[cesarb]

That would prevent a hazardous factory from being built next to residences, but wouldn't prevent residences being built nearby after the factory is already there. For that, you'd need restrictions on the residences and/or the land.

[Tiksi]

Maybe a hybrid solution would work? Have a zone tied to the factory, no residential buildings within a certain radius of the factory, but if the factory shuts down or moves, the zone goes with it.

[hodwik]

That's a really cool idea.