Explosion at Scaled Composites Kills 2, Injures 4

Animats writes "Details are scant at this time, but a explosion at the Scaled Composites rocket test facility has killed two people and seriously injured four more. The Los Angeles Times reports that the explosion was 'ignited by a tank of nitrous oxide.' This is Burt Rutan's facility, and the home of SpaceShip One and Virgin Galactic spacecraft development."

Comments

CNN

[Lithgon]

CNN is also reporting on this story: http://www.cnn.com/2007/US/07/26/spaceport.blast/i ndex.html

Strange for a hybrid motor

[sokoban]

The article's a little light on details, but explosive failure is pretty rare for hybrid rocket motors such as this, isn't it?

Usually mis-ignition will just cause rapid release of the N2O oxidizer, and designs are such that a clogged nozzle which would actually cause an explosion generally causes a safety valve to open and vent the excess pressure.

Yeah, everything I've seen on hybrid motors says they are non-explosive with a near zero TNT rating.

Re:Strange for a hybrid motor

[evanbd]

They weren't firing the motor; apparently this was some sort of handling accident. Which also explains why people were close enough to be hurt. Why the fireball, I don't know. Also, nothing actually *detonated* here -- just a big fireball and modest overpressure. (At least, that's what informed commentary on the pictures I've seen says.)

It's also worth noting that given sufficient provocation, it is entirely possible for N2O to detonate by itself -- it's an energetic compound. It's just fairly non-reactive under most conditions, and even if it does start decomposing in a self-sustaining fashion it doesn't normally detonate. But it can, and if you have enough of it you don't even need a detonation to kill people.

Re:Strange for a hybrid motor

[evanbd]

No, it most certainly does *not* need a fuel. It is an energetic chemical. In other words, 2N2O -> 2N2 + O2 + energy. Not TNT levels of energy, but not small amounts either. I don't have the numbers off hand, but the decomposition temperature is over 1000 Celsius. That reaction *can* happen in a detonation. However, the chemical is quite stable and relatively inert at normal temps (thermal decomposition starts a bit over 500C, iirc) -- at room temp it's far less reactive than oxygen. This accident may or may not have been that -- my understanding is it looks more like a pressure vessel burst and a fire from fuel + oxidizer, but we don't have enough details to know that. The trailer and tank you see overturned in that photo hold nitrous normally (I don't know what was full, or where the nitrous was at the time).

I've worked on that airport and seen these guys out testing. My condolences to the families.

Re:Strange for a hybrid motor

[sokoban]

2N2O -> 2N2 + O2 + energy. 104.20 kJ/mol of N2O at 298K to be exact.

The activation energy is high, but it can be lowered by use of a catalyst.

Re:Strange for a hybrid motor

[DesserttRatt]

I didn't see any fireball. Just a large explosion... A black cloud with lots of brown dust mixed in, shooting 3-400 feet into the air... Mostly straight up with one very large piece flying off to the south-southwest followed quickly by a loud BOOM (I was about 1/2 mile away at the time so the sound and pressure wave were a bit delayed) but it most certainly was a "detonation".

A couple more details

[evanbd]

I've been chasing news articles for a little while now.

Details are very scarce, but apparently this was a cold-flow test -- they weren't intending to light the motor, just flow nitrous through it. Tank ruptured, and a big fireball. Evidence visible from pictures etc suggests nothing detonated. Apparently people a couple miles away at the airport proper didn't hear an explosion -- they just saw clouds of dust and smoke, not abnormal for a motor test. I haven't seen anything about causes etc.

My condolences to the families.

Re:A couple more details

[evanbd]

In non-technical usage, explosion can refer to a detonation or a deflagration. The distinguishing feature is a detonation has a supersonic reaction front, a deflagration is subsonic.

A pressure vessel rupture is an explosion for most purposes in terms of the results; ditto a deflagration. This appears to have been a deflagration -- damage is too light for a mass detonation on that scale.

Damage from explosions can come both from the overpressure, heat, flame, etc caused by the combustion, and also from the shock wave of a detonation. The shock wave will shatter hardened structures, the overpressure "just" moves things around. Also, with a detonation, the pressure rise time is *much* faster, and the overpressure can be *much* higher, so a comparable mass of substance will do much more damage if it detonates rather than deflagrates.

Nitroglycerin doesn't "ignite" in that there isn't a "flame", but the reaction that occurs is a combustion reaction -- the complex molecule ends up as a mix of N2, H2O, CO2, CO, etc. That reaction propagates at supersonic speeds. Interestingly, it will burn quietly if lit -- there's no pressure wave, just thermally-induced decomposition, and it won't transition on its own.

Re:This has NOTHING to do with NASA

[kimvette]

http://news.yahoo.com/s/ap/20070727/ap_on_re_us/ai rport_explosion;_ylt=Atw8pinyLC7AW3ayUC4B.Eis0NUE

Aerospace designer Burt Rutan, who heads Scaled, was away at the time. He sounded distraught in a phone call with The Associated Press as he was en route to the scene.

"We've lost a couple of our employees. It's a very big deal," Rutan said.

Rutan is fine.