FFM in Technical Diving

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... And I have no idea why you say they can't be used on high O2 mixes. I used my OC setup with 100% for deco all the time...

WARNING, Dangerous Practice:
Rapid-opening valves generate high flow velocities that are sufficient to heat tiny particles glowing red, which is really dangerous on pure oxygen. NASA did tons of studies after the Apollo capsule fire. One study filmed the phenomenon with high-speed cameras. Fortunately, ball valves had not been very reliable with high pressure gases for very long at that point so the number of oxygen systems using them was pretty small.

Most "non-combustible" materials burn like crazy in high pressure pure O2 environments. Oxygen fires are really violent explosions that degrade into a raging fires as the pressure diminishes and Oxygen is diluted.

Causes of Ignition in Oxygen Regulators 2001 - YouTube



Some rapid-acting valves are acceptable at low pressures that vent to atmosphere like solenoid valves that add oxygen to a chamber or breathing loop because the velocity is low, pressure drops instantly, and the O2 level drops from dilution.

Unfortunately, the UDT/SEAL base at Coronado was one of the known fires. I was assigned to Submarine Development Group One's Mark II Deep Dive System in the early 1970s when the explosion occurred. We had one of the first clean rooms for Oxygen systems in the Navy so we had been trained in the latest research. A team was asked to help investigate and found that ¼" ball valves were used on the cascade panel used to charge the Oxygen CCR cylinders. The final report clearly stated that ball valves were the cause of the disaster.

Nobody has done the research necessary to quantify where the safe thresholds are; which would also depend on system cleanliness, pressure differentials, and oxygen level of the gas. Other than pure Oxygen, O2 mixes above 21% are rarely used in saturation diving. Therefore the lack of guidelines on how rich a mix we could use with ball valves wasn't a concern.

The accepted safe practice in the industrial gas industry is "no ball valves on Oxygen systems" and is prudent to follow until we know a great deal more.

Edit: Oxygen Safety for Haskel Booster Users. See page 3
 
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Sharing a FFM back and forth is a skill I have never seen, never practiced, never recommended, and in fact never heard of. No reason to ever do this.

I've seen it once in "Sanctum". Didn't end very well.
In real life I never heard of such practice but since I am a Ocean Reef FFM user, I do not think this is feasible. Too much time consumed to prepare the mask just to barely fit the face and empty it of water.
 
Akimbo, I appreciate the comments. But rapid opening of valves applies to a lot of things. I boost pure O2 to 3500 psi. I use an O2 tank on every dive. Pressing the O2 manual add valve on a rebreather opens an orifice very quickly. We are all aware of adiabatic heat and forces. We keep things on the O2 side very clean. We try to eliminate sharp bends in plumbing. And we open valves slowly. The number of O2 fires has been miniscule and have always had a precipitating factor or fuel source. Let's not overstate the danger of using high O2 with a FFM or a ball valve compared to a separate deco cylinder.
 
I have just had a flick through Jill Heinerths book on cave diving and I have noticed in quite a few of the photo's she is wearing FFM on cave dives. I'm not sure if this is because they were filming and needed comms to co-ordinate and set-up shots, I will have a read to see if it says anything more.

From my own perspective I am doing the FFM and surface supplied introduction in order to be better able to understand archaeological team diving as this is what I am moving towards, and for this comms are regularly used. The teams I have dived/worked with were (part from me) all using FFM and comms, I'm not sure what the OP's angle was though. - Phil.
Yes, in several films and TV programs Jill has worn a FFM, as did others on team. But remember, these films are shot with a crew of safety divers and many of the risks associated with hard core tech diving and raw exploration are mitigated. In at least one TV program, I think it was in the "Water's Journey" PBS series, Jill has a real life FFM failure while in a cave - and Wes Skiles continued to film while Jill and dive buddy Tom Morris deal with the emergency. Anyway, I guess it all comes down to the KISS principle.
 
I know I'm reviving my own ancient thread. I've got some more knowledge on the topic and wanted to share. I've done some tech training including cave classes, and I own a couple ocean reef full facemasks.

That said, there is a secondary port on the masks. You can attach a standard second stage regulator to the port. You could then put a QD and shutoff on both LP hoses so you could swap gasses as needed for either port. While breathing from one, you swap the other to whatever gas you need next. You should still have a secondary connected somewhere and a mask in your pocket in case you need to ditch the FFM for some reason. Once you're setup for it (and practiced), gas switches should be pretty trivial.

I've got my secondary port fitted with a surface air valve so I can breathe at the surface without removing the mask.

The ocean reef manual discusses it and has a photo of a mask with a second regulator connected.

As for the pros of using a FFM, @DevonDiver nailed it. Oxtox survival and comms.
The big con that's kept me from going that route is that the masks blow (they're positive pressure). As such they like to burp, wasting gas. This might be negated with a mask that sucks (negative pressure), but I've never used such a mask.

Also, if you were team diving then donating would require you to have some regular second stages or the other divers to have similarly plumbed FFM's. The latter might be nice as even if they were unconscious you could swap their gas around as needed.

Here's a page from the ocean reef manual with a photo of a mask with a secondary regulator connected:

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https://www.shearwater.com/products/swift/

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