It's not just toxic, it's incredibly toxic... the threshold for toxicity is below human sensitivity, i.e. if you can smell it, it's already too late. It's also flammable/explosive, poisonous, carcinogenic, catches fire without a spark, has no surface tension so it spreads faster than water, and it's generally the single most dangerous chemical known to man. In the words of Isaac Asimov:

anyone working with rocket fuels is outstandingly mad. I don't mean garden-variety crazy or a merely raving lunatic. I mean a record-shattering exponent of far-out insanity.

That's Hydrazine. The other liquid propellant, nitrogen tetroxide, which causes the signature red clouds, is slightly (!) less hazardous. It will still readily kill you. It's odd to see in the twitter photo that there was a fuming red cloud during takeoff, which suggests a problem with the burn ratios. Absolutely zero propellant should be allowed to pass unspent into the air, from engineering, safety and environmental perspectives.

kbotc

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They’re using the stuff the Soviets called Devil’s Venom and just letting it slam back into the earth with unburned chemicals?

canis_majoris

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Yeah I mean, why not. Who's going to stop them?

Fucking guys have their own space station they built by themselves.

kbotc

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The Nedelin catastrophe should be a warning at least?

SharkAttak

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Yeah, there's just people down there, they got a lot of 'em around.

sebinspace

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IIRC Hydrazine is generally only used, or was used as the RCS thrust fuel for the Apollo program. You know, outside of the Earth’s atmosphere.

crapwittyname

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Pure hydrazine maybe, as that's not all that common. But the derivatives MMH and UDMH (which are both equally devastating to humans/the environment) are certainly used in the atmosphere, even by western nations. It's common as an orbit raising fuel.