They still loft hydrazine on birds already designed, but plan to use a non-toxic, and otherwise actually better alternative in new designs.
Hydrazine is troublesome because it is readily absorbed through the skin, in liquid form, or the lungs, in vapor form, whence it destroys the liver and other internal organs. As vapor it is slightly heavier than air, so its vapor spreads out from point of release.
When you see dramatic videos of spilled ammonia, that is generally liquid, either boiling anhydrous or dissolved in water and spreading out on the ground. Purely gaseous leaks go up. But liquid spills can be pretty bad.
All that said, synthetic hydrocarbon fuels will clearly be better for small and consumer-grade use in places where batteries do not suffice.
Hydrazine is troublesome because it is readily absorbed through the skin, in liquid form, or the lungs, in vapor form, whence it destroys the liver and other internal organs. As vapor it is slightly heavier than air, so its vapor spreads out from point of release.
When you see dramatic videos of spilled ammonia, that is generally liquid, either boiling anhydrous or dissolved in water and spreading out on the ground. Purely gaseous leaks go up. But liquid spills can be pretty bad.
All that said, synthetic hydrocarbon fuels will clearly be better for small and consumer-grade use in places where batteries do not suffice.