AIr Embolism In Shallow Water

[Dive Kayak]

I am a certified recreational diver that is exploring the use of emergency air for whitewater kayaking, including extreme, big water conditions. There are a variety of hazards in whitewater that may cause the need for emergency air. It would be rare for a kayaker to ever breathe emergency air at a depth of ten feet, and most hazards would be in three feet of water or less. However, there are some situations where a kayaker ends up swimming in huge whitewater where the hydraulic forces would make his depth vary, but again, probably not more than ten feet. The theory being explored is that if a kayaker can increase the time between respirations (by holding his breath or breathing very slowly), his emergency air will last longer, increasing his chance for self-rescue, or rescue by others.

Are there any MD's, or other knowledgeable divers, that can comment on the chance of air embolism in 3-5 feet of water. My layman's thinking tells me that unless your lungs are completely full, the chance of air expansion sufficient to cause an embolism is pretty low in 3-5 feet of water. How about ten feet of water?

Thanks in advance for any constructive comments.​

 

[Duke Dive Medicine]

I can definitely see the utility of this idea. There would be a risk of gas embolism, even in relatively shallow water, but it would probably be outweighed by the risk of drowning without supplemental air. I think it would take a pretty clear-headed individual to have the presence of mind to deploy his/her emergency air then extricate himself/herself, all the while being mindful of breathing. I know of one case for sure where it would have been useful; we helped NatGeo with a documentary on this gentleman: 7 minutes without air: Surviving under white water - WTOP.com

Best regards,
DDM

 

[ewq]

Hi Dive Kayak,
Interesting post.
Couple of points for consideration:

1. The risk of (pulmonary) barotrauma and resulting Arterial Gas Embolism from air entering torn (pulmonary) capillaries is actually greatest in shallow water/closer to the surface rather than deep water.
-Examples:
A) When surfacing from 10m underwater, pressure changes from 2ATM to 1ATM which results in a doubling of gas volume
B) When ascending from 40m to 30m underwater, pressure changes from 5ATM to 4ATM which results in an increase in gas volume of only 25% (as compared to 100%)

This is as opposed to Decompression Sickness where dissolved inert gas/nitrogen bubbles out when supersaturation occurs after ascent.
If your max depth is going to be no more than 10 feet for a few minutes, you will have no risk of DCS from supersaturation

-Considering pressure changes and barotrauma leading to AGE, if your anticipated maximum depth is no more than 10 feet, that will lead to only a 0.33ATM change in pressure and 33% increase in gas volume.
-in a capsize situation where a kayaker may be trapped underwater, or under his kayak shell (am I assuming your scenario correctly?), the said kayaker is most likely going to be in a state of panic. Most individuals respond to panic by taking rapid shallow breaths (increased respiratory rate but smaller tidal volumes) instead of long deep breaths.
>hence, in a non-fully expanded lung a 33% increase in gas/lung volume should not lead to significant problems.

I personally do not forsee any major problems with Emergency Air for this application from a theoretical point of view as such

2. Emergency Air is used in other similar applications
-It was part of my Helicopter Underwater Escape Training course where all flight crew have a STASS (Short Term Air Supply System) Bottle attached to their flight/life jacket. (I am also a rescue diver so my experience with SCUBA is much more than the 15 min introduction to STASS Bottles during my HUET course)
-A sinking helicopter (that ditched into a water body) may obviously reach depths much greater than 10 feet, yet they never bothered to cover any aspects of barotrauma or air embolism for the trainees
>we were taught to use the STASS to continue breathing underwater(amongst many other things). This then increased available time to locate the exit of the sinking helicopter and effect an escape.
>a controlled "AAHHHH" or steady exhalation stream on ascent was not taught during the HUET course unlike what is taught during CESA sessions for Open Water Scuba Courses
>this is probably an intentional course design as the risk of drowning if one does not escape successfully is probably much worse than the risk of air embolism/barotrauma. In a panic situation, the individual should not be overloaded with too many tasks.
>though the depths involved may be different, I believe DDM's point still holds true in this case. The risk of drowning is still the same whether it's 10 feet or 100feet.

You will probably need to explore more and think about how emergency air may benefit the trapped kayaker in the situations you are anticipating.
From your brief description (and some personal assumptions), I do not personally see any big risks of air embolism with reasons as above.

Perhaps you could describe more about the exact scenarios/situations where you think emergency air may be beneficial as well as "worse case scenarios".
-we may perhaps be able to advise better.

Cheers!