[zeristor]

How could one tell if there were toxic hypergolic fuel residue in the debris?

[shantara]

The standard advice is to keep your distance and contact the authorities. The debris can easily have low enough level of hypergolics to be unnoticeable, but high enough to cause health problems

[colechristensen]

One wouldn't easily. But assuming it may is a necessary precaution. Hydrazine is common and harmful in rather small amounts.

[plugger]

I would like to think most of that would have been consumed, the thing was still on fire when it hit the ground.