Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Why May Bags On Oxygenmasks Not Inflate?  
User currently offlineHT From Germany, joined May 2005, 6525 posts, RR: 23
Posted (8 years 10 months 1 week 3 days 4 hours ago) and read 4302 times:

After a couple of flights the last days I´ve watched the usual safety demonstration over and over, however one question came up in me:
Everytime the use of pax-oxygenmasks is demonstrated it is said that "the bag may not inflate".
Q: Why is it so ? Which purpose does the bag have ?

-HT


Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
19 replies: All unread, jump to last
 
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 1, posted (8 years 10 months 1 week 3 days 3 hours ago) and read 4293 times:


O2 mask for GA Aircraft.

Quoting HT (Thread starter):
the bag may not inflate

If the Bag is Punctured or connecting hose Disconnects.Though very rare.Thats why a stby mask is provided in each PSU.

The bag holds a fixed qty of O2 when the Flow is activated.
regds
MEL



Think of the brighter side!
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 2, posted (8 years 10 months 1 week 3 days 3 hours ago) and read 4292 times:

My understanding was that it's a rebreather system. The bag holds mostly exhaled air, and inhaled air comes from a mix of the supplied oxygen and oxygen that was exhaled and stored in the bag.


Position and hold
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 3, posted (8 years 10 months 1 week 2 days 20 hours ago) and read 4247 times:

Quoting Bri2k1 (Reply 2):
My understanding was that it's a rebreather system

Not exactly as that usually implies the presence of carbon dioxide scrubbers in the system.

Actually the system is constant-flow, but the flow rate is not very high - a liter a week or so. (kidding) So while you are not inhaling, oxygen will pool in the mask. When you do inhale the first part is high O2 content, but when that is gone the little flapper valve in the back of the cup opens and you are inhaling cabin air plus smoke or whatever else it contains.

If you breathe rapidly the bag will never inflate because the flow rate is not high enough to fill the cup, then inflate the bag.

If you are not breathing rapidly you obviously have not grasped the seriousness of the situation.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineTimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 4, posted (8 years 10 months 1 week 2 days 6 hours ago) and read 4076 times:

Just about all systems (commercial aircraft) are NOT using bottled 02- they use solid chemical generators. I remember the early days they F/A's briefing included the words, "you may notice a slight burning smell". I don't think the generators can make enough volume to get the bag to inflate, but do cause enough flow to keep you going until the altitude gets to a level the atmosphere can sustain you. The cup has a small exhaust valve built into it, and the supply line. When you inhale, the valve closes and you get whatever is in the bag, and then on exhale the valve opens, letting out the C02.

User currently offlineLoggy From United Kingdom, joined Oct 2005, 15 posts, RR: 0
Reply 5, posted (8 years 10 months 1 week 2 days 5 hours ago) and read 4069 times:

So, if you breathed reeaaall slow the bag would inflate because you wouldn't be using all the ? Pure o2 ?, or just plain old high altitude, say 10000 Ft, air being supplied ? .
If it were pure o2 then the supply would be quite low ? . Enough to keep you conscious, panting, or enough to keep your vital systems going ? .

Obviously if the supply were low then unfit and smoker pax would suffer more, albeit temporarily, than fit healthy people.


User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 6, posted (8 years 10 months 1 week 2 days 4 hours ago) and read 4061 times:

Quoting TimT (Reply 4):
they use solid chemical generators



Quoting Loggy (Reply 5):
Obviously if the supply were low then unfit and smoker pax would suffer more, albeit temporarily, than fit healthy people

Unfit ok.But why would a Smoking Pax would suffer more.



Think of the brighter side!
User currently offlineLoggy From United Kingdom, joined Oct 2005, 15 posts, RR: 0
Reply 7, posted (8 years 10 months 1 week 2 days 3 hours ago) and read 4054 times:

Quoting HAWK21M (Reply 6):
Unfit ok.But why would a Smoking Pax would suffer more.

Well depending how long they have smoked would determine their lung capability for extracting the necessary oxygen from any air supply into the blood stream. I would imagine a moderate smoker noticing the effects of a reduced oxygen supply moreso than a non smoker due to the damaging effects on the lungs through smoking.


User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 8, posted (8 years 10 months 1 week 2 days 2 hours ago) and read 4046 times:

Quoting Loggy (Reply 7):
I would imagine a moderate smoker noticing the effects of a reduced oxygen supply moreso than a non smoker due to the damaging effects on the lungs through smoking.

Because of collapsed lungs.
regds
MEL



Think of the brighter side!
User currently offlineTod From Denmark, joined Aug 2004, 1724 posts, RR: 3
Reply 9, posted (8 years 10 months 1 week 1 day 21 hours ago) and read 4007 times:

Quoting TimT (Reply 4):
Just about all systems (commercial aircraft) are NOT using bottled 02

744 use gaseous oxygen and it is a customer option 772 and 773.

Tod


User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 10, posted (8 years 10 months 1 week 1 day 20 hours ago) and read 4001 times:

Quoting Bri2k1 (Reply 2):
rebreather

Your'e right, that was the wrong word. What I was trying to describe is that the flow of oxygen goes into the mask, and the bag is filled by exhaled air, which still contains oxygen. Then, eventually, inhaled air will be a mix of the supplied pure oxygen plus the exhaled air from the bag. When we breathe normally, we don't inhale pure oxygen, so this approximates normal breathing.

Am I closer?



Position and hold
User currently offlineElectech6299 From United States of America, joined Aug 2005, 616 posts, RR: 3
Reply 11, posted (8 years 10 months 1 week 12 hours ago) and read 3897 times:

Try this LINK from a report on the oxygen systems of a MD-11. It is supporting information for the TSB crash investigation of SR111.

It explains the masks in detail, and will answer most of the questions about the generators. It is a little thin on info about the reservoir bag, tho:

Quote:
Each passenger oxygen mask is fitted with a reservoir bag that is attached to the oxygen generator with a flexible hose. When a generator is initiated, the reservoir bag unfolds and may inflate (depending on the altitude) until breathing begins.

I assume this means cabin altitude- which is obviously above 14,000 feet if the masks have deployed. But basically, it is as described by Slamclick- a reservoir bag, that will inflate to provide pressure relief and a reservoir of O2 until the passenger starts breathing, but the bag is not intended to supply the breathing air. The passenger breathes cabin air, supplemented by O2 from the generator supply tube (or reservoir bag if any has accumulated there). Exhaled air is vented through the exhalation valve in the mask directly to the cabin, not into the bag.


But to answer the question directly- based on altitude. That's what the report says. I don't know which way the altitude affects it- I would think high altitude, thinner atmosphere, the bag inflates more. But perhaps lower altitude, denser atmosphere, more efficient operation of the canisters which provide more O2, inflating the bag more. I dunno

[Edited 2005-10-21 01:34:17]


Send not to know for whom the bell tolls...it tolls for thee
User currently offlineErj-145mech From United States of America, joined Oct 2001, 306 posts, RR: 1
Reply 12, posted (8 years 10 months 1 week 9 hours ago) and read 3869 times:

The most important function of the mask is that it muffles the screams of the wearer, other than that, it will provide enough oxygen to sustain life, not necessary consciousness.

User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 13, posted (8 years 10 months 1 week 8 hours ago) and read 3859 times:

Quoting Bri2k1 (Reply 10):
Am I closer?

Well, my only hangup was the word "rebreather" which, to me, conjures images of underwater or firefighter breathing gear using CO2 scrubbers.

I think we were thinking of the nosebags the same way, though.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineTod From Denmark, joined Aug 2004, 1724 posts, RR: 3
Reply 14, posted (8 years 10 months 6 days 20 hours ago) and read 3816 times:

Quoting Electech6299 (Reply 11):
But perhaps lower altitude, denser atmosphere, more efficient operation of the canisters which provide more O2,

Oxygen generator canisters are self contianed and effiency is not impacted by altitude.

Tod


User currently offlineElectech6299 From United States of America, joined Aug 2005, 616 posts, RR: 3
Reply 15, posted (8 years 10 months 6 days 12 hours ago) and read 3780 times:

Quoting Tod (Reply 14):
Oxygen generator canisters are self contianed and effiency is not impacted by altitude.

Well, you can see that I didn't read all the info in my link  embarrassed  Oops... I was more interested in the aneroid switches and door release, and glossed over the canisters. Glad somebody knows...

Quoting SlamClick (Reply 13):
Well, my only hangup was the word "rebreather" which, to me, conjures images of underwater or firefighter breathing gear using CO2 scrubbers.

Most of the firefighting gear I have worked with is strictly compressed air SCBA, I haven't personally seen or heard of rebreathers outside of underwater/submersible vehicle or contained HAZMAT site use (Like chemical dump cleanup). Do airport firefighters use them? Or cockpit crew? Any info you have on this would be welcome.



Send not to know for whom the bell tolls...it tolls for thee
User currently offlineHT From Germany, joined May 2005, 6525 posts, RR: 23
Reply 16, posted (8 years 10 months 6 days 5 hours ago) and read 3752 times:

Thanks for all the input !
-HT



Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
User currently offlineDC8FriendShip From United States of America, joined Apr 2005, 242 posts, RR: 3
Reply 17, posted (8 years 10 months 5 days 21 hours ago) and read 3725 times:

Quoting Tod (Reply 9):
744 use gaseous oxygen and it is a customer option 772 and 773.

For the flight crew, maybe. but i doubt that there are tanks onboard that hold enough O2 for over 250 people. They most likely use generators like most pax aircraft do.



Come fly the Friendly Skies of United
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 18, posted (8 years 10 months 5 days 3 hours ago) and read 3677 times:

Quoting DC8FriendShip (Reply 17):
For the flight crew, maybe. but i doubt that there are tanks onboard that hold enough O2 for over 250 people. They most likely use generators like most pax aircraft do.

Didn't the B742 have Piped O2 for the Pax system.
regds
MEL



Think of the brighter side!
User currently offlineTod From Denmark, joined Aug 2004, 1724 posts, RR: 3
Reply 19, posted (8 years 10 months 4 days 21 hours ago) and read 3675 times:

Quoting DC8FriendShip (Reply 17):
but i doubt that there are tanks onboard that hold enough O2 for over 250 people. They most likely use generators like most pax aircraft do.

Nope.

The pax oxygen tanks on 747 are located in the forward cargo compartment, right side just aft of the cargo door, next to the halon tanks. Additional oxygen tanks are sometimes installed between the main deck floor beams in the forward cargo compartment. I designed the installation of two extra tanks for the Corsair 744 fleet of ex-UA planes. Some of the asian operators such as SQ have as many as 14 extra bottles on their 744 to facilitate high pax loads and long range requirements.

On 777 gaseous oxygen is an option. About half the ones I've work on have gaseous systems.

Quoting HAWK21M (Reply 18):
Didn't the B742 have Piped O2 for the Pax system.

Yes

Tod


Top Of Page
Forum Index

Reply To This Topic Why May Bags On Oxygenmasks Not Inflate?
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Why No Papi On W/B Rwys At LAX? posted Wed Oct 18 2006 06:58:06 by Adipasqu
Why 12 Exits On This 757? posted Sat Apr 22 2006 21:26:05 by YoungFlyer
Why No Landings On posted Mon Sep 12 2005 11:29:01 by TheSonntag
Why No V2500 On The A318 posted Sat May 28 2005 13:52:30 by HAWK21M
Why The Forehead On Some A/c? posted Tue Apr 12 2005 08:23:56 by AR1300
Why No Winglets On The 777? posted Sun Sep 12 2004 12:19:58 by Regis
Why No HUDs On Large Aircraft? posted Tue Aug 31 2004 05:52:04 by AndrewAir
Why 40° Flaps On The Cessna 150? posted Fri May 14 2004 20:48:04 by Bragi
Why No Paint On Wings? posted Wed May 5 2004 12:55:05 by A380900
Why No FE On 737? posted Sun Apr 25 2004 16:36:12 by Checkerboard

Sponsor Message:
Printer friendly format