In an earlier thread, ICD came up as a decompression risk. ICD is basically a description of physical facts which play a role when you change breathing mixes. Dr. Simon Mitchell explained in this post how ICD can lead to IEDCS when going from a high helium mix (heliox/trimix) to a high nitrogen mix, using OC but the same applies when you have to bail-out from CC at depth.
Two strategies or rules-of-thumb to minimize IEDCS are to
Sheck Exley described his approach to prevent an ICD hit by taking 1 breath from his decogas, followed by 2 breaths of backgas, then 2 breaths of decogas followed by 1 breath of backgas and then breathing decogas. No vertigo, no vomiting, not narced.
Let's say that's a timespan of half a minute in which the partial pressures of all inert gasses in your lungs are more gradually changing than from one breath to the next. Is half a minute enough to prevent exceeding the critical supersaturation of the endolymph and the surrounding sensitive functional inner ear tissue?
Course material from agencies don't say much on preventing ICD either. It's limited to describing the mechanism that can lead to IEDCS and the two prevention stategies.
One organization ignores the ICD risks by stating that the use of standard gasses excludes this. Which I don't really understand since a change from standard gas 10/70 to standard gas 15/55 exceeds the limits from both strategies.
My experience sofar is all above 100m/330ft, but before passing that depth I want to know how to minimize the risks. There must be loads of succesful deco strategies from those depths and I'd like to better understand these upfront. So educate me from your experience!
Two strategies or rules-of-thumb to minimize IEDCS are to
- keep the rise of ppN2 within 0.5bar
- keep the change of He:N2 within a ratio of 1:5.
Sheck Exley described his approach to prevent an ICD hit by taking 1 breath from his decogas, followed by 2 breaths of backgas, then 2 breaths of decogas followed by 1 breath of backgas and then breathing decogas. No vertigo, no vomiting, not narced.
Let's say that's a timespan of half a minute in which the partial pressures of all inert gasses in your lungs are more gradually changing than from one breath to the next. Is half a minute enough to prevent exceeding the critical supersaturation of the endolymph and the surrounding sensitive functional inner ear tissue?
Course material from agencies don't say much on preventing ICD either. It's limited to describing the mechanism that can lead to IEDCS and the two prevention stategies.
One organization ignores the ICD risks by stating that the use of standard gasses excludes this. Which I don't really understand since a change from standard gas 10/70 to standard gas 15/55 exceeds the limits from both strategies.
My experience sofar is all above 100m/330ft, but before passing that depth I want to know how to minimize the risks. There must be loads of succesful deco strategies from those depths and I'd like to better understand these upfront. So educate me from your experience!
- When do the risks kick in?
- After how much bottomtime at what depth is the risk becoming an issue?
- For how much time after a switch is there an IEDCS risk?
- From what depth can you exceed the limits set by the mentioned strategies?