doubles in DIR diving wet....

[limeyx]

You're right. There is nothing dangerous about diving doubles. Nobody ever died from carrying too much gas.

If I was just starting out I would go with AL80s doubled up because they can be broken down into singles later for use as stage or deco tanks.

This is not really accurate as doubles have more complexity.

It would be easy to make a mistake with doubles if you dont have a mentor/training that is not possible with singles
- doubles filled with isolator closed resulting in a weird mix
- diving with isolator closed and not noticing

for instance.

Not to say they are inherently dangerous but you do need to know what is what.

it's also definitely possible to die from too much gas if that results in you having an unbalanced rig that you cannot swim to the surface in the event of a wing failure.

 

[Derek S]

Icarusflies -

Here's a little "test" you can give yourself. Borrow some AL80 doubles. Go on a shallow dive somewhere with a teammate (buddy) where you can stand on the bottom at 30'-50' FSW and not disturb the aquatic life. Dump every ounce of air from your wing. Attempt to manually swim rig up to the surface. If you encounter too much difficulty, add air to wing. Go about your dive, and buy a drysuit because you shouldn't dive doubles in a wetsuit.

When you get to technical types of dives, a drysuit will be a must anyway, so it's really a moot point.

 

[PerroneFord]

Are you suggesting that you have seen or heard of someone hooking up an oxygen whip on one side and an air whip on the other side of the isolator?

Diving with the isolator closed simply means the diver is using 1/2 their available gas. Essentially, they are diving a single 80 at that point. 40 minutes into the dive their SPG would still show full. Time to go...

I agree that you should have someone show you what's what. That was helpful for me. But I greatly prefer diving doubles even in shallow water. The LP85s are nice in that they get rid of some weight on the weightbelt for most divers, and yet have characteristics similar to AL80s. In fact, I think they are actually lighter than their Aluminum counterparts out of the water.

However, as someone mentioned, you can break that AL80 set apart later if you really wanted to. I wouldn't do that, just buy a couple AL80s if you need a stage or big deco tank.

 

[RTodd]

Are you suggesting that you have seen or heard of someone hooking up an oxygen whip on one side and an air whip on the other side of the isolator?

Yup, happens more than it should. Dive shop monkey closes the isolator valve thinking he is opening it, pure HE one one side, air and O2 on the other side, diving close to a normoxic mix, so it analyzes out okay. (Or any combination of a screwed up mix.) Once someone passes out on a pure HE mix, reviving them is really tough due to the greatly reduced O2 levels even if the team responds immediately. On nitrox, the risk is pure O2 which has the worst consequences. There are tons of fill procedures and pre-dive procedures designed to prevent this. But, newer divers have plenty of other pre-dive considerations, many of which usually aren't followed as well as they should, and don't need to add these yet.

And, if the answer is he is diving air with doubles, then there is no DIR answer for that dumb idea.

Diving doubles for more gas is not safer. Diving proper rock bottom is how you increase safety. Carrying a ton of extra gas so you "think" you don't have to worry about it inviting a problem. Carry only the equipment you need and this includes tanks. Take it to the extreme, carrying six stage bottles on a cave dive that only needs a single stage creates more potential problems than it fixes.

For recreational open water dives, the only thing newer divers should even be thinking about, all you need is a single tank. Plan gas usage conservatively and enjoy the dive.

 

[Soggy]

Are you suggesting that you have seen or heard of someone hooking up an oxygen whip on one side and an air whip on the other side of the isolator?

There have been several incidents over the past few years where mistakes were made and for one reason or another, the isolator was closed during filling causing weird mixes. In one case, it ended up with a diver breathing 100% He at 130 ffw in Eagle's Nest.

Contrary to common wisdom, if the tanks are filled with the isolator closed, opening the isolator will not result in the gases mixing. Pressure will equalize, but after that it takes a LONG time (days to weeks) for the gases to mix. This was actually tested by Rick Murchison...after 3 days of driving the tanks around in his car, the gases had not changed by more than a percent or two...one side was nearly pure helium, the other nearly pure O2....a potentially deadly problem.

The solution to this problem is very simple. Always check your isolator before and after filling and before jumping in the water. Always analyze BOTH posts before diving. I mark this on my analysis sticker by putting "LR" next to the O2 percentage, indicating I have analyzed from both the left and right.

Doubles are not rocket science and can be a huge added safety margin, particularly in cold water. I basically don't dive single tanks unless I'm in warm water weenie mode or if I'm shore diving. However, there are a few things you need to understand about them before jumping in and there are a few skills that need to be practiced.

 

[PerroneFord]

Soggy, I am aware of the Eagles Nest incident, spoke to one of the divers involved in that incident 2 weeks ago at Ginnie Springs, and my cave instructor was one of those involved in the on scene rescue. (By the way, the victim has returned to work.)

However, someone filling air in doubles for an openwater dive, and someone filling hypoxic trimix in doubles is slightly different. I am not saying that I think protocol should be lessened or broken but I have yet to see anyone doing PP mixing in a set of doubles by attaching two whips, especially one with pure o2.

RTodd, I hear ya. Believe me. And yes, protecting against pure o2 is the key. I guess I am just not used to some of the threats other divers face in their areas. Or I trust my protocols and just don't worry about some of this stuff.

 

[Soggy]

Soggy, I am aware of the Eagles Nest incident, spoke to one of the divers involved in that incident 2 weeks ago at Ginnie Springs, and my cave instructor was one of those involved in the on scene rescue. (By the way, the victim has returned to work.)

Yeah, I know the Eagle's Nest victim's best friend. It's good to hear she's back to work. She was in a coma for some time.

However, someone filling air in doubles for an openwater dive, and someone filling hypoxic trimix in doubles is slightly different.

No, it's exactly the same. Either way, you may not be breathing what you think you are breathing...The risk could be getting bent from too little O2 or toxing from too much O2. When you start dealing with mixing gases, which is DIR Day 1, you need to be diligent about this stuff.

I am not saying that I think protocol should be lessened or broken but I have yet to see anyone doing PP mixing in a set of doubles by attaching two whips, especially one with pure o2.

It's not about putting on two whips, it's about having the isolator closed at any point during filling. In one case, it was that the O2 was put in on one side, then later, the He was put in on the other. The isolator happened to be closed, so the gases never mixed.

Or I trust my protocols and just don't worry about some of this stuff.

As did Rudy and Janet at EN....

The lesson is simple, always analyze both posts. If the tanks are not in your possession for the fill, you don't know what has happened. I have slapped the hands of more than one fill station operator who started closing my isolator to fill my tanks. Incompetence is rampant and even competent people make mistakes.

 

[PerroneFord]

Yeah, I know the Eagle's Nest victim's best friend. It's good to hear she's back to work. She was in a coma for some time.

Yes, Rudy was giving us updates through the process. When I spoke to him last month, he was describing the therapy sessions. Harrowing stuff.

No, it's exactly the same. Either way, you may not be breathing what you think you are breathing...The risk could be getting bent from too little O2 or toxing from too much O2. When you start dealing with mixing gases, which is DIR Day 1, you need to be diligent about this stuff.

Which is why *my* protocol is to analyze the gas. However, I watch my tanks get filled. From the time they leave my hands until the time they are finished filling, I am watching what goes in them. Since I generally dive banked gas, one whip goes on, one comes off, and I analyze. In special cases when I am doing custom blending, the mix is analyzed after the fill, and again on site. If I did not personally witness my tanks get filled, I am a bit more anal about checking both posts. I also surface breathe both my regs on my walk to the water or in my pre-dive breathing procedure. I spend at least a minute on both regs before I hit the water.

It's not about putting on two whips, it's about having the isolator closed at any point during filling. In one case, it was that the O2 was put in on one side, then later, the He was put in on the other. The isolator happened to be closed, so the gases never mixed.

RIght. And we know what happened. However, the mix could have been wrong all day, or right. The gas was never analyzed. Which is where the diver failure was. Whether it's a deep dive or a dive to 50ft. Analyze the gas, and protect against this kind of thing.

As did Rudy and Janet at EN....

Their protocol did not include analyzing their gas. Had EITHER post been analyzed, it would have shown the mistake.

The lesson is simple, always analyze both posts. If the tanks are not in your possession for the fill, you don't know what has happened. I have slapped the hands of more than one fill station operator who started closing my isolator to fill my tanks. Incompetence is rampant and even competent people make mistakes.

I wholeheartedly agree. Which is why I tend to either fill my tanks myself, or I am present while they are being filled. If I can't be there, I am VERY anal about checking everything. Normally, I check everything anyway, but I will admit to being lazy on occasion when I have not let the tanks leave my sight.

 

[rjack321]

Back to the original issue.

Doubles are not rocket science but closed isolators during filling have killed people. And closed isolators at other times can do bad stuff too, like not knowing what you consumption should have been and noticing within a few minutes that your isolator is closed and you're breathing off one tank. Or having a pressurized but off left post. The OP does have to know these things because he should be diving 32% and it may get pp mixed (maybe not).

I am ok with people gaining doubles experience under a suitable mentor prior to taking a proper class in their use. Say 25-30 shallowish orientation/setup dives (<50ft). Basically get your trim and bouyancy down. After that you need training so that these things are an asset and not a liability at 100ft when you don't understand what's going on back there.

In a wetsuit the common DIR choice is AL80s. I found that in freshwater they required about 4lbs in my 7/5mm jumpsuit and 3mm vest. I'd need a bit more weight in saltwater. Get a 40lb wing for these, ~55lb is too big and floppy. An aluminum plate is good to keep from being head heavy in freshwater. SS can be used in salt.

Any larger tanks and you'll need a drysuit to help with some redundant lift.

 

[limeyx]

I'd argue that LP85s are fine too and would be my top choice. I went with AL80 doubles and like them a lot, but I sure wish I had some LP85s.

I am not sure the 85's with a wetsuit are a good idea.

Luxfer AL80 is -1.4 full, +4.4 empty
Faber LP85 is -6.7 full 0 empty

so you will need 8.8 pounds less weight on the fabers, but also be 8.8 pounds more negative at the start of the dive (maybe a little more due to more gas)

so unless you need a lot of ditchable weight with the AL80s (unlikely in a 3mm suit), you are (probably) going to be too negative in the steel tanks to swim it up.