Now that terrorists have demonstrated they're capable of carrying out unthinkable attacks of extreme devastation, some believe the United States should be on higher alert for a biological or chemical attack, or an assault on a nuclear facility.
ABCNEWS.com talked to several experts to learn about these weapons, the preparedness of the United States for such attacks and possible defenses against them, including:
Kyle Olson of Community Research Associates, an Alexandria, Va., consulting firm that specializes on domestic preparedness and terrorism Michael Allswede of the Department of Emergency Medicine at the University of Pittsburgh Kathleen Vogel of Cornell University Victor Weedn of Carnegie Mellon University Thomas Inglesby and Tara O'Toole of the Center for Civilian Biodefense Studies at Johns Hopkins University
Most agree that while a biological or chemical attack could be devastating in theory, the logistical challenges of developing effective agents and then dispersing them make it less likely a terrorist could carry out a successful widespread assault.
Here are some questions and answers on these issues:
Would a chemical or biological attack be more deadly? Questions on biological warfare Questions on chemical warfare Threat to Nuclear Power Plants Threat to Water Supply
Q: Would a chemical or biological attack be more deadly?
A: If cultured well, a biological weapon would have a more devastating impact since people infected with a biological agent can spread the disease for months and over a broad geographical region. One person infected with smallpox, for example, could pass along the disease to 20 or more individuals. In this way the disease could spread broadly and rapidly. A chemical weapon would only affect people who are near the place of its release and the chemical would dissipate with time.
Q: How easy would it be for a terrorist to launch a biological attack?
A: Experts say it remains very difficult to transform a deadly virus or bacterium into a weapon that can be effectively dispersed. A bomb carrying a biological agent could likely destroy the germ as it explodes. Dispersing the agents with aerosols is challenging because biomaterials are often wet and can clog sprayers. The Aum Shinrikyo cult, which released the nerve gas sarin in the Tokyo subway system in 1995, killing 12 people, repeatedly tried to produce and disseminate agents, including anthrax, but failed each time.
Some experts think suicide terrorists could resort to spreading smallpox by infecting themselves and then wandering and breathing among large groups of people. But in that scenario, large numbers of people still might not be affected since infection rates vary among people and because people infected by the virus are highly infectious only seven to 10 days following the outbreak of a rash.
Q: What biological weapons pose the biggest threat?
A: Right now, scientists are most concerned about smallpox and anthrax. Both are bacteria that can spread through the air in a powder and cause swift, deadly diseases. Smallpox could be even more lethal because it's easily spread from one person to another. Also worrisome are the bubonic plague, botulism, tularemia and ebola.
Q: How easy is it to develop a biological weapon?