Sealing off a room is an idiotic step and I've lost even more faith in the media for suggesting it.
The only people this would benefit in the least are people close to the epicenter of a chemical attack. A biological attack isn't obvious at first, so chances are, by the time people became symptomatic, you would have already been exposed to the weapon. With a chemical attack, if you're in the area (meaning one-to-two miles from the attack's origin), yeah, sealing MIGHT help, but so might running like hell away from where you are UPWIND.
As I said before, it would take a MASSIVE quantity of chemical agent to produce a lethal dosage for all those exposed in an open-air environment. Even the military has had trouble getting open air attacks to work properly. When you hear about things like "a single microliter of VX on your skin will kill you," it's bullsh*t. If you have 5-10 liters of VX or GB (AKA Sarin) and your target area is one city block, yeah, that might work. If you have 10 liters and your target is an entire city? Get real. Imagine if you would the weight and volume of the air encompassing a 20x20 mile (typical Metro area size) area to an altitude of 1000 feet (seeing as very few buildings in the US are higher than this, it's a good benchmark). That's 105,600ft (L) x 105,600ft (W). That is approximately 11,151,360,000 square feet, or x/5280^2 = 400 square miles. And somehow a terrorist, with a (most likely a crude tank + C4 setup) chemical device, filled with a binary mixture of a chemical agent most likely not exceeding twenty gallons/liters (due to prohibitive weight), who would most likely detonate it from a medium altitude during a morning commute or rush hour...is going to contaminate an entire metro area? Again, get real.
For a biological attack, all you have to do is limit your direct contact with others. Even a simple paper surgical mask would help. Biological agents, with the exception perhaps being anthrax or genetically-altered agents, do not do well in open-air environments and/or direct sunlight. Sufficed to say, going outside after a, let's say, a smallpox attack ISN'T going to kill you. Going to someplace where large quantities of people are gathered? Probably not smart, unless it's Anthrax, in which case people can't even transmit it to you if they cough in your face.
And about "genetically-altered" biological weapons. I honestly think the prospect of a country like Iraq or North Korea selling GA strains of smallpox or any other biological agent to terrorists is nil. Quite simply because the use of smallpox (especially a genetically-altered strain resistant to vaccination) is like dropping napalm into a forest of dry trees. It spreads like wildfire. So any nation that provides such a weapon could easily see the contagion coming back across their borders en masse in a week or two. The only thing that's kept smallpox contained the past 100 years, ending in the late 70s when it was "eradicated," is that it usually cropped up in isolated impoverished areas where the population had almost no way of infecting an outside population. One person gets on a plane headed for another country/coast/continent, and the fire spreads. Virologists and epidemiologists refer to the worldwide airline network as "the net;" once something as contagious as smallpox hits it...well, you get the idea.
Biological weapons exist for two reasons. One is to create a consequence so dire that attacking someone willing to use them will produce a Pyrrhic victory. The second (was) that in the event of a war with the Soviet Union, they would have probably used biological agents on "soft" targets (i.e. personnel) to not only demobilize but demoralize. Could you fight, wondering if you were going to die anyway from something you couldn't even see? Biological weapons were never meant as weapons to be used on populations of civilians (though powers have figured out ways and means to make them a viable weapon).
Since smallpox seems to be the virus everyone is scared sh*tless of, let's talk a little about that. Smallpox is a highly infectious virus which has a mortality rate of around 30%. So in an unvaccinated relatively unhealthy population smallpox would be expected to kill one in three infected. Your chances of survival increase exponentially with how good of shape you're in, and the condition of your immune system - those of you infected with autoimmune diseases or HIV/AIDS should take great care in the event of a biological attack to shield yourself from contracting the agent.
If you were vaccinated as a child (for you baby boomers in the crowd), your old vaccination should have a greatly reduced effiency, but that doesn't mean it's worthless. The more smallpox vaccinations you recieved prior to 1972, the better off you are...speaking statistically - no one knows how protected you are simply because there's no way to do a study on it. Me being born in 1981 doesn't help, since I've never received the vaccination. But I'd hardly call my attitude "panicked," would you?
In the event of an outbreak of smallpox in a heightened alert status, something called a "ring vaccination and quarantine" would take place. The affected area(s) would be completely sealed off and medical personnel would be sent in to care for those exposed and affected. This is the equivalent of slapping a tourniquet on a bleeding limb. As I said before, if you deny a pathogen hosts, you deny its survival.
Myth: Someone infected with smallpox is contagious before the scabs appear.
Fact: Someone infected with smallpox COULD be very minorly infectious a day or two before the scabs appear on or around Day 11 following initial exposure and infection.
Smallpox has an incubation period (which is the time it takes for the virus to build itself up and overcome the immune system) of 10-12 (though the range is anywhere from 7-17 days depending on varying circumstances) days. After that, telltale signs such as the infamous pusy rash will appear, followed by 2-3 days of very high fever, headache, and prostration (wanting to be nowhere but flat on your back). It's only on or around day 10+ that a person becomes infectious, the least amount on day 10 up until maximum infectiousness near the endstage of the infection. So to put it quite frankly - even those infected aren't contagious until they begin to show the physical signs of infection, and by then they're not going to want to be "up and at 'em" anyway.
Myth: You can catch smallpox from an infectious person, say, across the room.
Fact: It takes rather close proximity to an infectious person (about six feet) to be able to catch the virus.
Think about it...we've lived with tuberculosis for centuries. You can catch TB just about as easily as you can catch smallpox. Have you ever caught TB?
So, after that long tirade, duct-taping your house or "one room?" It's BS. Just be smart, don't panic, and exercise good use of common sense.