For what it's worth - using plastic sheeting and duct tape is pretty standard defense against airborn poison and radiactive dust. From what I've read, using it to create in home shelters is SOP in Israel where they've been worried about this for sometime.
In other words, good defense against the kinds of weapons terrorists are least likely to have. The only protection against modern chemical and biological agents is complete airtight protection and air recirculation; in other words, a full body suit and gas mask, or a sealed residence with some kind of air filtration system.
Otherwise, if you can seal off the air in your house enough to protect yourself, you will also suffocate. The only real prepardness in that case would be to have a real shelter with air filtration. Otherwise, the only option is to get out of the affected area, if possible.
Not that I believe these "warnings"; just as the Dems play politics with foreign policy, so do the Republicans. Bush's administration has been milking 911 for all it's worth. Giving endless scare-mongering but useless "warnings" serves to ratchet up the tension and to keep people convinced that war abroad and a police state at home are the only options left to them.
Otherwise, if you can seal off the air in your house enough to protect yourself, you will also suffocate. The only real prepardness in that case would be to have a real shelter with air filtration. Otherwise, the only option is to get out of the affected area, if possible.
Nope. If you shut off your a/c, your house should have neither positive nor negative ventilation. A mist like nerve gas or a dust like anthrax will only get into your house if there is a pressure differential, i.e. blowing air out one end of your house lowering the internal pressure, making air suck into cracks on the other end. (Note, if your house heats up or cools off a lot, this will cause some differential)
If you keep your air off and doors closed for a few days, you should still have plenty of air to breath in the volume of a normal house or apartment. If you really want to get fancy, you can make your house positive ventilation, which would blow air out any crevices. You'd need a blower bringing in air through a HEPA filter (a real HEPA, lots of crappy filters at walmart say HEPA on them). We do the reverse when working with radiological or chemical waste in a glove-bag, so that any opening is sucking air in, and the blower with the HEPA is blowing out. You're better off just caulking your windows and sitting tight for a few days.
If you have a swamp cooler, which is a big gaping hole in your house, then plastic sheeting and duct tape would work wonders.