Nitrox Tank

[ajduplessis]

Rather than admit defeat adjustscrewedthisup is backpeddling as quietly as possible.

Says the guys thay believes you dont need heat or ignition source to completed the 3 pilars of starting/sustaining a fire. Nice

 

[boulderjohn]

Says the guys thay believes you dont need heat or ignition source to completed the 3 pilars of starting/sustaining a fire. Nice

We believe what we do because we choose to believe authorities who tell us it is true. Take, for example, this safety bulletin[/URL] from Air Products, one of the primary supplier of gases to different users. Here is an excerpt:

In an oxygen-enriched environment, fire chemistry
starts to change. Materials become easier
to ignite because their flammable ranges start to
expand and their autoignition temperatures begin
to drop. This includes the materials of construction
used in oxidizer systems, such as metals.
This reactivity continues to increase not only with
the concentration of oxygen, but also with pressure
and/or temperature. In other words, oxygen
contacting a material at 2000 psig is more likely to
react with the material than at atmospheric pressure.
In the case of a contaminant in a system, the
contaminant may react and generate enough heat
to start another material reacting. This is called the
kindling chain. When temperature increases, it can
lower the amount of energy required to initiate a
reaction.
Let’s look at the basic fire triangle. All three legs of
the triangle must be present to produce a fire—a
fuel, an oxidizer, and an ignition source. If asked
to name some fuels, materials like wood, coal, oil,
and gas would be mentioned. But would anyone
list materials like aluminum, steel, stainless steel?
What is the primary reason we can light a piece of
wood with a match but not a steel rod? The ignition
temperature of the wood is much lower than
that of the steel rod and the heat from the match
is sufficient for ignition. Remember what we said
about fire chemistry and oxygen—as the oxygen
concentration increases, the autoignition temperature
decreases. So materials that cannot be ignited
in normal air may burn readily in oxygen-enriched
atmospheres. With this in mind, it is easy to see
that in an oxidizer system we have two legs of the
fire triangle present. All that is required for an ignition
is an energy source.
Now let’s consider ignition sources. Typical sources
of ignition would be fire, open flames, sparks, or
cigarettes. But that is in the world of normal air,
not oxygen-enriched atmospheres. Remember the
definition of autoignition temperature—the lowest
temperature required to ignite a material in the
absence of a flame or spark. Could gas velocity,
friction, adiabatic heat, or contamination provide
ignition sources? Yes.
In the case of gas velocity, it is not the flow of gas
that can cause ignition, but a particle that has
been propelled by the gas and impacts the system
with sufficient force to ignite. The heat generated
may be sufficient to start a fire depending on the
material impacted. Friction from a component malfunctioning
or operating poorly can generate heat.
Friction between two materials generates fine particles,
which may ignite from the heat generated.

Adiabatic heat is sometimes confused with the
heat of compression. The heat of compression
causes the temperature of a system to rise. An
example would be a tire pump. The barrel or compression
chamber builds heat as the pump compresses
air. This process occurs relatively slowly
and the system takes on the heat. Adiabatic heat
is caused by the rapid pressurization of a system
where the gas absorbs the energy and the gas
temperature rises. This heating occurs at the point
of compression or the point where the flow of gas
is stopped, such as at a valve or regulator seat.
Depending on the material in use where the hot
gas impinges, the heat may be sufficient to ignite
the material.

All of these energy sources can be enhanced by
the presence of a contaminant. Contaminants are
typically easier to ignite than the components of
the system. If they react with the oxygen, they may
generate sufficient heat to propagate a reaction to
the system.

As I said earlier, you should contact people like them to let them know they are wrong. They will be relieved to have you assure them that such safety precautions are unnecessary.

 

[idocsteve]

I hope that ajduplessis doesn't decide to open up his own dive shop.

The results would be disasterous.

 

[Akimbo]

You need fuel, O2 and heat/ignition to have a fire/explosion. Do you argree?

No, because scuba tanks that are contaminated and then filled with pure oxygen have been known to explode in the absence of heat/ignition. If they didn't well then there would be no point in having tanks 02 cleaned in the first place.
….

I was not certified as an oxygen cleaning tech in the Navy, but they trained all of us on the deep dive team on the basics and let is assist certified techs. It was really cool because there was a class 100,000 clean room in a converted trailer on the pier.

Oxygen, fuel, and a combustion source are required for an O2 fire or explosion, which is basically a really fast fire. The same question was asked in very class: where’s the ignition source? The answer is gas can flow through an orifice a very high speeds; the speed of sound is not unusual. A combustible particle, like a tiny piece of iron, can heat to glowing red at these speeds or cause sparks on impact. I could be wrong as to who, but I think it was NASA who actually photographed the phenomenon.

 

[ben_wilson3301]

See post 43 on heat.

One question on heat. Why dont the O2 tanks explode when they are delivered to my house on the back of the van, or when they are at the dive site? The sun bakes it during transport. We have heat?


I am really glad my tanks don't expand. Maybe thats one of your problems.

Well to put simply, the delivery guy was nice enough to remove one component from the triangle... the fuel. How did he do such a thing??? He made sure it was o2 cleaned before he filled it. This board is used to lend advise to those who are willing to learn. A. Do you really want to send out advise like this? B. Why aren't you willing to learn? Scuba is dangerous enough without adding unsafe practices to the mix. Take some classes on Enriched Air and Trimix, and when you do... Please, for the rest of us, listen.

 

[Orlando Eric]

Really? The dive shop won't give you a fill unless they cleaned the tank themselves even if it's got a sticker on it? According to your logic, then a shop tech won't fill a tank that has not been visually inspected or hydro'd by them because they would be foolish to trust any other. Maybe he shouldn't be intimate with his significant other unless she provides proof of a recent STD panel because she could be lying. Maybe the dive shop owner won't eat food he hasn't prepared himself because who knows what could be in there? Maybe when he gets his car back from the shop he's going to put it up on a jack to make sure the work was done properly?

Regs do not have to be 02 cleaned when used with recreational diving Nitrox mixes. Tanks DO need to be 02 clean when used with recreational diving Nitrox mixes.

If you use normal unfiltered air in your tank it will be need to be cleaned again prior to be filled with Nitrox (depending on whether it's banked or blended of course).

Somebody needs to go back through Nitrox class again and hint, it's not me!

:cool2:

I do not think this si the first time you took a simple concept and either did not understand it completly or just have a hard time putting the words in order to explain it.
Yes there are actually shops which will not honor inspection stickers they do not know.
Recreational Nitrox mixes DO NOT require O2 clean tanks. You say it does then at the bottom say Depending on whether it is blending or not.) Which is the fact everyone was jumping on. Starting around Jupiter south banked nitrox is easier to find in my diving area. JDC banks 34% all the time. As you get to Pompano it even gets better.

And when I get my car back from the shop I check the fluids... kick the tires and make sure the hood is latched.

 

[Slamfire]

Take, for example, this safety bulletin[/URL] from Air Products, one of the primary supplier of gases to different users.

...in the Navy, but they trained all of us on the deep dive team on the basics and let is assist certified techs.

Ajduplessis, I can certainly see how someone could develop a cynical/sceptical attitude towards nitrox and O2 handling practices promoted in the scuba industry. I can see how BS practices that are only aimed at scalping out some money from customers who have been misinformed with an aim to create fear in them can promote this attitude. I am referring to things like trying to have mandatory color coded regs, specific nitrox only non-standard valves, nitrox branded regs, and then telling you that it is "a must" to do all these things in order to dive nitrox or O2 safely. And it just so happens that you have to dish out a good amount of money to comply with these things, when your existing equipment can be made O2 safe at a fraction of the cost or incovenience.

That said, there's been good information presented here that has nothing to do with the scuba industry. There is no ulterior motive in trying to promote safe practices. On the other hand there is plenty of solid science, best practices, and sound advise. Nobody here is trying to sell you anything or trying to instil fear in you to profit from it. It's just plain simple reality: you get careless on this and things can easily go boom. If you distrust the traditional scuba distribution channels, get knowledge and training outside the traditional scuba channels. Build your own tumbler. Clean your own tanks and service your own equipment. Just be safe when handling O2 and don't turn a blind eye to the real risks.

 

[Akimbo]

See post 43 on heat.

One question on heat. Why dont the O2 tanks explode when they are delivered to my house on the back of the van, or when they are at the dive site? The sun bakes it during transport. We have heat?...

There is always heat until reaching 0° Kelvin (-459.67° F). More precisely, the minimum required ratio between oxygen, fuel, and heat are required to achieve combustion. In this case, the first two are always there. Sufficient heat is what limits reaching combustion — as mentioned already, usually from a particle in the stream of moving O2 that heats high enough or impacts something to release sufficient heat.

 

[Orlando Eric]

Excellent job here of explaining the differences of blended and banked.

Point brought up though... many local dive shops that are nutso about nitrox O2 clean tanks clean them then pretty much accept that for life. Excellent point of the tank will pick up polluants over time. Some other shops are a PITA about the Nitrox bumper sticker and the rules etc. Then I take the tank in for VIP and get it back with the same scratched up half missing sticker. ViP's call for the stickers to be removed...

 

[idocsteve]

Recreational Nitrox mixes DO NOT require O2 clean tanks. You say it does then at the bottom say Depending on whether it is blending or not.)

Recreational Nitrox mixes require an 02 clean tank because there is a risk of explosion if contaminents are present depending on whether it's blended or not because depending on the way the Nitrox is created 100% 02 may come in contact with the tank and it's contents.

Now I'm not certain if it's by "law" or "convention" or by "industry standards" but regardless: all Nitrox tanks are required to be 02 clean and have stickers that attest to that fact.

Is that better, worse, or the same as something I said before?