What can’t Nitrox do?
A lot is said about Nitrox, some of it cannot be proven with the best will in the world. Do you feel fitter after diving with Nitrox? It may be, but whether it’s really the gas is more than questionable. You mean you could shorten your surface interval a bit because you are diving Nitrox? That certainly doesn’t make the next dive any healthier.
Can I shorten my surface interval with Nitrox?
We’ve already seen that with Nitrox we can increase our bottom time OR take on less nitrogen. You can’t do both together, even when diving with Nitrox we still absorb nitrogen.
The risk of getting DCS is not significantly reduced by using nitrox. This emerges from a study published by DAN in 2017. Among other things, they measured the occurrence of bubbles after the dive and were unable to find any relevant difference between dives with air and dives with nitrox. No wonder – most of the time you use Nitrox to dive a little longer, and of course bubbles form there as well.
Relevant to our risk of DCS, however, is the amount of bubbles still circulating through our bloodstreams after diving. In the measurements in the same study, it has been demonstrated (again) that the highest bubble load does not occur immediately after diving, but increases further at the surface during outgassing.
The graph shows the bladder load measured at different times after the dive. As we can see here, most bubbles are detectable in the body 30-45 minutes after the dive. If you go back into the water at this very moment, these are compressed and can spread further and grow with the nitrogen that comes in. After 90 minutes, the bladder load is relatively low again. Whether air or nitrox, at least 90 minutes surface interval is a very good idea to make the dive safer. To cut this short because you are diving Nitrox is really not recommended.
You can read the whole study here:
D. Cialoni et al.: “Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base”
(Front. Psychol., 19 September 2017 | https://doi.org/10.3389/fpsyg.2017.01587 )
Does nitrox wake you up? Or beautiful?
At times, nitrox is credited with things that go well beyond the clear benefit of taking in less nitrogen.
Very often it is claimed that you are less tired after dives with Nitrox. In principle, of course, this is quite conceivable: One takes up less nitrogen, has a lower load after surfacing than after the same dive with air. So when diving with air just along the limits where decompressive stress becomes apparent, nitrox may eventually make the difference. Decompressive stress in this context refers to measurable blisters and other markers that are not yet decompression illness, but show that the body is under some stress.
However, this only applies if you use nitrox but have dived to air limits. The moment you take advantage of the longer no-stop times possible with nitrox, you no longer have an advantage in terms of the nitrogen you absorb. In addition, with Nitrox you are always exposed to higher oxygen partial pressures than with air, and this also puts a strain on the body, so tends to lead to more fatigue.
Unfortunately, if one searches to see if there are any meaningful studies on the subject, one finds little. But at least there is one where 11 divers:inside were given either air or an EAN36 to breathe during simulated dives in a pressure chamber, without knowing which gas they were on. The dives went to 18m for 40 minutes, within no-decompression limits with air. Before and after, some tests were made to detect something like fatigue and exhaustion. The result: “Dives to 18 m revealed no measurable difference in fatigue, alertness, ability to concentrate […] after dives with either breathing gas.”
Harris et al 2003: “Measurement of fatigue following 18 msw dry chamber dives breathing air or enriched air nitrox.”
