Dry Hypoxia Training for Rebreather Divers

[Dave Sutton]

Howdy,

Just had a question come back to me by one of the manufacturers of a rig that I teach regarding a question on conducting optional dry-environment hypoxia training for students. Essentially the question regards the "ethics" for lack of a better term of allowing a closely monitored student to sit on the couch and breathe from an ever-decreasing PP02 loop while doing simple word and math problems until the first signs of hypoxia are noted.

This was done to me in training when I first qualified on rebreathers, and is done in a slightly different venue to me annually as part of my high altitude physiology training for my work as a test pilot. In both cases I felt/feel that the training is some of the most valuable that I have ever had. In fact, I can say without hesitation that I am alive as a result, having intercepted a hypoxia event at altitude in a jet that would no doubt have caused loss of conciousness within another minute, in a situation where I would have certainly crashed and died as a result.

Hypoxia training is conducted for aviation in hypobaric chambers, essentially a low pressure chamber where the students are exposed to low altitude conditons in a controlled environment, and are taught their personal hypoxia symptoms. Many become unconcious... and are simply put back on 02 by the attendant. This is part and parcel of becoming a military pilot, and course are offered by several organizations to civil pilots as well.

One of those other civil agencies, FlightSafety International, uses a ROBS system in flight simulators, (Reduced Oxygen Breathing System), which uses reduced 02 nitrox to simulate high altitude for pilots flying a simulator. In a different walk of my life, I managed this system for the FSI center where I instructed for 12 years, and we put over 1600 pilots thru the course under my direction. The US Navy now uses the same system, and I had an opportunity to participate as a student myself last week. The ROBS uses air and PP02 sensors and a solenoid (sound familiar?) to inject NITROGEN into the loop to maintain selectable LOW PP02, essentially a rebreather turned inside out. This training and equipment is well established in aviation training.

The question comes now to use of a rebreather in a DRY (not wet) environment to induce clinical hypoxia, in order to teach divers the sinister and very subtle signs of hypoxia. The method is to turn off the 02, and while being VERY carefully monitored to breathe the loop while safely seated and while NEVER using a gag strap, etc (in fact we do not let the student even place the mouth-bits of a mouthpiece inside the lips), and then to let them do word games and math questions until they first see symptoms of hypoxia. At that time they are recovered by dropping out the mouthpiece. This has been done 1000's of times and if monitored correctly is a safe and viable method of training.

Some links to other information:

This is the course that I ran for many years:

Altitude Chambers Don't Cut It For Pilot Training - Jetwhine - Jetwhine: Aviation Buzz and Bold Opinion

This is a civil-access chamber course:

High-Altitude Chamber Course: Why it is a Must for Any Pilot | Coast Flight Training | iflycoast

More on the ROBS system:

Training to Survive Hypoxia Without Actually Getting It - Office of Naval Research


I'm interested to hear how many people have had this done in training, have tried it at home (DO NOT!, but please anonomously let us know via the poll), how many never thought about it, how many would like to take such a training event, and how many say "No Way Jose'" .


Discussion?


Dave

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[matt]

Each to their own, but I'd rather the training focused on monitoring PPO2.

I'm not fully sure that a sat-on-the-couch experience is close enough to underwater conditions to be so valuable.

I never did it (either voluntary or otherwise) so I've no practical experience, for which I am grateful.

Matt.

 

[Simon A]

The realy scary thing about hypoxia training is when you "come round" and don't believe you were unconciouss untill they show you it on film...
Simon A

 

[Dave Sutton]

It's interesting to me to note that it's a routine training event for military pilots and an optional but highly useful and universally recognized training event for civil pilots, but that RB divers, who deal with the possibility daily, are not yet coded to think that this is a routine training opportunity.


The really scary thing after exposure to the event is how normal it all feels. That's the takeaway.... it's "pleasant". That and the fact that you CAN often (but not always) detect your symptoms in time to bail out if you have learned your own symptoms. In the aviation training, "bailing out" means putting your own mask on in the chamber before you need external assistance.


(and having actually been waterboarded in another school... that's not even a germane comparison).

I can't imagine any rebreather diver not seeing the value in this, thus my poll. It's a curious cultural difference between aviation and diving training. The cost for the ROBS course at FlightSafety was about $5000.... and we had flight departments lined up with a waiting list.



Dave

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[Dave Sutton]

The realy scary thing about hypoxia training is when you "come round" and don't believe you were unconciouss untill they show you it on film...
Simon A

Precisely. It's not an upsetting drill to undergo at all.

Simon, can you elaborate from any experience?


Dave

 

[GLOC]

Like Dave, I undertook this part of aviation medicine training and I think it is a very good idea. However, doing it in a controlled environment with a formal risk assessment is very different to letting any 'tom, dick and harry' instructor do it. That isn't meant to be too derogatory but how do you 'police' such an activity knowing some of the instructors that are out there who don't provide proper and robust training.

Regards

 

[Dave Sutton]

^^^ To GLOC

(which in fact describes another hypoxia-induced altered state: G- Induced Loss of Conciousness, = GLOC)


A: Fill out the darned poll, dammit.. I know I'm not the only one who went thru it in aviation physio, but there's only ONE poll answer here...:brickwall

and

B: The methodology for use by the RB training community is what I am trying to figure out. I use the same methodology that I used when using the RBS system at FlightSafety as an Instructor. I also recognize that this is a propriatary course and that it's not completely suitable for use by a lay-instructor who does not have the same background.

With that said, after teaching the course for 100's and 100's of pilots, and having passed out or at least greyed out flying fighters literlly dozens of times (including once on Monday ) it's a remarkably safe thing to do if it's monitored correctly.


There's plenty of bad basic rebreather training going on too... policing things, well... it's impossible.



Dave

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[JacobT]

Sounds like something I would love to try.
But you would seriously need to trust the instructor, with this kind of "experiment" you are quite literally putting your life in the instructors hands, much more so than when "just" diving I think....

-jacob

Sent from my HTC Desire using Tapatalk 2

 

[erikradstrom]

Dave, if you do this the way you wrote in the beginning. The mouthpiece so that it will fall out if you pass out it will fall out of your mouth.

How big is the risk? You pass out without the mouthpiece and then what? You just wake up when you took a few breaths or do you need assistance?

 

[Johan Isaksson]

Hypoxia to the level of passing out on dry land is unlikely to cause any damage, unless you manage to hurt yourself falling. You will not stop breathing when you pass out so as long as it's monitored the risks should be minimal.

Pre-existing conditions could make it a tad more dangerous however and in the case of pilots undergoing this sort of training I'm assuming that they'll have been through fairly thorough medicals to screen for ischaemic heart disease and similar things.

 

[Dave Sutton]

Actually, in the USA, Private Pilots with a 3rd class medical are accepted for the courses on a "space available" basis by the military chambers. A 3rd class is a "fog a mirror" medical, meaning that it's just a basic health check. I've been in the chamber with 70 year olds.

One thing to note is that if you go past the point of self-rescue, you will not remember the symptoms, and the entire excercise is lost (to the subject). The bystanders are usually amused. The goal is to self rescue so you can remember the symptoms after the fact.


Dave

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[Dave Sutton]

Dave, if you do this the way you wrote in the beginning. The mouthpiece so that it will fall out if you pass out it will fall out of your mouth.

How big is the risk? You pass out without the mouthpiece and then what? You just wake up when you took a few breaths or do you need assistance?

First, we do this with 3-4 people present and we do not rely on gravity, we rely on self rescue backed up by three other people.

But, if you get past the point of self rescue, we grab off the loop and 5 seconds later you wake up and don't remember anything about it.

That's the terrifying part.... not feeling any distress.


When we have done this with divers (and when I have had it done to me), we spot one person in front of the subject, talking to them and assessing conciousness. Asking questions, asking them to draw a circle, then a box around it, then a star around that, etc. We get them off the loop before they are unable to assist themselves. We spot another person behind them to pull the loop up to break the cycle when appropriate. Usually we have 4 people present.

The ROBS system we used in flight training represented a cabin altitude of about 18,000, which gives a PP02 using air of about 0.10, which at rest for the average person gives a time of useful conciousness of about 20 minutes. During this period of slow onset, trainees are able to slowly see what is happening. In hypobaric chamber training we are routinely explosed to PP02's of 0.05, and have a TUC of about 3 minutes at rest. I've seen guys go funny after a minute, and one guy sitting there talking normally at 10 minutes as if there was nothing wrong with him. 0.05 is the absolute low limit I have even been exposed to in a couch-dive scenario. My own TUC there to self rescue without excercise is about 2 minutes, and at 3 minutes I am still responding to verbal questions but am unable to assist my own rescue.


See:

Time of useful consciousness - Wikipedia, the free encyclopedia


Just a data point: In the USA, 5 days a week, week after week after week, well over 1000 pilots are put into a chamber and taken to 0.05 PP02 for a training course, without any notable issues. At the base where I was flying last week, they ran 12 guys in the AM and 12 in the afternoon, for 5 days straight.


To be clear: This has never been a part of any sanctioned diving training course I have taught. It's always "friends gathered for advanced training". I'm trying to assess applicability to a more general enviroment.



Dave


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[erikradstrom]

Actually, in the USA, Private Pilots with a 3rd class medical are accepted for the courses on a "space available" basis by the military chambers. A 3rd class is a "fog a mirror" medical, meaning that it's just a basic health check. I've been in the chamber with 70 year olds.

One thing to note is that if you go past the point of self-rescue, you will not remember the symptoms, and the entire excercise is lost (to the subject). The bystanders are usually amused. The goal is to self rescue so you can remember the symptoms after the fact.


Dave

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Then I don´t see why its not a common practice during training. The only thing you get out of it knowledge how you body works and that can be bad

 

[PeterN]

I voted "no way" before reading Dave's explanation.

I would support the kind of session that Dave describes, but I doubt that the level of know how is generally available.

Peter

 

[erikradstrom]

I voted "no way" before reading Dave's explanation.

I would support the kind of session that Dave describes, but I doubt that the level of know how is generally available.

Peter

As I see it from reading both Johan and Daves answers the risks are so low that I would have no problem letting an instructur do it.

To be hones you put more trust in your instructor during a MOD 3 course dive then doing this.

 

[w ripley]

Dave, I'm curious what you think of what Kevin has done with the HH, giving it a safety override when the calculated average PO2 is 0.19 or less. Regardless of the mode, the solenoid starts firing at that point, the alarm lights start flashing, and the DIVA starts vibrating. I'ts pretty hard to ignore all of that going on at the same time.

I understand I'm asking about an electronic "safety" override, but I'm betting (my life) that the unit will recognize that I'm entering a hypoxic threshold before my body will.

I have had a CO2 hit on OC, but they tell me that not all CO2 hits have the same early symptoms. If it's the same with a hypoxic hit, in that you may or may not feel it coming, isn't a O2 sensor approach as valuable as what you are proposing?

 

[Dave Sutton]

Dave, I'm curious what you think of what Kevin has done with the HH, giving it a safety override when the calculated average PO2 is 0.19 or less.

Same thing a Shearwater controller does. Probably food for another thread. Essentially there is no "Off", it's just a system that recognizes "less than air PP02 by a smidge" and will keep things atmospheric if the diver goes dumb and does not change setpoint after closing up the rig. I'm not really sure it's an "underwater intercept the problem" mode, more a "I'm gonna keep you alive on the bench if you start your prebreathe without raising setpoint" mode.


Dave

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[w ripley]

. . . I'm not really sure it's an "underwater intercept the problem" mode, more a "I'm gonna keep you alive on the bench if you start your prebreathe without raising setpoint" mode.
Dave

What's the difference, if it triggers the solenoid to inject O2 and sounds the alarm - on land or underwater?

 

[Dave Sutton]

Short answer: Nothing, other than what scenario would trigger it:


(1): Loss of 02 underwater that is otherwise unrecognized by the diver. Running out of 02 underwater is about the only thing I can see that would trigger this.

(2): Failure to turn on system or raise setpoint when sitting on the deck that is otherwise unrecognized by the diver. Probably a more likely scenario.


Love to discuss this, let's start a thread if there is more hardware to discuss v/s the human pysiological training which is the focus of this thread.


Best,


Dave


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[matt]

That and the fact that you CAN often (but not always) detect your symptoms in time to bail out if you have learned your own symptoms.

I'd be concerned that people would use this detection as the trigger and become overly reliant on it.

I can't imagine any rebreather diver not seeing the value in this, thus my poll. It's a curious cultural difference between aviation and diving training. The cost for the ROBS course at FlightSafety was about $5000.... and we had flight departments lined up with a waiting list.

Indeed. Monster difference between regulated aviation industry and a recreational diver having a fun dive.

Certainly if I was offered the chance I would decline.

Matt.