Nitrogen Increase?

[tombiowami]

Question, I have about 36 dives, most with the Suunto Mosquito. Some days I have dove 5 times on nitrox in a day, or 3 or 4 dives on air in a day. I use the tables for planning, but then look at the graphs of the dive. The most I really get up to on the 9 compartments in the Suunto RGBM is about 25 per cent.

Last weekend I did two dives to 40' or less for an hour a piece, avg. depth was in the 20s. My nitrogen intake though hit 50 per cent on both dives according to the graphs. We did a SIT of an hour and a half between dives, air temp was in the 70s.

I usually dive in water that is 72 at the coldest, and this water was 58-61. Is that the reason for the increase?

Tommy

 

[Dr Deco]

Dear Tommy:

To the best of my knowledge, no dive computer takes into account air or water temperature. The gas loads determined by the computer are what they would be for those dives, independent of temperature.

What you see is what the algorithm actually calculated, and it was mostly the result of the somewhat long bottom times and the loading of longer halftime compartments.

Dr Deco

 

[tombiowami]

Thanks. I have been down that long before, but always on much higher 02 content, so that explains it. Have a good day.




Tommy

 

[TexasMike]

Tommy,

I've recently come across some good books that help to explain the physiology of diving and nitrogen uptake/off gas.

I'll try to remember to post the titles/authors tonight for ya.

 

[Liquid]

Doc-
I belive that RGBM formulae does take into consideration temperature, and that the new generation SUUNTO computers that use this formulas also use the temperature as a part of their computeaions. I'm not sure about it, but I read about RGBM thourioghly about a year ago and I belive it is so. Though, I confess it was long enough ago, that I may not remember correctly.

 

[Solomon]

The new UWATEC computers also factor in water temp as well as rate of breathing/workload.

 

[The Iceni]

Hi all,

I am no expert as you know, so I am little confused if there has been an attempt to incorporate water temperature into deco alogrithms used by computer manufacturers.

Work rate and stress, I can understand. Water tempreature, No.

The solubility of gasses is affected by temperture, but by the temperature of the solvent not of the gas. The hotter the liguid the less gas can dissolve. In addition the thermal capacity of any gas is much less than any liquid so is unlikely to cool an inert solvent significantly in any case.

Helium is perhaps the exception but in recreational divers?

Humans are warm-blooded creatures and even when diving in the cold North Sea we seldom deliberately allow our core temperatures to drop by significant amounts. Indeed I use a hefty dry suit and 200 g/M2 thinsulate undersuit and remain as warm as toast. I am reasonably confident my core temperature remains fairly constant for most of the time as do those diving under the ice in the antarctic.

It may have been a little different when I used a DIY 4 mm wet-suit in winter all those moons ago ( I did not dive again if I felt cold and victims of hypothermia - with a significant reduction in core temperature - will have long past the stage of feeling cold.)

If there is an attempt to control for water temperature in these manufacturer's deco algorithms how do they control for that unknown variable of the diver's attire?

I also feel fairly confident that gas use is also independent of water temperature, because it is heated by the mucus membranes of the respiratory tree to core temperature before it reaches the lungs, regardless of the water/cylinder/gas temperature.

(Clearly a cold cylinder filled to 232 bar contains more gas than a warm cylinder at the same pressure and will last longer but this bears no relation to finite gas consumption.)

 

[Liquid]

Doc paul- Since we're hot-blooded creature, when we'r in a cold inviorment, our body needs to heat us. It does by using nuscles and burning energy, i.e we are actualy more active than we would have in uncold enviorment, doing exactly the same thing. The more you stress your body, the more you risk bends. So the problem with the temprature isn't a direct one, since like you pointed out, cold liquids can contain MORE gas. Rather it's indirect- you get more stressed, and therefore more susceptible to DCS.

 

[BOOinTX]

Not sure ithat the Suunto RGBM model accounts for temperature but it does address things like:
- closely spaced repetitive dives
- dives deeper than the previous dive
- rapid ascents which produce high micro-bubble (silent-bubble) build up
see page 96

 

[Dr Deco]

Dear readers:

The water temperature by itself would not influence the gas uptake that much, since the body temperature is fairly constant. However, exercise that might accompany a cold diver in the attempt to remain warm would increase gas loads. This would be reflected in the meters that monitor gas consumption and input that information to the algorithm.:cold:

If this info were added, the algorithm would need to account for it. I am not aware, and do not believe, that such an adaptive computer exists. We do track such information on EVA astronauts during oxygen prebreathe at NASA, but this is a very controlled situation.

Dr Deco
:doctor: