Pass rides after diving
Off home: How high should you go after diving?
Another question that often arises in connection with diving at altitude is the area around the mountain lake. It is not uncommon to have to go a little higher after the dive, over a pass, to get back home. At what point can this pose an additional risk?
Very often, another ascent after diving is seen as a big risk, kind of like getting right into an airplane. However, there is no evidence of a demonstrable risk, and when one considers the pressure differences that are being talked about, a small further increase seems quite unproblematic. If you have to go from 1000m to another 1500m and then down into the valley, you accept another pressure difference of about 0.05 bar. Under water, this would be just 50cm additional water column, a pressure difference that can also occur as a measurement inaccuracy. And: The range in which a table or a setting on the computer is valid covers e.g. 700 to 1500m altitude. If it doesn’t matter if I dive at 800m or 1500m, why would it be so critical to change altitude after the dive?
Certainly, such small height differences are nothing that can cause big problems on their own. Nevertheless, we should think about the height after the dive, because:
Bubbles continue to develop after the dive, more even than underwater. Most bubbles can be measured 30-45 minutes after the dive, only after that they slowly decrease. If you reduce pressure even further just when most bubbles are developing, that could theoretically “break the camel’s back.” So, if you were close to a DCS anyway, the ride could still provoke that little extra bubble growth that finally leads to crossing the line into an accident.
DCS symptoms usually appear after the dive, very often in the first hour. If you’re driving uphill, it doesn’t make things any better – but suddenly you might suspect the ride itself of having caused the DCS. This uncertainty can be avoided: If you have concerns about whether everything went well, there is nothing to be said against a break at sea level.