Dissertations and Theses

Date of Degree


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Environmental, Occupational, and Geospatial Health Sciences


Ilias Kavouras

Committee Members

Glen Johnson

David Prezant

Subject Categories

Environmental Health | Longitudinal Data Analysis and Time Series | Public Health | Statistical Methodology


firefighting, occupational exposures, smoke particles, pulmonary function, longitudinal data analysis, job exposure matrix


Background. Firefighters are habitually exposed to hazardous toxicants which place them at an elevated risk for numerous adverse health outcomes. An example of this is the associations observed in other works between inhalation of combustion byproducts from urban structural fires and both acute and chronic pulmonary dysfunction. To-date, the characterization of firefighters’ exposures to dangerous chemicals in smoke from non-wildfire incidents, both directly through personal monitoring and indirectly from work-related records is scarce. Prior works investigating the association between routine firefighting and pulmonary function have relied on crude metrics such as years of service and numbers of responses to quantify exposure. These surrogate measures tend to correlate poorly with true exposure to combustion, providing an impetus for use of more refined exposure indices when studying pulmonary function and other health outcomes. This dissertation aims to evaluate the association between routine firefighting exposures and longitudinal pulmonary function, first, as a function of active-duty service years before retirement and then, by developing and applying a framework for estimating quantities of exposure to smoke particles from routine fires. In chapter 2, the objective was to assess pre- and post-retirement lung function changes among World Trade Center (WTC)-exposed firefighters. In chapter 3, a refined job exposure matrix (JEM) based on fire incidents, response characteristics, and particle emissions data was developed for firefighters to estimate exposures to combustion byproducts from structural and non-structural incidents. In chapter 4, the JEM was applied to longitudinal pulmonary function testing (PFT) data to assess the effects of short- and long-term smoke particle exposure on pulmonary function.

Methods. The overall source population for this study included World Trade Center (WTC)-exposed firefighters that were actively employed on September 11, 2001 and retired before September 11, 2021. All outcome data were obtained via PFTs, or spirometry exams which are conducted approximately annually as part of routine medical surveillance. In chapter 2, repeated measurements of one-second forced expiratory volume (FEV1) were analyzed for firefighters during the 20-year follow-up period. Hierarchical piecewise linear mixed effects models were used to assess longitudinal trajectories by comparing slopes before and after retirement. PFTs were nested within individual participants. All covariates were included as fixed effects and intercepts as random effects to account for correlations between repeated measurements. Logistic regression was used to evaluate the association between retirement period and accelerated lung function decline (i.e., double the expected-age-related decline). In chapter 3, a refined JEM was developed for estimating exposure to smoke particles using fire incident data, individuals’ response data, and particle emissions data using a United States Environmental Protection Agency Framework (US EPA) used elsewhere for characterizing air pollution. This chapter included a subset of participants that responded to at least one incident between 2010 and 2021 (i.e., when data were available). Fire incident data included dates, type, severity (alarm level), and location. Response data included dates worked, firehouse, position-title, and shift-length for each firefighter. Temporal patterns of personal exposures (P) were assessed using fire incidents and responses. Correlations between years of employment, fire responses, and Pby firefighter were examined. Simple linear regression models were fit and corresponding R2 values were calculated. In chapter 4, the novel JEM was used as a surrogate measure for smoke particle exposure and was evaluated in relation to longitudinal FEV1 measurements to estimate both the short- and long-term effects on lung function. Since incident data were only available from 2010-2021, the study focused on this period for primary analyses. Rolling sums of P were calculated using 15 distinct intervals prior to the date of each PFT, ranging from 3 months to 12 years (i.e., the overall cumulative exposure). Linear mixed effects regression was again employed to estimate changes in lung function in relation to personal exposures.

Results. When comparing FEV1 trajectories before and after retirement, a significantly greater decline was detected post-retirement (βΔslope=-7.3 mL/year; 95% CI= -8.0, -6.6), after controlling for age on 9/11, race/ethnicity, height, weight, smoking, arrival time and duration worked at the WTC site. Participants that retired earliest (i.e., between 2001-2007) demonstrated the largest improvement in slope (βΔslope=+4.5 mL/year; 95% CI= 0.5, 8.5), however, had a two-fold greater likelihood of accelerated decline, over the full 20-year follow-up period (OR=1.96; 95% CI=1.59, 2.42). In characterizing exposures to fire incidents, participants were observed to have responded to a median of 424.7 (IQR: 202.3-620.0) annual incidents per person; 17.6% were fire incidents (median=77.1; IQR: 40.4-114.0). Structural fires were the most common type of fire incident (72.5% of annual incidents per person; median=55.9; IQR: 29.6-85.5). The median P was 2,922 (IQR: 882-10,424) kg of particles. Incident severity (alarm level) and firefighter engagement (position title) appeared to differentiate between high and low exposure regimes (R2=0.43). Incident severity explained most of the variability of particle exposures (R2=0.90). For participants that retired between 2019-2021, when evaluating change in FEV1 in relation to P, a -18.8 mL/1000 kg (95% CI=-30.44, -7.20), -6.01 mL/1000 kg (95% CI=-9.23, -2.79), and -12.43 mL/1000 kg (95% CI=-13.27, -11.59) in the 3-months, 18-months, and overall period prior to each repeated PFT measurement, respectively. Similar results were observed for participants that retired before 2019. When comparing P within 3 months after the exam among retirees from 2019-2021, a -23.05 mL/1000 kg (-35.83, -10.26) was observed for those that arrived at the WTC site within the first two days compared with 3.47 (-23.90, 30.83) mL/1000 kg among those that arrived later. Comparisons for all other time intervals evaluating exposure before PFTs demonstrated insignificant differences between early and late arrivers.

Conclusions. Retirement was associated with declines in FEV1 slope greater than what was observed pre-retirement. This finding may be attributable to changes in health behaviors after retirement given the reductions in occupational exposures to smoke emissions after leaving the workforce were expected to result in improved lung function. Using the JEM, incident-specific and cumulative exposures to smoke particles were estimated overall and by individual allowing for evaluation of exposure-response associations with varied health outcomes including pulmonary function, cardiovascular disease, and cancer in future studies. Firefighting exposures were observed to have a modest short- and long-term negative association with lung function, with a brief period of recovery in the intermediate period, when examined as a function of P. This finding was most pronounced among participants that had the highest levels of WTC exposure, as measured by early arrival at the disaster site. Future work examining the association between P and lung function among non-WTC exposed firefighters will be essential for disentangling the effects of routine aging, firefighting, and WTC-exposures.

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