Deep diving with a FFM

[DeepSeaExplorer]

CO2 retention is a potential issue with FFM, so is air consumption. Commercial divers FFMs with surface-supplied air to avoid these problems. Those same issues make them suboptimal for deep dives with SCUBA.

If you eventually decide to go tech, it’s a lot easier to switch to O2 for deco in regular SCUBA gear - assuming you can even find another tech diver willing to dive with someone in FFM.

 

[Akimbo]

Do you have any material on FFM and co2 retention?

There are too many variables to effectively quantify CO2 retention of a FFM. Military and commercial divers are trained to compensate for the added dead air space in an oral nasal mask compared to a mouthpiece by breathing deeper and ventilating the mask or hat.

As others have alluded to, greater dead air space inherent in an oral-nasal mask coupled to a demand regulator requires more gas exchange to dilute CO2. Valid reasons to consider a FFM include:

• The need for audio communications or recording. Wireless communications is far less reliable than hardwire used in surface supplied diving. It can also be a PITA to fit ear phones to FFMs used in recreational diving. Commercial FFMs have earphone pockets built into the attached hood:
  
  
• Cold and contaminated water, which is the main reason PSDs (Public Safety Divers) favor them.
• Deeper and/or long duration pure O2 in-water decompression where the risk of a convulsion is high. A rare example would be an IWR (In Water Recompression) treatment system that a trained and experienced team might consider in very remote locations. A whole lot more than just a FFM is involved though.
• Facial deformation or neurological disorders that make using a mouthpiece impractical — useful for divers with certain disabilities.
• Although it is rare, personal preference. There are pros and cons but the cons add up to a lot of complexity, especially when things go wrong.

 

[Nick_Radov]

The FFM creates a dead air space that does not get fully flushed on each ventilation cycle. That promotes some CO2 retention.

Bingo. For those who want the details, read this article.

Warkander DE, Lundgren CE. Dead space in the breathing apparatus; interaction with ventilation. Ergonomics. 1995 Sep;38(9):1745-58. doi: 10.1080/00140139508925224. PMID: 7671854.​

Dead space in the breathing apparatus; interaction with ventilation

Dead space in breathing apparatus may cause increased ventilation and/or CO2 retention. Interactions between ventilation and dead space were tested in the breathing apparatus of three divers: a ful...

doi.org

A FFM is suspected to have been one of several factors that contributed to the death of Jane Orenstein on a tech dive back in 1998.

Diver Death in Pompano B. Fl......"Murder on the IANTD Express" ---student killed by instructor

groups.google.com

 

[Fishdip]

Interesting read!

 

[Fishdip]

There are too many variables to effectively quantify CO2 retention of a FFM. Military and commercial divers are trained to compensate for the added dead air space in an oral nasal mask compared to a mouthpiece by breathing deeper and ventilating the mask or hat.

As others have alluded to, greater dead air space inherent in an oral-nasal mask coupled to a demand regulator requires more gas exchange to dilute CO2. Valid reasons to consider a FFM include:

• The need for audio communications or recording. Wireless communications is far less reliable than hardwire used in surface supplied diving. It can also be a PITA to fit ear phones to FFMs used in recreational diving. Commercial FFMs have earphone pockets built into the attached hood:
  View attachment 730252
• Cold and contaminated water, which is the main reason PSDs (Public Safety Divers) favor them.
• Deeper and/or long duration pure O2 in-water decompression where the risk of a convulsion is high. A rare example would be an IWR (In Water Recompression) treatment system that a trained and experienced team might consider in very remote locations. A whole lot more than just a FFM is involved though.
• Facial deformation or neurological disorders that make using a mouthpiece impractical — useful for divers with certain disabilities.
• Although it is rare, personal preference. There are pros and cons but the cons add up to a lot of complexity, especially when things go wrong.

Thank for the info!

 

[SlugLife]

So been reading a bunch about deep diving 130+ and I noticed a trend or lack of using a full face mask. Why is this? Would a FFM not be safer option due to risk of blacking out and such?

I don't know what people are blacking out from, and ideally you REALLY don't want that happening underwater. However, some people (myself included) make a regulator-necklace out of bungie, which can be tightened to prevent the regulator from falling out of your mouth, or drifting off if knocked out of your mouth.

FFMs tend to use more air, are expensive, have special training requirements, and don't work well for regulator-switching which is why they're less common. With deep / deco, side-mount, multiple-tanks, etc running a FFM quickly becomes impossible or impractical to manage.

FFM are neat for underwater coms, and stuff like commercial diving. However they do have their drawbacks. And if your only goal is preventing a reg from falling out, the bungie-method works fairly well. That said, I probably would avoid any dive I thought my regulator might fall out, that's more of an unexpected emergency-management kind of thing.

 

[BoundForElsewhere]

After reading the title I realize I watch too much porn.

 

[Bigbella]

The immediate problems that come to mind are the required gas switches for deco, stage, and possibly travel gases. Instead of just verifying the gas and switching regs, now you're into more complicated plumbing, with the attendant risk of breathing the wrong gas and dying.

One can make that FFM situation as complicated or as streamlined as they like -- simply verifying the available gases on hand is no hard work, any more than that of the casual diver who tests a tank of nitrox.

I have used gas manifolds for years, over thousands of dives, without ever accidentally switching to an inappropriate tank or mix. They are dirt-simple devices; in my experience, cannot be accidentally switched; and safe when used properly . . .

 

[jawaputih]

I don't know what people are blacking out from, and ideally you REALLY don't want that happening underwater. However, some people (myself included) make a regulator-necklace out of bungie, which can be tightened to prevent the regulator from falling out of your mouth, or drifting off if knocked out of your mouth.

This is not helping, if someone would blackout, a regulator stuck in someone's mouth is not going to prevent him from drowning, a FFM does (see thai cave rescue soccer team).

A modern FFM/IDM is great for diving and provide a lot of comfort however, in-case of a failure it does add a lot of complexity, specially on a dive exceeding recreational limits.

 

[Nick_Radov]

This is not helping, if someone would blackout, a regulator stuck in someone's mouth is not going to prevent him from drowning, a FFM does (see thai cave rescue soccer team).

A modern FFM/IDM is great for diving and provide a lot of comfort however, in-case of a failure it does add a lot of complexity, specially on a dive exceeding recreational limits.

Hold on. Why would someone blackout in the first place? Let's address the root cause here instead of trying to work around it by introducing additional risks and convolutions with a FFM and gas switching block.

The Thai cave rescue was a unique circumstance with little relevance to sport diving. In regular ocean tech diving, a blackout is unlikely to be survivable regardless of what kind of mask or regulator arrangement you have. I mean we practice rescuing an unconscious diver by managing the airway and bringing them up in a controlled ascent, but the actual odds of success are pretty low.