Inert Gas in Fuel Tanks

From:         "P. Wezeman" <pwezeman@blue.weeg.uiowa.edu>
Organization: The University of Iowa
Date:         Tue, 22 Oct 1996 23:48:53 GMT
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   I would like to thank everyone who answered my question about the
use of inert (non oxygen containing) gasses in the ullage spaces in
aircraft fuel tanks to prevent fuel-air explosions. This question is
naturally related to the loss of TWA flight 800, where investigators
have been reported to have found evidence consistent with such an
explosion in the center fuel tank.

   To summarize the information I received, many aircraft have
successfully used inert gas systems. In particular, the C-5 and C-17
transports flown by the United States Air Force use nitrogen gas for
this purpose. The newer of these two aircraft, the C-17, has a device
that separates ambient air into its two main constituents, oxygen and
nitrogen, and sends the nitrogen produced to the fuel tanks. As I
understand it, this is the same basic process that has been used on
other aircraft to produce breathing oxygen for the crew.

   Military air transport does not, of course, have exactly the same
economic constraints as an airline, but still the C-17 is similar to a
large airliner in several respects, including size, type of engines
and number of flight crew (excluding cabin attendants), and the C-17
is said to have been designed to strict specifications of total
lifetime cost, including maintenance. McDonnell Douglas in fact is
currently offering the C-17 for sale to commercial operators, although
the civilian version will lack the on board inert gas generating
system as well as in-flight refueling equipment and some other
systems.

   Is there any reason that it would be impractical to put a nitrogen
fuel tank pressurization system similar to that on the C-17 on an
airliner?  Could it be retrofitted, or would it have to be
incorporated in new models only? Aside from the weight and space, I
can't see any drawbacks, in that the failure of such a system would
not in itself endanger the aircraft.  Ambient air would still be
available for venting, so it would be no more dangerous than present
practice, as long as maintenance on the electrical system was kept to
the current standard.
            
                       Thank you in anticipation,

                        Peter Wezeman, anti-social Darwinist

                             "Carpe Cyprinidae"