I was there for those "scary little incidents" at XCOR and saw the fireball
from the fatal Scaled Composites accident. It's the ones that don't go bang
that come back to you at 3AM.
After using a bottle for N2O service for a couple of years, filling it with
liquid and tapping vapor from it, I removed the valve to replace it with
the correct type (CGA 540 to CGA 660) and I looked inside the bottle.
It had the measles inside there. Thousands of small black dots. Of grease.
Egad. I had refilled and used that bottle a dozen times. With about 8 kg of
N2O when full. Each time the liquid was loaded in with everything it had
dissolved at every step in the supply chain, then gave it up when the vapor
was tapped off.
If you use N2O, I suggest *distilling *the N2O from the rental bottles into
your own, well-cleaned bottle. Never ever fill it with the greasy mess that
is commercial non-medical grade N2O.
There's not a lot of old, bold pilots.
On Wed, Jan 13, 2021 at 11:41 AM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 13 Jan 2021, Jack Hanna wrote:
...so i'm wondering what
are some best practices for nitrous oxide handling...
Aside from the obvious basics of handling a liquid that has to be kept
under high pressure, the key things to understand about nitrous are that
(a) it's a monopropellant, capable of decomposing energetically and maybe
violently, and (b) it's terribly sensitive to contamination.
Pure nitrous is fairly benign and will take a lot of abuse and just sit
there. Even a little bit of organic contamination makes it much touchier,
more likely to do something violent if mistreated slightly. And it's an
extremely good solvent for almost anything organic -- lubricants,
sealants, minor ingredients of plastics, etc. -- and *will* pick up
organic contamination if you give it the slightest chance.
After several scary little incidents with surprise decomposition of
nitrous, XCOR instituted LOX-grade cleaning for all nitrous plumbing, and
had no more.
In fact, you could do a lot worse than to read up on LOX safety practices,
and apply them to nitrous. Almost every LOX hazard has some sort of
equivalent for nitrous, although sometimes not as bad. For example, in
LOX plumbing, any space where LOX can get trapped between two closed
valves needs a relief valve, because it will eventually start to boil, and
without a relief valve, pressure will go up until something bursts.
Nitrous won't do that... but the liquid *does* have a very high
coefficient of thermal expansion, so if it's a hot day, and your nitrous
comes out of a tank that's still cold, and then the liquid sits trapped
between valves, warming up, its pressure *can* rise quite impressively.
Beware of "we got away with it repeatedly so it must be okay"; that's what
killed the crews of Challenger and Columbia, and probably also the three
people who died in the Scaled Composites nitrous explosion. You need to
learn from the people who did have accidents, not just the ones who
didn't. The single most dangerous thing about nitrous is the widespread
belief that it's as safe as mother's milk. Treat it as dangerous and keep
it clean, and it will behave itself.
Henry