ascents were identical, despite one person ending the dive with, say, 500 psi and the other with 1500 psi (I actually had this happen - instabuddied with the boat's divemaster and he came up with 500 psi and me with 1500 psi). I would assume that the heavier breather would have taken in more nitrogen, but I guess it doesn't make that much of a difference in recreational diving?

What about with tech diving and mixed gas? Or is replacing nitrogen with helium or hydrogen only done to eliminate nitrogen narcosis?

 

[boulderjohn]

Your assumption is not correct. The rate at which you breathe does not matter for nitrogen loading. The only way it does is if you are breathing heavily because you are working hard and your blood is flowing extra hard.

 

[fuzzybabybunny]

Your assumption is not correct. The rate at which you breath does not matter for nitrogen loading. The only way it does is ITV you are breathing heavily because you are working hard and your blood is flowing extra hard.

So nitrogen loading is pegged to metabolism? And the individual differences in metabolic rates among relaxed divers isn't enough to demand compensation by the computer?

 

[runsongas]

most computers don't have information on your heart rate and body temperature to adjust the calculation. scubapro sells a hrm band that works with some of their higher end computers and the garmin descent has hrm. mainly just adds more deco when the easier option is just swim in circles at your stops.

 

[rongoodman]

Nitrogen loading has nothing to do with metabolism, since N2 isn't active in the body. It just passively diffuses in and out of the various body tissues.

 

[tursiops]

Also, the pressure in the tank is irrelevant, because the pressure you are breathing is ambient at one's depth...so all you need to know is depth and time (and gas mixture...).