soontobepilot
Posts: 267
Joined: Thu May 25, 2000 9:18 am

What Is An Oxygen Door?

Tue Oct 14, 2003 6:42 am

Hello,

I recently had a somewhat scary experience aboard a Frontier Jet Express (Mesa) CRJ flying from DIA to OKC. We took off normally, but levelled off at about 3000 ft. AGL and began descending. The f/a came on the PA and told everyone to prepare for a precautionary landing at DIA. The approach back to DIA seemed mostly normal, but the glideslope and power settings were extremely eratic. We landed on the opposite runway we took off on (with the wind!) and taxiied right back to the gate. It turns out, as the captain later told us, that the oxygen door came unlatched and swung out, blocking the pitot tube. As we all know, this makes some vital instruments stop functioning (namely airspeed indicator). So, the captain just made a downwind landing with no airspeed indicator! I wished I had had my scanner on at the time...

Anyway, I am very curious about what the oxygen door is and why it would be placed in a location that could cause pitot-tube blockage. had this been at night or in IMC, the situation could have been much worse. Any ideas?

-STBP
 
sushka
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 7:23 am

Scanner on in flight? Will the F/As allow that?

Interesting experience
Pershoyu Spravoyu Litaki!
 
jetstar
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 10:52 am

The aircraft oxygen system, if it the old fashioned high pressure oxygen bottle setup as opposed to the newer type oxygen generators is serviced from outside the aircraft.

Somewhere along the fuselage these is a small hinged door that when opened allows access to the external oxygen service port. The aircraft oxygen bottles are filled from a portable oxygen cart consisting of a few large high pressure aviators breathing oxygen. This is a slightly different type of oxygen from what is used in hospitals.

All oxygen servicing has to be done externally because of the potential fire hazard if pure oxygen comes in contact with any oil or grease. Only personnel trained in servicing oxygen systems are allowed to service the oxygen bottles, and extreme caution must be used to make sure the operators hands are clean, the oxygen service line and the wrenches used have not come into contact with oil or grease.

More than one airplane has been destroyed by an oxygen fire because of improper servicing.

After the oxygen cart service line is attached to the aircraft service port, the oxygen cart regulator is slowly opened and oxygen from the higher pressure oxygen cart bottles flows into the aircraft oxygen bottles. Normal pressure in the aircraft bottle when filled is 1800 psi, but on some airplanes the bottle pressure can be higher.

In this case someone left the oxygen service door open and it should have been noticed. The oxygen may not have been serviced, but it may be a preflight item to open the door and make sure the oxygen service port cap is on and secured. The cap is usually held on by a safety chain so it does not get lost when the oxygen is being serviced.

The external service doors or panels are usually mounted with the hinge on the forward side of the door so if the door open in flight, it will not rip off and possibly be ingested by one of the aft mounted engines. The door will usually open a bit but remain in a faired position, but the airflow from the slightly open door could have an effect on the pitot or static ports if it effects the airflow over these items.
 
avioniker
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 12:59 pm

Scanner below 10K ft? Nope...
Who in the commercial world still services O2 bottles on the aircraft?
I'm under the impression that it is not allowed any more and the bottles must be removed for service, at least in the US. This, of course brings up the question how did the door get unlatched and how did the crew miss it?
The MESA guys used to do it that way too last time I looked (that was 3 years ago)
That's a question not a blanket statement. I'm really curious. To the best of my knowledge the 737NG's don't even have provisions making removal of the bottle from the E&E bay necessary.
Someone please enlighten me.
Tanks bunches
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
L-188
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 1:31 pm

Boy that would be a pain in the ass, dropping O2 bottles out to refill them.

BTW I suspect that the F/A was running a line of garbage, I can't think of any aircraft that would have the pitot tubes located behind a door, for obvious reasons.

Thank goodness that everything I work with is older, so the bottles are refilled from the service port provided.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
JBirdAV8r
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 1:59 pm

CRJ's have dual pitot/static systems for just this kind of situation.....if you look closely you can see the starboard pitot tube in this picture.

View Large View Medium
Click here for bigger photo!

Photo © Jayson Romeo


IIRC there does seem to be some sort of door in front of that pitot tube...you can barely see its outline there. I will look for a better picture.

So, no matter what happened, I doubt that your flight came in without a reliable airspeed indication  Smile/happy/getting dizzy
I got my head checked--by a jumbo jet
 
saintsman
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RE: What Is An Oxygen Door?

Tue Oct 14, 2003 8:35 pm

'Door' also gives the wrong impression. It was most likely an access panel that came open which would be much smaller (I would guess at not more than 12" square).

It is bad design though if it came open and blocked a pitot tube.
 
E1FAIL
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 1:49 am

Who in the commercial world still services O2 bottles on the aircraft?
I'm under the impression that it is not allowed any more and the bottles must be removed for service, at least in the US. This, of course brings up the question how did the door get unlatched and how did the crew miss it?
The MESA guys used to do it that way too last time I looked (that was 3 years ago)


ERJ's get serviced through a port on the right hand forward side of the fuselage. Removing the bottle on those things would be impractical because of the way they mounted it and the frequent servicing that plane requires.
 
jetstar
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 6:26 am

Removing an oxygen bottle every time to service it would create more problems because of the wear and tear on the oxygen bottle fittings and lines every time the bottle is removed, this would be a major source for leakage.

Most oxygen bottles are located outside of the pressure vessel, usually in the nose forward of the pressure bulkhead and behind the radar unit.

By opening the radar dome access to the bottles would be very easy especially if there was a leak in the system, the first place would look at is the oxygen bottle fitting.

Also oxygen bottles have a shut off valve mounted right on the bottle fitting and it would be shut off if the aircraft was in for major maintenance or if the bottle was to be removed for hydrostatic tests. All oxygen bottles must be hydrostatic tested every few years, I believe it is 5 years, this is a DOT and FAA regulation.

On oxygen bottle equipped airplanes, the masks are deployed by oxygen pressure, the oxygen lines to the masks are empty and when the masks are required, oxygen pressure from the regulator opens the valves and allows the masks to deploy.

There are 2 ways for the mask to deploy. They will deploy automatically if the cabin pressure reaches a certain altitude, usually around 12 to 14 thousand feet.
Also the pilot can deploy them manually from a switch in the cockpit. This switch is known by some in the aviation industry as the “Oh Shit” switch, because that’s the comment uttered by whoever accidentally hits this switch and then has to call maintenance to stow the masks.

One interesting side note, on the Payne Stewart LearJet crash investigation, one theory they believe caused the crash is that the airplane lost pressurization, but the crew and passengers was unable to receive oxygen through their masks because the oxygen bottles were not opened after the airplane was returned to service after maintenance. This cannot be proved because the airplane was literally smashed to smithereens because of the velocity of the high-speed impact.
 
L-188
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 12:22 pm

Yeah everybody got real paranoid about the 02 bottles after that.

On the 35 it is mounted in the nose, and the angle it sits at makes it really easy to screw up and turn it off when you actually mean to turn it on.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
Guest

RE: What Is An Oxygen Door?

Wed Oct 15, 2003 12:56 pm

FWIW, I just returned from my 6-month recurrent training at FlightSafety. During our discussion on pressurization systems we had the obligatory discussion on the Payne Stewart accident. The thing that always puzzled me about the accident was that, in my opinion, they overlooked one item - the Lear 35 pressurization system has automatic cabin altitude limiters designed into it that make it impossible for the cabin altitude to go above 14,000' or so in a structurally sound airplane. (The Lear 35, while only certified to FL450 has the same pressurization system that is certified to FL510 in their other airplanes.) Remember, the chase airplanes saw no evidence of airframe damage. 14,000' is hardly an altitude that will bring on terminal hypoxia.

I'm typed in the Lear series and have nearly 3,000 hours PIC in the Lear 35. It didn't make any sense to me until the instructor mentioned that they have recently uncovered the fact that the passengers had loaded some frozen fish in the baggage compartment in the cabin behind the rear bench seat. There are now witnesses who say that there were several pounds of dry ice packed with the fish. That changes everything. Dry ice is a VERY dangerous commodity to carry in the passenger compartment. It will readily displace the oxygen in the space and easily explains the accident. It wouldn't be the first fatal aircraft accident involving dry ice.

As for the "O2 Door" causing a major problem. I have to agree that it was at best an over statement or exaggeration by the crew. All transport category aircraft have at least two separate pitot/static systems - the one the left side of the fuselage typically drives the copilot's instruments and the one on the right hand side drive the pilot's. If the "O2 Door" did indeed totally block one side's pitot tube, the crew would still have accurate indications from the opposite side - hardly an emergency situation. IMHO, there was something else going on, probably a screwup that they didn't want to admit to. Hey it happens.

Jetguy


[Edited 2003-10-15 06:16:10]
 
avioniker
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 1:22 pm

E1FAIL
Thanks for the fill in.

Jetstar
What kind of planes are you talking about? I don't know of any with the bottle outside of the pressure vessel.

The last plane I worked on with the pressure deploy system was a 727-100.

Actually when I was working on a new combi 727 pax installation in 1996 the FAA and CAA refused to certify a pressure activated system and we had to get new PSU's with solenoid drop mechanisms. It made the CG and MAC easier to calculate too since we didn't have all that concentrated weight in one location like used to be with the bottles all in the side wall of the bag pit.

Very few modern commercial airliners have been outfitted with Gasseous Oxygen systems for the Pax in the last ten or so years. Way too impractical and expensive. Generators are cheap and don't leak. They can be changed in under 20 minutes when some fool pulls the pin. Takes at least that long to service a bottle.

The 737 and 727 bottles have been in the front pit for decades. I've done many many deactivations of external servicing ports and doors on those fleet types.

The NG bottle is in the E&E bay with access through the front pit. No external service port that I know of.

What rationale would you use for lifting the radome to service oxygen? There are plenty of other access ports on any plane.

HP services the crew bottle by removal on all fleet types. AA does the 737's that way. Anyone out there from CO and DL?

I agree with you about removing the bottle but the cost of the servicing equipment vs the fair wear and tear on the bottles and valves isn't out of line.
The only problems I'm aware of is when someone doesn't open the valve fully after reinstallation and you get a neck leak. The planes I used to service at service ports suffered chronic leaks in the service lines so I don't see the problem with not using an external port. I don't know of any bottle drop incidents yet either.
I don't have to like it. Just do it. Safely...and carefully...Like everything else I do on an aircraft. I've never been afraid to ride on anything I've worked on.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
L-188
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 2:04 pm

I hadn't heard of the dry ice theory before.

That makes a lot more sense then some of the other theories mentioned.

You are correct as dry ice, "melts" it gives of co2 gas. That is one of the reasons that we where never supposed to put dry ice in the same cargo compartment as live animals.

Since there is no bulkhead between the behind the seat there is nothing to prevent the gas permeating the cabin.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
challengerdan
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RE: What Is An Oxygen Door?

Wed Oct 15, 2003 3:26 pm

the oxygen servicing panel is right in line with the copilot pitot/static tube on the forward right hand side of the A/C. I would doubt though that the "erratic"
landing was caused by this event, because the pilot still has his good altimeter AND airspeed indicator AND the stanby instrument. Those are all on the left hand side. You can see the panel right in front of the tube on this photo.


View Large View Medium
Click here for bigger photo!

Photo © Brett B. Despain



I guess Canadair must know that this can be a problem with some operators caused they moved the panel lower on the fuselage on the 700/900 series.
There's the crew oxygen servicing port and and gauge in this panel, so it is probably opened during pilot walk-around. The pax o2 system is of cartridge type so it doesnt require any servicing and access panel.

Avioniker:
The Challenger corporate aircraft has two oxygen cylinders int the forward avionic bay, outside of the pressurized vessel. I guess it has to do with certification rules because on the CRJ they moved it to the lower avionic bay (pressurized, pretty much under the fwd galley) and replaced it with a bird-strike protection panel just in front of the fwd pressure bulkhead.
if your flight goes MX in YUL, I might be called to fix it!
 
wilcharl
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RE: What Is An Oxygen Door?

Thu Oct 16, 2003 1:24 am

looking at that door in the picture it looks like it would close inward (the hinge being torwards the nose of the aircraft) and as a result the airspeed would close it if left open in flight... this makes logical sense to me, and most the aircraft ive worked around had service panels designed that way... it also looks like the door is not in line with the pitot tube but below it.... but none the less if one of the pitot tubes became obstructed, i dont see why a precautionary ladning wouldnt be advised since you are now down one ...
 
avioniker
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RE: What Is An Oxygen Door?

Thu Oct 16, 2003 9:13 am

Challengerdan,
Thanks for the info. So they are now in the pressure hull? I knew the all-in-one type radar installation was unpressurized but I didn't realize the actual avionics compartment was unpressurized.
(So many airplanes, so little time...)
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
soontobepilot
Posts: 267
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RE: What Is An Oxygen Door?

Thu Oct 16, 2003 2:48 pm

Hello,

I am finding this conversation very interesting. I don't know anything about what happened with the door/pitot for sure, I am just reporting the info given by the f/a and captain over the PA. I agree with the point that the backup pitot would have provided a perfectly sound airspeed indication. There may well have been other factors that led to the return to the airport. Thanks for the information about oxygen systems!

-STBP
 
challengerdan
Posts: 145
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RE: What Is An Oxygen Door?

Thu Oct 16, 2003 3:03 pm

The hinge is on top of the panel, by the way. And the hinge is pretty much right in line with the tube. I was looking at a CRJ in the hanger, today, and I can't exactly guess what the panel will do if left open, because of the nose curve or "slope"...

I never heard of any incident concerning that panel where I work which I must say is kind of surprising... I've seen un lock radomes, open aft equipment bay doors, ground lock pins forgot...
if your flight goes MX in YUL, I might be called to fix it!
 
Mr Spaceman
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RE: What Is An Oxygen Door?

Sat Oct 18, 2003 6:12 am

Hi guys.

JETSTAR, you mentioned something very interesting to me in your first reply. You made the following statements .........

"All oxygen servicing has to be done externally because of the potential fire hazard if pure oxygen comes in contact with any oil or grease".

.... "and extreme caution must be used to make sure the operator's hands are clean, the oxygen service lines and the wrenches used have not come into contact with oil or grease."

"More than one airplane has been destroyed by an oxygen fire because of improper servicing."

My question to you (or anyone) is .......

Why can a fire start if pure oxygen comes in contact with oil or grease?

I've never heard of this before. Obviously the answer involves chemistry, and thus may not be easily explained, however, I would love to learn the basics about what chemical reactions causes this hazard.

The closes I've come to dealing with oxygen in a greasy environment was when using a torch in auto shop. The only warnings I was taught back then was to remember the phrase .... "A before O, or up you'll go" when first lighting the torch. I guess the oxygen we used was not "pure".


View Large View Medium
Click here for bigger photo!

Photo © Corey Robinson



Any info about this hazard would be great!  Big thumbs up

Chris  Smile
"Just a minute while I re-invent myself"
 
air2gxs
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RE: What Is An Oxygen Door?

Sat Oct 18, 2003 6:32 am

I never learned the science behind it but the warnings are very clear. Spontaneous combustion can occur if pure o2 comes in contact with greases and oils. I've heard that the o2 has to be under pressure, but this is something I wouldn't want to test.

The horror stories are out there, most probable embellishments, but who knows?

The B757 AMM says:
warning: keep materials that will burn away from the pressurized oxygen. Oil, grease, flammable solvents, dust, lint, metal filings, or other combustible can explode if it gets near pressurized oxygen.

Anyone know the science?
 
Mr Spaceman
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RE: What Is An Oxygen Door?

Sat Oct 18, 2003 7:04 am

Hello Air2gxs.

Thanks for that information.

The warning in the B757's AAM does sound like a chemical reaction between pressurized oxygen & certain materials can occur causing spontanes cumbustion!  Wow!

The warning isn't worded in a way that would suggest an open flame would be needed for an ignition source to trigger an explosion.

Chemistry is pretty crazy stuff!

Chris  Smile
"Just a minute while I re-invent myself"
 
jetstar
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RE: What Is An Oxygen Door?

Sat Oct 18, 2003 11:41 am

There are different types of oxygen, the purest is hospital oxygen ,which I believe is called USP oxygen. Aviation uses what is known as aviators breathing oxygen, which is not as pure as hospital oxygen, and there is also welders oxygen used with acetylene torches which is not to be used for breathing. Liquid oxygen is one of the main propellants of liquid fueled rockets.

As others have stated, when any pure form of oxygen comes in contact with oil or grease, spontaneous combustion can occur. I do not know the reason for the chemical reaction between the two and maybe there is someone on this board with a chemical background who can explain why.

I spent my aviation career in general and corporate aviation and the training in the handling and servicing of oxygen systems was not anywhere as strict as in the airlines. Basically it was on the job training.

When I serviced an oxygen system, I had a clean degreased wrench that I kept in a plastic bag and used only for oxygen servicing. I also washed my hands with soap and water before I handled the oxygen lines because hands have lanolin, which is an oil. I probably went to the extreme with this, but I rather side with caution.

Because the oxygen is under very high pressure, the line from the oxygen service cart to the bottle is a 3000 psi steel braided hose. I heard stories that some untrained personnel would take the line off a cart and use it for hydraulic servicing and put the line back on the cart when finished. If the hydraulic fluid was the old type red fluid, MIL H 5606, this is an oil based fluid and when the next person used the oxygen cart, the line would explode and the high pressure oxygen escaping from the ruptured line would burn. In the shops where I worked we kept a close watch on our oxygen cart and lines to make sure it did not come in contact with oil or grease.

Other stories I heard was the mechanics would use a wrench with grease on it and when they went to disconnect the service line, the oxygen would come into contact with the grease on the wrench and catch on fire, usually burning their hands.

Also the oxygen tank would heat up if the tank were serviced to fast. If the tank was just being topped off with a few hundred psi of oxygen, there was no problem with heat, but if the tank was empty and serviced to the full 1800 psi limit, then the tank could get very hot if serviced to fast.

Aircraft oxygen tanks are light weight aluminum tanks, not like the steel tanks used in scuba diving and must be handled carefully when removed for maintenance.

I spent many hours troubleshooting leaking oxygen systems using a little bottle of oxygen leak detector, basically a soapy water solution and spraying all the lines and connections until I found the leak. It does not take much of a leak to deplete an oxygen bottle over a few days.

I can see why the airlines went over to the oxygen generators instead of bottles. No leaking lines or bottles to worry about and when they time expire just replace them with new units.

 
Guest

RE: What Is An Oxygen Door?

Sat Oct 18, 2003 1:10 pm

There is only one type of oxygen - it all comes out of the same tank. There is NO FAA requirement to use "aviators breathing oxygen".

Jetguy
 
L-188
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RE: What Is An Oxygen Door?

Sat Oct 18, 2003 1:34 pm

I read an arcticle a while back in some airplane rag about the different types of O2.

Aviators oxygen is supposed to have very little water in it, as in "dry". Medical oxygen is not supposed to be as dry as aviation O2, since the human body can't handle it. Welding O2 allegedly isn't as pure.

That being said lets leave theory and go on to reality.

No gas supplier is going to have 3 different gas miner setups to produce three different' oxygen types.

They are going to have one and use it for all three types. Which was the basis of the arctle, that proposed that pilots buy cheaper medical or welding oxygen for their private aircraft to save a few bucks.

OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
jetstar
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RE: What Is An Oxygen Door?

Sun Oct 19, 2003 12:27 am

The gas supplier to one company I worked for told me that they get only one type of oxygen, the only difference is how it is mixed when the oxygen cylinders are filled.

Our oxygen cylinders we got from our gas supplier, as all oxygen cylinders are painted green, but were stenciled “Aviation Breathing Oxygen” on them and were only used for this type of oxygen.

 
Guest

RE: What Is An Oxygen Door?

Sun Oct 19, 2003 1:15 am

There are several misconceptions associated with Aviators Breathing Oxygen (ABO):

Misconception #1: ABO is Different. This is probably the most common misconception about ABO and includes the incorrect notions that it’s drier than medical oxygen or welder’s oxygen, it’s cleaner and it’s made by ATP-qualified elves in the Black Forest. No matter what you’ve been told, the truth is that all commercial grades of oxygen produced today, including ABO, are exactly the same. There are ultra-pure grades used for science and research purposes but this variety is outside the normal distribution chain. Welding oxygen is the same. Medical oxygen is the same. Industrial oxygen is the same. All such oxygen is produced by the same distillation process, in the same plant and with the same equipment to the same specification. It’s shipped in liquid form to major distribution centers. There are no separate tank cars or trucks for ABO. It all comes out the same port; it just goes into different (often identical) cylinders with different labels. The only difference is the paperwork, the distribution system—and the cost. The purity requirements for industrial and welding oxygen today are actually more stringent than the old mil-spec for ABO. Decades ago, there were differences because the methods of production differed; today there are none. If you don't believe me, go to a gas production plant and watch. If that doesn’t convince you, you probably still believe in Santa Claus and the Tooth Fairy.

Misconception #2: FARs Require ABO. Wrong. There’s no FAR that requires you to use ABO. The only place the FAA says anything on the subject is in some old Advisory Circulars. AC 43.13-1A (Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair) lists a maximum moisture content specification for ABO. All oxygen currently produced exceeds this specification by a mile. It’s absolutely dry by virtue of how it’s produced (distillation) and distributed (as a liquid). Those who claim medical oxygen is different because it has more moisture so it doesn’t dry out patients’ pulmonary systems haven’t been to a hospital in the past few decades. They bubble the oxygen through water to moisturize it because it’s so dry. So, there’s no water to freeze up your aircraft’s oxygen delivery system, portable or otherwise, as some mistakenly believe. AC 65-9A (Airframe And Powerplant Mechanics General Handbook) says “Only oxygen marked ‘Aviator’s Breathing Oxygen’ which meets Federal Specification BB-0-925a Grade A or equivalent may be used in aircraft breathing oxygen systems” (emphasis added). For portable, non-TSO’d oxygen systems, even this recommendation (remember, the “A” in AC stands for advisory) isn’t applicable. However, my point is to again look at the reality of Misconception #1; there’s no difference between oxygen, so by default, it’s equivalent. And, in any case, all oxygen made today is far superior to that antiquated specification.

Misconception #3: No ChapStick. This is another Old Wives Tail. The theory is that you can’t use ChapStick or lipstick when using an oxygen mask because the oil in them will cause it to spontaneously ignite in the presence of pure oxygen. No doubt that’s why so many emergency medical patients have ended up with burned lips, the EMTs didn’t wipe off the lipstick—not. While you do have to be very careful about introducing oil into the oxygen refill and delivery system because of the dangers of combining high-pressure oxygen and oil and the potential for rapid and significant temperature rises that could cause spontaneous combustion, by the time it gets to your lips, it isn’t an issue. The guy filling and handling oxygen bottles needs to worry about this, you don’t.

Misconception #4: Only FBOs Can Fill Cylinders. Nope. There’s no federal regulation that prevents you from refilling your own oxygen cylinder.

Hope this helps.

Jetguy

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