sudden
Posts: 3934
Joined: Fri Jul 13, 2001 5:20 pm

Oxygen Mask.

Wed Jun 12, 2002 7:38 pm

I did a search, but did not found anything about this.

Anyone that can tell me how the oxygen mask system works?
Also, what is it that actually makes the masks drop down? I know it's due to sudden lost of cabinepreassure, but in more depth perspective, please.

Thanks in advance.

Sudden
When in doubt, flat out!
 
dragogoalie
Posts: 1172
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RE: Oxygen Mask.

Wed Jun 12, 2002 11:00 pm

My first flight instructor was a graduate of the University of North Dakota's commercial aviation program (which I will soon be a part of). One time after my night cross country we went to grab something to eat and we were talking about this. He learned at UND that the oxygen is created by some sort of a chemical reaction and only produces enough Oxygen to sustain life, not to keep the passengers concious, because in theory, if the pilot is doing what he/she should be doing, they will soon be in air that is breathable, so they will only need the oxygen masks for a little while. Needless to say the pilots are given enough oxygen to keep them awake. Or at least I'd hope so  Wink/being sarcastic. Thats all I know about this (or think I know about this). If I'm wrong, someone please correct me.

--dragogoalie-#88--
Formerly known as Jap. Srsly. AUSTRALIA: 2 days!
 
Guest

RE: Oxygen Mask.

Wed Jun 12, 2002 11:03 pm

Like most things aviation related, the O2 system can vary from aircraft to aircraft. The most common form is a gaseous O2 system. Typically, the mask will drop on receiving a signal from an aneroid. On the aircraft I flew, the masks would drop if the cabin altitude exceeded 14,000'. The crew could also drop the masks with a switch in the cockpit. The 727 also has a manual lever to deploy the masks. When the system is activated, the oxygen lines are pressurised and the pressurised O2 line in the PSU moves a plunger that trips the latch on the PSU door. Since the latch mechanism can be sensitive, the mask would sometimes drop if the landing was harder than normal. Hope this helps. Some aircraft use oxygen "candles" or some other chemical form of O2 generation. A lot of military aircraft use liquid oxygen. Hope this helps.
 
OPNLguy
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RE: Oxygen Mask.

Thu Jun 13, 2002 1:38 am

Just to expend on what 727pfe said, the older types (727, 737-100/-200, and I presume the early DC-9s) have the plumbed systems with a tank located inside the foward cargo bin, on the Boeings, anyway.

When the DC-10 came out, it went to the individual chemical generators, and Boeing went to them on the 737-300 and subsequent variants. There are actually a few 737-200s towards the tail end of the production run that also have generators versus a plumbed system.

These generators can create alot of heat when they react, which is ordinarily no problem, since they're installed in insulated enclosures in either seatbacks or overheads. ATA had a DC-10-30 burn-up on the ramp at ORD some years ago when a row of seats (being worked on down in one of the cargo decks) had a generator trigger, and un-noticed, it proceded to burn through. Of course, everyone recalls how generators factored into the Valujet 592 crash into the Everglades back in the mid-1990s.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
OPNLguy
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RE: Oxygen Mask.

Thu Jun 13, 2002 2:01 am

Forgot to add this link... and it was a DC-10-40, not a -30

http://aviation-safety.net/database/1986/860810-0.htm
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Guest

RE: Oxygen Mask.

Thu Jun 13, 2002 3:01 am

To supplement what had already been provided herein, and to answer the question "Also, what is it that actually makes the masks drop down? "...the logic is rather simple, as 727pfe stated, an aneroid (barometer) will close, connecting the circuit, at a predetermined cabin pressure (14,100 ft for the DC-10). To avoid false indication, there's a 5-second timer. After 5 seconds of closed circuit, solenoids are activated to open the latches, dropping the masks. Passengers still need to pull on the lanyard to activate the oxygen (in DC-10 case, it's a chemical unit).

As a tidbit of info, for aircraft operation that can go above 30,000 ft, FAA requirements (14 CFR 25.1447) require automatic (mask drops) before the cabin pressure altitude exceeds 15,000ft. Most airplanes activate mask drops at 14,000 ft as a margin (to pass the tests).

Regards,
Nut
 
sudden
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RE: Oxygen Mask.

Thu Jun 13, 2002 5:26 pm

Thanks for your replys guys. Pleasure reading them.  Smile
When in doubt, flat out!
 
JETPILOT
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RE: Oxygen Mask.

Thu Jun 13, 2002 6:11 pm

Just to clear up a few loose ends.

There are two types of masks....the ones up in the cockpit are pressurized. They create a pressure environment in the system to allow air to enter the bloodstream.

The masks for the passengers arent pressure masks. The mask is only there to revive you when atmospheric pressure allows air to be absorbed into the blood stream.

The passenger masks do not suport sustained conciousness at low atmospheric pressure.

The cockpit masks are switchable from diluter/demand to 100% flow.

Just a tidbit.... oxygen generators in the cargo hold caused the ValueJet crash in the everglades.

JET
 
flashmeister
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RE: Oxygen Mask.

Thu Jun 13, 2002 9:17 pm

Regarding the seatback generators in the DC-10...

Wasn't the design of the bracket and harness of the generator considered a design flaw? I remember reading of cases where people yanked too hard on the lanyard and pulled the generators into their laps, or where the generators got so hot that they burned through the headrest and then injured the person sitting in the forward seat...

Did the L-1011 have a seatback or ceiling system?
 
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VIflyer
Posts: 452
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RE: Oxygen Mask.

Fri Jun 14, 2002 9:38 pm

Well I know that the O2 masks on our EMB's are triggered once the cabin ever gets to 14,000 Ft and the flight crew uses a separate 02 bottle that must be keep at a certain psi (I can't remember right at this moment). But the Saab's and the ATR's are different. On the Saab's the 02 masks are located below the aisle seats (those on the 2 seat side have two masks with a single point y connection) and the pax actually have to plug the connection on the mask to a port above there seat. On the ATR's (depending on the model) either there are masks below the F/A's jumpseats or a pop down compartment above certain seats. The thing about the ATR is that there is more pax than Masks, and this is because the FAA at the time only required that 30% (I think I'm going on 2 year old tired memory) of the passenger needed to have O2 in a depressurization situation because the aircraft is only certified to 25,000ft. On both the Saab and ATR the pax O2 is turned on via the Cockpit.

just my 2 cents
I reject your reality and subsitute my own
 
sudden
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RE: Oxygen Mask.

Sat Jun 15, 2002 12:58 am

If you mean the SAAB 2000/340 I have flown both, and nothing was mentioned about plugging it yourself during the safety instruction of the F/A.
Did I misunderstood you, or do you mean those A/C's?
When in doubt, flat out!
 
TechRep
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RE: Oxygen Mask.

Sat Jun 15, 2002 2:28 am

http://imageevent.com/techrep/328fireprotection

Have a look but I have much to add to this system. Feel free to look at the rest of the site as well.

TechRep
 
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VIflyer
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RE: Oxygen Mask.

Tue Jun 18, 2002 12:51 pm

Well I know that on our Saabs 340B/B+ (AE) that the paxs have to plug in the O2 masks, I don't know about other airlines the only other airline Saab I've been on was Mesaba and the FA didn't even bother to mention the O2 mask. In our safety demo the operation of the masks is told.
I reject your reality and subsitute my own
 
Metwrench
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RE: Oxygen Mask.

Tue Jun 18, 2002 1:25 pm

Most items posted here are correct except the statement about oxygen keeping pilots awake. In the event of loss of pressurization, oxygen keeps the pilots, and pax alive! From 35,000' to 15,000' @ 2.500' per minute of emergency decent takes 8 minutes. Yes, the average person will survive that without permanent damage. However your reasoning, logic, and basic motor skills will be affected. The pilots need to have access to quick donning oxygen masks to stay alert to respond to whatever emergency got them in this situation to begin with.

P.S. I like to slam pilots, but once or twice in their careers they might need every second available to respond to an emergency, never it be said that MX didn't give them every chance to overcome it. You guys want your O2 bottle topped off before departure, no problem!

Just curious though, where does all that O2 go when there aren't any leaks in the system???????????
 
JETPILOT
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RE: Oxygen Mask.

Tue Jun 18, 2002 3:40 pm

Gotta disagree with you Metwrench if I understand you correctly.

The pilots mask forces oxygen into the lungs under pressure allowing absorbtion by the body.

You could depressurize the plane don your mask and fly up there "concious" until the oxygen runs out.

If you had 100 passengers in the back and all donned masks they would all be dead. Why? the oxygen wasn't underpressure.

JET
 
FredT
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RE: Oxygen Mask.

Tue Jun 18, 2002 4:14 pm

JETPILOT,
those masks aren't pressure breathing. That's a very questionable pleasure reserved for the military and other users with similar demands. What matters is the oxygen pressure in the inhaled air. If you go to 100% O2, the oxygen pressure at a cabin altitude of 92,000' will be the same as it would with the normal 21% O2 at 8,000' cabin altitude. Unless you plan to do a lot of flying at 92'000', or pull a lot of G's, you don't need pressure breathing.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Metwrench
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RE: Oxygen Mask.

Tue Jun 18, 2002 4:15 pm

Jet, two conditions, two answers. I would encourage experienced flight crews to join in and correct me.

1st)

Pilot masks. They are designed to be quick donning and of a design to fit very tightly over the nose and mouth. The slightest inward breathing causes a low pressure area that allows a check valve to open and provide a positive flow of pure O2. There is also a microphone that is already plugged into a jack which allows for voice communication over the Comm system.

When the person stops breathing inwards, the flow stops, on exhale the breath exits through a separate valve, similar in principle to scuba gear.

The hose to the mask has a visual indicator, green, that repasts positive flow of O2. I have never not seen a pilot test this system during preflight.

2nd)

Pax O2 masks.

Have you ever flown on a commercial flight???? Obviously you were asleep or ignored the Flight Attendants briefing!! In the event of an unlikely deployment of Pax O2 masks, blah, blah. The bag will not inflate but O2 will be flowing. You're not swimming 60' under water! You just need enough O2 not to die!!! The Pilots need more!!!! If you need O2 to stay coherent, they need it to make sound judgements to keep you alive!

Gawd, I can't believe I'm defending pilots!!! What a pathetic state you are in that Metwrench has to step up to the plate to protect you!!!
 
FredT
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RE: Oxygen Mask.

Tue Jun 18, 2002 4:36 pm

Oh yeah, and you might very well be looking at having dead pax if they don't get oxygen. You don't have all that much time available either. I did a web search to get some figures, and found this article on AVWeb giving a time of useful consciousness (TUC) at 25,000' of "three to six minutes with death following not long after that" which is consistant with what I remember. I recall a TUC of around ten seconds at 40k'... don't take the recommendation to don the mask first of all lightly!

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Metwrench
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RE: Oxygen Mask.

Tue Jun 18, 2002 5:06 pm

Okay Fred, so what you're saying is that I should grab the 1st mask that swings my way and by all means prevent that obnoxious brat that has been kicking the back of my seat the last two hours from getting some O2?

Thanks, I was looking for some absolvment!!! Should I strangle the lathargic Mother too??? Please can I???

Met
 
erasmus
Posts: 256
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RE: Oxygen Mask.

Tue Jun 18, 2002 5:31 pm

Interesting discussion,

Metwrench,

I just wanted to say that in "my company" and the two other companies I've previously flown for it is common practise to check the quick donning mask, the mic in the mask, the O2 pressure and the Oxygen flow before the first flight.

I think it's common practise in every airline!

Just curious though, where does all that O2 go when there aren't any leaks in the system
Answer: probably because every pilot uses a small amount of oxygen when testing the system!

Regards,
Erasmus
 
sudden
Posts: 3934
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RE: Oxygen Mask.

Tue Jun 18, 2002 6:30 pm

Is it really necessary to argue, or whatever it is you are doing?!
You all have a lot of knowledge, which I appreciate, so why not share the knowledge instead of acting out like you are doing.
Don't turn this forum into another civil av. forum where argues belongs to the topics.

Have a great day and thanks for all your replys!
When in doubt, flat out!
 
FredT
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RE: Oxygen Mask.

Tue Jun 18, 2002 7:10 pm

Met,
grab the mask dropping down on you, then help the passed out kid (yes, I know it will seem like a relief that the brat finally passed out, but try to do it anyway  Smile) and the lethargic mother, even though it won't make much of a difference.

Isn't it peculiar, how you always get the obnoxious kid with the lethargic mother in the row behind when flying? Do they have thousands of those flying around fulltime, occupying every other seat row? It's a conspiracy, I tell you! Big grin

But if you do choose to follow your original plan of action... I was looking out the window the entire time and didn't see a thing.  Big grin

Sudden,
I don't think we're arguing anything but the facts - yet. We're trying to work our way up to some good old civilised name-calling, but it's a slow process at times, y'know...  Big grin

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
sudden
Posts: 3934
Joined: Fri Jul 13, 2001 5:20 pm

RE: Oxygen Mask.

Tue Jun 18, 2002 7:19 pm

Well,
I wrote it now, before it gets out of hand.  Smile
By the way, are you at ARN?
Have worked at got myself.
When in doubt, flat out!
 
erasmus
Posts: 256
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RE: Oxygen Mask.

Tue Jun 18, 2002 9:28 pm

Hi,
have a look at what the A320 operating manual says about the fixed oxygen stytem in the cockpit:



and also:



So what jetpilot said about "overpressure" oxygen is correct.
OK, it's probably not the same "overpressure" system the military might use, but it does use an overpressure of some kind.

Friendly regards to everybody,
Erasmus
 
Guest

RE: Oxygen Mask.

Tue Jun 18, 2002 10:34 pm

Jet is of course correct. The standard "Pressure-Demand" type regulator supplies 100% O2 under pressure when selected to emergency, or above a preset cabin altitude. The passenger masks do not supply O2 under pressure, and would do no good if the pilot elected to remain at altitude after a depressurization.
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Oxygen Mask.

Tue Jun 18, 2002 10:47 pm

Erasmus,
that's a slight overpressure to avoid having smoke enter the mask. Not The pilots mask forces oxygen into the lungs under pressure allowing absorbtion by the body at all, which would be pressure breathing. Pressure breathing equipment also includes a vest with a chest bladder to help get the air back out of the lungs. And still, people sign up to become fighter pilots. Unbelievable.  Smile

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
FredT
Posts: 2166
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RE: Oxygen Mask.

Tue Jun 18, 2002 10:56 pm

Sudden,
no, I'm at ESSL (LIN) these days. I used to worke on the ramp at ARN though.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
erasmus
Posts: 256
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RE: Oxygen Mask.

Tue Jun 18, 2002 10:59 pm

Hi Fred T,
I did think that this military system was something completely different.
However, the fact that my A320 OM says:
"Overpressure supply is started automatically when cabin altitude exceeds 30000 feet."
makes me suspect that there's is more to this slight overpressure then just to remove smoke from the mask or keeping (toxic) fumes out of the mask.

Why would this feature be automatic only above 30000 Ft if it's sole purpose was to clear smoke from the mask? Maybe the slight overpressure DOES help in breathing?

Does anybody have more information about this feature?

Regards,
Erasmus.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Tue Jun 18, 2002 11:16 pm

There are two types of O2 masks for cockpit use:


1. Pressure demand - these masks are typically used on high g capable, military a/c. In use, the O2 is supplied at pressures that actually interfere with speaking. In other words, much more than the slight over pressure of the second mask:

2. Diluter demand - most common on airliners and business a/c. Typ has 3 positions: Normal, 100% and Emergency. Normal will dilute the O2 w/ambient air up to a specific pressure alt, above which 100% O2 is delv'd. 100% delivers, of course, 100% O2 even at lower alts. Both "normal" and "100%" positions only provide flow when a breath is drawn. "Emergency" provides continuous flow, 100% O2 (ie very slight positive pressure) in order to clear the mask/goggles if smoke is present. A diluter demand mask WILL NOT force O2 into the lungs.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Tue Jun 18, 2002 11:28 pm

I agree w/ FredT here for the most part. JET is incorrect b/c he's confusing the 2 types above (and so therefore is 727pfe) and/or doesn't understand the amount of pressure required to force air into human lungs. The constant "dribble" flow of O2 out of a diluter won't do it in a 1g environment, so one can imagine the flow pressure req'd for a 9 g turn.

If you've ever worn a pressure demand, as I said, it's literally hard to talk when it's functioning and requires a technique. Believe me, it's a night and day diff b/t the 2 types.

cheers
 
Bellerophon
Posts: 516
Joined: Thu May 09, 2002 10:12 am

RE: Oxygen Mask.

Wed Jun 19, 2002 12:21 am

Essential Powr

Correct!

Anyone who has used both types, knows what "Pressure Breathing" means, and it is very different to the systems fitted to Boeing and Airbus aircraft.

Learning to use a pressure breathing mask is an acquired art, and can be very disconcerting at first, as oxygen is forced down into your lungs, an experience that takes some getting used to. Likewise, talking is difficult, as you have to expel sufficient air, against the inbound rush of oxygen, to generate any sound at all.

I have pressure breathing equipment on my current (civil) type, due to the altitudes we fly at, and its use is trained for very carefully. We do not have the benefit of a military pressure suit (that FredT refers to) to assist in exhalation or to prevent over-inflation of our lungs.

When practising its use on a rig during the annual Safety Equipment Training day, we are required to have an aviation specialist Doctor in attendance.

Regards

Bellerophon






 
Guest

RE: Oxygen Mask.

Wed Jun 19, 2002 2:19 am

I did not say that civil aviation regulators or those in military cargo/transport aircraft were the same as installed in high performance jet fighters. If you read FAA TSO-C84, you will see that there are three types of regulators in civil aircraft. The three types are "Demand, Diluter Demand, and Diluter Pressure Demand". The pure demand regulators are not used in many aircraft. The other two are the most common. The confusion factor is they are both often refered to as simply "diluter demand". The difference is that one will supply O2 under pressure, and one will not. Every aircraft I've ever flown in has had a "Diluter Pressure Demand" regulator. That means that they will supply positive pressure above a certain cabin altitude. The pressure is normally between 50-75 psi. The higher than atmospheric pressure is essential to allow the law of gaseous diffusion to occur in the lungs for O2 tranfer to take place. It probadly won't inflate the lungs in a 9 g turn! (I don't know for sure, never been in a 9 g turn). BTW the regulators in our aircraft are labeled "Pressure Demand".
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Wed Jun 19, 2002 2:43 am

I don't have any confusion on the issue. All 3 of the above referenced diluter types are civil, and WILL NOT force air into a pilot's lungs.

JET pilot said:

"The pilots mask forces oxygen into the lungs under pressure allowing absorbtion by the body."

in describing a diluter demand system evidently b/c it supplies just enough pressure to a mask to clear it or the goggles of smoke. You erroneously agreed with him, and did not catch the distinction. The 50-75 psi you ref on a diluter demand is the LINE pressure prior to the regulator. The regulator then drops the pressure to approx 15 psi or less. That's certainly not pressure breathing.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Wed Jun 19, 2002 2:58 am

727pfe,

The statement: "...The higher than atmospheric pressure is essential to allow the law of gaseous diffusion to occur in the lungs for O2 tranfer to take place." is a gross conceptional error in aviation physiology.

You're implying that a diluter demand mask is pressure breathing, based upon your reference to the lungs. All the diluter demand system does, as opposed to pressure demand, is:

1. Supply sufficient O2 pressure to the "intake", commonly referred to as the nose and/or mouth in the case of the full mask types. The pressure difference created by the diaphram still enables respiration in the lungs.

2. Desmoke the mask or goggles

If a diluter demand system did what you are describing, then that is "pressure demand."

A diluter demand system will not respirate for you. A pressure demand system will.
 
Guest

RE: Oxygen Mask.

Wed Jun 19, 2002 3:06 am

After more research, primarily in Air Force Pamplet 160-5, the important factor is the partial pressure of O2 in the alveoli. To prevent hypoxia you need to maintain 60-100 mm hg of O2 alveolar pressure. As the cabin climbs higher the pressure required will also increase. That pressure is not just to clear smoke or fumes. I was agreeing with Jet that the O2 is delivered under positive pressure above a certain altitude. I don't know the exact PSI. I don't agree that the O2 will be "forced into" the pilots lungs. Just that the pressure in the the system will be higher than ambient, once the regulator goes into it's pressuirzed mode.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Oxygen Mask.

Wed Jun 19, 2002 3:28 am

pfe:
"As the cabin climbs higher the pressure required will also increase..."

...if the concentration of O2 in the inhaled air remains the same. As I stated initially, if you increase the concentration with the altitude up to 100% O2, you will have the partial O2 pressure of a normal atmosphere at 8,000' up to 92,000' at ambient total pressure. Up to this altitude, any pressure above ambient is not necessary to maintain the proper blood O2 level.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
vc10
Posts: 1342
Joined: Thu Nov 15, 2001 4:13 am

RE: Oxygen Mask.

Wed Jun 19, 2002 3:39 am

A web site that might be of interest on this subject is :-

www.vnh.org/fsmanual/01/05positivepress

As far as I know [ I could be wrong though ] The only civil aircraft that requires and has pressure breathing for the flight deck crew is Concorde, and it is a requirement that Concorde crews have regular training sessions on how to use pressure breathing as Bellerophen has already reported. Now some of the modern Biz jets which have operating ceilings well above 40,000ft might have true pressure breathing also. No civil aviation Oxygen system is meant to sustain life at high altitudes continuously, but merely to sustain it long enough for the crew to get the aircraft to descend to lower altitudes [15,000ft] where life can be sustained. If a crew of an aircraft do not have to be trained to use their oxygen masks, and rechecked on a pressure breathing rig then believe me their aircraft has not got pressure breathing in the true sense.

regards little vc10
 
Guest

RE: Oxygen Mask.

Wed Jun 19, 2002 3:40 am

Sorry Fred, I disagree with you. Any aviation physiologist will tell you that you have to have O2 under pressure above FL 340. My information comes right out of AFP 160-5 Physiological Training. It's true that you will increase the blood O2 saturation level with 100% O2, but eventually you will have to decend if you do not have O2 under pressure. The normal amount of Alveolar pressure at sea level is 100 mm hg. As you can see from my post, it can go down to 60 mm hg, without hypoxia onset. On our aircraft without pressure demand regulators for the Pax, you must descend the aircraft to prevent hypoxia. But, even though we disagree thanks for keeping it civil.
Cheers,
Kevin
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Wed Jun 19, 2002 10:05 am

727pfe,

Jetpilot's statement: "The pilots mask forces oxygen into the lungs under pressure allowing absorbtion by the body." is flat out wrong, and the reason I introduced the physiology aspect to the discussion.

Your direct response to Jetpilot: "Jet is of course correct. The standard "Pressure-Demand" type regulator supplies 100% O2 under pressure when selected to emergency, or above a preset cabin altitude."

Your further statement:

"The pressure is normally between 50-75 psi."

Implies you thought the delivery pressure is 50-75 psi (in the face) on a diluter demand. It's not! A diluter demand mask DOES NOT provide O2 downstream of the regulator at 50-75 psi. As I stated, it's 15 psi or less, which is certainly not enough to sustain, or even cause, respiration.

You were apparently under the impression that a diluter demand mask forces O2 into the lungs at 50-70 psi, or else you wouldn't have agreed with Jetpilot or quoted the 50-70 psi LINE pressure prior to the regulator. There is no way the breeze of O2 in the face provided by a diluter demand mask accomplishes anything related to respiration past the face.

Why, then, didn't you draw these distinctions? It's clear your grasp of how the diluter demand mask works was not sufficient.
 
Guest

RE: Oxygen Mask.

Wed Jun 19, 2002 10:46 pm

EP,
And yet you provide no documentation or references to back up your claims. Every post you get involved in turns into a fur ball. Have you ever used an O2 mask? Have you ever been unpressurised at 43,000' and felt the "breeze in the face" It feels like a lot more than 15 psi. But I have to admit I had no way to measure the pressure. Just what are your credentials? Why don't you do a search on Diluter pressure demand regulators or read the references I mentioned? Erasmus provided documentation showing the A320 regulators begin pressurised functions above 30k cabin altitude, you've show us noting other than your vast knowledge. When you place the switch in the emergency position, the positive pressure is substantial. Is it 15 psi? Or 50 psi? To me it doesn't matter, as long as the pressure provided is greater than ambient. Why do you feel the need to pick apart posts for spelling and other minor things? Are you a lawyer? The original post was how do the masks work and how do the Pax masks drop. Why don't you stick to the subject instead of trying to prove what an expert you are by trying to "correct" other posts.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Thu Jun 20, 2002 1:18 am

727pfe,

1. I can expand on any topic I choose; as you can and have done on this one.

2. The reason this has turned into a furball is b/c you simply don't have the integrity to state, "Gee. I learned something." You agreed with Jetpilot's statement: The pilots mask forces oxygen into the lungs under pressure allowing absorbtion by the body. Wrong!! A diluter demand mask DOES NOT do this. Period. So, instead you choose to redirect and continue the argument.

3. You don't have a clue what pressure breathing is, and you admit you haven't done it. Maybe you should think about that for a moment. What's the diff? The masks look the same...Could it be DELIVery Pressure???

My response was:
There are two types of O2 masks for cockpit use:

Pressure demand - these masks are typically used on high g capable, military a/c. In use, the O2 is supplied at pressures that actually interfere with speaking. In other words, much more than the slight over pressure of the second mask:

Diluter demand - most common on airliners and business a/c. Typ has 3 positions: Normal, 100% and Emergency. Normal will dilute the O2 w/ambient air up to a specific pressure alt, above which 100% O2 is delv'd. 100% delivers, of course, 100% O2 even at lower alts. Both "normal" and "100%" positions only provide flow when a breath is drawn. "Emergency" provides continuous flow, 100% O2 (ie very slight positive pressure) in order to clear the mask/goggles if smoke is present. A diluter demand mask WILL NOT force O2 into the lungs.

To which Bellerophon and FredT strongly concurred. As Bellerophon and I both stated, if you've ever used a pressure demand mask, you'd know the distinction, which makes the difference b/t the two types blatantly clear. The fact that you still think that a diluter demand mask is in ANY way pressure breathing, or has any impact on human respiration donwstream of the nose, indicates you haven't experienced the distinction and are ignorant of the difference. Yet you argue.

So try this, and report the results:

Go sit in your seat. Put on your mask, and try to let it force air into your lungs. Talking or not. Stand/sit; whatever. What you'll find is, with a diluter demand mask, no matter what you do,
*****until you decide to INHALE (conciously or sub conciously!), NO O2 will get to your lungs. The mask WILL NOT do it FOR YOU.*****

That would be PResure Breathing, and that is the distinction you have missed in stellar fashion.

 
Guest

RE: Oxygen Mask.

Thu Jun 20, 2002 1:49 am

The only thing I've learned is that you have no clue. Once again, give some reference. The Delta 767 maintenance training manual states that the output pressure from the regulator is nominally 70 psi. It is labelled a Diluter Demand regulator, but it supplies positive pressure above 28k. I obviously am not going to convince you that you are wrong, and you won't convince me. And I have used pressure breathing, have you?. I will agree that the pressure output is different with different regulators, aircraft that have a higher service ceiling use a high pressure regulator. Why don't you take a couple of Human factor classes? Maybe lean a little about human physiology. Have you ever been a crewmember, or just an aviation know it all? Have you ever been to an altitude chamber? The only reason this thread turned argumentative, is you, because every thread you get involved in is the same. Do you see a PAttern?
 
Guest

RE: Oxygen Mask.

Thu Jun 20, 2002 2:59 am

Try reading this article.
http://www.avweb.com/articles/highalt/
 
Guest

RE: Oxygen Mask.

Thu Jun 20, 2002 3:49 am

Another good source of information is a booklet published by the FAA titled "Aviation Physiology".
You can get it by contacting the FAA at:
FAA
Civil Aeromedical Institute
Aeromedical Education Division, AAM-400
Mike Monroney Aeronautical Center
P.O. Box 25082
Oklahoma City, OK 73125

All my statements have been backed by research, not conjecture.
Our DC-8, DC-9, and 767 manuals all refer to "Diluter Demand Positive Pressure Breathing" regulators. Is this the same "Pressure Breathing" mentioned here?
I don't know for sure, we might be arguing over semantics. According to the FAA, straight Demand type regulators are only good to 40,000'. Above that a Demand pressure regulator is required.
The statement "Go sit in your seat, put the mask on and see if it forces O2 into your lungs" is in invalid statement. We are talking about what happens at altitude, you can't duplicate the pressure differential in the cockpit. I would CONJECTURE, that at 40,000' and 2.73 psi, even a relatively low pressure of 15 psi, might just do that. But, everything I can find in our manuals state the system output pressure to be between 50 -70 psi. Again, since I've never measured this, I will believe it until proven otherwise.
PS. Putting speculation in CAPS, or acerbic language, does not make it a fact.
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Thu Jun 20, 2002 4:42 am

727pfe,

It seems like you are the one learning aviation physiology at about the rate this thread is progresing, particularly since you agreed with the now classic "The pilots (diluter demand/typ transport) mask forces oxygen into the lungs under pressure allowing absorbtion by the body." I notice Jetpilot has been rather absent from the discussion, but two other members have directly agreed with me.

You have said: "I don't agree that the O2 will be "forced into" the pilots lungs. Just that the pressure in the the system will be higher than ambient, once the regulator goes into it's pressuirzed mode." So that statement agrees exactly with what I'm saying, ie that a diluter demand mask won't respirate for you. But you don't seem to know what your position is. Technically speaking, .00001 psi greater than ambient is pressure breathing. Do you think you mask in the 727 engineer's seat can respirate for you with the seat belts locked tight? I don't care what the ambient altitude is. A diluter demand mask still requires the human to inhale. Why you don't get that is beyond me.

My reference is altitude chamber training (been there - have you?) at CAMI in OKC. The class DEFINES and teaches the distinction b/t the 2 masks I have described.

Human Factors? Do a word search on this forum for that very phrase and figure out for yourself what my qualifications are.

Technical Competence? Same thing. I pick and choose the topics I respond to typically b/c I see a glaring error in the logic. Yours and Jetpilots was blatant in this case, and it went the way it typically does when someone who holds himself in high regard can't learn something. Don't blame me for holding your feet to the fire, that's the purpose of the forum.

cheers-
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Oxygen Mask.

Thu Jun 20, 2002 4:56 am

727pfe,

You refereed a topic previously about "windshear" audible alerts. I made my argument, and prefaced with a ref to part 121 ops...the person opposed to me whined about what does or doesn't happen in Canada, which I had already excluded with the phrase "Part 121." the thread went on and on, and I just restated what I originally had.

You agreed with me...Is this similar?
 
Guest

RE: Oxygen Mask.

Thu Jun 20, 2002 5:11 am

Facts:
FAA 25.1443 requires a mean tracheal oxygen partial pressure of 149mm Hg for continuous flow equipment, 122 mm Hg for demand equipment. This is for the crew. For pax, 100mm below 18.5K, 83.8 mm Hg above.

1. 149mm Hg is the normal oxygen partial pressure at sea level (reads: unpressurized). One can deduce that oxygen equipment DO NOT have to be pressurized.

2. With 100mm/83.8mm, the intent of the FAA requirements is to keep the pax from hypoxia or from passing out.

Regards,
Nut
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Oxygen Mask.

Thu Jun 20, 2002 7:22 am

MD11nut "1. 149mm Hg is the normal oxygen partial pressure at sea level (reads: unpressurized). One can deduce that oxygen equipment DO NOT have to be pressurized."

EXACTLY.... that applies to sea level and 40,000 feet. So as ambient pressure decreases the pressure in the mask increases and provides sea level pressure breathing environment.

If I'm wrong correct me.

The question isnt weather the mask would respirate for you. If it forced air into your lungs you wouldn't be able to exhale. The statement is that whe nyou inhale your respiratory system becomes part of the pressurized environment until the mask valve coses again upon exhalation.

JET
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Oxygen Mask.

Thu Jun 20, 2002 8:31 am

Thx, MD11.

If you want to maintain the sea level static partial O2 pressure, as opposed to that you're in with a cabin altitude of 8000', you'll need slight overpressurization above 40k. IOW, you need to be breathing 100% O2 at the 40k feet ambient pressure.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Guest

RE: Oxygen Mask.

Thu Jun 20, 2002 8:55 am

JetPilot & FredT - agreed with you both. That was what I was trying to put out so people will see the subtleties. You didn't see me calling anybody as being wrong  Smile/happy/getting dizzy. It's just how you look at it.

Regards,
Nut

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