Ummm... look, don't take this wrong man, and don't take it as a criticism, but: That's sort of not correct. Or better yet, not the full story. What would govern things in this case is not
merely the availability of oxygen but also the aluminum oxidation
rate. It's actually surprisingly low (
Source 1.
Source 2).
I really,
really would need a real chemist here to explain the details well (too bad Maldach doesn't play in the CT subforum
; I merely took undergrad classes and don't have his experience... ). But: Despite the fact that aluminum oxidation releases quite a bit of energy, it's not normally a quick reaction at all, at least not when you're talking oxidation with air (with iron oxide, well, that's another story but it's also a different reaction with different kinetics). Once an oxide layer forms on an aluminum "particle" (grain, seed, whatever) the aluminum underneath is sealed off from further oxidation. And that's why there's
so much research into particle size for aluminum oxidation reactions: Researchers are trying to get a feel for the subtle aspects of the aluminum oxidation reactions in order to fine-tune the rate as well as the completeness to which it reacts. Remember Mackey's mention of Tillotson in reference to the thermite stuff? He's done some research noting that depth of oxidation layer on aluminum particles most definitely affects oxidation "completeness" in ways that aren't immediately apparent; beyond a certain point, smaller particles actually
reduces the energy release because a greater proportion of the aluminum particle surface becomes unavailable to combustion due to the depth of the oxidation layer relative to the particle size. That's not immediately obvious, yet it's understandable in hindsight.
Whoops, I'm starting to blabble
. Anyway, what must be understood is that a fire of office contents (and in the beginning, jet fuel) in the area would quite obviously be proceeding far faster than an air-aluminum oxidation. And without aluminum being consumed at a fast rate, oxygen won't be consumed in an aluminum oxidation at a high rate. That's the bottom line. I wouldn't want to even think about modeling local oxygen concentrations in a fire
, but when you're talking about the oxidation of aluminum, you must remember the reaction kinetics and compare
that against the rate of other oxidations that don't involve aluminum. If you're talking about the atmosphere, there's probably enough oxygen in the air relative to the surface of any given aluminum piece to not be considered "scarce". At least I would guess that's the case; I'm obviously subject to correction by our fire experts here. They'd know better than I would.
Tri, since I opened that door: How exactly
would local oxygen concentrations vary in a room where there's a roaring fire? I can mentally picture eddies and swirls, and many areas of CO2 and other gaseous products all mixing chaotically, but I'd guess that you as a firefighter would have a better grasp on how that all works that I would.
