Eighth Circuit Affirms Exclusion of Expert Testimony on Specific Causation in Toxic Exposure Case
The Eighth Circuit recently issued a Daubert opinion that provides a good reminder that in toxic tort cases, experts must pay attention to issues of actual exposure and dose before they can have an admissible opinion on "specific" causation (i.e., that the plaintiff's exposure to the chemical caused his injury).
In Barrett v. Rhodia, Inc., No. 09-3115, Slip op. (8th Cir. May 24, 2010), the plaintiff worked for a company that disposed of hazardous waste. Plaintiff's job was to assist in ash fixation -- making waste materials stable enough to be disposed of in landfills. Plaintiff worked in a three-story facility with steel grating floors. One of his co-workers would open a barrel of phosphorus pentasulfide and load it into a chute on the third floor. Plaintiff's job was to open the door of the chute on the second floor and let the phosphorus pentasulfide flow down to the first floor, where the waste materials awaited treatment.
Phosphorus pentasulfide is a powder that defendant delivered in barrels. It reacts with water and water vapor, forming toxic hydrogen sulfide gas. If the dust is enhaled, it interacts with moisture in the lungs to form the gas. High concentrations of hydrogen sulfide gas (500 to 1,000 ppm) can cause unconsciousness and death.
Because of its known toxicity, OSHA advises that workers who use the chemical wear protective clothing and a self-contained breathing apparatus. On the date in question, the employee on the third floor wore a breathing apparatus, put plaintiff and his colleagues on the lower floor did not. The employee on the third floor loaded the chute. When plaintiff went to open the second-floor chute, he collapsed. He subsequently was diagnosed with dementia resulting from lack of oxygen to the brain.
Plaintiff's employer hired someone to investigate the incident. They opened the drums of phosphorus pentasulfide and found hydrogen sulfide gas in the headspace of the drums at a concentration as much as 5,500 ppm.
Plaintiff sued the defendant chemical supplier, claiming that the drum was defectively designed to allow hydrogen sulfide to build up in the headspace and that defendant failed to warn of the risk of harm from hydrogen sulfide in the headspace of the drum. Plaintiffs' experts were prepared to testify that it was the act of third floor employee in opening the drum that caused plaintiff to be exposed to enough hydrogen sulfide to pass out and be injured.
Defendant moved to exclude plaintiff's expert testimony under Daubert, arguing that although some of the experts might be qualified to testify to general causation -- i.e., that hydrogen sulfide can cause the type of injury that plaintiff has -- none were able to testify to specific causation with the requisite degree of scientific reliability because they did not establish that plaintiff was exposed to hydrogen sulfide from the drum's headspace and, if so, in what dose. In fact, the defendant hired its own expert who conducted drum opening experiments in the employer's facility, including gas dispersion calculations to determine how much hydrogen sulfide gas a person standing twelve to fourteen feet below the drum (on the second floor) would receive. Defendant's expert concluded that the plaintiff could not have been exposed to a sufficient concentration of hydrogen sulfide gas to cause plaintiff's reaction. The defendant's expert concluded that the more likely explanation was that plaintiff -- who wore no breathing apparatus -- inhaled phosphorus pentasulfide dust when he tried to open the chute. This, of course, was a danger that was amply warned about.
Plaintiff's primary expert was an experienced allergist who was board certified in toxicology. She had never treated anyone with exposure to hydrogen sulfide gas. And she "conceded that she did not know how hydrogen sulfide disperses, the distance between [plaintiff] and the . . . drum alleged to be the source of the gas, or the concentration of hydrogen sulfide gas, if any, in the drum." Slip. op. at 8. She also testified that she did not rule out other potential causes of plaintiff's injury -- such as the inhalation of phosphorus pentasulfide dust -- prior to forming her causation opinion, which she admitted was "based on assumption, without any scientific testing or analysis." Slip op. at 8-9.
The court stressed that "[t]he plaintiff in a toxic tort strict liability case needs to establish causation through expert testimony," which in this case meant both general causation and "that [plaintiff] was exposed to hydrogen sulfide gas which dispersed from the . . . drum manufactured by [defendant] in sufficient concentration to cause his injuries." Slip op. at 7. Without admissible expert testimony on this point, plaintiff failed to establish a prima facie case.
The court affirmed the trial court's grant of summary judgment for the defendant based on plaintiff's failure to offer admissible expert testimony on specific causation:
[Plaintiff's experts] had presented insufficient evidence, and no expert evidence, on specific causation. They had not shown that hydrogen sulfide gas released from [defendant's] drum was the source of [plaintiff's] injuries. The [district] court also noted that appellants had offered no evidence to refute [defendant's] expert, who had testified in his deposition on the basis of chemical analysis and modeling that [plaintiff] had actually inhaled [phosphorus pentasulfide] dust as a result of not wearing any protective equipment.
Slip op. at 13.
Plaintiffs tried to rely on temporal relationships and the employer's investigator's finding of gas in the drums to get to a jury on the question of specific causation. But the Eighth Circuit said no; expert proof on dose and exposure is required in toxic tort cases: "Although a mathematically precise quantification of exposure level is not required, [plaintiff and his employer] were required to present expert evidence that [plaintiff] was exposed to toxic levels of hydrogen sulfide gas, as opposed to [phosphorus pentasulfide] dust." Slip op. at 14.
Barrett is a strong reminder that experts must do their homework on the basic questions of exposure and dose, and work to eliminate potential alternative causes, in order to have admissible testimony that meets a plaintiff's prima facie burden of proof in a toxic tort case.
