Trimix and FFMs.

[Finless]

Just wondering if there are any trimix divers in the world that use recreational FFMs (not commercial gear) and, presumably, a 3 way gas switch?

 

[DA Aquamaster]

I will on occasion use a FFM when using a deco gas. It requires switching to a backup (non FFM) mask when you switch to the deco gas. Other than adding a bit of time to the gas switch there is no real downside.

Some divers carry the backup around their neck facing aft so that all they need to do is spin it around and pull it up. Others carry it in a pocket. Carrying it on the neck is strap dependent and creates more potential to lose it, while carrying it in the pocket creates more potential to lose it without knowing it (although a zippered pocket is pretty secure). In either case, you need to plan for the contingency and have a plan to decompress off the backgas or to make other arrangements.

Gas switching blocks can also be used to route all the gases to the second stage in the FFM and are either pre connected to all the deco bottles or allow the deco bottles to be connected to the block individually with a quick disconnect. This approach works well and avoids a mask switch but has obvious training requirements, is more equipment intensive and requires a great deal of care to ensure you do not connect the wrong bottle to the block or use the block to inadvertantly switch to the wrong gas. They also pose some potentially serious problems if you have to share gas with a buddy, and with buddy compatibility in general. At a minimum, a backup mask is still a good idea.

A mask like the Kirby Morgan M-48 Supermask is another very good option. It uses a pod in the lower part of the mask to hold the primary second stage. This pod can be folded down to expose the lower portion of the face to allow the use of other second stages in a normal manner.

 

[Finless]

I currently wear my FFM and use a 2 way switch for back gas and deco gas. I wear contact lenses so I prefer the gas switch method to bail out and ......

I am planning on doing trimix this year and wondered IF there were any trimix FFM divers and whether they go for a 3 way gas switch or the quick connect hose method of gas switching.

I am thinking at the moment of keeping my 2 way switch and using the quick connect hoses. That way I am still breathing something whilst connecting up the correct hose for the next gas switch.

Quite equipment intensive but it just takes discipline. Of course there is still the bail out option if confusion reigns.

 

[MikeFerrara]

I think it makes a mess out of gas swotches. A diver toxed and died fairly recently and it isn't the first time he toxed. I wish I could remember who it was.

I'm also convinced that the reg in your mouth is the one to donate and that's a little hard with a FFM.

Personally I'd limit their use to long decompression on O2 and a fun toy for Sunday afternoons at the quarry (or where ever).

 

[diverbrian]

I think it makes a mess out of gas swotches. A diver toxed and died fairly recently and it isn't the first time he toxed. I wish I could remember who it was.

I'm also convinced that the reg in your mouth is the one to donate and that's a little hard with a FFM.

Personally I'd limit their use to long decompression on O2 and a fun toy for Sunday afternoons at the quarry (or where ever).

Mike,

To be fair, there is a legimate use. FFM's make good underwater comms with the other divers in the water and the boat possible. If you need gas (from the boat to do deco if a real foul-up happens)/help, this is a great way to communicate EXACTLY what is going on instead of completely relying on light/hand signals.

I don't have the bucks for this kind of system, but it would be nice for just that reason. You are correct that most training as tech divers involves handing off the primary on a long hose and that involves a culture change. Many tech divers successfully use them for long dives, though. A rebreather would involve a similar culture change. I couldn't see handing off THAT primary, LOL.

 

[MikeFerrara]

Mike,

To be fair, there is a legimate use. FFM's make good underwater comms with the other divers in the water and the boat possible. If you need gas (from the boat to do deco if a real foul-up happens)/help, this is a great way to communicate EXACTLY what is going on instead of completely relying on light/hand signals.

What follows is of course my opinion...

If you switch to the wrong gas at your 120 ft gas switch and tox or your switch block gives you the wrong gas at the bottom and tox, no one on the boat will be able to help you and you will almost certainly die. All voice communication will do is let divers on the surface hear your last gasp.

If I feel a dive calls for additional support I'd rather plan on having them in the water. In OW, in theory, a signal to the boat could get more gas sent down but the signal could be a bag and without a bag they won't find you anyway unless you're on the line.

Talking to a boat won't help you if you're in a cave. LOL and commercially available comm systems are ultrasonic and need a clear, unabstructed path to communicate. Even a thermocline can mess you up...sometimes we have several.

I own 2 FFM's equiped with comms but after looking at gas switch options we only use them for playing around on shallow qaurry dives and stuff. When faced with the issues of up to three decompression gasses, one or more stage bottles, the potential need to shut down a valve and switch to a backup or donate air, I just don't see how it's really workable.

Think about it. With a stage or two and multiple decompression gasses, how many gas switches are we talking about? Ive counted a dozed or more including back gas breaks. This is the procedure that needs to be ABSOLUTELY bullet proof. Bad gas switches have probably killed more technical divers than anything else. If you can reliably switch to the right gas and donate gas to some one who needs it then it's pretty likely that every one will come home.

I don't have the bucks for this kind of system, but it would be nice for just that reason. You are correct that most training as tech divers involves handing off the primary on a long hose and that involves a culture change. Many tech divers successfully use them for long dives, though. A rebreather would involve a similar culture change. I couldn't see handing off THAT primary, LOL.

Don't worry about the money. I'd sell you mine cheap if you promis not to use them on a big dive and get killed.

Maybe some one is using them but I haven't come accross them. Wes Skiles uses FFM's with comms for making TV shows but that's TV and it's a special system built by Brian Peace that's radio rather than unltrasonics so it works in a cave.

The arguement for comms to the surface for safety got real loud after that stupid book but a little helium and sensible equipment configurations would have solved almost all of their problems better than screaming for help to people sunning themselves on the boat.

 

[DA Aquamaster]

Well said, Mike.

 

[JS1scuba]

FFMs were being used very early on in Tech Diving. Many were using the AGA with custom switch blocks, others opted for the more rugged Kirby Morgan EXO mask. Kirby Morgan came out with the SuperMask 48 which is a great tool with a removable pod for gas switching but requires multiple pods (which are large) to complete the "lower half" of the mask. Some use the SuperMask for just the bottom mix and then remove the pod and use conventional regulators for the deco. Frankly, if you are going to use a FFM the key is for the high oxygen mixes.

Switch Blocks. -- there is ABSOLUTLY no reason to mess with Quick Disconnects under water. First, even the best Hansen connectors are difficult to use while pressurized. Second why on earth would you want to have a FFM spidered to your head and not have a continuous gas supply?

The best route is with a switch block. Simple to make (we make them custom) and reasonabley easy to use once you have the procedure down. Though if you dont its an ugly day.

Three valves into a block --- one line out to mask, one line out to back up regulator on long hose. Put valves in order of Bottom Middle Top and you know the gas sequence. With check valves you open the new gas then close the old gas .. dont worry about "flushing" since that will happen naturally when you take in the new gas and dump the old one out by exhalation. Visually confirm the switch before you do it.

You want to make sure you have envriomental kits on all the first stages, should your FFM go to positive pressure you can have freeze up (not fun) also you want OPVs on all your regs as well and an OPV on the block. An LP on/off for the FFM and Back up reg is nice too.

But as you can see from a few short paragraphs this is not a task for the inexperienced.


Regards,

 

[diverbrian]

Mike,

I see your points. I also know that many of the divers with a commercial background swear by the FFM and voice comms.

Personally, I am at the point where I wouldn't buy anything that was only useful in the quarry. By the end of the spring, I will be having to buy helium and that stuff (as we all know) isn't cheap. I have enough crud already that I bought and no longer use since the bulk of my diving is beyond recreational limits in either violating NDL's and (soon) recreational depth limits.

Also, I don't see myself doing any diving that involves more than a travel gas and a deco gas. Why? The weather in the Great Lakes is too volatile for my taste in terms of leaving a boat stuck on station while the divers below are commited to a super long deco. Also, I will likely go to a rebreather in a couple of years. You can carry a lot of gas with you in terms of gas management with one of those.

 

[MikeFerrara]

Mike,

I see your points. I also know that many of the divers with a commercial background swear by the FFM and voice comms.

Commercial divers are doing work while a crew on the surface monitors and manages the dive. If you're going to use surface supplie gas and HARD wired comms I guess you're good to go for commercial diving. Like I said the unltrasonic comms typically used don't transmit through obstructions even thermoclines very well.

As JS1 points out there is equipment available but it sounds like a mess to me. We don't select gas by the position of a tank or the order of valves. We visually verify MOD...and we do it for eachother. A mistake here might be your last.

Also, in a cave we don't carry our decompression gas so it would be a little hard to keep it plugged into a switch block. In any case, even in OW, we keep stages/deco gas stowed and off when not in use. It would be a shame to go to use it and find that it all leaked out while you weren't looking.

To each their own but I don't see any sense in making something so critical and so simple and mistake proof into something complicated. Having a couple stages and a couple decompression bottles plugged into a switchblock that you may have to oporate by feel and trust the order of the vales seems like an unbelievable mess.

Personally, I am at the point where I wouldn't buy anything that was only useful in the quarry. By the end of the spring, I will be having to buy helium and that stuff (as we all know) isn't cheap. I have enough crud already that I bought and no longer use since the bulk of my diving is beyond recreational limits in either violating NDL's and (soon) recreational depth limits.

I've kept mine around thinking that I might someday use them for long deco but so far it hasn't seemed worth the trouble.

Also, I don't see myself doing any diving that involves more than a travel gas and a deco gas. Why? The weather in the Great Lakes is too volatile for my taste in terms of leaving a boat stuck on station while the divers below are commited to a super long deco. Also, I will likely go to a rebreather in a couple of years. You can carry a lot of gas with you in terms of gas management with one of those.

There are plenty of Great Lakes wreck dives where we typically use 2 decompression gasses and we still limit our run time to between 60 and 90 minutes. We also use a stage sometimes to help get through 2 dives on one set of doubles when there isn't room on the boat to more than one set of doubles each. If you're going to use a bottom mix that temps you to use a travel gas you'll be wanting more than one decompression gas.

Travel gas...

I guess every one has their own way of doing things but we don't use a travel gas in OW. Even with the most hypoxic mixes we use we only need to decend a short way before the gas is good. We do sometimes use one in a cave where we have a long shallow swim to get to the deep stuff. When we do use a travel gas we use one of our decompression gasses.