Re: Chemistry of Oxygen Generators

From:         bradg@io.org (Brad Gillies)
Organization: Internex Online (io.org), Toronto, Ontario, Canada
Date:         25 May 96 14:40:21 
References:   1
View raw article
  or MIME structure

In article <airliners.1996.708@ohare.Chicago.COM>, Bob Standaert <standaert@chemvx.tamu.edu> wrote:
>I remember reading a post which mentioned that emergency oxygen in
>modern aircraft is generated chemically by "perchlorate candles," and I
>was curious about how they worked.  The recent ValuJet crash renewed my
>curiosity; can anyone please provide more detailed information about how
>the O2 generators work?  I would be most interested to know the exact
>chemical reaction and how it is initiated, but any help, insight, or
>history would be appreciated.

The oxygen generator "Burns" a mixture of sodium chlorate
and iron to produce pure oxygen.
sodium chlorate, when heated to 892 deg F, decomposes into ordinary salt and
oxygen.    The fuel to produce heat for the decomposition of the sodium
chlorate is iron.  When sufficient heat is applied to start the burning of the
iron with a portion of the released oxygen, the burning continues until the
chemical process is completed.
The generators are either activated electrically or by a percussive "cap" or
squib.
Assuming the generators on the aircraft, in the hold were of the latter type,
the cargo would have to have been shipped with the squibs intact.  This alone
would be illegal as it would be the equivalent of carrying live ammunition.
If the generators are the electrical variety they would need a supply of
electricity to activate.
The liklyhood that these generators started the fire is somewhat remote BUT
the possibility that they were activated by a cargo fire is not so remote.
There could have been any number of things to start a fire but heat would
activate the generators and make the fire a thousand times worse.

This is just the way I look at it.  I'll wait until the NTSB finds probable
cause then I'll know more, as will we all.

--
Brad GIllies		Bradg@io.org
PPASEL		AME (CANADA)	A&P
	HTTP://www.io.org/~bradg