Thoughts about the EEBD hood without exhaust valve

[mando]

I posted this on the exit bag and inert gas thread, but i think it is more relevant in this forum.


I bought two EEBD (Emergency Escape Breathing Devices) hoods, but I discovered they didn't have an exhalation valve. I initially assumed, partly due to everything I read on this forum, that a hood with an exhalation valve is a better solution.
However, I have since changed my mind.
To begin with, I have personal experience with forced air masks where the overpressure ensures that no air from outside can flow inwards.
I also read in the PPH handbook that various masks are recommended, all without an exhalation valve.

All these bags, the exit bag, eebd masks, and several commercially available masks like 3M versaflow,etc. are also not equipped with an exhalation valve.
They are all suitable for use, as long as there is some space at the bottom of the neck seal, and since CO2 is heavier than nitrogen, it will naturally sink downwards. I would be keen to hear what others think about this.
PPH:

"The bag will be filled with nitrogen/argon/helium before you pull it down over your head. When you pull it down, you will start to exhale CO2. The heavier CO2 will be purged down to the bottom of the bag by the lighter nitrogen, and out the small gap in the bottom(there'll be a tube going into the bag). You will be unconscious in 30-60 seconds. Any CO2 that hasn't been purged out the bottom won't be enough to cause hypercapnia (excessive CO2 in the lungs). You will be inhaling the inert gas."

I know AI gives some weird answers sometimes, but when I fed this query to Gemini I got the following response :

EEBD Hoods: With or Without an Exhalation Valve?
Experience and Practice

* Many EEBD hoods (Emergency Escape Breathing Devices) are indeed designed without an exhalation valve.
* The reason for this: these hoods work with a constant overpressure of supplied breathing air from a cylinder.
This prevents contaminated outside air from leaking in, because the overpressure pushes air (and possibly CO₂) outwards naturally through the openings at the bottom of the neck seal.

Exhalation Valve: Necessary or Not?
* An exhalation valve is not necessary with overpressure EEBDs, because the overpressure itself ensures the expulsion of exhaled air and prevents contaminants from entering.
* The absence of a valve is therefore not a safety risk, as long as the hood fits well and there is space at the bottom of the neck for exhaled air to escape.

CO₂ and Nitrogen
* Your observation is correct: CO₂ is heavier than nitrogen and will sink downwards through the openings at the bottom of the hood. This happens naturally due to the overpressure and gravity, as long as the hood does not completely seal airtight at the bottom.
Conclusion
* EEBDs without an exhalation valve are safe and effective according to international standards (such as SOLAS and FSS code), provided they are used correctly and the neck seal does not completely seal off.
* Your experience with forced air masks aligns with the design principle of these hoods.

In short: An exhalation valve is not necessary with overpressure EEBDs, and many approved models do not have one.
Your conclusion is therefore broadly supported by practice, regulations, and design[1].

I would like to hear your thoughts

 

[k1w1]

As long as the elastic is snug to the neck you will be fine. Sure my chinese yellow hood has an exhalation valve, but the ori-nasal cup is made of the hardest rubber so Ill be adding an external strap to hold it closer to my face. A few of the Chinese hoods really could have been made with silicone inner cups for an easier fit. Which brings me back to your enquiry. You are essentially using an exit bag, it will be inflateable, where mine is not, so you can prime it. All of us are just doing what we can and hoping for the best. The likelihood should be considered that Vizzy used SN in addition to gas. Bless him, he was a nice guy.

 

[mando]

So I believe the consensus should be that exhalation valves are actually not necessary at all ln EEBD hoods.

 

[locked*n*loaded]

Did either Vizzy's or GasMonkey's setups use an exhalation valve (I'm too lazy to go look)? If so, that's what I would go with then.

 

[mando]

Vizzy ,'s had a exhalation valve, Gasmonkey had a SCBA setup.
Although i respect the knowledge of these guys, ( i exchanged pm's with Gasmonkey regarding SCBA ), i fail to see why one could not argue the merits of needing a valve.

 

[JonCody]

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