Deadly blasts: explosion experts use forensic science to investigate crimes committed by bombers.
One moment everything is quiet, and then, KABOOM! A huge fireball fills the air with smoke and scatters twisted pieces of metal, glass, and rubble. Minutes later, firefighters are putting out the flames. Then, detectives arrive on the scene to look for casualties and search the debris for clues about what caused the explosion.
Like the actors on television crime-investigation dramas such as CSI, NCIS, and Bones, real-life forensic scientists can learn a lot about a bomb by examining what's left behind (see Prime-Time Science, p. 18). By collecting evidence, forensic scientists can determine everything, from what type of device caused the explosion to who planted it. These scientists can also find clues to identify suspects when bombs fail to go off, like in the case of the attempted car bombing at New York City's Times Square last spring. It's their job to use their knowledge of explosives to help the police and other law-enforcement agents catch bombers--both those who have and haven't yet succeeded in their explosive endeavors.
Most criminals work with explosive chemicals like TNT or plastic explosives like C4. These chemicals are made of molecules, or combinations of two or more atoms that are bonded together, that contain nitrogen, hydrogen, and carbon (see Nuts & Bolts, above right). Together, these elements serve as the fuel for combustion. Combustion occurs when oxygen reacts with a fuel to release energy.
Some fuels release more energy than others when they bum. "In the case of a forest fire, the fuel is wood and the oxygen comes from the air. But it's a very slow process," says Jay Siegel, a professor of forensic science and an explosion expert at Indiana University-Purdue University Indianapolis. Compare that with an electrical spark or a timed fuse that sets off explosive chemicals instantaneously. This is called a detonation. The blowup creates a shock wave that propels gases through the air faster than the speed of sound.
The hot gases push everything away from the place where a bomb was planted, known as the bomb seat. This is where forensic scientists go to collect the charred bits of rubble that hold valuable clues. "Recovery of evidence is the hardest part of forensics. If you don't recover the right evidence, you're not going to get the right answers in the lab," says Siegel. It might surprise would-be bombers that an explosion won't destroy all the evidence of their crime.
Back at the lab, the first thing an explosion specialist attempts to find out is which explosive was used. Sometimes not all of the explosive material ignites. If they're lucky enough to find some of this unexploded material, the specialists can easily determine what it is. If not, they have to do some sleuthing.
During combustion, predictable chemical reactions take place. Depending on the type of fuel burned, different residues will be left behind. New Mexico Tech's Energetic Materials Research and Testing Center has a 104-square-kilometer (40-square-mile) test range in the desert, where it can explode as much as 18,000 kilograms (40,000 pounds) of explosives at a time. "We test everything, from homemade bombs to military rockets," says chemist Chrism Hockensmith.
After a test explosion, they collect all the debris and return to the lab. There, they examine residues with a device called a mass spectrometer to determine their chemical makeup. Then they repeat the experiments with different explosives and build databases for government agencies that investigate bombings.
Once the experts know the type of explosive used, the detective work can begin. Much like how certain artists are known for their specific style of painting, each bomb maker has his or her own bomb style. "There are
some forensics people who are so knowledgeable in these explosives f and bomb makers that they can tell who made it from an examination of the device--or even fragments of the device," says Siegel.
If the bomb doesn't go off, it's even easier for the forensic scientists to find a suspect. In the case of the attempted Times Square bombing, there was a lot of evidence left at the scene. Not only were investigators able to track the bomber with video footage from security cameras and the identification number on the car that was supposed to blow up, but there was also DNA evidence. DNA is the chemical that carries hereditary information and is unique for every person (except identical twins).
"DNA evidence has really increased our ability to solve crimes that we couldn't solve before," says Siegel. Students from his lab have even been able to collect DNA from some of the exploded bombs they tested. Improvements to technologies like these help explosion scientists build better databases of information, allowing them to stay one step ahead of criminals. With any luck, someday they'll be able to solve crimes as quickly as the supersleuths on TV.
nuts & bolts
TNT: EXPLOSIVE MOLECULE
TNT, or trinitrotoluene, is one of the most common explosives. It's also the standard by which an explosion's power is measured using s unit of energy called a ton of TNT. The amount of energy released by Mount St. Helens's eruption in 1980 equaled 20 million tons of TNT.
CSI: NY writers and actors turn to technical advisor Bill Haynes to make their show as authentic as possible. Haynes was a forensic scientist with the Los Angeles County Sheriff's Department for six years before he started working on the CSI television series.
Haynes not only makes sure that the forensic science used in each episode seems realistic, but also shows the actors how to look like they are collecting evidence and analyzing forensic data the proper way. "I know the science lingo and forensic procedures," he says. This season, you might even see some fantastic explosions on CSI: NY. Tune in to watch the show's prime-time detectives use forensic science to catch the culprit.
* How realistic do you think the procedures that forensic scientists use on TV shows like CSI, NCIS, and Bones are?
* What kind of clues do you think can be found on the scene after an explosion?
* Would you want to become an explosion expert? Why or why not?
DID YOU KNOW?
* Gunpowder, or black powder, is a mixture of sulfur, charcoal, and saltpeter (potassium nitrate). It was the first commonly used explosive. A Chinese text from the 9th century describes how a mixture of sulfur, realgar (sulfur and arsenic), saltpeter, and honey ignited when heated.
* Famous Swedish engineer Alfred Nobel was the inventor of dynamite and amassed a large fortune from its sale. In his will, he left most of his money to create the Nobel Prizes to atone for causing so much damage with his invention.
* An explosion from a bomb occurs as a result of an endothermic chemical reaction, which is one that releases vast amounts of energy (usually in the form of heat) and takes place very quickly.
* Explosion expert Jay Siegel said, "DNA evidence has really increased our ability to solve crimes that we couldn't solve before." How is that so? What makes DNA such a good tool for finding suspects? What are some new ways forensic scientists might use this tool in the future?
LANGUAGE ARTS: Have students read about the various jobs in the arson and explosives department of the Bureau of Alcohol, Tobacco, Firearms, and Explosives here: www.atf.gov/explosives/enforcement. Then have them pick a specialty and create a brochure to recruit prospective explosion experts.
You can access these Web links at www.scholastic.com/scienceworld.
* WEB EXTRA: Watch a slow-motion video of an explosion of a car bomb conducted at New Mexico Tech's Energetic Materials Research and Testing Center at: www, youtube.com/user/nmimt#p/a/94B70420FE66CFE4/1/37ITOm51XOI.
* CSI: The Experience is an exhibit currently traveling around U.S. science museums. Rice University made an interactive Web site to accompany the exhibit where you can become a deputy investigator to help solve their cases: http://forensics.rice.edu.
* Find out what it takes to be a forensic scientist at the American Academy of Forensic Sciences' career Web site: www.aafs.org/choosing-career.
READING COMPREHENSION SKILLS
The Science of Fingerprints
In "Deadly Blasts" (p. 16), you read about the forensic scientists who search through rubble for clues to solve bomb-based crimes. Read the passage below to learn more about how fingerprints are used to solve crimes, and then answer the questions that follow.
Fingerprinting for Identification
No two people share the same set of fingerprints--not even identical twins. This fact was first recognized more than 100 years ago, and identifying people using their fingerprints has remained an important tool for law-enforcement officials.
Each person's hands, feet, fingers, and toes have features called friction ridges. These ridges help them grip objects. Every time a person touches something, a small bit of sweat and oil from their fingers leaves a friction ridge impression on the object. This is called a latent fingerprint.
Although a person's appearance changes over time, their fingerprints don't. Even if the skin of a person's fingertips was somehow temporarily removed, their same fingerprints would return when the skin grows back. Interpol, the international law-enforcement agency, estimates that between 5 and 15 percent of the world's population have their fingerprints on file in government-run databases. Each day, computers analyze millions of fingerprints each second, looking for matches to help police officers catch criminals.
1. Which of the following BEST summarizes the passage above?
(A) Fingerprinting is an outdated tool that people no longer use to catch criminals.
(B) Collecting the correct fingerprints at a crime scene is hard work.
(C) Forensic scientists need to find better tools than fingerprints for identifying suspects.
(D) Although it has been around for nearly a century, fingerprinting is an integral tool that police officers use every day.
2. What is the purpose of the second paragraph?
(A) to describe how investigators collect fingerprints
(B) to state what Interpol does
(C) to describe how fingerprints are made
(D) to argue the usefulness of fingerprints
3. Interpol estimates that what percentage of the world's population has fingerprints on file?
(A) 1 to 5 percent
(B) 5 to 15 percent
(C) 10 to 20 percent
(D) 15 to 25 percent
4. Latent fingerprints are impressions made by--.
(D) both a and b
5. Which of these statements is NOT a fact from the article?
(A) Identical twins have the same fingerprints.
(B) Friction ridges allow people to grip things.
(C) Interpol is an international law-enforcement agency.
(D) Each day, computers analyze millions of fingerprints for matches.
6. Complete the following on a separate sheet of paper: The passage above describes how fingerprinting is an important tool for catching criminals. DNA analysis is another tool. Using information from the passage and the article, argue which method you think is most useful to detectives searching for clues.
1. d 2. c 3. b 4. d 5. a 6. Answers will vary.