Nitrox production guideline - Continuous blending

[IyaDiver]

Hi Gang,

I been dying to get answers from the experts in the field. So here goes..............

We know that Nitrox production, say up to 36% EAN , must have air "cleaner", less oil trace etc etc than normal 21% 02 for the sake of prevention of fire hazard. There is no mention that Nitrox should be very low oil trace because it is healthier for us , I wish they would say that and the regular air users will be pissed then.......

How would one achieve that kind of super low oil trace in the air, when doing continuous blending, using a compressor with oil lubrication ?

What I mean is, the moment we inject X% of oxygen and mix it with ambient air, technically the nitrox is already produced at 1st stage of the compressor. We have then violated the standard because the compression chamber has lots of oil vapor and we introduced EAN into it. Even worse, the amount of oil trace is obscenely massive in respect to part per million or thousands of oil trace in that compression chamber in relation to the capacity of the 1st stage compression chamber for air at 7-8 BAR.


With each and every stage more and more oil vapor is introduced to the production air, again we violated the standard. Perhaps in a 3 stage compressor, stage 2 could be the cleanest of all, since it is after the water and oil separator of stage 1.
The only time the air is really "very oil clean", is after the filter towers, assuming the filter tower has the suitable medias for that.

Unless there is a ban on continuous blending with oil lubricated compressor and only allow partial blending with extremely clean purified output of an oil lubricated compressor or oil-less compressor like RIX, where is the safety or how to achieve : very very very low oil level in the air is required for Nitrox when cont-blend is the method chosen ?

Let alone very low oil trace, oil lubricated compressor being used for cont-blend is the same as mixing the EAN with LOTS of oil and later being cleaned ..........how safe can that be ? Ok explosions are not so common, but why are we taking risk doing cont-blend using oil lubricated compressor ?

Even a nitrox generator EAN air output plumbed to an oil lubricated compressor, it is no different than a continuous blending with 99% 02 bottle set at X% 02........

I am very confused ..........:shocked2:


Thanks guys.........

 

[Blue Abyss]

Iya Diver you are confusing a few things here. The main reason that we make a big deal about having oxygen compatible air/modified E grade etc... (really, really, clean air) is if we are using that air to blend with 100% oxygen at high pressures when we are partial pressure blending. When we are dealing with 100% oxygen at high pressures that is when we need to be really careful about possible ignition sources.
The reason that we get away with continuous blending in an oil lubricated compressor is that the compressor never is exposed to high percentages of oxygen. The typical 32% -36% that is run through a compressor using synthetic oils typically will not generate an ignition. There is always that risk and most of the compressor manufactures say not to do it. But we get away with it every day.
If we were to run 100% oxygen through our oil lubricated compressor it would be a very different story. Big bang, maybe a flash and that would be the end of that compressor.
The reason we continuous blend is it is easy, cheap, and we can use almost every scrap of O2 in a bottle.

As far as the safety of breathing nitrox which has been run through a compressor it is no more or less safe than air that has been run through the compressor, it all depends on your filtration.

That is the simple version I am sure someone else will jump in with all the physics and temperatures required for things to burn.

 

[IyaDiver]

Blue,

I guess u can say I am kind of confused .
Is the 40% rule which made u think cont-blend is still safe ? Is there any documented proof behind 40% rule , other than so far so good ?

My friend does partial and cont-blend all the time when we do 1 week live on board. Its just me scared looking at it because I know how hot cylinder head ( that means the compressed air too ) gets in the tropics during a cont-blend and the reduced oil AIT in higher 02 level. My friend does 32% all the time. All I can do is to get a very powerful blower to extra cool the compressor.

Yes, I agree, many seems to get away with cont-blend and very few explosions reported. The same as I see dock workers doing welding with acetylene and oxygen and smoking while preparing them


Thanks
.

 

[Blue Abyss]

I don't claim that continuous blending is without risk. Are there instances of people burning up compressors when doing continuous blending, sure there are, but the vast majority of hours which people run 32% - 36% through compressors are without incident.
If you take this to the logical conclusion if you get air hot enough with enough pressure and fuel present it will ignite too.
The process works because the air fuel mixture is generally well below the ignition point.

 

[clownfishsydney]

I do Nitrox through my Junior II without any problems. I do up to 40%, but mostly around 30-31%.

 

[frogman62]

I have been building compressors for over 40 years. I have customers that have been building and using nitrox sticks for at least 8 years with less than 40 % O2. Technically speaking Oxygen supports combustion: it does not burn BUT when added to a fuel source like natural gas, petroleum oil in large concentrations you have the making of a large intense fire.
In the compressor you have air (nitrogen, oxygen ,CO2 and others) but no gaseous hydrocarbons so the chance of fire is extremely low.
I compress natural gas to 4500PSi in my compressors. Your home has natural gas and ONLY when you have a gas leak and the gas mixes with air(oxygen) do you have a fire hazard (explosion). IF you follow the Oxyhackers direction and build a good nitrox stick with proper monitors in place, you don't have any more hazard than running the compressor with air only.
Jim Shelden

 

[iain/hsm]

I have been building compressors for over 40 years. Jim Shelden

1. In that time how many have you built specifically for nitrox and to what percentage?

I have been building compressors for over 40 years. Jim Shelden

2. In that time how many have you tested to a percentage greater than 40%, say 60-80%?

I have customers that have been building and using nitrox sticks for at least 8 years with less than 40 % O2. Jim Shelden

3. In that time how many of then have you actually independently tested and certified for Nitrox 40%?

Technically speaking Oxygen supports combustion: it does not burn BUT when added to a fuel source like natural gas, petroleum oil in large concentrations you have the making of a large intense fire.
In the compressor you have air (nitrogen, oxygen ,CO2 and others) but no gaseous hydrocarbons so the chance of fire is extremely low.Jim Shelden

4. Do you have any test results on your compressor to back up this claim? Have you ever done an crankcase blow-by spectrographic analysis of your nitrox test percentage. Also on your range of recommended lubricants? Please share your results.

I compress natural gas to 4500PSi in my compressors. Your home has natural gas and ONLY when you have a gas leak and the gas mixes with air(oxygen) do you have a fire hazard (explosion). IF you follow the Oxyhackers direction and build a good nitrox stick with proper monitors in place, you don't have any more hazard than running the compressor with air only.Jim Shelden

5. Just keeping to the nitrox side of compression. Please explain how you removed the additional oxidised oil breakdown gaseous components? Also on the crankcase analysis, or the list of specific gas component carry-over not adsorbed by traditional activated carbon/charcoal of molecular sieve in oil oxidation breakdown. Im intrigued by this claim, no more hazard than compressing Air. Iain Middlebrook

 

[frogman62]

I have never built a compressor specifically for nitrox. The compressor is not modified in any way because of Nitrox use.

1. In that time how many have you built specifically for nitrox and to what percentage?



I spent 6 years in EOD in the Navy in the early 60's and was a second class/EOD diver certified for rebreathers and "Hard Hat". We used nitrox, trimix , and 100% Oxygen in rebreathers for specific dive conditions. We were required to have oxygen tolerance tests every 6 months in a chamber at 60 feet equivalent on 100% oxygen for 30 minutes. The standard at that time on mixed gas was to never exceed 100% partial pressure (compensated) of Oxygen at a depth of 30 feet. Since Oxygen poisoning does not seem to be an issue in normal recreational diving, the use of 31 to 36% Oxygen levels in nitrox seems to be reasonable to me.

2. In that time how many have you tested to a percentage greater than 40%, say 60-80%?


I have never certified a compressor for any level of Nitrox. I have had independent labs check the purity and content of air for fire departments and many of my customers have their air samples tested to be sure their calibration of their nitrox stick is correct

3. In that time how many of then have you actually independently tested and certified for Nitrox 40%?



NO, Just 40 years of operation. Since the military started recommending the reformulated Mobile Jet II for air compressors producing air for breathing applications. I believe the testing done to confirm this was sufficient.
During my career with Beech Aircraft and Raytheon ( retired Director of Target Missile Division) I believe that testing of military equipment is well above that required for most commercial products.

4. Do you have any test results on your compressor to back up this claim? Have you ever done an crankcase blow-by spectrographic analysis of your nitrox test percentage. Also on your range of recommended lubricants? Please share your results.



Iain, you may be very smart, but the critical issue is "IS the gas being delivered through a commercial filter system safe for the diver" . All the testing and certification completed by filter cartridge manufacturers and compressor manufacturers for many years have for the most part given all of us that dive a sense of safe air production. The biggest issue I have is the dive shop that takes poor care of their equipment and never tests the air or nitrox component content for accuracy.
I have seen several compressors completely destruct due to poor maintenance, but the check valves and commercial filters did not blow up and hurt anyone. The compressor itself has very little internal volume so if it destructs , you have an oily mess and pieces to clean up about the same as a car engine throwing a rod out the side of the block. II DON'T CLAIM ANYTHING, I AM JUST RECORDING MY EXPERIENCE. Jim Shelden

5. Just keeping to the nitrox side of compression. Please explain how you removed the additional oxidised oil breakdown gaseous components? Also on the crankcase analysis, or the list of specific gas component carry-over not adsorbed by traditional activated carbon/charcoal of molecular sieve in oil oxidation breakdown. Im intrigued by this claim, no more hazard than compressing Air. Iain Middlebrook

 

[NAM001]

I can not gie you the documented proof. I will offer legend info for what it is worth. Nasa ,after the i think apolo fire onthe pad, did the reserch to see what they could do to reduce the chances of another capsule fire. they found that above 60% all acted like pure o2 and below that it acted like air. After adding 20% buffer zone we were left wirth the 40% rule. which at the time accomodated noaa 32 and 36.

Blue,

I guess u can say I am kind of confused .
Is the 40% rule which made u think cont-blend is still safe ? Is there any documented proof behind 40% rule , other than so far so good ?

My friend does partial and cont-blend all the time when we do 1 week live on board. Its just me scared looking at it because I know how hot cylinder head ( that means the compressed air too ) gets in the tropics during a cont-blend and the reduced oil AIT in higher 02 level. My friend does 32% all the time. All I can do is to get a very powerful blower to extra cool the compressor.

Yes, I agree, many seems to get away with cont-blend and very few explosions reported. The same as I see dock workers doing welding with acetylene and oxygen and smoking while preparing them


Thanks
.

 

[IyaDiver]

Hello Guys,

Sorry, so long no write back.
Anyway, if there is anyone competent or competent body in USA or the world, I would say US Navy data depository will be a good place to start searching for my Nitrox question and I did. Not easy find as they are not Google friendly.

No one is USA has the database, money, amount of experiments done and etc etc as US Navy. Dang, if there is any experiment King, it would be the US Navy.

So I found it and once for all, I close the case :
http://www.supsalv.org/manuals/diveman5/13512-001h/css/vol2/chap10.pdf

Page 10-10 Fig 10.3 and it has that fire red warning too
Page 10-12 Fig 10.4

Its clear that US Navy does not allow cont-blend or even nitrox generator output to be fed to an oil-lubricated compressor.
It stated OIL-FREE COMPRESSOR.

So as someone who is 0.00000001% as knowledgeable as US Navy experts, I am following their guide lines.
Case closed.

Thanks for those who have assisted and gave your comments and input.

And to IAIN/HSM , this is very much in line with the European Standard BS8478:2006 Breathing Gases Component Concentration. Is US Navy and the British or EN somehow sharing information Iain ?

Thanks & Later,

IYA