Diagnosing The Risks

In the three weeks since the Sept. 11 attacks, Americans have become increasingly concerned that the next one might be even worse. In the TIME/CNN poll taken last week, 53% of those surveyed feared a chemical or biological attack; 23% a nuclear strike. Among terrorism experts, however, the focus has shifted from a single large-scale assault--which would be difficult to pull off--to a series of smaller attacks that could be just as damaging to the U.S. economy and public morale. How serious are these threats? What form might they take? The best guesses of the experts consulted by TIME offer both reassurance and fresh cause for alarm.

Biochemical Attacks
Smallpox
It doesn't take an exotic virus like Ebola to transform the U.S. into a hot zone. A single case of smallpox could put the entire nation at risk. The smallpox virus is highly contagious and would spread quickly because Americans are not vaccinated. Routine inoculations were halted in 1972. People vaccinated before 1972 lost most of their immunity within 10 years.

A terrorist who wanted to launch a smallpox attack, however, would probably have a very hard time getting hold of the virus. Smallpox was eradicated in 1980. Officially, only two stores of the virus exist, for research purposes, in secure locations in the U.S. and Russia. There may be covert stashes in Iraq, North Korea and Russia, but these countries would be reluctant to release them, fearing a smallpox epidemic among their own unvaccinated people. Even if a terrorist were successful in obtaining the virus, his plans could backfire: smallpox is so contagious that the first victims are likely to be the members of his own terrorist cell.

Anthrax
Many bacterial agents can be used as bioweapons, including Clostridium botulinum (botulism) and Yersinia pestis (plague). But anthrax stands out because its spores are particularly hardy; they are resistant to sunlight, heat and disinfectant, and can remain active in soil and water for years. Anthrax occurs naturally in both wild and domestic animals--including cattle, sheep and camels. Infection from direct contact with affected animals is fatal in 20% of cases. If inhaled, however, anthrax spores cause death almost 90% of the time.

Yet manufacturing sufficient quantities of any bacteria in a stable form is a technical and scientific challenge; plague bugs, for example, degrade within hours when exposed to the sun, and anthrax spores tend to clump together in humid conditions. The Japanese cult Aum Shinrikyo sprayed anthrax and botulism eight times over parts of Tokyo without effect.

Despite all the attention being given crop dusters, using one to spread germs is not as easy as it sounds. The planes are designed to spray pesticides in heavy, concentrated streams, whereas bioweapons are ideally scattered in a fine mist over as large an area as possible. The nozzles in crop dusters are best suited to discharging relatively large particles--100 microns in diameter--not tiny 1-micron specks of bacteria.

Sarin
Unlike biological agents, which are living organisms that require proper conditions to survive, chemical weapons such as the nerve gases sarin and VX are relatively easy to acquire and stockpile. Chemicals are difficult to manufacture in sufficient quantities for a large-scale attack, however; more likely are isolated assaults such as the 1995 sarin attack on a Tokyo subway that injured thousands and killed 12.

Water
Reservoirs
Poisoning your enemy's well is an ancient tradition, but would-be terrorists would find it extremely hard to inflict widespread casualties through our water supply. Chlorine in treated water kills most microbes, and huge quantities of chemical toxins would have to be dumped into a reservoir to make many people sick, let alone kill them. (A U.N. study estimated that it would take 10 tons of potassium cyanide.) Drinking water might be threatened locally, however, if someone managed to tap the pipe going into a building or neighborhood or infiltrate a water-treatment facility. With this threat in mind, municipal water authorities have stepped up security.

Dams
If poisoning the water supply doesn't work, terrorists might try to cut it off or disrupt it. On an even grander scale, they might blow up a dam, causing widespread flooding damage downstream. Compounding the impact would be the loss of hydroelectric-power generation. With security beefed up at major dams across the country, however, especially at landmark behemoths such as the Hoover and Grand Coulee dams, it would take a very determined effort to carry out such an attack.

Hazardous Materials
Chemical plants
Some 850,000 facilities in the U.S. handle hazardous chemicals. Many substances that have benign industrial uses, such as metal cleaning or photo developing, can in theory be turned into dangerous weapons. But gaining access to plants, either for sabotage or to get raw materials, is difficult. Employees handling hazardous materials undergo security background checks, and chemical manufacturers across the country last week were double-checking their employee rolls. Since Sept. 11, most facilities have barred outside visitors and allowed only authorized personnel to enter.