A reaction between Aluminum and Iron Oxide will produce toxic nerve gasses? React with relatively inert agents used in fire extinguishers?
The stuff burns so hot and fast there wouldn’t be time to put it out, and the molten Iron it produces will melt most anything in an airplane. Any toxic fumes will be burning foam and plastic nearby.
Yeah, they need to be trained to spot a powdered mixture of Aluminum and (black) rust. But there has to be an initiator to get it up to kindling temperature.
Pretty basic chemistry, really.
There are many more types of thermite than just aluminum and magnetite. Cadweld is aluminum and copper oxide.
One can even mix aluminum, calcium sulfate and water and cast it into a solid block of thermite.
Have you seen the TSA agents? Do you really think they took chemistry in high school .... in fact do you really think they even finished high school? From the ones I’ve seen, it probably takes two of them to go to the bathroom.