Orange Grove fatality?

[bamafan]

Larry, I have never been on a breather even in a pool so I sure can't debate the specifics of rebreather diving. I can tell you I think people are being unsafe. I was taught in my very first cave class to plan for any 2 failures. That if you have more than 2 you are done for. I see people on breathers who with 2 failures are done for. People are free to make up their minds and do whatever they want but none of the dives you listed require a breather. Have you seen the videos from Dema where the Sidewinder is being marketed to inexperienced divers because it is so easy to dive? I disagree and feel that people should be competent OC divers before getting a rebreather because when it fails they are now OC divers. Are you aware of the diver in Mexico who died on a Sidekick due to bad gas? A single tank for dilulent and bailout. It has happened and from what I am seeing the single tank as bailout and dilulent is becoming the norm. What amazes me is there is generally only a single first stage. Would an H valve not provide more redundancy? No oc diver would go cave diving with a single first stage. I don't even feel comfortable reef diving with a single first stage anymore. Oh well have fun and I might join you some day on a breather. Maybe I will find out I am wrong. And by the way I know the Flex has 2 counter lungs while the Sidekick and SF2 have one.

 

[DA Aquamaster]

I agree with you that some CCR divers are probably being unsafe, but it's more complicated than just redundant diluent.

One of the safety advantages of OC is that over the years most of the ways you can cack yourself have become pretty well known. CCR on the other hand has a larger number of potential failures, and with a great deal of variety in configurations, there is much less standardization in how those failures can or should be dealt with in an overhead environment.

In that regard, I think one of the major killers of CCR divers is a lack of imagination regarding all the ways they could potentially get in over their head and die.

That's often exacerbated by a lack of in depth knowledge how their CCR really works, the ways it can fail and the available in water work arounds. Classes teach some basic procedures, but that's not really enough to troubleshoot the unit and come up with solutions and work arounds on the fly.

But redundant diluent and bags of bailout gas on the diver are not cure all solutions.

For example, bad gas isn't always, or even often, going to be solved by having a second source. If it's the same bad gas, and if you're renting tanks in MX form the same source, having the same problem in two tanks is very likely. And if you are unlucky enough to a second bailout / source of diluent that was also filled from the same source, your redundant dil source will do nothing for you. Using a reliable source of gas and backing that up with proper analysis of the gas is what prevents this kind of accident, not a redundant source of diluent.

 

[DA Aquamaster]

Let's also discuss the benefits of a redundant first stage with an H valve, and with a fully redundant tank.

An H valve in my opinion is a really had idea, in OC or CCR. It does not offer true redundancy as an extruded neck o-ring or blown burst disc will lose all the gas, making the second first and second stage a moot issue. What it does do for you is give you much messier hose routing that can and will reach out and grab line in a wreck or cave, it adds a couple more o-rings that can fail (increasing the potential for gas loss in the first place, and it instills a false sense of security.

It's also a solution for a non-problem, or at least an extremely low occurrence problem. In 32 years of diving and 20 years of regulator servicing for a number of shops, I've never encountered a first stage failure that resulted in a failure to deliver at least some gas - and on a CCR you don't need much flow rate to supply adequate diluent. I had an old Scubapro Mk V come in the shop with a broken piston spring and it still delivered gas to an OC diver. The customer complaint was it breathed a little hard. Hard breathing is not surprising given the almost zero intermediate pressure that results when the spring breaks, yet there was still adequate downstream bias to allow gas flow.

 

[tbone1004]

@DA Aquamaster the H-valve shouldn't give any extra o-rings that can give total gas loss because the valve plugs have the same o-rings. I can't say I've ever seen or heard of a valve failure where it wouldn't shut itself off aside from knobs coming out. The valve failures I've seen multiple times are the ones that leak like a sieve when they are opened but they'll always seal when they shut off.

I have had a first stage failure that wouldn't deliver any gas to the second stage for reference. Hog D1, early in the production, HP seat failure that blew the enviro seal out *still have the donut and donut hole from the silicone* and pushed the main diaphragm out so it wouldn't seal. Was quite messy indeed. Since then I bring an IP gauge with me and check all of my regs before I leave the house.... Super rare, but it can and has happened....

 

[DA Aquamaster]

A couple thoughts on H-valves.

First, there's a difference between a plug and a valve hanging in the port. You'd br hard pressed to break the plug with a hammer, but a valve isa bit more fragile.

Second, with left and right hand valves, there isn't any need to use modular valves in a side mount system, or as bailout in CCR, so it really is added a couple of extra o-rings that can leak. Having had a few leak over the years, I'm not anti-modular valve enough to retire them, but I'm also not inclined to buy them anymore as I replace older valves.

Regarding first stage failures, way back in the day before the earth cooled (late 1960s, early 1970s) there were a few instances of piston regs with very sharp pistons and too soft seat materials where the piston could cookie cutter the seat and plug the flow through piston. But that has not been a problem in 40 years, due to better seat materials and more rounded knife edges on pistons.

I wasn't aware of the issue with the Hog D1, but in general I've never been a fan of Hog regs. You get what you pay for and what Hog gets are parts with rather wide tolerances. Some work great, others not so much.

Those issues aside, with modern, good quality regulators a failure to deliver failure is still an exceedingly rare failure mode for a first stage.

The usual failure mode for a first stage is still a "too much gas scenario", usually with a leaking high pressure seat and creeping IP, or a boom scenario where an o-ring fails or a hose bursts. The former can be dealt with feathering the valve, and the latter almost never happens with a LP hose without warning in the form of a bubbles or a casing that is in poor condition. High pressure hoses can fail with no warning, but those are slow gas loss events given the small orifice in the HP port and in the hose.

The exception here is a low pressure hose bursting as a result of no pressure relief mechanism in the system, if a downstream second stage or OPV is not connected. Any first stage regulator has to have a second stage or OPV attached to prevent a rupture in the event of a HP seat leak, as that can be a catastrophic gas loss failure.

On a dive with my Sidekick, I had a leaking HP seat in the diluent reg which resulted in a slow creep in the intermediate pressure. I noted the ADV (an upstream design) got harder to activate the longer it went between activations, and eventually, after a long enough time at a constant depth, I could not inhale hard enough to activate the ADV. But that just meant I had to reach back and press the ADV paddle. The excess gas would have eventually vented though the OC bailout second stage, but since it's also a sidemount configuration with an easy to reach tank valve, feathering the valve was also an option to prevent the IP increase. That's probably one of the more typical first stage failures, but armed with a little knowledge of how the unit works, that "failure" was very manageable and a non issue for a safe end to the dive.

 

[DA Aquamaster]

Obviously, I've been diving in caves with a single diluent / bailout tank and a single first and second stage regular. As noted above, I am not overly concerned about a first stage failure as they are virtually always "too much gas failures" not "failure to deliver gas" failures, so the real threat, and the one that should be managed is losing all your diluent / bailout gas for other reasons, not a first stage failure.

I am also not all that concerned about a second stage failure. I am personally aware of a single instance of a second stage failing to deliver gas and that was on an old Scubapro Adjustable where an old lever with the feet spread one to many times allowed the poppet to jump the lever. I have had one instance where I had a rock in a second stage that resulted in very wet breathing, but I could have still exited the cave on that reg - and in any event it also only took about a minute or so to remove the rock in the water.

For a failed second stage to be a problem in CCR, I'd have to first have a failure that required me to bailout to open circuit, and then discover that the second stage I just checked at the start of the dive was no longer working. That's two significant failures on the dive, which is a very, very low probability event.

However in the event that low probability event ever happens, I also have a team mate with a long hose bailout reg I could use. Plus, we both configure the long hoses on our diluent regulators with a Omni QD fitting, so that we can swap the second stage from system to system, or remove the second stage to use the long hose to donate diluent as it's the same fitting that plugs into the rebreather. I also carry a compact second stage (an old but well maintained Dacor Viper that is only about 1 1/4" thick and takes up very little space) in a pocket on my dry suit with the same QD fitting. It is a spare team second stage that can be used on any first stage we have. So again, despite 2 major failures (a CCR failure forcing me off the loop, and a second stage failure), I still have 3 viable options to deal with that failed second stage to complete the OC bailout - even with just a single diluent tank and regulator.

 

[DA Aquamaster]

Don't get me wrong, redundant diluent is still important, but there are multiple ways to accomplish it.

As noted above, we dive as a team and we can donate diluent to one another via the long hose in an emergency, as well as OC bailout gas. That's really not much different than a back mount OC diver relying on his or her buddy to have reserve gas he can use in an emergency. You can argue there is a difference between OC and CCR, but diluent is not something that needs to have a continuous flow. It's something that gets added for an increase in depth, or to flush a high PPO2, or to replace loop volume lost through mask clearing, etc.

If you are diving a single source of diluent then it clearly is possible to lose both your diluent and your OC bailout. However, given the extremely low probability of a "failure to deliver gas" first stage failure, that won't happen suddenly or pose an immediate threat. For example, let's say you blow a burst disc and are going to lose all the gas in under a minute. Your first actions are going to be to dump the wing and get fat on diluent in the loop, while making sure you are in close proximity to your team mate, and thus your redundant diluent in the event you need more to complete the exit.

A more insidious way to lose all your diluent is an artifact of having a redundant diluent source that is not truly separate - and not having the systems knowledge to realize a potential vulnerability.

As back ground, way back in the day when I did inland commercial diving, I'd sometimes have a surface supplied gas source feeding my EXO-26, as well as a back mounted bailout bottle. The mask was fed from an M&J gas block that had two positions - surfaced supplied or bailout. There was no intermediate position for the very good and very simple reason that if both gas sources were feeding the mask, the gas source with the highest IP would feed the second stage, and if that was the bailout bottle, it would be used before the surface supplied source was tapped. That defeats the purpose of having bailout, so it was important to keep each system isolated.

If a CCR diver is using a simple manifold to plug in both the on board and off board diluent/bailout gas, there's the potential to lose all the gas in both the on and off board systems. Consequently, unless they systems are isolated via a gas switch block, or by shutting off the on-board diluent tank valve, there is a need to ensure that the IP in the diluent regs are such that the on-board diluent is kept in reserve, rather than used first. Even then, in a gas share situation, the CCR diver will want to shut off the on-board diluent valve to ensure at least some it is saved as a reserve. If a team mate comes calling for OC bailout gas, and exhausts it, a CCR diver who did not shut off the on board diluent valve first to keep at least some of it in reserve, is going to be in for a really nasty surprise when the OC buddy sucks both the on board and off board tanks dry. That's a scenario for a potential double fatality.

Personally, I'd much rather plug into my old M&J gas block than a manifold in an on and off board diluent situation, but it's a moot point with the Sidekick as redundant diluent gas is truly redundant and plugged directly into the rebreather when/if needed

 

[DA Aquamaster]

I'm not anti-redundant diluent, and it's not a major problem to just carry a redundant source of diluent for emergency purposes, but there's still an issue of balance.

It's not much of an imposition to butt mount an AL 6 with the sidekick, and I moved my can light to my hip to accommodate that method. An AL 6, a short hose and a QD fitting and you're in business with a small supply of redundant diluent to get you out.

Obviously if exiting will require a substantial increase in depth one the way out, 6 cu ft might not be enough, and an AL 30 or AL 40 carried as a stage is a better solution.

I can also carry an AL72 or AL80 as a stage for redundant diluent, but realistically at that point I'm just carrying more OC bailout with me all the time, as it's serious overkill for redundant diluent purposes. In that regard, it's needless extra work and an approach that tends to be self limiting. I'm probably better off with an AL 6 I won't mind carrying than an AL 72 or AL 80 that gets in the way and tempts me to leave it behind.

On a larger dive, you really only need to have the diluent needed to get to nearest pre-placed staged gas, so I think there's a balance that has to be maintained.

On a smaller dive, you have to look at the impact on the dive as a whole. For example, if I'm in the Worm Hole at Ginnie, I really don't want to carry an AL 72, and even an AL 30 is way more than I need given the minimal depth change. But there is a depth change whether you exit at the Hill 400 end, or go back out through the Worm Hole and you'll need diluent. Here an AL 6 is nice as it doesn't impede movement through the cave, and it's nice to have as there are only a handful of spots where share diluent via a 5 ft hose can be done without impeding the exit.

But for larger cave passage, where my team mate is close at hand and accessing her diluent is not an issue, redundant diluent is more of an added level of safety than a necessity, provided we are maintaining good team integrity.

 

[victorzamora]

I agree with you that some CCR divers are probably being unsafe, but it's more complicated than just redundant diluent.

I could be wrong here, but I feel like I'd be more concerned with lacking redundant bailout than I would redundant diluent. I've never taken a rebreather into a cave, and my experience is limited, but redundant bailout is much less of a reason to carry an extra tank with me. Maybe it's my OC-cave mentality, but I don't like the idea of having to rely on one tank for both CC and OC in a cave.

 

[Bennno]

@DA Aquamaster
With only one tank for DiL and BO, you're in trouble when the burst disk craps out or you rip a hose badly. Seems unnecessarily risky, imho. Why not just take a 2nd tank?