Date: Fri, 30 Aug 2002 05:14:39 -0500
Reply-To: John Rodgers <j_rodgers@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <j_rodgers@CHARTER.NET>
Subject: Re: Re: Fire Extinguishers
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Stan Wilder wrote:
> The Magnesium isn't really a hazard.
It's good stuff in the right applications. Lighter than aluminum. Strong. In
earlier years prone to inner-granular corrosion. Maybe modern metalurgy has
resolved that. Beech Aircraft Corporation used the stuff on the ailerons and
elevators on their Bonanza Series. With the passage of time the corrosion
became a problem for them. It was also brittle and fatigue cracking was a
problem. And it was hard to get paint to stay put on its surface.
Magnesium aircraft engine cases were used extensively in WWII. Many a plane
was lost due to an engine fire where the magnesium got hot enough to burn. No
way to put that out. Can you imagine a magnesium fire being fanned by a 200
mph wind???
Magnesium will burn in many atmospheres because it gets hot enough to cause
separation of of any O2 molecules from the surrounding gasses. A burning
magnesium strip, when thrust into a pure carbon dioxide atmosphere - one
which would extinguish most flames - simply strips away the O2 molecules
from the carbon leaving a pure black carbon soot. Very messy! Same reason
magnesium burns underwater. Tears the oxygen atom away from the H2O
molecule.
> Also aircraft tires that fly at high altitudes are filled with nitrogen.
> Won't freeze, Won't hold moisture,
> Won't expand at altitude
What altitude? One foot above sea level? 30,000 feet above sea level? All
gases respond to Boyles Law. Reduce the pressure and the gas will expand to
the limits of its container. Nitrogen will expand in a tire to the mecanical
limits the tire imposes. The reason nitrogen is used in Aircraft tires is
that nitrogen , being an inert gas under pressure in the tire, does not
oxidize - ie, rot - the rubber in the tire as rapidly as would occur with an
air filled tire. And it is less hazardous in the even of a brake/wheel fire.
No oxygen is present to do the job or feed the fire. The oxygen present in
air, and under pressure in a tire acts more rapidly that at normal
atmospheric pressure. There's just more oxygen molecules pressent in the
compressed air. More oxygen molecules present, more oxidation.
John Rodgers
88 GL Driver
