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Author Topic:   Spacecraft atmosphere and fire prevention
moorouge
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Posts: 1490
From: U.K.
Registered: Jul 2009

posted 12-27-2012 01:30 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Having just finished watching the first of the Royal Institution Christmas lectures, I was impressed by a demonstration that showed how it was impossible for fire to be present when the oxygen content of our atmosphere was reduced from 21% to 15%. This reduction has no effect on us.

This set me wondering what the oxygen content is on spacecraft atmospheres where either a nitrogen/oxygen or normal air is used. Do spacecraft using these mixes have reduced oxygen content as fire prevention? If not, has this simple method of preventing cabin fires ever been considered?

Robert Pearlman
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From: Houston, TX
Registered: Nov 1999

posted 12-27-2012 05:16 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Gravity, apparently, plays a role in how fires burn — on Earth and in space.

Based on experiments performed on the International Space Station, flames in space burn at a lower temperature, slower and with less oxygen than in normal gravity. As a result, 'simply' lowering the oxygen content as described may not be an option at all.

The space station maintains an atmosphere of about 21% oxygen, 78% nitrogen at 14 lbs. per square inch.

moorouge
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From: U.K.
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posted 12-27-2012 06:11 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Thanks for the input Robert. However, the impression given during the lecture was that it was impossible for a fire to start as there was insufficient oxygen at 15% to sustain it. This, I assume, was regardless of whether there was gravity present or not.

On edit - the lecture may be watched either on the Royal Institution website or on BBC iplayer.

garymilgrom
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From: Atlanta, GA, USA
Registered: Feb 2007

posted 12-27-2012 07:37 AM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
What's the name of the lecture showing this? Thanks.

moorouge
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Posts: 1490
From: U.K.
Registered: Jul 2009

posted 12-27-2012 09:00 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Gary - sent you email. To update. It seems that the lectures haven't been posted yet on either BBC or Royal Institution sites. But they will be shortly. Keep an eye out for them. The reduced oxygen demonstration has to be seen to be believed as does the floating of a foil boat on an atmospheric gas.

The series of lectures are called 'The Modern Alchemist'.

Robert Pearlman
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Posts: 27327
From: Houston, TX
Registered: Nov 1999

posted 12-27-2012 11:32 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
To quote Wikipedia:
The limiting oxygen index (LOI) is the minimum concentration of oxygen, expressed as a percentage, that will support combustion of a polymer. It is measured by passing a mixture of oxygen and nitrogen over a burning specimen, and reducing the oxygen level until a critical level is reached.
The Flame Extinguishment Experiment (FLEX) was aimed in part in measuring the LOI index for polymers in a microgravity environment. From the results:
The ambient oxygen concentration was systematically lowered from test to test so as to approach the limiting oxygen index (LOI) at fixed ambient pressure. At one atmosphere pressure, ignition and some burning were observed for an oxygen concentration of 13% with the rest being nitrogen.

Gonzo
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From: Lansing, MI, USA
Registered: Mar 2012

posted 12-27-2012 01:35 PM     Click Here to See the Profile for Gonzo   Click Here to Email Gonzo     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by moorouge:
I was impressed by a demonstration that showed how it was impossible for fire to be present when the oxygen content of our atmosphere was reduced from 21% to 15%. This reduction has no effect on us.

I would question this statement about it having "no effect on us". The human body not only evolved to survive at roughly 20.5% oxygen, many studies show that mental capacity starts to diminish at concentrations as high as 18%. Lack of coordination and any ability for strenuous work diminishes as well as the percentage drops. At 15%, most people can survive as long as physical work or critical decision making is not needed.

For myself, having spent a fair amount of time at extreme elevations (15,000+ feet), these conditions certainly hold true. In fact, these are some of the very symptoms to watch for with Acute Mountain Sickness (be it HACE or HAPE) among others. Left untreated it can be fatal. So, I'd question this assertion and probably the study in general.

moorouge
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Posts: 1490
From: U.K.
Registered: Jul 2009

posted 12-27-2012 02:10 PM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Gonzo:
I would question this statement about it having "no effect on us".

Take this up with Dr. Peter Wothers. It is his statement. I was merely quoting him.

All times are CT (US)

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