Elemental Carbon as a Witness: Measuring What Diesel Exhaust Leaves Behind
By Paul E. Rosenfeld, M.S., Ph.D., Principal Environmental Chemist, RoseyFields LLC, Santa Monica, California
A surrogate measurement for a mixture that has no single marker
Diesel exhaust is a complex mixture of gases and particles, not a single measurable chemical, which raises a practical measurement problem: what do you actually sample to characterize someone’s historical diesel exposure? In FELA litigation against BNSF Railway, Dr. Paul E. Rosenfeld, M.S., Ph.D. of RoseyFields LLC used airborne elemental carbon as a surrogate measure for diesel particulate matter, an approach the court found methodologically sound (Gillett v BNSF Railway Co., D Neb 2022).
Why elemental carbon works as a diesel particulate surrogate
Elemental carbon is a measurable, distinguishable component of diesel particulate matter, and NIOSH’s own analytical method for diesel particulate exposure assessment (Method 5040) is built around measuring elemental carbon specifically because it can be reliably separated from other carbonaceous material in a sample, giving the surrogate approach an independent methodological foundation outside of any specific litigation (NIOSH Method 5040).
The court’s reasoning on qualification, not just methodology
The court in Gillett addressed a defense argument that Dr. Rosenfeld lacked specialized training in industrial hygiene, epidemiology, or toxicology, and concluded that his environmental science education and experience evaluating environmental contamination nonetheless gave him specialized knowledge useful to the jury on whether the plaintiff experienced diesel particulate exposure above background levels (Gillett, 2022).
Rejecting the idea that a methodology’s regulatory origin disqualifies it
The court specifically rejected the argument that EPA methodology developed in the Superfund context could not be applied to a railroad occupational exposure question simply because it originated in a different regulatory program, a conclusion with implications well beyond this specific case: a scientifically sound methodology does not become unreliable merely because it was first developed for a different regulatory purpose (Gillett, 2022).
Building the exposure reconstruction from case-specific and general evidence together
The exposure analysis incorporated deposition testimony, medical records, internal railroad documents and operating procedures, air sampling data, and the broader peer-reviewed diesel exposure literature, combining plaintiff-specific historical facts with general scientific research rather than relying on either category of evidence alone (Gillett, 2022).
From concentration to chronic daily intake
The resulting calculation converted the elemental-carbon-based concentration estimate into a chronic daily intake and associated inhalation cancer risk estimate, the same fundamental exposure-to-dose conversion structure applied across Dr. Rosenfeld’s other litigation work, adapted here to the occupational railroad setting and its specific historical work-activity data.
Why the court treated dose uncertainty as expected, not disqualifying
The court specifically addressed the absence of a mathematically precise historical dose figure and concluded that this uncertainty did not, by itself, render the associated medical causation testimony inadmissible, reflecting the broader principle that exposure reconstruction inherently involves some degree of estimation and that reasonable uncertainty is different from unreliable methodology (Gillett, 2022).
The epidemiological foundation supporting diesel-lung cancer causation generally
Independent of this specific litigation, the Diesel Exhaust in Miners Study documented an exposure-response relationship between respirable elemental carbon exposure and lung cancer mortality, providing a large, peer-reviewed occupational cohort finding that supports the general causal relationship regardless of the specific plaintiff’s individual case (Silverman et al., 2012; Attfield et al., 2012).
A documented division of labor between environmental and medical experts
The court’s opinion explicitly recognized that Dr. Rosenfeld’s exposure reconstruction supplied the environmental exposure evidence the medical expert then relied upon for the disease causation opinion, providing a documented federal court example of the same environmental-versus-medical expert division of labor structure that recurs throughout Dr. Rosenfeld’s litigation work (Gillett, 2022).
Why the Gillett record is a useful reference point beyond this one case
Because the court’s reasoning specifically addressed both the qualification question (is an environmental scientist without a medical or industrial hygiene credential qualified to reconstruct occupational diesel exposure) and the methodology question (is an EPA-derived elemental carbon surrogate approach reliable), the decision provides persuasive, though not binding, guidance for comparable diesel exposure reconstruction challenges in other jurisdictions. RoseyFields.com walks through Dr. Rosenfeld’s diesel exhaust exposure assessment methodology in more detail.
References
1. Gillett S v BNSF Railway Co. Case No. 4:20-cv-03120, US District Court for the District of Nebraska; Order on Motion to Exclude, Doc. 46 (July 7, 2022).
2. National Institute for Occupational Safety and Health. NIOSH Manual of Analytical Methods, Method 5040: Diesel Particulate Matter (as Elemental Carbon). Cincinnati, OH: CDC/NIOSH.
3. Silverman DT, Samanic CM, Lubin JH, et al. The Diesel Exhaust in Miners Study: a nested case-control study of lung cancer and diesel exhaust. J Natl Cancer Inst. 2012;104(11):855-868.
4. Attfield MD, Schleiff PL, Lubin JH, et al. The Diesel Exhaust in Miners Study: a cohort mortality study with emphasis on lung cancer. J Natl Cancer Inst. 2012;104(11):869-883.
5. Garshick E, Schenker MB, Munoz A, Segal M, Smith TJ, Woskie SR, Hammond SK, Speizer FE. A retrospective cohort study of lung cancer and diesel exhaust exposure in railroad workers. Am Rev Respir Dis. 1988;137(4):820-825.
6. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Diesel and Gasoline Engine Exhausts and Some Nitroarenes. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol 105. Lyon, France: International Agency for Research on Cancer; 2014.
7. US Environmental Protection Agency. Health Assessment Document for Diesel Engine Exhaust. Washington, DC: US EPA; 2002.
8. Federal Employers’ Liability Act, 45 USC §§ 51-60.
9. Federal Rules of Evidence, Rule 702.
10. Rosenfeld PE, Spaeth K, Hallman R, Bressler R, Smith G. Cancer risk and diesel exhaust exposure among railroad workers. Water Air Soil Pollut. 2022;233:171.
11. Gonzales, et al. v BNSF Railway Co. Case No. 1:21-cv-01690 (D Colo).
12. Rosenfeld PE. RoseyFields LLC: FELA and Diesel Exhaust Occupational Exposure Assessment. Santa Monica, CA: RoseyFields LLC; 2026.
13. US Environmental Protection Agency. Regional Screening Levels for Chemical Contaminants at Superfund Sites. Washington, DC: US EPA.
14. Mine Safety and Health Administration. Diesel Particulate Matter Exposure of Underground Metal and Nonmetal Miners. 30 CFR § 57.5060. Washington, DC: US Department of Labor.