Expertly Speaking


Don’t Blame the Design!

Robert J. Nobilini, Ph.D., Biomechanical Engineer

Case Synopsis: A bartender slipped and fell on a wet ceramic tile floor, fracturing her patella. The plaintiff’s expert claimed that the design of the plaintiff’s footwear was the primary cause of the fall.

Expert Analysis: Plaintiff’s expert opined that the design of the footwear’s sole reduced its contact area with the floor, which reduced the slip resistance of the footwear. It was shown that slip resistance is independent of surface contact area. Therefore, the plaintiff’s expert’s opinion contradicted the laws of physics. Plaintiff’s expert stated that the midsole stiffness of the footwear increased the push-off force between the footwear and the floor. However, he failed to provide any scientific basis to support his opinion. In fact, the design of the incident footwear was shown to be similar to other footwear on the market. It was also shown that the expert made certain assumptions about the plaintiff’s fall mechanics that were incorrect. Therefore, the stiffness of the footwear was determined not to be a factor.

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Coal Mine

Underground Coal Mining Train Derailment

Paul Moore, Mining Safety Engineer

Case Synopsis: This case involved a train derailment in an underground coal mine. The train consisting of 2 mining locomotives each operated by an experienced coal miner (the plaintiffs) was hauling 2 flat cars loaded with mining supplies. As the train was traveling down grade, the miners lost control and were unable to slow or stop the train. Both miners jumped from the locomotives and the train derailed in a turn near the bottom of the slope. The miners suffered serious injury as a result of having to jump from the train.

In general the plaintiff’s alleged negligence on the part of the locomotive manufacturer and the mining company in allowing the existence of unsafe locomotive operating conditions and requiring the miners to transport supplies in excess of the capabilities of the locomotives, resulting in serious injury to the miners.

In this case, the locomotives were operating beyond their safe capacity for the conditions encountered as evidenced by the fact that the miners lost control. Conditions that could account for this include the track rail condition, the steepness of the track grade, the performance capability and operating condition of the locomotives, the weight of the flat cars with supplies, and the locomotive operator’s knowledge and ability.

The complaint and case file provided by the client (attorney for plaintiffs) was reviewed for information in support of the allegations. Additional resources including Federal and State mining regulations and reports; records of enforcement actions against the manufacturer and mining company (defendants); engineering references related to locomotive performance capability; and information from plaintiff interviews were also reviewed.

Regarding track rail condition – The case file included the mining company’s accident investigation reports indicating that the track rail had been wet and the need to sand the rails in areas of steep grades after extended period of time to prevent similar occurrences. Wet track rail significantly decreases a locomotive’s braking ability. Application of sand to the rails helps the locomotive wheels gain traction enabling the locomotive operator to safely control the speed of the train. Federal and State regulations require mining companies to examine underground workings for unsafe conditions on a regular basis and to eliminate such conditions when found. The client was advised that obtaining records of these examinations for time intervals prior to the accident could support allegation of the company’s prior knowledge of wet rail condition.

Regarding steepness of descending track grade – The case file did not contain sufficient information to fully evaluate the locomotive’s ability to safely negotiate the grade. Grade profiles documenting the degree of slope are typically included in surveyor reports possessed by mining companies. The client was advised that a grade profile would be necessary to evaluate the impact of track grade on the accident.

Regarding the performance capability of the locomotives – Engineering methods are available to evaluate the locomotive’s ability to safely haul the train down the grade. However the case file lacked sufficient information to support this type of evaluation. A list specifying the information required for the evaluation was given to the client.

Regarding the operating condition of the locomotives – Based on the mining company’s records of weekly maintenance exams in the case file and plaintiff statements made during interviews it appeared that on the date of the accident, the locomotives were operating correctly with the possible exception of a brake control switch. Additional information was needed to address the brake control switch operation.

Regarding the weight of flat cars and supplies – The case file lacked information to describe the weight of the flat cars and supplies. According to the plaintiffs the flat cars and supplies weighed 16 tons and exceeded the locomotives performance capabilities for the track conditions and grade. The client was advised of the specific information needed to fully assess the validity of this claim.

Regarding the operator’s knowledge and ability – The plaintiffs had operated the locomotives for several years prior to the accident and mining company training records verified that they had been appropriately trained. This indicated that both plaintiffs had the requisite knowledge and ability to safely operate the locomotives. The client was advised of additional information that could be used to enhance this conclusion.

Results: The client was provided a comprehensive report detailing the additional information needed to support further analysis of the accident factors. In response to the client’s request, further information was obtained; however, the case was settled prior to analysis of the additional information.

Paul Moore, Mining Safety Engineer with DJS Associates, Inc., can be reached via email at or via phone at 215-659-2010.

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ADA Shower Seat Collapse

John R. Yannaccone, P.E., Senior Mechanical Engineer

Case Synopsis: A hotel guest was taking a shower in a handicap accessible guest room. He was sitting on the wall-mounted shower seat when it collapsed, causing the guest to fall onto the floor of the shower. His wife contacted the front desk who sent hotel employees to assist her in helping her husband off the shower floor. Initially, the man reported he was uninjured but was later taken to an urgent care center when he indicated he was experiencing pain from his fall.

Expert Analysis: Photographs of the shower and shower seat, from the time of the incident, showed the upper portion of the shower seat had separated from the wall of the shower. Additionally, the photographs showed the support structure of the seat was still intact and appeared to be undamaged.

The specification for the shower seat indicated a maximum occupant weight of 360 pounds. Medical records for the plaintiff indicated he was between 260 and 270 pounds, which was well within the design limits. The instructions for the seat provided some guidance for installing the shower seat. The shower wall on which the shower seat was mounted was a hollow, studded wall. The manufacturer’s installation requirements for mounting to a studded wall indicated there had to be a backer board installed between the studs and that the seat itself had to be attached to the wall with #14 screws. Local building codes required a backer for shower seats capable of supporting the shower seat with a 250-pound occupant, as opposed to the allowable 360-pound occupant for which the subject shower seat was designed.

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Are Screenshots Sufficient Evidence?

Timothy R. Primrose, Mobile Forensic Analyst

Text messages, photographs, and call lists accessed directly from a cell phone reveal only a fraction of usage data stored within the device. Accessing additional data, unattainable by scrolling through the device, requires sophisticated software that collects a detailed timeline of phone events. This metadata, or data that gives information about other data, can assist in distinguishing between, whether a text message was received or was received and read.

The image on the left provides a text message conversation snapshot displayed on a cell phone. The image on the right shows data about the same conversation, provided by a forensic extraction.

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Automated Metalworking System Jams and Injures Worker

Thomas Cocchiola, P.E., CSP, Mechanical Engineer

Case Synopsis: A maintenance worker sustained severe head injuries while assessing the extent of a jam in the scrap conveyor feed chute of an automated metalworking system. The manufacturer designed the system to operate continuously; however, operators routinely experienced jams that interrupted production. The system was equipped with a window to monitor the flow of scrap material through the conveyor feed chute, which was located under a reciprocating table. After de-energizing and shutting down the machine, the maintenance worker knelt down and looked through the feed chute window. Unfortunately, the table unexpectedly reciprocated and struck the plaintiff in the head.

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A Shocking Design Failure

Colin Brigham, CIH, CSP, Safety Management and Ergonomics Expert

Case Description: A high school science teacher was using a hot plate on the top of her laboratory bench in a demonstration to the class. The hot plate was being used to heat and mix material in a glass vessel. While the hot plate was still turned on, she bent over and began to unplug the hot plate and received an electrical shock that threw her back, causing her to strike the back of her head on the tray of a large dry erase board. The teacher sustained brain damage.

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