Duct tape and plastic sheeting.

If terrorists use chemical weapons, they will probably affect a tiny area at worst, because terrorists would have chemical agents in relatively small amounts. Though any amount of chemical agent might seem ghastly, in actual use chemicals have proved no more deadly, pound for pound, than conventional bombs.

The British and Germans used one ton of chemical weapons per fatality caused during World War I. The 1995 release of the nerve gas sarin in the Tokyo subways by the Aum Shinrikyo sect killed 12 people, fewer than a small, standard bomb might have killed in that crowded, enclosed area. An estimated 5,000 Kurds died in Saddam Hussein's chemical attack on Halabja, Iraq, in 1988, but this involved dozens of fighter-bombers making repeated low passes over the town. It's hard to imagine that terrorists could pull off such a coordinated heavy military maneuver.

A terrorist release of chemical weapons in an American city would probably have effects confined to a few blocks, making any one person's odds of harm far less than a million to one.

Last week, a Washington talk radio host discussed what listeners should do if "a huge cloud of poison gas is drifting over the city."

None of this means bioweapons are not dangerous. But in actual use, biological agents often harm less than expected, partly for the simple evolutionary reason that people have immune systems that fight pathogens. Also, as overall public health keeps improving, resistance to bioagents continues to increase.

Conceivably, being in a duct-taped room could protect you if a plane dropping anthrax spores were flying over. Smallpox, on the other hand, must be communicated person to person. Those in the immediate area of an outbreak might be harmed, but as soon as word got out, health authorities would isolate the vicinity and stop the spread. By the time you knew to rush to your sealed room, you would either already be infected or the emergency would be over.

Another point skipped in the public debate: smallpox is awful and highly contagious, but with modern treatment usually not fatal. Anthrax doesn't necessarily kill, either, as the nation learned in 2001. Only in movies can mists of mysterious bioagents cause people to drop like stones. In reality, pathogens make people ill; medical workers rush in and save most of the exposed.

If germs merely leave sick people whom doctors may heal, terrorists may favor conventional explosives that are certain to kill.

While government officials now emphasize improbable events involving chemical or biological arms, less is being said about how to be ready for two macabre threats the public is unprepared for: atomic explosion, and the radiological, or "dirty," bomb.

The chance that a crude atomic device will someday detonate on American soil is, by a large margin, the worst terror threat the nation faces. Yet the new Department of Homeland Security has said little about atomic preparedness.

To think the unthinkable, if an atomic device bearing about the yield of the Hiroshima weapon went off outside the White House, people for roughly a mile in each direction might die. But most people in the District of Columbia would survive, while the main effect on Washington's suburbs would be power failures and broken windows. So the majority of people in Washington and its suburbs who would not die would need to know what to do. But do they? Generally not, because there has been scant discussion.

(Here's what to do: Remain indoors at least 24 hours to avoid fallout; remain on ground floors or in the basements of buildings; if you are upwind of the explosion stay put; if downwind, flee by car only if roads are clear since buildings provide better fallout protection than cars.)

(Stay indoors; if upwind do nothing; if downwind, drive away only if roads are clear; take potassium iodide pills to prevent some effects of fallout.) The Department of Homeland Security Web site, for one, has loads of information about anthrax, but offers essentially zero on what to do in the event of radiological explosions.

Increased presence of police and military units in cities may help deter terrorists, and by being more visible and waving bigger weapons, law enforcement is doing what it can think of. But government officials who are advising people to buy plastic sheets create unnecessary anxiety while achieving little beyond helping hardware stores.

Was this color campaign ever anything other than an attempt to give the Admin cover in case an attack happens again?

Oh brother au, I don't suppose you were out there with the black block over the weekend?