A fire as a resMaterials engineering expert for fire casesult of lightning destroyed a home in Missouri. The homeowners’ insurer reimbursed them for their loss, received an assignment of their rights, and filed a diversity products liability action against a manufacturer of corrugated stainless steel tubing (“CSST”) that brought propane gas from an underground storage tank into the home.  Both sides retained materials engineering experts to support their claims.  A jury found in favor of the manufacturer.

All of the experts agreed before trial the start of the home fire was a lightning strike of a tree near the underground propane tank, which caused electric energy to enter the home and ignite combustible materials.

Fire investigators found two holes in the CSST where the fire ignited. Insurer’s experts opined that lightning traveled along the CSST, caused the two holes by melting the CSST, and ignited escaping propane, starting the home fire. The Manufacturer’s expert testified that the lightning strike did not generate enough energy to create holes in the pipe or to ignite propane escaping from the tubing. Instead, the defendant’s expert theorized that the fire started when lightning entered the home and ignited other combustibles. The fire then energized a nearby aluminum feeder wire, which arced to the tubing, creating the holes in the CSST.

Prior to trial, after the exchange of expert reports, the Manufacturer moved to exclude the Insurer’s materials engineering expert testimony, and the Insurer did likewise. The district court granted in part the Manufacturer’s motion to exclude Insurer’s testimony and denied the Insurer’s motion to exclude the Manufacturer’s expert testimony. The Insurer appealed both rulings.

Insurer’s expert witness was a professor of materials engineering and engineering systems at MIT. During a 30-year academic career, he published hundreds of articles on metallurgy and arc physics, and his expertise in those fields was undisputed. In its motion to exclude, the Manufacturer argued that this expertise did not make the Insurer’s expert qualified to opine that the pipe caused the fire in the home, or that the product was defectively designed.

The trial court ruled that the Insurer’s expert could testify as to the matters within his areas of expertise—metallurgy and arc physics—and denied the Manufacturer’s motion to exclude opinion testimony as to home fire causation. The court granted the motion to exclude opinion testimony regarding “product design and warnings” because “[the expert] specifically disavowed such expertise and his areas of expertise bear no more than a remote relationship to product design and warnings.”

On appeal, the Insurer argued the district court erred by barring the Insurer’s expert from offering at trial his expert opinions concerning material selection and the design of CSST. Manufacturer noted that Insurer never identified which opinions Insurer’s expert was allegedly erroneously precluded from offering at trial.

The Eighth Circuit agreed. Circuit Judge James B. Loken’s stated in his opinion that in order to preserve a claim that the trial court erred in excluding evidence, a party is to inform the court of its substance by an offer of proof, unless the substance was apparent from the context. Federal Rule of Evidence Rule 103 says that if the court “rules definitively” before trial, “a party need not renew an objection or offer of proof to preserve a claim of error for appeal.” In this case, the judge noted that the trial court’s only “definitive” pretrial ruling was that the Insurer’s expert could not offer opinion testimony relating to product design. The trial court offered an opinion, testifying to the thickness of the tubing and opining that it was “too thin.” So what, asked Judge Loken, was excluded?

When the Manufacturer raised this issue, counsel admitted that, during trial, the Insurer waived an offer of proof on the issue, but argued it preserved the claim of error. That reference was sufficient for the district court to deny insurer’s motion on the merits. But on appeal, Insurer did not identify or explain this to the court, making no attempt to explain what opinion testimony was excluded until the middle of its Reply Brief—stating what Insurer’s expert would have opined, without citation to the trial or appellate record. For this reason alone, Judge Loken held that the district court’s evidentiary ruling would be affirmed.

However, despite this failure to preserve, the Eighth Circuit combed insurer’s 1124–page Appendix looking for excluded opinions by Insurer’s expert relating to product design. Without success, Judge Loken wrote that nonetheless, even if properly preserved, the district court did not abuse its discretion in excluding this conclusory opinion. Insurer’s expert denied expertise in the design and installation of Manufacturer’s systems. As a result, the Eighth Circuit said that the district court correctly noted that the exclusion of the admission of expert design testimony has been upheld where it was beyond the expert’s expertise.

Insurer’s expert also opined that the tubing was unreasonably dangerous unless grounded differently, an opinion that did not address the product’s design, but instead addressed the ultimate issue of whether the tubing was an unreasonably dangerous product. While such expert testimony is permissible, Judge Loken explained that courts must guard against invading the province of the jury on a question which it was capable of answering without the benefit of expert opinion. Here the district court held that, in the absence of specific design expertise, Insurer’s expert’s conclusory opinion would provide little assistance to the jury, as required by Rule 702(a). The trial court also noted that this might run afoul of Rule 403 if the jury afforded it more weight than warranted because of the Insurer’s expert’s expertise in other areas.

However, despite this, the district court denied Manufacturer’s summary judgment because the Insurer’s expert’s testimony on causation based on the vulnerability of thin tubing to lightning, along with other experts’ testimony on the cause of the fire provided evidence from which the jury could have determined that the product design was defective. So, Insurer was able to submit its design defect and unreasonably dangerous claims to the jury.

Also, in light of the detailed scientific and causation opinions that the expert did express to the jury, the exclusion of his ultimate opinion was not a prejudicial abuse of discretion. Any equally prestigious academic “expert” provided with the expert’s scientific testimony could have expressed the same ultimate opinion. The Circuit Court found that the district court’s careful parsing of the expert opinions that Insurer’s expert could reliably provide for the jury was a proper exercise of its gate-keeping function “to ensure the reliability and relevancy of expert testimony.”


The Manufacturer’s expert was a Vice President of the Thermal Sciences at an engineering and scientific consultant firm. He held academic and research positions at various universities and published many articles on the subjects of fire origins and liquefied natural gas transportation. He was involved in hundreds of fire investigations and was a Certified Fire Investigator and a Certified Fire and Explosion Investigator. However, he had not published on the specific tubing at issue and could not recall working on any fires that involved lightning. He was not a metallurgist but studied the strength of materials and the characteristics of metals. The district court qualified him as an expert in materials, mechanical engineering, home fire, cause and origin, code reviews, and electrical causation.

This Expert’s Testimony primarily addressed fire causation, disagreeing with the Insurer’s experts as to the cause of the fire. In developing his opinion, the Manufacturer’s expert reviewed the depositions of expert and fact witnesses and the photographs taken of the home, and personally inspected the tubing. He also conducted some general scientific tests that he used to challenge Insurer’s expert’s opinions. The district court denied the Insurer’s motion to exclude Manufacturer’s expert’s opinion testimony, concluding that he had sufficient expertise in fire causation and that his opinions were sufficiently grounded in scientific literature and testing.

On appeal, Insurer argued that the district court unevenly applied the law when it excluded part of its expert’s testimony yet allowed Manufacturer’s expert to testify. Not so, said the appellate court, as the district court properly applied Daubert’s flexible standard to the distinct issues on which each expert would opine, and neither testified on the ultimate issue of product defect.

The Eighth Circuit has consistently upheld the admission of expert testimony as to the cause of a fire when the expert applied specialized knowledge to observations of a fire scene that had support in the record. Manufacturer’s expert’s extensive credentials qualified him as an expert in fire causation, and he based his opinions on that experience and his examination of the fire scene and the tubing involved. Manufacturer’s expert was not a metallurgist or lightning expert, and his testimony only touched upon those fields as relevant to the subject of fire causation, his area of expertise. Citing Eighth Circuit precedent, Judge Loken wrote that gaps in an expert witness’s qualifications or knowledge go to the weight of the witness’s testimony, not its admissibility.

The Eighth Circuit held that the Insurer failed to identify any deficiency in either the district court’s application of Rule 702 or its discharge of the ‘gatekeeping function’ under Daubert and Kumho Tire.