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The day before the Pad Abort test attempt (May 5, 2015) SpaceX test fired the SuperDraco engines in a hot fire. Similar to how they test the Falcon 9 a day or three before launch, the engines spin up and fire, the booster/capsule is mechanically held down for the test.

But normally, SpaceX burns LOX/RP1 whose exhaust is carbon dioxide, water, and some sulfur by products. Basically car exhaust, just lots more of it.

For the Pad Abort vehicle, it is Nitrogen Tetroxide and MMDH which are astonishingly nasty nasty fluids. They are horribly corrosive and dangerous to humans. The products of full combustion are not very bad (water, ammonia, and other benign things) but you cannot guarentee 100% full combustion, and this stuff is just plain nasty. (Potential additional question will be for capsules landing on land, how much work will be needed before they can leave the capsule safely. Shuttle had people in Hazmat suits cleaning up, before the crew were allowed to leave from its NTO/MMDH thrusters.).

How much cleanup was required at the pad after the test?

Looking at the pictures, they did use the Niagara water deluge system. Was that sufficient to wash away any issues? (If so, do they process the deluge system water before letting it flow back into the Florida waterways?)

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  • $\begingroup$ My impression is that the products it forms when burned (completely) are not toxic. The unburnt fuel actually injured astronauts pretty bad (unconsciousness) in the Apollo-Soyuz mission. $\endgroup$ – LocalFluff May 6 '15 at 13:47
  • $\begingroup$ Another example of the problem with (incompletely combusted) N2O4/UDMH is a Proton launch failure in 1969 which made the entire kosmodrom toxic and unusable for some time. And a similar accident happened again with the 2013 Proton failure. Russia, China and India use this fuel on big launchers today, but except for India, they are about to replace those launchers. $\endgroup$ – LocalFluff May 6 '15 at 15:58
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The Nitrogen Tetroxide fuels are quite toxic because they react with h2o to form nitric acid. For that reason, you don't want to breath the stuff in, burning the lungs. But the same high reactivity also means that the stuff will break down quickly.

In the case of the shuttle, the landing team had a giant fan to blow whatever fumes away. The people in the hazmat suites are there for emergency rescue, leak checks and to make sure that the stuff has been properly dissipated.

There us a bit more at http://en.wikipedia.org/wiki/Dinitrogen_tetroxide#Chemical_reactions

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