FFM advice

Shas · 18th May 2006, 00:21

We have been asked questions recently about using FFMs with the PRISM, this is what Peter had to say.

An opinion on diving Rebreathers with Full Face Mask – Peter F. Readey

In shallow water a standard Full Face Mask (FFM) with a low dead space or oral nasal is appropriate for communications and for some cold-water applications with communications. It has been our experience if an oral nasal type system has a weeping seal (nicked seal, debris etc), the user often does not recognize slow water ingress into the system, which can result in serious flood in the case of inversion, or any significant change in body position.

Furthermore, a standard, open-circuit type, oral nasal design has proven to be inappropriate for deep-water heavy exertion diving leading to considerable problems of CO2 build-up.

A “T-bit” design alleviates some of these problems to a large extentbut does not resolve the large air volume typically associated with a FFM. On some systems it is not possible to completely clear the FFM with a single lungful of gas. Kirby Morgan Super Mask with Rebreather pod and ScubaPro low volume masks are a good combination of T-bit style FFM, with low dead space designs.

Although the T-bit FFM assemblies with the lowest volume will function at depth, bailout to open circuit with a switchover block are often problematic as the regulator orientation, being far away from the users mouth has hydrostatic issues ranging from positional free flow to extremely high inhalation resistance at a given body position. Not to mention single point failure at the regulator.

A retaining strap attached to a neutrally buoyant mouthpiece has proved acceptable in many extreme environments.

This is a contentious issue as there is not a single or simple solution to the problem. Although some of our customers use a FFM with the PRISM™, Steam Machines, Inc does not recommend the use of a full face mask with less than 100 hrs of Rebreather specific dive time and only for specific application with extensive, appropriate training for that purpose.

Bubble Boy · 18th May 2006, 02:42

Hi Shas,

Thanks for the input on FFMs, please could you elaborate on your thoughts around OC/DSV mouthpieces?

18th May 2006, 00:21	#1 (permalink)
Shas New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Mar 2005 Location: Lebanon, TN Posts: 12	FFM advice We have been asked questions recently about using FFMs with the PRISM, this is what Peter had to say. An opinion on diving Rebreathers with Full Face Mask – Peter F. Readey In shallow water a standard Full Face Mask (FFM) with a low dead space or oral nasal is appropriate for communications and for some cold-water applications with communications. It has been our experience if an oral nasal type system has a weeping seal (nicked seal, debris etc), the user often does not recognize slow water ingress into the system, which can result in serious flood in the case of inversion, or any significant change in body position. Furthermore, a standard, open-circuit type, oral nasal design has proven to be inappropriate for deep-water heavy exertion diving leading to considerable problems of CO2 build-up. A “T-bit” design alleviates some of these problems to a large extentbut does not resolve the large air volume typically associated with a FFM. On some systems it is not possible to completely clear the FFM with a single lungful of gas. Kirby Morgan Super Mask with Rebreather pod and ScubaPro low volume masks are a good combination of T-bit style FFM, with low dead space designs. Although the T-bit FFM assemblies with the lowest volume will function at depth, bailout to open circuit with a switchover block are often problematic as the regulator orientation, being far away from the users mouth has hydrostatic issues ranging from positional free flow to extremely high inhalation resistance at a given body position. Not to mention single point failure at the regulator. A retaining strap attached to a neutrally buoyant mouthpiece has proved acceptable in many extreme environments. This is a contentious issue as there is not a single or simple solution to the problem. Although some of our customers use a FFM with the PRISM™, Steam Machines, Inc does not recommend the use of a full face mask with less than 100 hrs of Rebreather specific dive time and only for specific application with extensive, appropriate training for that purpose.
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18th May 2006, 02:42	#2 (permalink)
Bubble Boy PRISMs are kewl Current Rebreather/s: Prism Topaz MK 15.X Other CCR Dolphin Ray Other Rebreather/s: Other CCR Dolphin Ray Join Date: Mar 2005 Location: Sydney Australia Posts: 132	Re: FFM advice Hi Shas, Thanks for the input on FFMs, please could you elaborate on your thoughts around OC/DSV mouthpieces?
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