I'm assuming that a chemical or biological attack would come without any warning. There would not be enough time to escape to a bed & breakfast in a rural area.
if there is no warning, then you won't know to seal up the house, will you. and if you have any warning, then you have enough time to get in the car, turn off the heater and close the vents, and drive away.
i actually expect that there will be a few swine flu vaccine moments, where people who have sealed themselves in rooms and then suffocated.
dep
duct tape your auto.then go t b&b.