A professional approach to legal investigations

Issue July/August 2016 By Fahmida Hossain and Veda-Anne Ulcickas

Irrespective of the failure, the pattern of a forensic analysis is well established. While the tests and analyses selected for individual cases can vary widely based upon materials of construction, the overall method of proceeding from naked eye to detailed microscopic examinations remains the same.

Guidelines of general forensic procedures

The primary role of a failure analyst in determining the root causes of a failure is to identify the sequence of events involved. At the beginning of an investigation the failure analyst should start with an open mind without any bias, and let the data and evidence collected paint a picture of the incidents which caused or led to the failure. The generally accepted basic steps in an investigation are:

  • Collecting data
  • Identifying the different damage patterns/modes present
  • Planning and performing different tests on the components to find the actual mechanisms which contributed to the failure
  • Differentiating between primary and secondary mechanisms involved in the subject failure
  • Identifying the possible root causes after analysis of the data collected from the different experimental procedures
  • Identifying the primary root cause leading to the failure by refining the possibilities

Many times during an investigation the data may suggest a different root cause for the failure than the one initially hypothesized. All the physical evidence, background information and experimental data has to lead to the actual failure mechanism. Often we call the failure investigation a "puzzle," and after the analysis all the puzzle pieces have to fall into place.

The failure analyst/forensic engineer needs to understand the physical behavior of the failed component and what different scenarios could cause that particular type of failure. All the physical evidence present in the failed component, in the mating component(s) and the adjacent areas requires careful documentation to identify the failure mechanism. Sometimes the expert witnesses or failure analysts are contacted by lawyers in the beginning of an investigation. This is the best case scenario. However, many times, the experts are brought into a legal case after the initial phase of the investigation. As long as the photographs and all the evidence can be reviewed, the experts may get a good idea of the initial scenario.

Generally the lawyers, investigators and insurance companies involved in the initial phase of examination keep the evidence for later examination. As long as the evidence is kept in proper condition, most or all of the required testing can be performed. It is of utmost importance to keep the components involved in an investigation in a protected environment so that the failure features of the components are not altered during the storage. In most of the cases, the pieces are not examined right away and it may take a few years before the actual examination can happen. For example, a failed iron pipe, if kept in an outside environment will rust, destroying valuable fracture information. However, if the failed pipe pieces are kept in a controlled environment, most of the features associated with the failure can usually be analyzed and identified.

When a laboratory receives components for a legal investigation, it is the lab's responsibility to inform the lawyer or the client if destructive tests are going to be performed on the components. All interested parties should be invited to participate in an investigation that includes destructive testing. A specification provided by the American Society of Testing Materials (ASTM E 860) clearly identifies this requirement. If the lawyer involved is not aware of this, it is the investigator's or lab's responsibility to educate him/her. The lawyer is then expected to notify all interested parties involved in the particular case and agree upon on a date on which all the parties can meet at the particular lab for the analysis. The lab performing the analysis provides a protocol outlining the different steps necessary to determine the root cause of the problem. This protocol is then submitted to the lawyer who circulates it to the other interested parties who may or may not have any feedback or comments. These comments can be addressed before or during the investigation. Many times after doing one or a few steps of the investigation, the proposed protocol may have to be changed due to some evidence present on the components which was not expected before the examination.

Generally the investigation starts with photographic documentation, dimensional measurements and identification of the overall macro-features associated with the failure. Then the different pieces of evidence are examined carefully and primary areas of interest are identified. In-detail examinations of the identified areas are performed by sectioning the pieces as needed and examining them closely.

It should be mentioned here that a failure analyst or forensic engineer should not be a "hired gun" of the lawyer. The role and opinion of the failure analyst should be independent of any bias and should be strictly based on the facts and data gathered from the investigation. It is a general practice for the expert to discuss the findings with the lawyer before writing a report. We have had many cases where the lawyer did not want a complete report with all the data and findings together with a conclusion as the findings were not in favor of the side that lawyer was representing.

After the investigation and reporting, the next phase might be to provide a deposition or appear as an expert witness in court. At this time the expert witness is expected to present the findings in a simple enough manner so that the lawyers, the juries and the judges can understand the report and the findings. This is very important for an expert to do correctly as the outcome of the case may be altered based on these presented facts.

Case History Example

A few years ago, Massachusetts Materials Research, Inc. (MMR) performed a litigation investigation on the failed back of a wheelchair that was designed to provide support to the user. The seat back was attached to the upper canes of the wheelchair via four cane clips. The upper two clips contained a latching mechanism to hold metal pins that protruded from the sides of the seat back. The two bottom clips were notched to hold the metal seat back pins. The clips were attached to the canes with a hex bolt which, when tightened, pulled the two sides of the clip toward each other and maintained a tight fit against the cane. The failure of one of the cane clips caused the subject seat back to fall out while the wheelchair was occupied. Head trauma and subsequent hospitalization led to the death of the 40 year old owner.

Material analysis identified the clips to be a blend of polycarbonate/acrylonitrile butadiene styrene (PC/ABS). This was the intended material of the clips per the manufacturer. Additional extraction type analysis performed on a fractured clip piece yielded an aliphatic liquid. This compound indicated some kind of lubricant, e.g., mineral oil, etc. Note that this was not detected on pieces analyzed away from the fracture. The composition of the clip material was the same at and away from fracture, which was confirmed with different analysis techniques.

The owner bought the wheelchair in February and the accident happened during Thanksgiving weekend in November. There was a presence of spider-web cracks (known as craze patterned cracks) at the failed locations. The presence of mineral oil at the primary failure location would indicate an environmental stress cracking (ESC) situation. This type of oil can be found in sunscreen, moistening lotion, etc. Our analysis indicated that exposure to an ESC agent caused numerous surface cracks from which cracks progressed with application of normal service loads. Note that these surface cracks would act as stress raisers. Polycarbonate plus ABS type material is known to show ESC when exposed to sunlight, temperature variations and mineral oil type compounds. As personal care products can reasonably be expected to come in contact with these clips, the ESC failure here indicates a poor design vis-a-vis material selection.

The owner used his chair very regularly both indoors and outdoors including transportation. He weighed about 180 pounds and was very active. The seat back was also designed to recline. Combination of an inadequate design and improper material selection caused ESC failure of the seat back and death of the owner. It should be noted here that a few years later the manufacturer completely changed the design of the clips and used aluminum metal instead of the polymer material.

The investigation performed at MMR helped the family of the deceased person to win the case.