From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: Unadvisable Rocket Science
Date: Fri, 2 Aug 1996 15:23:02 GMT

>>   While I concede the cryo point without contest, don't you get
>> relatively nasty byproducts from burning N204 and hydrocarbons (all
>> those nitric oxides)?  Or are these nitric oxides not toxic, but just
>> smog-causing?

The N2O4 decomposes enthusiastically, given the slightest chance (like all
the nitrogen oxides).  You won't get any oxides of nitrogen in the exhaust,
except the minor amounts which inevitably appear when hot exhaust hits air.
Although it's not a common combination, N2O4 burns hydrocarbons just fine.

>I seem to recall from high school chemistry that there are five common nitrogen
>oxygen combinations of which three kills you, one makes you laugh and the other
>just decomposes into O2 and N2 in your lungs.

It's not quite that simple.  For one thing, in high concentrations these
things have an annoying tendency to be in equilibrium with small (or not
so small) quantities of each other.  In particular, there is basically no
such thing as pure N2O4, it's always in equilibrium with NO2.

>If my brain hasn't died overnight and failed to inform me I think the dangerous
>ones are 
>N2O4
>NO2 
>and
>N2O

Not quite -- N2O is laughing gas, the one used as an anesthetic.  NO2 is
another story.

>I seem to recall NO2 being a major component in urban smog.

Oxides of nitrogen feature prominently in smog, but fortunately there isn't
a lot of NO2 present -- it's seriously poisonous.
-- 
 ...the truly fundamental discoveries seldom       |       Henry Spencer
occur where we have decided to look.  --B. Forman  |   henry@zoo.toronto.edu