Rebreathers and Full Face Masks

[ShoalDiverSA]

Hi,

I watched the movie The Cave a few nights ago, and the obvious voice-overs during the diving sequences got me thinking.

They are diving with rebreathers, but the fact that they have mouthpieces precludes them from using a (standard) electronic communications system. This is surely also the case where rebreathers are used for expedition dives similar to this.

One solution seems to be to attach a FFM to a rebreather(?). I was wondering whether this has been tried in the past, or if it is not even theoretically viable due to safety or practical concerns? Is this option merely excluded as it creates further possible failure modes?

One of the concerns may be the flow characteristics of the air through the mask leading to poor/unpredictable recycling of air through the breathing loop. Another may be that the loss of a FFM versus a conventional mask would result in water ingress into the breathing loop.

Other than a FFM, what other techniques are used during expedition dives on rebreathers for communication (other than hand signals)?

I was just wondering about this, came up with nothing through the search feature, and thought I would put it to the rebreather gurus!

Cheers,

Andrew

 

[caveseeker7]

I watched the movie The Cave a few nights ago, and the obvious voice-overs during the diving sequences got me thinking.

Andrew, for movie productions voice-over is indeed the choice of adding conversations UW.
There are however UW comm systems like the 2010 from Ocean Technology Systems thant can be plugged into UW video housings and allow actual communications to be recorded.

They are diving with rebreathers, but the fact that they have mouthpieces precludes them from using a (standard) electronic communications system. This is surely also the case where rebreathers are used for expedition dives similar to this.

If you have a look at OTS' webseite/catalog you'll find pictures of Dräger LAR V rebreather (and MK15.5 I believe) where the microphone is actually integrated into the RB's DSV. Much harder to actually speak and understand, but good enough for short signals.

One solution seems to be to attach a FFM to a rebreather(?). I was wondering whether this has been tried in the past, or if it is not even theoretically viable due to safety or practical concerns? Is this option merely excluded as it creates further possible failure modes?

For decades the Carleton Technologies MK16 has been the mainstay of the US and other navies, and has been in use with FFMs. Either adapted Interspiro AGA masks or lately Kirby-Morgan M48 Supermasks. Dräger in Germany builds the Nova FFM in a rebreather version available for all their military and civilian rebreathers, as well as Closed Circuit Research's Ouroboros.

If you ever watch Deep Sea Detectives, you'll see the K-M M48 FFM hooked up to Kohler's Evolution CCR and Chatterton's Ouroboros.

One of the concerns may be the flow characteristics of the air through the mask leading to poor/unpredictable recycling of air through the breathing loop.

Depends on the mask. Different designs have a different gas flow path. The M48 was designed for RB use, as are above mentioned Dräger or the Divematics Widolf FFM. For masks like the AGA or Poseidon conversion kits are available.

Generally speaking, FFMs for use with rebreathers have a bite piece inside the mask to reduce dead space/CO2 buildup.

Another may be that the loss of a FFM versus a conventional mask would result in water ingress into the breathing loop.

Loosing a FFM is less likely to happen as they usually are held in place by 4 or 6 straps. Much harder to get knocked of your face. They're also attached to the rebreather (and second stage in some cases), so loosing them is rather unlikely.

They still have DSVs to close the loop of, and likely are equiped with Bail Out Valves, DSVs that have an open circuit second stage build into it. When the loop is closed, the second stage can be used with the same mouthpiece.

Other than a FFM, what other techniques are used during expedition dives on rebreathers for communication (other than hand signals)?

In caves, light signals are much more common than comm systems.

 

[ShoalDiverSA]

caveseeker7,

Thank you for taking the time to give me such a comprehensive answer. I appreciate it and you have certainly cleared up my questions. I was pretty certain that someone must have tried hooking a FFM to a rebreather - particularly for expedition (or military as you have mentioned) purposes.

I am going to do some reading on the equipment you have cited.

Thanks again!

Andrew

 

[caveseeker7]

You're welcome.

I already posted the link to OTS, they build the comms and are dealers for most FFMs. Divematics USA is also worth a look, they make RB conversion kits for FFMs, BOVs and the Widolf. If you follow the link in my signature and head for the library and gallery, RB Acessories, you'll find some articles and plenty of pictures on the subject.

 

[SA-Diver]

Andrew

I was going to answer until I read caveseeker's reply.

Hijack begins{}

I will be in your part of the ocean from Wednesday till Monday next week.
Will PM you my mobile #. Maybe we can hook up for a dive or a beer.

Kobus

Hijack ends{}

 

[ShoalDiverSA]

Excellent!

If my stuffy head clears up, a dive it will be. [And no, I don't normally speak like Yoda].

Cheers,

Andrew

 

[danielswaite]

Hollis PRISM 2 Rebreather has a Kirby Morgan MOD-1 FFM with BOV and Scuba POD Options, which I own both PODS. MOD-1 has a Comms Package.

 

[Enevoldsen]

SF2, GUE set up, Kirby Morgan mod-1 with Golem Gear BOV. Love it

 

[Haaginheimer]

I used a meg with a dsv and a side regulator as a MAV/ADV for dil add on a panorama nova and loved it.