What is the primary objective of pre-breathing a manual CCR?

[fullytek]

Just spitballing here, but I thought the primary objective was to avoid death.

This

 

[lostsheep]

So hear is an example of an experiment that supports the original assumption that a pre-breath may alert the diver to an issue with the scrubber. I think it's funny how 1 article produced by a questionable source is taken as gospel and so many divers are quick to use that as an excuse for skipping a critical safety check.

Pray tell, what do you find questionable about a peer reviewed paper published in a professional journal by actual experts?

Mitchell has done more to progress our knowledge using analytical methods than most of us combined ever will; if you’re going to come out swinging like that you better make it good.

ETA: the conclusion is not that one shouldn’t do a pre-breathe , the conclusion drawn is that a 5 minute pre breath is an insensitive test of co2 scrubber function.

 

[fullytek]

Did anyone bother to actually read the study?
I like the part whare the majority of contents detected a missing scrubber.

Also note durring the summary that the author clearly stated that they are not advocating for the omission of pre breathing.

But the inexperienced experts on scuba board have cherry picked parts of the study and used them as justification for skipping a critical step that they were trained to do.


So perhaps the study isn't questionable but the sloppy interpretation definitely is.

 

[lostsheep]

So perhaps the study isn't questionable but the sloppy interpretation definitely is.

Your complete retraction is duly noted.

 

[Snusmumrik]

The flowmeter is part of our assembly checks. Even so I have orifice problems non the less. (Use a .003 orifice so it doesn't take much)

So, there's a benefit for needle valves vs orifices. Me use needle.

 

[Geo7]

Quoting a 2014 post by Dr Mitchell:

"No subjects terminated when a normal scrubber was in place (as you would expect).

25% of subjects did not terminate the prebreathe when there was no scrubber present despite dramatic changes in the physiological parameters.

90% of subjects did not terminate the prebreathe in the partial failure condition despite significant CO2 break through and some changes in the physiological parameters."

I read this as a 75% chance to detect gross mistakes related to scrubber function (including flapper valves?), and 10% chance to detect a minor breakthrough (with major effects during the dive). My conclusion: I am doing a pre-breathe, but don't trust that test blindly.

(edit: IMHO that was an eye-opening study and important contribution to our community, and did not suggest we should skip the pre-breathe. The beauty of science is that the data are there for anyone to make up their own mind.)

 

[KBlack]

Ok while it is recognised by research of experts like Simon Mitchell that a 5 minute pre breath MAY NOT detect scrubber BREAKTHROUGH it is also recognised that it MAY detect scrubber bypass. I remember years ago as a new CCR diver feeling unwell during a pre-breath. I incorrectly put it down to seasickness however it cleared as soon as I went off the loop. On further inspection my unit was missing a critical O-Ring that was allowing scrubber bypass.

I teach this lesson (and others) to my CCR students. Investing 5 minutes of time on doing a proper pre-breath confirming proper operation of your life support unit is essential. If in doubt pre-breath longer. Over the years I have seen the pre-breath detect may problems that are better fixed on the surface than under water on both mechanical and electronic units.

 

[fullytek]

Your complete retraction is duly noted.

It's not a retraction. People skipping the pre breathe are stupid and statistically more likely to die

What else are they skipping? Like the rebreather praticily annalizes the gas for you so although you are trained to do it you all know its really just a waste of time on a hot day.

 

[lostsheep]

It's not a retraction. People skipping the pre breathe are stupid and statistically more likely to die

What else are they skipping? Like the rebreather praticily annalizes the gas for you so although you are trained to do it you all know its really just a waste of time on a hot day.

Alright let me try this again because you seem to not understand my objection to your post.

I prebreathe my unit before every dive in addition to a full flow check and monitoring o2 stability.

I called you out for calling a knowledgeable , reputable, and respected member of the science community, the diving community , and the SB community, “questionable.”

Calling a paper “questionable” without a properly formatted rebuttal detailing methods, data , references and citations does not lend much credibility to your claims, quite the opposite.

I do not refute the claims you have made in this thread but I do reject your methods as they are fundamentally flawed.

I quoted your retraction , discerning readers can make up their own minds.

Edit: I bet Mitchell would welcome you questioning his work if done in a professional manner ; that is why so many of us respect him and his conclusions as it is the mark of an actual scientist and not some inexperienced SB expert. Those are your words not mine and I am NOT calling your expertise into question as I know little to nothing about you.

 

[fullytek]

Alright let me try this again because you seem to not understand my objection to your post.

I prebreathe my unit before every dive in addition to a full flow check and monitoring o2 stability.

I called you out for calling a knowledgeable , reputable, and respected member of the science community, the diving community , and the SB community, “questionable.”

Calling a paper “questionable” without a properly formatted rebuttal detailing methods, data , references and citations does not lend much credibility to your claims, quite the opposite.

I do not refute the claims you have made in this thread but I do reject your methods as they are fundamentally flawed.

I quoted your retraction , discerning readers can make up their own minds.

I concider the study questionable because despite the data, somehow people interpret it as prebreaths are unnessasary. So clearly its poorly written. See part of science is defending your results and presenting them in such a way that even the dumbest amongst will agree with the findings and reccomendations. In this case the author failed to convince a lot of people.