Smoke: Mask 100% or EMER?

[ImbracableCrunk]

I'm in ground school (again) for the B737, and brought this up to my instructor today:

"Why does the memory item for smoke/fumes say Oxygen Mask . . . On/100% and not On/EMER"?

Having talked to an engineer from Avox/Scott years ago I came away with the impression that the 100% is meant as 100% O2 at 100% pressure (EMER), not simply 100% O2 content.

The engineer explained that the pressure in the mask helps to seal the mask and provide a positive pressure to keep irritants out.

We're got the EROS masks in our 737s, but I'd imagine the concept is the same.

Thoughts?

[westhawk]

My Lear 60 (EROS mask) cabin fire checklist memory items are worded exactly the same as yours. The systems description states that 100% mode supplies oxygen only when demanded unless the cabin altitude reaches 37,000 ft, in which case positive mask pressure will be maintained. In EMER mode, 100% oxygen is supplied under a slight positive pressure at all times, thus preventing smoke ingress.

I guess doing what the checklist says is okay for checkrides and up until you get real smoke in your mask. Then maybe it's time to exercise some initiative! I'd rather train for how I'll REALLY do it though.

[FullWings]

Having had the cockpit fill with smoke/fumes on rotation recently, I can confirm that an Eros mask on 100% is pretty effective at keeping the nasties out, although I don't have any face furniture. I was aware that if I needed to clear the mask out I could give a little twiddle and/or push on the knob to remove any unwanted fumes/aerosols.

I agree that a better quiescent state for the mask would be to have "EMER" selected as you can always unselect it after the event but our checklist (777) says to have it on 100%... :confused:

[ImbracableCrunk]

Having had the cockpit fill with smoke/fumes on rotation recently, I can confirm that an Eros mask on 100% is pretty effective at keeping the nasties out

I flew with a gent who, after 2 go-arounds, thought he was in need of a cigarette. I said, "Do whatever you need to do to get us on the ground." I put on the mask, and I could still smell the smoke. EMER kept the smoke out better.

[DongJoon Choi]

The oxygen regulator has three modes:
Normal: Red latch on left is up - Gives air/oxygen mix on demand. Use if no fumes are present eg decompression.
100%: Push red latch on left down - Gives 100& oxygen on demand. Use if smoke or fumes are present.
Emergency: Rotate red knob clockwise - Gives 100% oxygen under pressure. Used to clear mask & goggles of fumes and should also be used if aircraft is depressurised above 39,000ft.

Is there anybody here that knows why EMER mode should be used above 39000ft ???? How about 38000, 37000.........or 30000???

[ImbracableCrunk]

Mr Choi,

The regulator has some schedule built in to the mask. Above a certain altitude, it supplies 100% oxygen content at 100% pressure (the same as EMER mode).

Maybe for your mask (KAL? Jeju?), the altitude where the diluter/demand is at 100%/100% is FL390. Where did you find the FL390 reference?

According to the Avox/Scott engineer, they want crews to go to EMER first when there is a problem, and then sort it out after.

So you're climbing out, MASTER CAUTION, CABIN ALT, etc, you don the mask and go to EMER. If you're still conscious after that, you can go to 100% or NORM.

[DongJoon Choi]

Dear ImbracableCrunk,

I think maybe that a certain altitude you said is 27000ft. FCOM(-800) says that Pressure breathing occurs above 27,000feet. However, I have no idea whether or not the pressure breathing means the same as you said( Above a certain altitude, it supplies 100% oxygen content at 100% pressure (the same as EMER mode). Also there is no explanation regarding the function as you said in AMM.

FL390 is from 737 Emergency Equipment (http://www.b737.org.uk/emergency_equipment.htm#Flight_Crew_Oxygen).


If you can, please let me know the reason why people at the pointy end of the tube should use EMER mode above 39000ft.

[ImbracableCrunk]

Mr. Choi,

I think the reason for going directly to EMER is to bypass the diluter/demand regulator. Also, as the FCOM states, the EMER position is for smoke/fumes, not simply for clearing the smoke goggles. The positive pressure inside the mask prevents flow into the mask.

p.s. Have a Halla-San soju for me, please.