Scientific Aspects of Terrorism

The Science of Terrorism

The Biology of Anthrax

Anthrax is a serious disease caused by the bacterium Bacillus anthracis. Bacteria are single-cell microorganisms known as prokaryotes because they lack a nucleus housing the DNA. Instead, the DNA floats in a region of the cytoplasm of the cell called the nucleoid.

The DNA macromolecules contain the genetic information that a cell needs to perform its various functions. The cytoplasm is a gel-like, water-based medium permitting the flow of materials within the cell. Located in the cytoplasm are plasmids, or small loops of DNA, which may be exchanged with other bacteria in what amounts to microbial sex. A combination of protein and RNA, the ribosomes synthesize proteins by translating the information in messenger RNA into protein sequences. Separating the cell contents from its environment is the cell wall. Just inside the cell wall is the cytoplasmic membrane, which is selectively permeable allowing some material to flow in and out of the cell. Having no flagellum, Bacillus anthracis is not motile. A flagellum is a flexible, spiral-shaped structure that generates motion by rotating like a corkscrew or propeller. Pili, the external hair-like projections indicated in the Figure, allow a bacterium to interact with its surroundings.
Although many people are fearful of bacteria believing that they are a source of disease, bacterial are essential to the health of Earth's ecosystem. They are responsible for the breakdown of organic substances: Soil quality, for example, depends crucially on their existence. Bacteria have a symbiotic relation with animals, living in their stomachs and intestines and using enzymes to break food into useful smaller components. It is doubtful that humans could exist in the absence of bacteria. Indeed, there are more bacterial cells than human cells in the human body: About one-hundred-trillion (10¹⁴) bacteria are present in each of us! Only about 10% of bacteria are pathogenic, producing disease through the release of toxins. There is fossil evidence that bacteria have been present on Earth for more than 3.5 billion years.

Efficient deployment of anthrax
could cause more deaths
than from a nuclear bomb explosion.

     Bacteria come in different shapes of which the most common are spherical (cocci), rod-shaped (bacilli), spiral (spirilla) or comma-like (vibrios) forms. They may live in isolation but most (estimated to be 99%) live in clusters or colonies. For example, chains of spherical bacteria have the generic name streptococci – they resemble bead-lets and certain strains cause sore throats. As its name implies, Bacillus anthracis is rod-shaped. Individual bacterium cells are usually a few microns (10^-6 meters) in size. Anthrax spores and bacteria are of this dimension.
     Bacteria thrive in warm, moist environments. Once a bacterium has been cultured to increase immensely their number by introducing such favorable conditions, tests and identification can commence. Bacillus anthracis is anaerobic meaning that it does not need oxygen to grow and multiply. Many bacteria can live only in the presence of oxygen – they are aerobic. It is possible to distinguish bacteria by visual examination with a microscope.
     The French chemist Louis Pasteur (1833-1895) determined that bacteria are the cause and not the result of illness. The German physician Robert Koch (1843-1910) discovered a large number of bacteria including Bacillus anthracis and established procedures for isolating and identifying them. Scientists have only classified a few percent of the Earth's bacteria. They divide them into two broad classes: Gram positive and Gram negative react differently to a certain dye, reflecting a different absorptive property of the cell wall. This test was developed by the Danish bacteriologist Hans Gram. Bacillus anthracis is Gram positive.
     Bacteria reproduce by having one cell divided into two. Under ideal conditions, this happens roughly every 20 minutes, so that in six hours one bacterium can become 2¹⁸ = 262144 bacteria (more than a quarter of a million individuals). Without an immune system, an infected person would soon be overwhelmed by a multitude of bacteria. The rapid rate of growth is one of the reasons why microbes are potentially medically dangerous.
     Pathogenic bacteria may enter the human body through the lungs if inhaled, through the skin by contact, through the digestive tract if eaten and through the genitourinary system during sex. Anthrax does so by the first three methods: Inhalational anthrax is quite serious and often fatal with an initial flu-like reaction followed by high fever, restricted breathing and shock; cutaneous anthrax is most common, quite treatable and manifests as a raised, itchy bump on the skin that eventually becomes black; intestinal anthrax is rare but life-threatening and initially causes diarrhea, vomiting and fever. Inhalational anthrax is an occupational hazard of slaughterhouse and textile workers and, for this reason, it is also called woolsorter's disease.
     Anthrax mostly affects livestock. In the 17th century, about 60,000 cattle died in Europe in what is known as the Black Bane. People become inflected by inhaling spores released by an animal that has died from anthrax or by handling the meat, wool, hide or waste from such a diseased animal, or through human generated means: acts of bio-terrorism, biological warfare or accidents.
     In 1979 in Sverdlovsk, 66 Soviet citizens died from an accidental release of anthrax from a Russian biological weapons plant. It is believed that the biblical account of the fifth plague of Egypt was anthrax generated. Sizeable outbreaks in human populations are rare but, between October 1979 and March 1980, more than 6,000 people contracted anthrax in Zimbabwe. Most cases were cutaneous.
     When livestock die of anthrax, carcasses should be burned, not buried. Nearby animals and people should then be vaccinated.
     Evolution has devised a rather vicious survival mechanism for Bacillus anthracis: Anthrax spores rest dormant in the soil for years, waiting for a grazing animal to ingest, inhale or absorb them. If the animal is unlucky, an immune-defense white blood cell engulfs a spore, and before it transports it to a lymph node, the spore germinates into an active Bacillus anthracis, which then divides and reproduces. These few anthrax bacteria slice through the cell wall thereby entering the blood stream. Once in the blood, they multiply and release toxins that cause immune-defense macrophage cells to release excessive amounts of inflammatory hormones. The toxins are also able to defeat the animal's immune system. Massive inflammation causes widespread hemorrhage, and organs fail. Death follows usually within 36 hours. The anthrax bacteria then feed on the organic material of the dead animal and multiply to incredible numbers: more than a million anthrax cells per milliliter of blood. When the food source is exhausted, the bacteria turn back into environmentally resistant spores, which lay dormant and wait for the next victim.

In just a few hours on September 11
as many people died as 1/10th of the American solders
in Vietnam over a ten-year period!

Bacterial inflections are treated with antibiotics. Some, like penicillin, kill bacteria by breaking sections of a bacterium's cell wall. Water usually then enters the cell causing it to burst. Other antibiotics, such as tetracycline, halt bacterial growth, allowing the body's immune system eventually to dispense with the disease. Finally, antibiotics such as streptomycin prevent the production of proteins needed for a bacterium's survival. If detected sufficiently early, an anthrax infection can be defeated with antibiotics such as ciprofloxacin and penicillin. Anthrax is not contagious.
Bacteria are very adaptable and new strains can develop that are resistant to specific antibiotics. Weapon-grade anthrax is achieved by genetically manipulating it to be antibiotic resistant. In such a form, it is particularly lethal. Quantities are easily generated using cultures. Dried spores can be stored for long periods in weapon containers and are readily released as an aerosol spray. Efficient deployment of anthrax could cause more deaths than from a nuclear bomb explosion.

The Physics of the 2001 World Trade Center Terrorism

The terrorist attack of September 11, 2001 produced enormous destruction and killed thousands of people. To put the loss of life in perspective, in just a few hours on September 11 as many people died as 1/10th of the American solders in Vietnam over a ten-year period!
The World Trade Towers initially withstood the impact of the Boeing 767 jets, which they were designed to do, but the subsequent fire generated by burning jet fuel melted steel eventually causing an implosion in which upper level floors fell upon lower level floors to create a complete collapse, like a toppling row of dominoes. Here is some physics of the catastrophe.
A jet typically travels at around 500 miles per hour, which is equivalent to about 225 meter per second (=500 miles x 1600 kilometer per mile / (60 minutes per hour x 60 seconds per minute)). The weight of a Boeing 767 is about 400,000 pounds, which is roughly 180,000 kilograms (= 400,000 pounds x 0.45 kilograms per pound). The kinetic energy KE of a moving object is determined from the formula

KE = 1/2 mv²
Using, m = 180,000 kilograms and v = 225 meters/second, one finds that a jet's kinetic energy is about 4.5 billion Joules (a Joule is a unit of energy often used in physics). Since almost all this energy was deposited into a tower at impact, the equivalent of a little more than a ton of TNT was released in the crash (one ton of TNT is equivalent to about 4 billion Joules).

In effect, the terrorists
dropped a mini atomic bomb on New York.

     The ensuing fire raged havoc on the structural supports of the tower. Each jet could carry a maximum of approximately 24,000 gallons of fuel, and for a transcontinental flight each tank would be about 2/3 full. Thus there was about 16,000 gallon of fuel aboard, whose energy content is approximately 130,000 BTUs per gallon ("BTU" stands for British Thermal Unit, a unit of thermal energy for which one BTU is a little more than 1000 Joules). The net result is that about two trillion Joules were released in each fire, the equivalent of about 525 tons of TNT. About 10% of the fuel exploded at impact, so that the initial explosion was equivalent to releasing about 50 tons of TNT.
     The building's demise was the final collapse. In a fraction of a minute, the entire structure came tumbling down. The gravitational potential energy originally stored in the standing skyscraper was converted into microscopic kinetic energy in the form of heat and sound, into the macroscopic kinetic energy of flying debris and into the potential energy resulting from the deformation of building parts (twisted steel, distorted beams, crushed furniture and building parts, etc.). The formula for the potential energy PE of a uniform standing object is

PE = mgh
where h is half the height of the object, m is its mass and g = 9.8 meter/sec². Each tower weighed about 600,000 tons, which is roughly 550 million kilogram (= 600,000 tons x 2000 pounds per ton x 0.45 kilograms per pound). Since the height of a World Trade Tower skyscraper was just over 400 meters, h is about 200 meters. One finds that the energy released in each implosion was about a trillion Joules, which is equivalent to exploding about 250 tons of TNT.
     Summarizing,

Event	Energy Released	Image
Jet crash Initial fuel explosion	1 ton of TNT 50 tons of TNT
Fire	475 tons of TNT
Collapse	250 tons of TNT

The destruction in each tower was equivalent to about 775 tons of TNT. Thus, the September 11 terrorist act was equivalent to exploding about 1550 tons of TNT, which is approximately 1/13th the destructive power of the atomic bomb dropped on Hiroshima in 1945 (it was a 20 kiloton TNT-equivalent nuclear weapon). In effect, the terrorists dropped a mini atomic bomb on New York.

This report was prepared by the staff of Jupiter Scientific, an organization devoted to the promotion of science through books, the internet and other means of communication.

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