Hypothetical question

[RyanT]

Ok, this whole thread really got me thinking a lot about this. Something occurred to me last night that makes me think I got it wrong and @doctormike might be on to something here. I suggested that a change in pressure alone would not generate bubbles, that you need a gas concentration gradient. When you crack your knuckles, this increases the volume of the joint cavity, resulting in a coincident drop in pressure of the synovial fluid. The "crack" occurs from cavitation, that is bubble formation, in the synovial fluid. So assuming you haven't been diving, your PN2 is at equilibrium with the surrounding atmosphere. Here there is no gas gradient, yet the resultant drop in pressure results in bubble formation.

Pertaining to the specific situation described by the OP, however, I would go immediately to the airport. You would not have on-gassed any more nitrogen than what you would have had at atmospheric sea-level anyway. Thus should have no greater risk from flying compared to not having made the dive.

 

[Dominik_E]

RyanT, incidentally, the same basic process that makes your knuckles crack is also one suspect (although unconfirmed) for microbubble formation in diving ("tribonucleation", if in search for a technical term). This because bubble nucleation in the free liquid would require greater pressure gradients than can normally be reached in real dives...

 

[CT-Rich]

I don’t know if this has come up, but I like rolling grenades into the room. What was the nitrogen load on this hypothetical diver prior to the dive? This was a fairly benign dive and I am wonder why would he be using EAN 60 on a 30’ dive? I could see a diver grabbing a tank of EAN 32, because it was laying around, but 60%?

I know dive and let dive, but 60% at 30’ for 90 minutes right before you get on plane?

 

[CT-Rich]

I don’t know if this has come up, but I like rolling grenades into the room. What was the nitrogen load on this hypothetical diver prior to the dive? This was a fairly benign dive and I am wonder why would he be using EAN 60 on a 30’ dive? I could see a diver grabbing a tank of EAN 32, because it was laying around, but 60%?

I know dive and let dive, but 60% at 30’ for 90 minutes right before you get on plane?

Edit: Are you doing this with your personal gear or with rental? I would worry about resort gear bursting into flames on a dive like this, just sayin’

 

[RainPilot]

It’s a hypothetical to, I suspect, trigger some discussion around some of the perceived wisdom around flying after diving.

I have done some shallow cleanup dives on high O2 gases in the past, my shearwater has shown me to be on gassing on the surface afterwards but I’m starting to suspect there may be some additional factors at play.

 

[RyanT]

@Dominik_E, cool thanks. I was just reading a paper on tribonucleation in knuckle cracking, which is what further sparked my response above. Can you explain your statement (below) a little more, I'm not sure I'm quite following... thanks!

This because bubble nucleation in the free liquid would require greater pressure gradients than can normally be reached in real dives...

 

[seeker242]

What is your answer, and why?

Calculating the EAD and then referring to US Navy air dive table and the US Navy ascent to altitude table, that dive does not violate permission for immediate ascent to 8,00ft. Therefore, no wait necessary.

 

[boulderjohn]

I don’t know if this has come up, but I like rolling grenades into the room. What was the nitrogen load on this hypothetical diver prior to the dive? This was a fairly benign dive and I am wonder why would he be using EAN 60 on a 30’ dive? I could see a diver grabbing a tank of EAN 32, because it was laying around, but 60%?

I know dive and let dive, but 60% at 30’ for 90 minutes right before you get on plane?

This was a hypothetical question, so questions about the likelihood of it happening in the real world are not relevant. For the purposes of this question, the diver has 60% on hand, is certified to use it, and has the proper equipment. I have personally been in a similar situation in which I have done a shallow dive while breathing a gas mix that was intended for decompression and happened to be handy at the moment.

As was pointed out earlier, the mix and depth was carefully selected to create a situation in which the diver's nitrogen loading would be approximately equal to what it would have been had he or she stayed in bed. That would only be true, however, if the diver was at the maximum depth for the entire dive. If the diver spent time shallower, then the diver would have less nitrogen loading in all tissues than at the surface. The diver would thus be on-gassing in all tissues during an air-breathing surface interval following the dive, and the diver would arguably be better off to fly as soon as possible. This would be similar to astronauts and U-2 pilots breathing pure O2 prior to taking off.

 

[CT-Rich]

This was a hypothetical question, so questions about the likelihood of it happening in the real world are not relevant. For the purposes of this question, the diver has 60% on hand, is certified to use it, and has the proper equipment. I have personally been in a similar situation in which I have done a shallow dive while breathing a gas mix that was intended for decompression and happened to be handy at the moment.

As was pointed out earlier, the mix and depth was carefully selected to create a situation in which the diver's nitrogen loading would be approximately equal to what it would have been had he or she stayed in bed. That would only be true, however, if the diver was at the maximum depth for the entire dive. If the diver spent time shallower, then the diver would have less nitrogen loading in all tissues than at the surface. The diver would thus be on-gassing in all tissues during an air-breathing surface interval following the dive, and the diver would arguably be better off to fly as soon as possible. This would be similar to astronauts and U-2 pilots breathing pure O2 prior to taking off.

I pretty much get all of that, but if this hypothetical diver went to his hypothetical job as an airline pilot, he would probably be grounded until he was in compliance with FAA and Airline policy. You can do a lot of stuff on paper, but in practice, you shouldn’t really try to lawyer your way around best practices.

 

[doctormike]

= The diver would thus be on-gassing in all tissues during an air-breathing surface interval following the dive, and the diver would arguably be better off to fly as soon as possible.

So.... as long as you don't ongas, ascents don't cause bubbles?

Is that "safe to fly because I'm assuming that the effect of those bubbles is trivial", or "safe to fly because the only thing that increases the risk of DCS with air travel is whether or not you have increased your N2 loading from your baseline"