Introduction to forensic engineering
1 Engineering quality
1.1 A growth area
The subject of this unit is forensic engineering, a branch of engineering that has grown substantially in recent years as consumers have demanded ever-increasing levels of quality. Premature product failure not only deprives the user of that product, but can also lead to personal injury and other detrimental effects. If a ladder suddenly collapses due to the fracture of a key part, the user may be thrown off and injured. If the radiator of a new car suddenly runs dry and the engine seizes up, the owner will want redress. When a patent for a new product is copied by others, the patentee will lose control of his or her invention unless action is taken against the infringer. They are all examples of the kinds of problem to which the forensic engineer can make a neutral and objective contribution.
The subject has grown with the application of new investigative tools such as Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), techniques also used widely by forensic scientists (Box 1).
Consideration of documentary evidence, which accompanies any dispute, is also a task the forensic engineer can perform. So any engineering drawings of a product that becomes available during a dispute may need to be interpreted for dimensional tolerances, or other features that may have caused a problem.
Box 1 Forensic sciences
The work of forensic scientists is well known because of high-profile murder trials, where forensic evidence was crucial in determining the truth. DNA analysis has become so sensitive a method that old, unsolved cases have been re-opened with new evidence obtained from traces of tissue still preserved from the original crime scene. While such cases have undoubtedly been spectacular successes, we should not forget that other cases have been equally spectacular failures.
There has been a series of major blunders where innocent individuals have been wrongly convicted on the basis of poor forensic analysis. Many of those cases were associated with IRA bombing campaigns, where misinterpreted forensic results combined with false confessions to produce unsafe convictions. Simplistic tests for traces of oxidized nitrogen – the nitro group – were used on clothing and limbs to show the individuals had handled explosives, for instance in the McGuire and the Birmingham Six cases. In fact, such traces could be reproduced from a wide range of common products, such as playing cards coated with cellulose nitrate, and even staples held together as a strip with cellulose nitrate polymer.
Forensic scientists practice in a variety of fields, ranging from fingerprint detection and analysis, to document examination and chemical analysis of drugs and poisons. The results of their work are widely used by the police in proving physical connection between suspect individuals and the crime scene. They are based mainly at several large and well-equipped sites supported by the government or police authorities, although they accept commissions from defendants who wish to test prosecution evidence independently.
Many of the techniques used by forensic scientists can be valuable to forensic engineers, who tend to work mainly on civil cases involving product failures, and accidents. In disputes involving intellectual property such as patents, forensic scientists are not involved at all, because such cases involve interpretation of the function of machines or devices.
Forensic engineers can help in criminal cases where sample examination and interpretation of a special kind is needed. The scanning electron microscope (SEM), frequently used for the inspection and analysis of fracture surfaces, can prove equally valuable for analysing traces of contaminants on products from a crime scene. Analytical methods such as spectroscopy have reached levels of sensitivity unavailable before 1990. Nevertheless, such methods also need the checks and independent corroboration that are an essential part of thorough sample examination. Such checks include calibration of the analytical machines, and the use of standard specimens to check machine function, as well as protection against contamination of the original samples.
Both forensic scientists and engineers can appear in criminal or civil cases, and as expert witnesses, can provide opinions to courts or lawyers. This privilege is normally denied to witnesses of fact, who can only give evidence of their direct involvement in an incident or crime. An eyewitness can give testimony about an accident she has seen personally, but cannot normally give an opinion as to why that accident happened.