# oxygen masks on airlines

**URL:** <https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101>\
**Category:** Factual Questions\
**Created:** [July 3, 2001, 4:57pm UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101 "2001-07-03T16:57:32Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![satanslawyer](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@satanslawyer](https://boards.straightdope.com/u/satanslawyer)\
**Post date:** [July 3, 2001, 4:57pm UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101/1 "2001-07-03T16:57:32Z")

</div>

On airliners they tell you after boarding all about the emergency proceedure. One of the things they tell you is when the oxygen masks come down they will have a bag on them, and that the bag does not inflate. What is the purpose of this bag?

---

<div class="post-metadata">

**Author:** ![Colin\_Trainer](https://avatars.discourse-cdn.com/v4/letter/c/958977/32.png) [@Colin\_Trainer](https://boards.straightdope.com/u/Colin_Trainer)\
**Post date:** [July 3, 2001, 5:09pm UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101/2 "2001-07-03T17:09:22Z")

</div>

When you wear an airline oxygen mask, why doesn’t the plastic bag inflate?  
URL: [http://www.straightdope.com/classics/a3\_140.html](http://www.straightdope.com/classics/a3_140.html)

---

<div class="post-metadata">

**Author:** ![ricepad](https://avatars.discourse-cdn.com/v4/letter/r/b38774/32.png) [@ricepad](https://boards.straightdope.com/u/ricepad)\
**Post date:** [July 4, 2001, 8:50pm UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101/3 "2001-07-04T20:50:02Z")

</div>

I heard another explanation for this. Sometimes, the decrease in cabin pressure can force material out of your stomach (especially if you’ve just eaten). The bag gives the vomitus someplace to go, so you don’t aspirate it.

---

<div class="post-metadata">

**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\
**Post date:** [July 4, 2001, 9:45pm UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101/4 "2001-07-04T21:45:21Z")

</div>

> [@](#):
>
> \*Originally posted by ricepad \*  
> \*\*I heard another explanation for this. Sometimes, the decrease in cabin pressure can force material out of your stomach (especially if you’ve just eaten). The bag gives the vomitus someplace to go, so you don’t aspirate it. \*\*

But the bag is connected to the facemask by a narrow tube that more likely than not would not open directly in front of the mouth, and the mask does not fit totally tight, so any vomitus would likely spill out the sides.

jrd

---

<div class="post-metadata">

**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [July 5, 2001, 1:51am UTC](https://boards.straightdope.com/t/oxygen-masks-on-airlines/71101/5 "2001-07-05T01:51:23Z")

</div>

> [@](#):
>
> \*Originally posted by ricepad \*  
> **I heard another explanation for this. Sometimes, the decrease in cabin pressure can force material out of your stomach (especially if you’ve just eaten**

The physics of this doesn’t make sense. If the cabin pressure drops, pressure on your mouth decreases, but so does the pressure on your belly. There will be no net force to push material out of your stomach. Air in your lungs is a different story - since gas is compressible, when the pressure drops it expands and escapes from your mouth or nose.

Of course, if the plane went out of control, the motion may very well make you airsick.