Forensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law cases, although it may be of use in criminal law cases. Generally, the purpose of a forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident. It can also involve investigation of intellectual property claims, especially patents.
As the field of engineering has evolved over time so has the field of forensic engineering. Early examples include investigation of bridge failures such as the Tay rail bridge disaster of 1879 and the Dee bridge disaster of 1847. Many early rail accidents pioneered the use of tensile testing of samples and fractography of failed components.
With the prevalence of liability lawsuits in the late 1900s the use of forensic engineering as a means to determine culpability spread in the courts. Edmond Locard (1877–1966) was a pioneer in forensic science who formulated the basic principle of forensic science: "Every contact leaves a trace". This became known as Locard's "exchange principle".
Vital to the field of forensic engineering is the process of investigating and collecting data related to the materials, products, structures or components that failed. This involves inspections, collecting evidence, measurements, developing models, obtaining exemplar products, and performing experiments. Often testing and measurements are conducted in an Independent testing laboratory or other reputable unbiased laboratory.
For medical device incidents, a clinical engineer (CE) can be called to arrive on scene and investigate from a medical device perspective--"why?" He or she may be summoned to court cases as a consultant or subject matter expert (expert witness) to fill in those questions that need answered as to why the device may or may not have malfunctioned. These professionals must adhere to the local and state (or country) requirements in which they perform these services.
In general, clinical engineers will take notes, photograph the scene to include pictures taken of the medical device (i.e. knobs, dials, missing parts, or components), the supplies used (i.e. manufacturer name, lot/batch number, expiration date), , and its surrounding environment (i.e. facility damage, utilities used, interference from other devices) for evidence. The CE will interview witness (i.e. nurses and technicians) to figure out the course of events leading up to the incident as well as what happened afterwards. The CE will impound the device in question, look up its historical record for previous problems, run a series of diagnostic tests, and calibration/certification checks to determine in fact was the device the problem leading up to or had the potential to cause the reported incident. It is always prudent to conduct these investigations with another CE, BMET, or non-partial staff to be present who can also corroborate the facts along with the leading CE on the scene.
Failure mode and effects analysis (FMEA) and fault tree analysis methods also examine product or process failure in a structured and systematic way, in the general context of safety engineering. However, all such techniques rely on accurate reporting of failure rates, and precise identification, of the failure modes involved.
There is some common ground between forensic science and forensic engineering, such as scene of crime and scene of accident analysis, integrity of the evidence and court appearances. Both disciplines make extensive use of optical and scanning electron microscopes, for example. They also share common use of spectroscopy (infrared, ultraviolet, and nuclear magnetic resonance) to examine critical evidence. Radiography using X-rays or neutrons is also very useful in examining thick products for their internal defects before destructive examination is attempted. Often, however, a simple hand lens may reveal the cause of a particular problem.
Trace evidence is sometimes an important factor in reconstructing the sequence of events in an accident. For example, tire burn marks on a road surface can enable vehicle speeds to be estimated, when the brakes were applied and so on. Ladder feet often leave a trace of movement of the ladder during a slipaway, and may show how the accident occurred. When a product fails for no obvious reason, SEM and Energy-dispersive X‑ray spectroscopy (EDX) performed in the microscope can reveal the presence of aggressive chemicals that have left traces on the fracture or adjacent surfaces. Thus an acetal resin water pipe joint suddenly failed and caused substantial damages to a building in which it was situated. Analysis of the joint showed traces of chlorine, indicating a stress corrosion cracking failure mode. The failed fuel pipe junction mentioned above showed traces of sulfur on the fracture surface from the sulfuric acid, which had initiated the crack.
Extracting physical evidence from digital photography is a major technique used in forensic accident reconstruction. Camera matching, photogrammetry, and photo rectification techniques are used to create three dimensional and top-down views from the two-dimensional photos typically taken at an accident scene. Overlooked or undocumented evidence for accident reconstruction can be retrieved and quantified as long as photographs of such evidence are available. By using photographs of the accident scene including the vehicle, "lost" evidence can be recovered and accurately determined.
Forensic materials engineering involves methods applied to specific materials, such as metals, glasses, ceramics, composites and polymers.
Most manufacturing models will have a forensic component that monitors early failures to improve quality or efficiencies. Insurance companies use forensic engineers to prove liability or nonliability. Most engineering disasters (structural failures such as bridge and building collapses) are subject to forensic investigation by engineers experienced in forensic methods of investigation. Rail crashes, aviation accidents, and some automobile accidents are investigated by forensic engineers in particular where component failure is suspected. Furthermore, appliances, consumer products, medical devices, structures, industrial machinery, and even simple hand tools such as hammers or chisels can warrant investigations upon incidents causing injury or property damages. The failure of medical devices is often safety-critical to the user, so reporting failures and analysing them is particularly important. The environment of the body is complex, and implants must both survive this environment, and not leach potentially toxic impurities. Problems have been reported with breast implants, heart valves, and catheters, for example.
Failures that occur early in the life of a new product are vital information for the manufacturer to improve the product. New product development aims to eliminate defects by testing in the factory before launch, but some may occur during its early life. Testing products to simulate their behavior in the external environment is a difficult skill, and may involve accelerated life testing for example. The worst kind of defect to occur after launch is a safety-critical defect, a defect that can endanger life or limb. Their discovery usually leads to a product recall or even complete withdrawal of the product from the market. Product defects often follow the bathtub curve, with high initial failures, a lower rate during regular life, followed by another rise due to wear-out. National standards, such as those of ASTM and the British Standards Institute, and International Standards can help the designer in increasing product integrity.
- ↑ ACCE. Certification Guide. 2007. p. 132.
- ↑ USAF, AFI 41-201: "Managing Clinical Engineering". 18 April 2011. p.49.
- ↑ Extracting Physical Evidence from Digital Photographs for use in Forensic Accident Reconstruction, David Danaher, P.E., Jeff Ball, Ph.D., P.E., and Mark Kittel, P.E, 6-15-12.