What makes a unit safe?

Mark Chase said:
Ability to connect off board gas is a bonus feature and I am happy with the BOV having access to off board gas I can use in the loop
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Mark, more than one way to do this. Probably worth a separate thread almost, but I have certainly seen some offboard solutions that do not seem safe and appear to not provide sufficient gas flow.... For instance the APD solution is only rated to work to 50m! and most others are unknown? Pointless having a BOV with good WOB if the offboard QC solution kills it.....
I am very interested to see what Poseidon have come up with for their deep test divers doing 150m dives on the Seven?

Mark Chase said:
However I have to admit that i am liking the idea of having my needle valve on my ECCR. If the Eccr fails I can just run the needle valve. Very useful. If required the needle valve can be left off or very low so the unit runs ECCR all the time. Simple mechanical device. The kind I like
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Mark, I understand the un-safe bit about them is that under mechanical shock - like being banged by a stage at 100m for example - they can inject a slug of O2, due to movement of the needle. Just something to watch for!

Doole said:
Well rumours are that the design of the poseidon bov, killed a guy who acted very wrong.
So I don't think it's such a great example
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Doole, can you point to on which incident the design of the Poseidon BOV was a factor?
http://mkvi.poseidon.com/downloads/Rebreather_Diver_Safety_White_Paper.pdf
http://mkvi.poseidon.com/downloads/To_whom_it_may_concern_2013-04-26.pdf
http://mkvi.poseidon.com/downloads/In_regards_to_the_South_African_fatality.pdf
http://mkvi.poseidon.com/downloads/Accident_information_2013-03-22.pdf
http://mkvi.poseidon.com/downloads/Accident_Report_IR-2010-05-31-1.pdf
http://mkvi.poseidon.com/downloads/Safety_bulletin 20090625-1.pdf

Manufacturers publishing accident analysis probably also helps make a safe unit!

rjack said:
As the owner of 2 Newfoundland dogs (if you don't know the breed they are hairy!) any unit which is so sensitive to hair is "unsafe" to me. Sorry, but being required to assemble a unit in a veritable clean room is a really foolish assumption which should be engineered out through better sealing surface/o-ring design.
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Nice dogs. Surely identifying if that has been considered in the design is just something to read up on from the respective rebreathers published FMECA! For example:
Apoc http://www.deeplife.co.uk/or_fmeca.php
Meg http://www.megccr.com/rebreather-products/
 
As said this is a rumour.

But the story goes like this. Diver goes down to about 30 meters with the unit in OC mode, figures out that something is wrong and switches to CC mode.
Due to the differential pressure in the loop, his tongue gets sucked in to the mouthpiece and seals tight so that air can´t pass from the ADV part.

As said this is a rumour but i think the source is pretty reliable.
 
Brad_Horn said:
Inversely proportional works better for me!
The simpler something is to use as a system, the less there is to go wrong or the easier to see it has gone wrong.
Take the Poseidon BOV: it combines a DSV, ADV and second stage. So compared to having those parts individually distributed around the rb you now reduce the number of hoses, o-rings and separate parts that could have a failure, reduce the total bulk and weight of the rig and everything is to hand in one place in case of an issue! What is less complex for the diver? What engineers 'stupid' out more!

If you had said "complexity of the design and testing behind the unit is directly proportional.....", now that is something different. Sometimes the simplest things are the hardest to design....

I could give you my CCR field stripped as a box of bits. It might take you a while to figure out where everything goes, but there is only one way you could put it together that allows it to be dived!
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I have not seen the Poseidon BOV, and expect that it is very well done, but it is everything I try to avoid with my dive gear.

It is very complex. Combining all these functions into one gizmo is the opposite of redundancy. Maintenance and service are most likely to be very involved. Generally items that are more complex are less likely to be reliable than items that are less complex. This is particularly the case in the marine environment where we deal with salt water and liberal amounts of goo. Throw in some electricity and every thing is a battery, like it or not.

In terms of functional appropriateness, the cumulative effect of how we use these things matters a lot. Having bog simple single purpose items for the above noted functions means, they are very easy to keep going, and as there is almost no ambiguity as what the problem is when there is a fault, the fault is easy to fix.

For a short while I had everything connected to everything on my rig. Gas from here could be gas to there etc. Then some minor fizzing and I decided to go back to basic principles. I have had a total failure on one side of a side mount rig, but I am still here as the fix was so simple, go to the other side.

Part of what makes my set up safe is that mostly the parts just have to be clean to function well. When I need to fiddle something I require few tools or expertise.

I sometimes get to dive in remote places and at the back of caves. The ability to simply fix or bodge up bits is very important to me. Too clever by half is the way I view some of the elaborate kit out there.

Peter
 
I think as many people here, what makes a unit safe is the head that dives it...





Sent from my HH using stamps...
 
Brad_Horn said:
Mark, I understand the un-safe bit about them is that under mechanical shock - like being banged by a stage at 100m for example - they can inject a slug of O2, due to movement of the needle. Just something to watch for!
Click to expand...


Thats right up there with being attacked by man eating shark during a dive

Possable but very very unlikley and would require a specific set of circumstance.

I have had free flow 02 into the loob via failed first stages and failed solinoids. A failed needle valve is right up there and thats why I have an inline isolator on my 02 feed to manula inject/ needle valve

ATB

Mark
 
Brad_Horn said:
Mark, more than one way to do this. Probably worth a separate thread almost, but I have certainly seen some offboard solutions that do not seem safe and appear to not provide sufficient gas flow.... For instance the APD solution is only rated to work to 50m! and most others are unknown? Pointless having a BOV with good WOB if the offboard QC solution kills it.....
I am very interested to see what Poseidon have come up with for their deep test divers doing 150m dives on the Seven?
Click to expand...


I ment off board for the unit

Like the Inspo counterlungs with off board attachement so I could conect my bailuts to the unit with a simple suit hose.

I am not a fan of gas blocks

I only have my BOV conected to a single OC off board gas and at switch id go full OC

If I needed to SCR my bailouts I can unscrew the BOV feed and screw on off board gas as I keep the regs loose at the hose joint

Thats plan Z -1

ATB

Mark
 
Gordon dived the KISS without any o-rings save the display pods and wasn't forced to call the dive cause of a flood. A very simple and well made unit.

My idea of a safe unit is one that doesn't make decisions for me but just provides information. As the old axiom goes, a THINKING diver is a SAFE diver

Cam
 
Very true.
Cameron said:
Gordon dived the KISS without any o-rings save the display pods and wasn't forced to call the dive cause of a flood. A very simple and well made unit.

My idea of a safe unit is one that doesn't make decisions for me but just provides information. As the old axiom goes, a THINKING diver is a SAFE diver

Cam
Click to expand...
 
There is not such thing as a safe ccr.

As others pointed out, key word here is simplicity, besides diver training and attention.

Simplicity makes the machine less prone to failure AND in most cases if something goes wrong, it is obvious for the diver almost im the moment that happens. And probably he/she will know how to react because a simple unit needs, aside of periodic diver monitoring, a diver that can handle it.
 
andrespp said:
There is not such thing as a safe ccr.

As others pointed out, key word here is simplicity, besides diver training and attention.

Simplicity makes the machine less prone to failure AND in most cases if something goes wrong, it is obvious for the diver almost im the moment that happens. And probably he/she will know how to react because a simple unit needs, aside of periodic diver monitoring, a diver that can handle it.
Click to expand...

Very much so
 
I think that the only thing that makes a unit safe, is the diver him/herself.

There's an olde saying in IT land Build a System Only a Fool can't use, and only a fool will use it. :)
 
megdiver792 said:
I think that the only thing that makes a unit safe, is the diver him/herself.

There's an olde saying in IT land Build a System Only a Fool can't use, and only a fool will use it. :)
Click to expand...

True. I believe the diver is very important but alerting cues are great for awareness of the diver. I like the vibrating DIVA and OLED screens that stay lite all the time even in dark environments.

There are some things about a rebreather other than the diver which I'm sure you would agree with. Adequate batteries for electronics/monitors. Etc.

I would say the diver is the most important piece of the kit but others help.

Garth


Sent from my iPhone using Tapatalk
 
the only safe unit is the one that does not get used!


However we all have way to reduce some of the associated risks with using it but making mods, carrying bailouts etc.
 
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