Gas masks?
But its not just a Muggle army, its a Muggle-Wizard alliance. The wizards counter the subtle threats, like this, while the muggles defend against a brute-force assault. Specifically, the Maurauder's map, if it can be recovered, would detect Tom Riddle, and I'd guess there would be other methods.
Also, he has stated that he doesn't want to kill students, he wants to rule them.
The gas doesn’t have to be poisonous. It could be an explosive (or simply oxygen, which returns to its original solid form, while it is in someone’s lungs …)
Also, Voldemort is flexible about not killing people. He doesn’t want to rule over a pile of ashes, but he won’t abandon his plans just because they force him to kill someone. Even Harry abandoned the superhero morality after the first victim …
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 112.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: