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Archives of Business Research – Vol. 9, No. 8
Publication Date: August 25, 2021
DOI:10.14738/abr.98.10784. Tannen, M. B. (2021). The Effect of Diesel Exhaust Exposure on Railroad Worker Health and Mortality: A Survey of Somewhat
Competing Evidence. Archives of Business Research, 9(8). 181-189.
Services for Science and Education – United Kingdom
The Effect of Diesel Exhaust Exposure on Railroad Worker Health
and Mortality: A Survey of Somewhat Competing Evidence
Michael B. Tannen, Ph. D.
School of Business and Public Administration
University of the District of Columbia
4200 Connecticut Ave NW, Washington DC 20008
ABSTRACT
Hazardous work conditions expose employees to health and safety risks, and
employers to potentially higher expenses including the possibility of a prolonged
series of expensive litigation.Indeed, recognition of this in individual and organized
(collective) bargaining over higher pay and health benefit coverage, and of course,
government regulation involving improved safety measures and equipment design
is common. It is easier for all to deal with such risks when they are recognized, and
the extent of that risk known. Often, though, risks may appear uncertain, with
contradictory evidence supporting opposing views. Such is the case for the
exposure of railroad workers to diesel exhaust, a subject that has been investigated
for decades with considerable disagreement. This paper contains a focused survey
of published studies in the past thirty-five years using observational data and
epidemiology (laboratory studies on animals) to review the extent to which
disagreement has or not been abated.
Official concern over the adverse health effects of diesel exhaust on workers was evidenced as
least as far back as 1988, when the U.S. Occupational Safety and Health Administration (OSHA)
issued a bulletin to its field officers that read “Recent animal studies in rats and mice confirm
an association between the induction of cancer and exposure to whole diesel exhaust. ... Limited
epidemiologic evidence suggests an association between occupational exposure to diesel
engine emissions and lung cancer. The consistency of these toxicologic and epidemiologic
findings suggest that a potential occupational carcinogenic hazard exists in human exposure to
diesel exhaust.” 1In contrast, an article published in the U.S. National Institutes of Health (NIH)
National Library of Medicine in 1995 challenged this position based upon epidemiological
evidence.2An Environmental Protection Agency (EPA) assessment finished in 2002, meanwhile,
concluded the issue would require a more complex consideration than might first seem when
it reported “long-term (i.e. chronic) inhalation exposure is likely to pose a lung cancer hazard
to humans, as well as damage the lung in other ways depending on exposure. Short-term (i.e.,
1 OSHA “Safety Hazard Information Bulletin on Potential Carcinogenicity of Diesel Exhaust, Memorandum for
Regional Administrators, November 30, 1988. 2 “Diesel engine exhaust and lung cancer: an unproven association,” by J.E. Muscat and E.L. Wynder, 1995
Sep;103(9):812-8. doi: 10,1289/chp.95103812.
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acute) exposures can cause irritation and inflammatory symptoms of a transient nature, these
being variable across the population.” 3
The American Cancer Society website in 2010 emphasized “Men with the heaviest and most
prolonged exposures, such as railroad workers, heavy equipment operators, miners, and truck
drivers, have been found to have higher lung cancer death rates than unexposed workers.“4
The following year, the U.S. Occupational Safety and Health Administration (OSHA)
prominently noted “Diesel exhaust is a pervasive airborne contaminant in workplaces where
diesel-powered equipment is used... workers ... exposed to diesel exhaust ... face the risk of
adverse health effects, ranging from headaches and nausea to cancer and respiratory disease.
Such workers include ... railroad workers...5 In 2013, OSHA followed up by issuing an alert on
its website (still present today), stating “The exhaust from diesel engines contains a mixture of
gases and very small particles that can create a health hazard when not properly controlled.”6
Despite this evidence and the related policy pronouncements, the OSHA webpage noted “There
are currently no standards for diesel exhaust as a unique hazard. However, exposures to
various chemical components of diesel exhaust are addressed in specific standards for the
general industry and shipyard employment.”7 The complexities of diesel exhaust and both
known and uncertain interactions with the site-specific environment are presumably
responsible for OSHA’s reluctance to issue a single diesel exhaust standard. This complexity is
explained in the 1988 bulletin, which stated “emissions from diesel engines consist of both
gaseous and particulate fractions.... several of which are carcinogens8.
The OSHA statement draws upon references to laboratory studies of animals. The EPA study,
however, is a Health Risk Assessment, implying how individuals located in different vicinities
and locations from concentrations of diesel-fueled vehicles and equipment are likely to be
affected by carcinogens released in such exhausts, based upon laboratory findings, climatic
patterns, and other evidence.
3 HEALTH ASSESSMENT DOCUMENT FOR DIESEL ENGINE EXHAUST (FINAL 2002), UNITED STATES
ENVIRONMENTAL PROTECTION AGENCY, NATIONAL CENTER FOR ENVIRONMENTAL ASSESSMENT,
POSTED ON THE EPA WEBSITE JANUARY 6, 2011. 4 “Diesel Exhaust,” American Cancer Society website, posted on November 8, 2010. The American Cancer Society
statement draws upon observational evidence on actual workers, but the OSHA statement is references to laboratory
studies.
5 U.S. DEPARTMENT OF LABOR, OCCUPATIONAL SAFETY & HEALTH ADMINISTRATION SAFETY AND
HEALTH TOPICS INTERNET PAGE ENTITLED “DIESEL EXHAUST,” UPDATED APRIL 22, 2011. QUOTED
AS APPEARED ON OCTOBER 2, 2011. 6 OSHA Hazard Alert (still on website) “The exhaust from diesel engines contains a mixture of gases ... (diesel exhaust
or DE) and very small particles ... (Diesel Particulate Matter or DPM) ...that can create a health hazard when not
properly controlled.” 7 OSHA, IBID, 2011. 8 “THE GASEOUS CONSTITUENTS INCLUDE CARBON DIOXIDE, CARBON MONOXIDE, NITRIC OXIDE,
NITROGEN DIOXIDE, OXIDES OF SULFUR, AND HYDROCARBONS (E.G., ETHYLENE, FORMALDEHYDE,
METHANE, BENZENE, PHENOL, 1,3-BUTADIENE, ACROLEIN, AND POLYNUCLEAR AROMATIC
HYDROCARBONS). PARTICULATES (SOOT) IN DIESEL EXHAUST ARE COMPOSED OF SOLID CARBON
CORES THAT ARE PRODUCED DURING THE COMBUSTION PROCESS AND THAT TEND TO FORM CHAIN
OR CLUSTER AGGREGATES. AS MUCH OF 15% TO 65% OF THE MASS OF PARTICULATE EMISSIONS
(SOOT) OF DIESEL ENGINES IS MADE UP OF ORGANIC COMPOUNDS ...SEVERAL OF WHICH ARE
CARCINOGENS.” OSHA, IBID, 1988.
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Tannen, M. B. (2021). The Effect of Diesel Exhaust Exposure on Railroad Worker Health and Mortality: A Survey of Somewhat Competing Evidence.
Archives of Business Research, 9(8). 181-189.
URL: http://dx.doi.org/10.14738/abr.98.10784
HEALTH RISK ASSESSMENT STUDIES
Several studies of diesel emissions in and near railyards in the United States have focused on
particulate matter, not gases 9 A widely-used methodology to assess potential health
consequences due to harmful and/or excessive pollution is known as a Health Risk Assessment
(HRA). These studies have looked at the railyard’s emissions inventory, local meteorological
conditions including wind patterns and typical weather, where people live in relationship to
the yard, and related factors that can be used to a ‘diesel cancer risk’ based on the toxicity of
diesel emissions.10
In 2011, The Impact Project 11 issued its policy-related study regarding the adverse health
impacts of growing goods movement on persons living near railyards. The piece was written
primarily to detail the influence of current and projected railyard pollution on surrounding
communities in Southern California, though there is also mention of harmful diesel pollution
near railyards in other places–e.g. Chicago, Kansas, and Australia. The Report noted “Of
particular concern are diesel particulate emissions, which have been linked to lung cancer and
other health effects.“12 These emissions are identified as emanating from a number of sources,
namely trucks, cranes, yard hostlers, switch locomotives and line-haul locomotives, other
vehicles, and a variety of equipment. The Report emphasizes that passage of thousands of diesel
trucks every day through communities on their way to the ports and rail yards impacts health
not only in the railyards, but in adjacent communities.
Diesel particulate pollution is a greater health hazard to those who are subject to is
concentrated effects on a regular, continuing basis. According to the report, most railyards in
the United States already operate round-the-clock and close to capacity, and so the
geographically concentrated effect of emissions continues over the entire day. The anticipated
substantial growth in railyard traffic due to increased global trade13 is likely to exacerbate
diesel particulate pollution in and near these railyards, with corresponding increased health
risks, unless policy is dramatically changed.
9 The concentration of the latter in a particular location being more affected by varying climatic conditions such as
wind.
10 More specifically, (BNSF, loc. cit. below, p. ), “an HRA consists of three major components: the air pollution
emission inventory, the air dispersion modeling, and an assessment of associated health risks. The air pollution
emission inventory provides an understanding of how the air toxics are generated and emitted. The air dispersion
modeling takes the emission inventory and meteorology data such as temperature and wind speed/direction as its inputs,
then uses a computer model to predict the distributions of air toxics in the air. Based on this information, an assessment
of the potential health risks of the air toxics to an exposed population is performed... Potential cancer risk from a given
carcinogen estimated from the health risk assessment is expressed as the incremental number of potential cancer cases
that could be developed per million people, assuming the population is exposed to the carcinogen at a constant annual
average concentration over a presumed period.” 11 TRACKING HARM: HEALTH AND ENVIRONMENTAL IMPACTS OF RAIL YARDS, THE IMPACT
PROJECT POLICY BRIEF SERIES, #1, OCTOBER 2010, BY JOCELYN VIVAR, MARK VALLIANATOS, AND
ANDREA HRICKO. THE PROJECT IS A CALIFORNIA-BASED, COMMUNITY-UNIVERSITY
COLLABORATION FUNDED BY THE CALIFORNIA ENDOWMENT AND THE KRESGE FOUNDATION. 12 Ibid, p. 4. 13 According to the study “recent port projections see a steady growth in cargo growth and is projected to triple by
2030.”
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This Report, as is the case with HRAs in general, did not present new direct evidence of diesel
particulates on individual health, but instead relied upon results from other studies in forming
its health-risk projections. In particular, considerable reference was made to a 2007 BNSF- Hobart study (considered more fully later) and the 2005 California Air Resources Board Health
Risk Assessment for each of the 18 major California railyards.14 The impetus for these latter
studies followed a 10-year scientific assessment completed in 1998, when the California Air
Resources Board identified diesel exhaust particulates (diesel PM) as a toxic air contaminant
with potential to cause cancer and produce other health maladies such as respiratory illnesses
and increased risk of heart disease. According to the Board, “Population-based studies in
numerous cities in the U.S. and around the world demonstrate a strong link between elevated
particulate matter levels and premature deaths....many of these studies have linked the health
effects to diesel PM... Subsequent research has shown that diesel PM contributes to pre mature
death.”15
The 2005 assessments, collectively, found the railyards responsible for “210 tons of diesel
pollution emissions a year, posing a significant public health risk and putting more than 3
million people at elevated risk of cancer.”16 Five of the railyards were identified, individually,
as posing “an excessive cancer risk chances of 500-3,300 chances per million, well beyond the
level EPA considers acceptable.”17 Much more information and detail is available from the
BNSF-Hobart study.
In the BNSF - Hobart Railyard study the Board conducted a voluminous health risk assessment
(HRA) of impacts associated with toxic air contaminants emitted in and around the very large
BNSF Railway’s Hobart Railyard, located in Commence, California.18 As the report explains “a
HRA uses mathematical models to evaluate the health impacts from exposure to certain
chemical or toxic air contaminants... HRAs ... are estimates for the potential health impacts on
a population at large.”19 This particular study focused on railyard emissions (separately and
collectively) from locomotives, on-road trucks and other off-road vehicles and equipment used
to move cargo. The authors note diesel PM emissions are usually found to be dominant toxic air
14 “THE COUNTRY’S TWO LARGEST FREIGHT RAILROADS OPERATE PRIMARILY IN THE WESTERN U.S.
THESE ARE BNSF RAILWAY COMPANY, WHICH OPERATES 32,000 ROUTE MILES IN 28 STATES AND
UNION PACIFIC CORPORATION, WHICH OPERATES 32,100 ROUTE MILES IN 23 STATES. IN
CALIFORNIA, THESE TWO RAILROAD COMPANIES OPERATE 18 MAJOR RAIL YARDS.” 15 IBID 16 Ibid, p. 4. 17 IMPACT, IBID, P.4. 18“Health Risk Assessment for the BNSF Railway Hobart Railyard,” California Environmental Protection Agency, Air
Resources Board, by Wei Li with contributions from Jing Yuan, Eugene Yang, Chan Pham, Hector Castaneda, et. al.,
November 2, 2007. BNSF Hobart Railyard is the largest intermodal railyard in the United States focusing on the
distribution of international containers. HRAs do not consider health data on specific individuals, but address overall
risks for groups of individuals. 19 THE REPORT CONTAINS WHAT SEEMS LIKE A STANDARD DISCLAIMER “THE RISK ESTIMATES
SHOULD NOT BE INTERPRETED AS A LITERAL PREDICTION OF DISEASE INCIDENCE IN THE
AFFECTED COMMUNITIES BUT MORE AS A TOOL FOR COMPARISON OF THE RELATIVE RISK
BETWEEN ONE FACILITY AND ANOTHER.” DESPITE THIS DISCLAIMER, MUCH OF THE TEXT OF THE
REPORT, SUCH AS THE SENTENCE QUOTED ABOVE, SEEMS TO IMPLY THAT THE ESTIMATES SHOULD
BE TAKEN MORE LITERALLY.
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Tannen, M. B. (2021). The Effect of Diesel Exhaust Exposure on Railroad Worker Health and Mortality: A Survey of Somewhat Competing Evidence.
Archives of Business Research, 9(8). 181-189.
URL: http://dx.doi.org/10.14738/abr.98.10784
contaminant in and around railyards, and this is found to be so in this study.20 How far away
from railyards are the cancer risks considerable has been a bone of some contention. The HRA
2004 study for UP Roseville Railyard, for example, indicated that cancer risk associated with
on-site diesel PM emissions is substantially reduced beyond a one-mile distance from the
railyard. The 2007 BNSF-Hobart study stated “the areas with the greatest impact has an
estimated potential cancer risk of over 1000 chances in a million, occurring in the area right
next to the boundaries of the railyard fence line.”21
EPIDEMIOLOGICAL STUDIES
Clinical trial evidence on health is seldom available from to human workers regularly exposed
to diesel exhaust. 22 One epidemiological study, though, conducted by a team of medical
researchers from Imperial College London and the New Jersey School of Public Health23 focused
on the short-term effect of this exhaust on persons with asthma. In this study, the researchers
recruited 60 non-smoker adults, approximately half with mild and half with moderate asthma.
Each of the subjects walked two hours per day, alternating daily between two locations, one, a
busy London street in which the only vehicular traffic was diesel-fueled buses and cabs, and the
other through a nearby city park over several months. The conclusions of the study were
walking on the city street “induced asymptomatic but consistent reductions in forced
expiratory volume...effects were greater in subjects with moderate asthma than mild asthma...
our observations serve as a demonstration and explanation of epidemiologic evidence that
associates the degree of traffic exposure with lung function in asthma.”24
In 2012 the U.S. National Institutes of Health published a review of seven of the more recent
epidemiology studies on the possible linkage of diesel exhaust and lung cancer.25 The evidence
did not specifically focus on railroad workers. Two concluded “significant exposure-response
(E-R) trends between cumulative diesel exhaust and lung cancer were unlikely to be explained
by bias or confounding” but the authors of the review article maintained this conclusion (of an
apparent cause and effect relationship) was ‘non-definitive.’ All remaining studies presented
some degree of apparent evidence, but were said by the review authors to be flawed because
of failure to control for general exposure to air pollution, smoking, and other possible
environmental health risks. Specifically, the review authors maintained “weak and inconsistent
E-R associations..could be explained by bias, confounding or chance, exposure misclassification,
and often inadequate latency.” In the authors judgment “the weight of the evidence considered
inadequate to confirm the diesel-lung cancer hypothesis.”
20 NON-DIESEL PM TOXIC AIR CONTAMINANTS HAVE LESS THAN A THOUSANDTH OF THE POTENCY
WEIGHTED EMISSIONS AS COMPARED TO DIESEL PM. 21 BNSF-HOBART, IBID, P. 17. 22 Still, the EPA in 2002 “described the risk of diesel exhaust-related lung cancer based on human epidemiologic
studies,” according to Garshick, et. al. “Lung Cancer in Railroad Workers Exposed to Diesel Exhaust,” Eric Garshick,
Francine Laden, Jaime E. Hart, Bernard Rosner, Thomas J. Smith, Douglas W. Dockery, and Frank E. Speizer,
Environmental Health Perspectives • VOLUME 112 | NUMBER 15 | November 2004, second page.
23 “Respiratory Effects of Exposure to Diesel Traffic in Persons With Asthma,” James McCreanor, et. al., Imperial
College Papers, and Science Daily, also published in The New England Journal of Medicine, December 6, 2007.
24 Ibid, p. 5. 25 “Lung cancer and diesel exhaust: an updated critical review of the occupational epidemiology literature,” John F
Gamble, Mark J Nicolich, Paolo Boffetta, 2012 Aug:42(7):549-98. doi: 10.309/10408444.2012.690725
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STUDIES OF RAILROAD WORKERS SURVIVAL AND MORTALITY RATES
Other studies specifically focused on the effect of diesel exhaust on railroad worker health and
mortality, based upon observational, not experiment-generated data. These studies may be
considered “long-run,” even though they actually rely upon cross-sectional data at a point in
time. Each study is a snapshot of mortality rates by age at a date, rather than a “panel data”
follow-up of the same cohort of individuals (e.g. those newly hired in the same time period),
evaluated at several later dates in their careers. Because individuals in this cross-sectional
snapshot have worked for railroads for varying number of years, it is possible to relate
mortality rates to years of railroad experience and age (not necessarily the same thing), and
some other factors, including occupational group (available in the data) and cigarette smoking
(asked of friends and relatives of those in the sample who are deceased).
Major advantages of these studies are that they consider a substantial period of worker’s lives,26
allow for consideration of accumulated diesel exhaust effects, reflect actual work-life situations,
and cover a substantial number of individuals. But their design also presents greater statistical
challenges than experimental epidemiological studies in ferreting out what is controlled from
what cannot be controlled for in a non-experimental situation.27
None of the results in these studies is thoroughly definitive, but the statistical methodology
used has been improved over time, yielding generally consistent results. These studies provide
a body of consistent evidence indicating that railroad workers who have been regularly
exposed to diesel fumes over decades are more likely to die from lung cancer than either other
railroad workers or the general population, by a substantial margin. Recent research on chronic
pulmonary diseases by some of the same authors, moreover, demonstrates that lung cancer is
not the only disease or malady that can be linked, statistically, to diesel emissions.28
26 THE DATE AT WHICH WORKLIFE AND DIESEL EXPOSURE BEGIN IN THESE U.S. STUDIES IS 1959. BY
WAY OF BACKGROUND, IN 1946, 10% OF THE LOCOMOTIVES IN SERVICE WERE DIESEL, BUT BY 1959,
THE TRANSITION TO DIESEL ENGINES WAS NEARLY COMPLETE, AT 95%. 27 Clinical trials, properly conducted, are truly “experimental” in that they rule out systematic confounding influences
from other possible causes of a disease or mortality, usually by random assignment of subjects to the suspected hazard.
Clinical trials of exposure to diesel exhaust with random assignment of individuals, observed over a long-enough period
of time to satisfactorily track the progression of a disease have not yet been undertaken. Observational studies are based
upon existing data sets are not truly experimental because the possibility of confounding effects can, at best, be partly
controlled for. Such studies have difficulty with satisfactorily controlling, for example, a type of selection bias known as
the “healthy worker effect.” This may be interpreted as the phenomenon of employed persons to be healthier than
unemployed persons who are comparable on other characteristics. Continuing employed persons, therefore, are less likely
to succumb to a toxic substance, yielding the surprising and probably misleading conclusion that those who are exposed
longer have lower mortality rates. 28 ACCORDING TO A MARCH 2011 POLICY PAPER [“GLOBAL TRADE IMPACTS: ADDRESSING THE
HEALTH, SOCIAL AND ENVIRONMENTAL CONSEQUENCES OF MOVING INTERNATIONAL FREIGHT
THROUGH OUR COMMUNITIES”] WRITTEN BY AUTHORS FROM OCCIDENTAL COLLEGE
&UNIVERSITY OF SOUTHERN CALIFORNIA, [P. 15], “U.S. RAILROAD WORKERS HIRED AFTER THE
INTRODUCTION OF DIESEL LOCOMOTIVES HAD A 2.5% INCREASE IN CHRONIC OBSTRUCTIVE
PULMONARY DISEASE (COPD) MORTALITY RISK FOR EACH ADDITIONAL YEAR OF WORK IN A
DIESEL-EXPOSED JOB. REF: HART JE, LADEN F, EISEN EA, SMITH TJ, GARSHICK E. CHRONIC
OBSTRUCTIVE PULMONARY DISEASE MORTALITY IN RAILROAD WORKERS. OCCUP ENVIRON MED
2009;66(4):221-6.”