Why is the max depth of Helitrox 150ft, while air goes to 180ft???????

[rjack321]

Why would you see a problem? The only issue is whether you would see an advantage.....

Accelerated oxidation for the slightly increased O2. Tires actually have percent quantities of antioxidants in them, the most widespread is a chemical called 6-PPD, which sadly, is remarkably toxic to fish.

 

[tursiops]

Accelerated oxidation for the slightly increased O2. Tires actually have percent quantities of antioxidants in them, the most widespread is a chemical called 6-PPD, which sadly, is remarkably toxic to fish.

Yes, increased oxidation is the fear, but I'm not aware of any evidence that it is a significant effect. The antioxidants you mention are to prolong the life of the bulk of the rubber tire, not mainly the inside touching he air. I understand that tire life is determined more by usage than by age. I guess the test would be to fill with 100% O2 and see if the tires actually have a shorter life....

 

[The Chairman]

But really if I am planning on that, the rebreather is just going to get used (with Helium).

My SF2 always has a bit of helium in it. It helps with EOB (ease of breathing). I can set my PPO₂ to maintain 1.3, which can only work if I dive to those depths with mixtures that do not support life on the surface. Ergo, I have to carry a bail out that would be safe not only at depth, but also a bail out that is safe when shallow.

 

[The Chairman]

I guess the test would be to fill with 100% O2 and see if the tires actually have a shorter life....

Dramatically and it's been done. All tires flex, generating heat, even when properly filled. Reduce that pressure, and the higher ppO₂ wreaks havoc on the inside of the tire. Most blowouts look like someone had a torch inside the tire, and that's with normal air. Usually it's start with a simple nail, and low tire pressure. Increasing the ppO₂ almost five times increases the likelihood of a catastrophic tire blowout.

 

[tursiops]

Dramatically and it's been done. All tires flex, generating heat, even when properly filled. Reduce that pressure, and the higher ppO₂ wreaks havoc on the inside of the tire. Most blowouts look like someone had a torch inside the tire, and that's with normal air. Usually it's start with a simple nail, and low tire pressure. Increasing the ppO₂ almost five times increases the likelihood of a catastrophic tire blowout.

Is there an observed difference between 21% O2 and 32% O2 in a tire? Ae you saying that ANY O2 is bad?

 

[Tigerpaw]

Thanks for the replies. But I'm wondering is the max depth truly at 150ft? Could you safely go deeper with Helitrox?

 

[lowwall]

Thanks for the replies. But I'm wondering is the max depth truly at 150ft? Could you safely go deeper with Helitrox?

Of course. 151' will be fine.

How much deeper depends on what you consider to be your safe limit on pp02, END (narcosis), and gas density.

 

[rjack321]

Thanks for the replies. But I'm wondering is the max depth truly at 150ft? Could you safely go deeper with Helitrox?

Depends on what mixes you're actually able to get with the card. The training mix, and the mix someone is will to sell you are unlikely to match exactly. Plus you can exceed training ppO2, END or gas density limits if you decide to.

 

[The Chairman]

Ae you saying that ANY O2 is bad?

I am. Given that any tire is supposed to be @32psi, that means that the pp O₂ is over 0.63 atm when it's air, and 0.96 atm with EAN32. Autogenous ignition is a real problem and results in tire fires, which are incredibly hard to put out. Consider that gas pressure is what supports a car, not the tire. An underinflated tire creates heat with the over-flexion of the sidewall as well as increased friction. The heat generated by an underinflated can easily burn you. Consider having a pp O₂ of close to pure oxygen with really hot rubber? See the heat damage caused to the sidewall of this tire? That's the thinnest part of a tire.

 

[Tigerpaw]

Of course. 151' will be fine.

How much deeper depends on what you consider to be your safe limit on pp02, END (narcosis), and gas density.

Depends on what mixes you're actually able to get with the card. The training mix, and the mix someone is will to sell you are unlikely to match exactly. Plus you can exceed training ppO2, END or gas density limits if you decide to.

Ok, thanks for the clarification. I was just curious as how deep I could go. I was planning on doing trimex until I heard the OC cost of it. 150's is good enough for me! LOL