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From Building Design to Prime Time: Forensic Engineering
(Released July 2008)

 
  by Marianne Stanczak  

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Basic Tools and Common Applications

Contents

magnifying glass
Visual processing is an important aspect of forensic engineering. One may think of Sherlock Holmes and his trusty magnifying glass or the sharp eye of a crime scene investigator. Although these "simple" techniques must not be ruled out, many technological advances have come along the way.

Basic photography is often a first step in a forensic engineering examination. For example, photographs of vehicle damage and skid marks (Bartlett) can aid in a traffic collision investigation. Various types of microscopy allow for more sophisticated visual exams. A stereomicroscope (Nunes) for example may help uncover a weapon's serial number that has been removed.

Even more technologically advanced is digital imaging. One use of this technique is pinpointing the source of a document's printing (Tschan). Banding effects of an image on paper are measured.

two pictures of parrots Top image: without banding

Bottom image: with banding

The bottom picture has "white" lines streaked through (horizontally). The banding could be due to less dpi (dots per inch) or low resolution or a clogged ink cartridge

Just as these bands can point to unique printers, fax machines or photocopiers, certain "security features" are put into place that act as a fingerprint (Smith). For example, in compact disk manufacturing, the molding process leaves a unique marking on the CD's surface. By using machine vision and pattern-matching, one can tell if a CD has been counterfeited. Also, material distributors may mark copies with an individual "virtual" fingerprint. This allows for easier discovery of a criminal (Schaathun).

Another "sense" used in some forensic engineering is hearing/sound or acoustics. One common example is the use of the "black box" or flight data recorder in aircraft. In addition to holding flight data such as speed and altitude, it may contain the flight crew's words (Spacecraft), information pertinent in the event of a crash or other catastrophic failure.

Other common acoustic tools include tape recorders or microphones, which are commonly thought of as being used in surveillance (Hollien). Such techniques are referred to as forensic phonetics. Forensic psychoacoustics deals with how sound is perceived.

The US Geological Survey (USGS) determined a unique way to use sound forensically since,"sound waves traveling through the air away from a gunshot are basically similar to the source (seismic) wave traveling through the ground away from an earthquake."

sound waves emanating from shot
A gun is fired . . . .

With this information it is possible to determine where a gun has been fired, and is far more reliable than human witnesses.

Once the "bigger picture" is analyzed, sometimes it must be broken down into many "smaller pictures." One way is by using mass spectroscopy (Lesney), which identifies chemicals by weight (mass) and charge, enabling one to see the chemical makeup of a compound. To analyze carpet fiber evidence, for example, mass spectroscopy results are assisted by chromatography and electrophoresis.

Again, it would take volumes to list and describe all the tools used in forensic engineering, but one of the most important is the computer. From displaying digital photographs to compiling databases of fingerprints to creating complex computer models, computers are an invaluable asset to the forensic engineer.

There is even an entire aptly named field of study devoted to this - computer forensics. In the current atmosphere of hackers and identity theft, methods of investigating these cyber crimes are needed. One such method is Fine-Grained, Active and Scalable Access Control (FASAC) (Hallahan). Failure Modes and Effects Analysis (Bowles) (FMEA) acts as a checklist of failures and the consequence of those failures.

possible causes of failed power devices
Example of a Fault Tree

In manufacturing or product design, one may be able to pinpoint the location where an error or failure occurred by using a combination of reverse engineering the "tool-path" and a Computer Aided Design (CAD) model (Chui). Such devices can be helpful in the field of product liability (Gagg, Smith) by narrowing a given failure to design, manufacturing or even consumer misuse.

In one case regarding product liability, an exploding aerosol can (Fox) unfortunately blinded a man. An extensive forensic engineering panel of tests was performed, including the following:

A natural segue from product liability is the use of forensic engineering in the automotive industry, where a great deal of accident analysis and reconstruction comes into play.

Crash tests, computer simulation and real accidents are studied to prevent accidents and/or improve the way cars/parts are manufactured. For example, investigating an accident in which a vehicle crashed into a wall (Zhang), engineers were able to improve upon the design of the hinge of the car hood to improve its energy absorption properties.

Reconstruction includes input from the accident itself - the condition of the vehicle, skid marks, witnesses, and police reports (Young). In the event that one needs to determine whether someone was wearing a seat belt or not - as in a lawsuit - the seat belts themselves can be examined (Gorski). The pressure from a person's weight creates loading marks that can determine the exact positioning of the person or if the seat belts were tampered with (Gorski).

seat belt buckle
Seat belt loading marks
Another important usage of forensic engineering is in the aviation industry. As mentioned earlier, the flight data recorder is one of the most important tools in aviation forensic engineering. If, however, damage occurs to the flight data recorder, the National Transportation Safety Board can perform a simulation in addition to using radar data and any available flight recorder data (Kakar). In the event that an aircraft does not have a flight data recorder at all - as in the case of an aircraft with a less than ten passenger load (Slane) - a makeshift Flight Data Recorder, or FDR, can be constructed using a global positioning system and an accelerometer.
red flight recorder box
Flight Recorder: Do Not Open
With the help of mathematical analysis, "important parameters such as roll angle, airspeed, altitude and acceleration can be accurately reproduced" (Slane).

Another technique used in aviation forensic engineering is a Vertical Motion Simulator (VMS) (Tran). As the name implies, this device simulates the motion of an aircraft as well as incorporating information from both the flight data recorder and the cockpit voice recorder (CVR).

Other aviation forensic engineering applications are concerned with structural defects such as corrosion and cracking. A visual inspection is usually performed, potentially leading to the aircraft's disassembly (Forensic).

It seems that for every field of study, there is a corresponding field of forensics. Additional fields not mentioned include (but are certainly not limited to):

  • Forensic geotechnical engineering
  • Forensic seismology
  • Microbial forensics
  • Environmental forensics

(Atimtay) According to an American Society of Civil Engineers article, "visiting an earthquake damaged town is like visiting a gigantic structural laboratory. A carefully conducted forensic engineering can reveal much insight into the nature of earthquakes and the fundamental principles of seismic design."

devastated building
A future laboratory? May 2008 Chinese earthquake

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