We face many fires every summer in Southern Oregon, where I live. It's timber country, and there is always a massive amount of forest duff (the old twigs and leaves and such which accumulate on the forest floor) dried out by our 100-degree-plus, rainless summers, just waiting for a lightning strike, careless camper, or, yep, arsonist to cause misery for countless miles around.
It gets so bad here that smoke from a long, long ways away will still get into your house and there's really nothing you can do but wait it out. It's worse than it sounds, because it can be thick enough that even young healthy people start coughing A LOT, and god knows what it's doing to pets like dogs, who pant constantly anyway and do it even more in the summer heat. I came close to crashing my car from it once, and it wasn't any better in the house.
Around here, hardware stores, Walmart, and the like carry cloth and paper breathing masks and put masses of them out come the fire season -- and sell out quickly Even the dollar store sells small ones -- but it's not something you want to go too cheap on. Cough long and hard enough, and it's just not funny anymore. You'll have wished you spent whatever it took.
If you can leave, leave early. It can get so bad you are not at all safe driving your way out. Not even because you can't see; because you can't breathe.
