This study evaluated the association of bladder cancer risk and fire scene investigation within a cohort of white male criminal investigators with the United States Bureau of Alcohol, Tobacco, Firearms and Explosives that was found to be at increased risk for bladder cancer. Medical surveillance data were used in a nested case-control study to determine odds ratios (ORs) estimating the relative risk of the cancer associated with post-fire investigation. The study comprised seven bladder cancer cases and 1525 controls. Six of the cases reported holding assignments associated with post-fire investigation. The OR for bladder cancer was 19.01 (95% confidence interval = 1.94–186.39) for those holding any one or more of these assignments for one to four years versus zero years and 12.56 (1.14–138.58) for those holding any one or more of these assignments for five or more years versus zero years. The risk for bladder cancer is significantly elevated for those holding post-fire investigation assignments compared to those not holding these assignments.
As presented in Part 1 of this epidemiologic study, a bladder cancer cluster occurred within a cohort of white male criminal investigators working with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), United States Department of Justice, between 1994 and 2005 [
Most scenes investigated by ATF are post-fire rather than post-blast and involve municipal structures. Although ATF employees who investigate post-fire scenes typically wait until the fire is out to enter the scene to search for origin and cause, the work still puts them at risk for exposure to a mix of hazardous chemicals and products of incomplete combustion which potentially includes known and suspect bladder carcinogens such as aromatic amines and polycyclic aromatic hydrocarbons (PAHs) [
Independently, ATF sponsored two efforts to characterize exposures occurring during fire scene investigation by ATF employees, (1) a health hazard evaluation performed by NIOSH in 1997 [
As no two fire scenes are alike and specific exposure risks vary from one scene to another, these industrial hygiene findings may not typify investigator exposures at all present-day fire scenes and may not characterize exposures occurring at fire scenes 10 to 20 years ago. Investigator variables such as time spent on scene, use of personal protective equipment, and adherence to cleanup procedures will also influence exposure risks. Potential for internal exposure to PAHs during firefighting activities has been demonstrated in a study on firefighters exposed to burning diesel fuel during training exercises [
No epidemiologic study on bladder cancer risk in fire investigators has been previously reported. Since firefighters and fire investigators share a potential for similar exposures, and firefighters may participate in fire investigation, a review of the epidemiologic studies on bladder cancer in firefighters is appropriate. Since the mid-1980s numerous epidemiologic studies [
Part 2 of this study uses data from the ATF medical surveillance program to evaluate the association between post-fire/post-blast investigation and bladder cancer risk within the study’s white male cohort through an internal nested case-control analysis which controlled for both age and tobacco use history.
Part 1 [
All seven bladder cancer cases identified in the ATF cohort study of Part 1 [
The selected control group, by definition, included all white males in the ATF cohort of Part 1 who had at least one medical surveillance exam during the period 2003–2007 with complete data on all study parameters and no self-reported history of any type of cancer. Thus, study controls were representative of all noncases in the population.
Since risk for bladder cancer increases with age, this study controlled for age. Dates of birth for cases and controls were self-reported through the medical surveillance program and then verified through cross-referencing with dates of birth obtained from annual ATF staffing rosters. Year of diagnosis of bladder cancer for cases was self-reported through the medical surveillance program and then verified through cross-referencing with a pathology report, as available. For study purposes, case age was the age the case turned in the year of diagnosis and control age was the age the control turned in the year of the most recent complete examination in the database.
As cigarette smoking is a significant risk factor for bladder cancer, this study controlled for tobacco use history. Tobacco use history for cases and controls was self-reported through the medical surveillance program and included the following: (1) yes or no if tobacco products were ever used, (2) whether use was current or past, (3) if past, the year quit, (4) type of product used (cigarettes, pipe/cigar, snuff/chew), (5) number of years used, and (6) amount per day. For study purposes, tobacco use data for the cases reflected tobacco use status in the year of diagnosis and tobacco use data for the controls reflected tobacco use status in the year of the most recent complete examination in the database. For cases diagnosed prior to 2003, historical medical surveillance data was accessible to verify tobacco use status in the year of diagnosis. Tobacco use status of cases after year of diagnosis was excluded from study as it was not relevant.
The selected work history parameters for this study included (1) number of years reported working on team assignments and with special designations relevant to post-fire/post-blast investigation (special assignment years), (2) number of years reported working post-fire/post-blast scenes (fire scene exposure years), and (3) number of days reported working post-fire/post-blast scenes (fire scene exposure days). As ATF investigations are predominately post-fire, these work history parameters serve as surrogate measures or variables of exposure to products of combustion associated with fire scenes.
These parameters applied only to work with ATF and did not include work with prior employers. The team assignment and special designation categories included (1) National Response Team (NRT), (2) Division Response Team (DRT), (3) Arson Task Force, (4) Certified Fire Investigator (CFI), and (5) Certified Explosives Specialist (CES). The terms NRT, CFI, and Arson Task Force were clarified in Part 1 of this study [
Work history information was collected through the medical surveillance program in the same way for both cases and controls. For cases, work history data reflected the reported number of years worked or number of days worked up to the year of diagnosis. A projection was used to calculate the number of days worked on fire and explosives scenes up to the year of diagnosis, if this information was first reported after the diagnosis year. This projection was based on the assumption that the days worked were evenly distributed over the years worked on fire scenes. For controls, work history data reflected the reported number of years worked or number of days worked up to the year of the most recent complete examination available in the database.
Evaluation of the association between post-fire/post-blast scene investigation and bladder cancer incorporated a nested case-control study design to compare the work histories of the bladder cancer cases and the work histories of the controls with no history of any cancer. As stated earlier, since all identified bladder cancers in the study population occurred in white males, the nested case-control study focused only on white males. See Section
Odds ratios (ORs), based on logistic regression models, were computed to estimate the relative risk of bladder cancer associated with each fire scene exposure study parameter, while controlling for the confounding factors tobacco use and age. Analyses of the special designation and team assignment categories included both years worked in each category and years worked in any one or more of the five categories combined.
Controls were not matched with cases in terms of the exposure parameters under study in order to avoid overmatching bias. To control for age, cases and controls were grouped into 10-year age increments: less than 30 years, 30–39 years, 40–49 years, 50–59 years, and 60 or more years. To control for tobacco use, cases and controls were grouped into the following categories: non-user, user less than 10 years, and user 10 or more years. The small sample size limited more sophisticated covariate matched analysis involving age or further stratified analysis of tobacco use history.
During the period 2003–2007, 2549 members (68%) of the full roster cohort of 3768 individuals (previously detailed in Part 1 [
Table
Distribution of all self-reported cancers by gender and race among employees with surveillance examinations and work histories.
Race | Male | Female | Total | |||||||
---|---|---|---|---|---|---|---|---|---|---|
Bladder cancer | Other cancers | Number of employees | Bladder cancer | Other cancers | Number of employees | Bladder cancer | Other cancers | Number of employees | Percent of full roster* | |
White | 7 | 79 | 1771 | 0 | 13 | 253 | 7 | 92 | 2024 | 65.7% |
Nonwhite | 0 | 11 | 441 | 0 | 1 | 84 | 0 | 12 | 525 | 76.4% |
| ||||||||||
Total | 7 | 90 | 2212 | 0 | 14 | 337 | 7 | 104 | 2549 | 67.6% |
Table
Distribution of age and tobacco use history among cases and controls.
Cases ( |
Controls ( | |||
---|---|---|---|---|
|
% |
|
% | |
Age | ||||
<30 years | 0 | 0% | 85 | 5.5% |
30–39 years | 3 | 43% | 625 | 41.0% |
40–49 years | 3 | 43% | 640 | 42.0% |
50–59 years | 1 | 14% | 169 | 11.1% |
≥60 years | 0 | 0% | 6 | 0.4% |
Tobacco use | ||||
None | 3 | 43% | 715 | 46.9% |
<10 years | 1 | 14% | 506 | 33.2% |
≥10 years | 3 | 43% | 304 | 19.9% |
Among the seven cases, six reported work histories associated with investigation of fire scenes while employed with ATF, as mentioned in the introduction. These six cases also comprised the six cancer cases verified by pathology report. At the time of diagnosis, three cases were both CFIs and members of the NRT, one was a CFI but not a NRT member, one was a member of the NRT but not a CFI, and one was a member of the Division Response Team (DRT). Three cases were also members of the Arson Task Force and two of the CFIs with membership on the NRT were also CESs. None of the seven reported work histories associated with fire scene investigation prior to employment with ATF.
Table
Distribution of fire scene work history parameters among cases and controls.
Cases ( |
Controls ( | |||
---|---|---|---|---|
|
% |
|
% | |
Fire scene exposure days | ||||
0 days | 1 | 14% | 73 | 4.8% |
1–199 days | 1 | 14% | 1270 | 83.3% |
200 or more days | 5 | 71% | 182 | 11.9% |
Fire scene exposure years | ||||
0 years | 1 | 14% | 208 | 13.6% |
1–9 years | 3 | 43% | 785 | 51.5% |
10 or more years | 3 | 43% | 532 | 34.9% |
Any special assignment* years | ||||
0 years | 1 | 14% | 1034 | 67.8% |
1–4 years | 3 | 43% | 179 | 11.7% |
5 or more years | 3 | 43% | 312 | 20.5% |
NRT years | ||||
0 years | 3 | 43% | 1329 | 87.2% |
1–4 years | 2 | 28% | 83 | 5.4% |
5 or more years | 2 | 28% | 113 | 7.4% |
DRT years | ||||
0 years | 4 | 57% | 1434 | 94.0% |
1–4 years | 1 | 14% | 39 | 2.6% |
5 or more years | 2 | 28% | 52 | 3.4% |
Arson task force years | ||||
0 years | 3 | 43% | 1320 | 86.6% |
1–4 years | 4 | 57% | 109 | 7.1% |
5 or more years | 0 | 0% | 96 | 6.3% |
CFI years | ||||
0 years | 3 | 43% | 1440 | 94.4% |
1–4 years | 2 | 28% | 20 | 1.3% |
5 or more years | 2 | 28% | 65 | 4.3% |
CES years | ||||
0 years | 5 | 71% | 1297 | 85.1% |
1–4 years | 0 | 0% | 54 | 3.5% |
5 or more years | 2 | 28% | 174 | 11.4% |
Table
Odds ratios for bladder cancer risk associated with fire scene exposure parameters, while controlling for age and tobacco use.
Exposure parameter | Odds ratio (95% CI) |
|
---|---|---|
Fire scene days | ||
1–199 days versus 0 days | 0.05 (0.00–0.82) | 0.04 |
200 or more days versus 0 days | 4.50 (0.38–53.06) | 0.23 |
Fire scene years | ||
1–9 years versus 0 years | 0.78 (0.08–7.61) | 0.83 |
10 or more years versus 0 years | 1.22 (0.09–17.08) | 0.88 |
Any special assignment* years | ||
1–4 years versus 0 years | 19.01 (1.94–186.39) | 0.01 |
5 or more years versus 0 years | 12.56 (1.14–138.58) | 0.04 |
NRT years | ||
1–4 years versus 0 years | 12.74 (2.02–80.31) | 0.01 |
5 or more years versus 0 years | 9.87 (1.32–73.81) | 0.03 |
DRT years | ||
1–4 years versus 0 years | 8.21 (0.88–76.40) | 0.06 |
5 or more years versus 0 years | 12.71 (2.10–77.00) | 0.01 |
Arson task force years | ||
1–4 years versus 0 years | 16.88 (3.70–76.99) | 0.0003 |
5 or more years versus 0 years | — | — |
CFI years | ||
1–4 years versus 0 years | 43.84 (6.70–287.02) | <0.0001 |
5 or more years versus 0 years | 22.76 (2.52–205.91) | 0.01 |
CES years | ||
1–4 years versus 0 years | 3.15 (0.50–19.93) | 0.22 |
5 or more years versus 0 years | 0.47 (0.05–4.50) | 0.51 |
Analyses of years spent on any one or more of the special assignments combined and on each individual special assignment did, however, identify significant associations between special assignment work and increased risk for bladder cancer. For participation on any one or more of the special assignments, the OR was 19.01 (95%CI 1.94–186.39) for one to four years on any special assignment compared to zero years and 12.56 (95%CI 1.14–138.58) for five or more years compared to zero years. For individual team assignments, NRT work with both one to four years and five or more years, DRT work with five or more years, and arson task force work with one to four years exposure were all associated with statistically significant increase in bladder cancer risk. The CFI designation was associated with the highest ORs for both one to four years and five or more years compared to zero years. The CES designation was the only individual special assignment which was not associated with increased risk of bladder cancer.
As previously detailed in Part 1 of this epidemiologic study, a bladder cancer cluster occurred within a cohort of white male criminal investigators working with ATF between 1994 and 2005 [
Specifically, the nested case-control analysis showed participation on any one or more of the special assignments combined to be associated with a greater than 12-fold increase in bladder cancer risk for both one to four years and five or more years of exposure, when compared to zero years of exposure, as detailed in Section
As addressed in the introduction, known and suspect bladder carcinogens are potentially present in postcombustion products present at fire scenes, and the threat for exposure to postcombustion products from smoldering and off-gassing materials exists during investigation of those scenes. Primary routes of exposure to these products include inhalation and skin absorption. Exposure risk is dependent on a variety of factors including scene parameters (e.g., presence of smoldering hot pockets, amount of ventilation) and work practices (e.g., use of personal protective equipment, eating and drinking on site, maintaining adequate hydration, containment and decontamination of soiled clothing and equipment, timeliness of personal cleanup upon leaving the scene). While the use of self-contained breathing apparatus (SCBA) and firefighter turnout gear is an established practice during fire suppression, the use of respirators and other personal protective equipment during post-fire overhaul and investigation activities is less routine and is generally based on a judgment call made at the scene. As such, exposure to hazardous chemicals may in fact be greater during post-fire overhaul and investigation than during fire suppression. Some fire investigators with ATF have in the past described clearing their nose of “black mucus” for several days following a three to five day post-fire investigation or experiencing their vehicles reeking of smoke from soiled clothing and equipment. This anecdotal information appears to support the findings of this nested case-control study by illustrating that fire investigators could potentially be exposed to bladder carcinogens through both inhalation and skin absorption. Even though the air-monitoring industrial hygiene studies reviewed in the introduction did not find bladder carcinogen concentrations of concern, the studied fire scenes may not represent all fire scenes and may not adequately define investigator risk for exposure to bladder carcinogens, especially historical risk occurring during the years prior to bladder cancer diagnosis. With each fire scene being unique, investigator use of respirators and other personal protective equipment, adherence to housekeeping measures related to personal hygiene and cleanliness, and decontamination of clothing and gear can be expected to moderate potential internal exposure to combustion products and any associated cancer risk. After concern was first raised that fire investigation appeared to be associated with increased risk for bladder cancer, ATF elected to take precautionary actions to raise awareness among investigators, formalize a respiratory protection program, and improve work practices associated with fire investigation to reduce potential for exposure to hazardous chemicals while at and upon leaving fire scenes. It has now been over six years since the most recently reported case of bladder cancer.
This is the first known epidemiologic study to evaluate the association of bladder cancer risk and fire scene investigation. The odds ratios generated in this study are relatively high when contrasted with findings of individual epidemiologic studies of bladder cancer risk in other occupations and industries. In these other studies, statistically significant increases in bladder cancer risk are typically found in the 1.1-fold to fivefold range but also occur in the sixfold to tenfold range, as addressed in the discussion section to Part 1 [
In the interim, the findings of both the incidence study and the nested case-control study support ATF’s preliminary initiatives to educate the employee population regarding the potential cancer risks associated with post-fire investigation, monitor the health of the employee population through the medical surveillance program, perform bladder cancer screening as part of the medical surveillance program, provide appropriate personal protective equipment to those investigating fire scenes, and establish guidance for appropriate cleanup and decontamination measures following fire scene work. Continued monitoring of current employees through the medical surveillance program for another five to 10 years is warranted to track the future pattern of bladder cancer occurrence in the population. In addition, with cancers being typically associated with latency periods, inclusion of retirees in some form of health-monitoring program should be a consideration.
One strength of this nested case-control study is that work history data were available on 87% of the 2928 members of the full roster cohort who were employed with ATF for one or more years during the period 2003–2007, when the work history questionnaire was part of the medical surveillance program. With this level of participation in the program, any significant bias in study outcome from nonparticipants is unlikely.
Another strength of the study is that the ATF employee population under study was fairly stable during the time frame of both the cancer incidence study of Part 1 [
The small number of cases is a limitation of this study and can be expected to contribute to statistical instability and wide confidence intervals of the ORs, but the large size of the control group counters the effect of the small case size and restores some statistical stability to the ORs or the confidence intervals would be even wider.
Another limitation of this nested case-control study concerns employee self-reporting of bladder cancer diagnoses. As presented in a prospective cohort study by Bergmann et al. [
Employee self-reporting of all exposure parameters, with potential for recall bias, also presents a study limitation. In this study, several work history parameters were selected for evaluation as surrogate measures of exposure to products of combustion associated with fire scenes. The most reliably reported work parameter is conceivably the number of years spent working on special assignments associated with fire scene investigation, where assignment membership is formally established. This work parameter was the only one in the study found to be associated with statistically significant increased bladder cancer risk and appears to qualify as a surrogate measure of fire scene exposure. The reported number of years spent working on fire scenes might also be a reliably reported work parameter, but unlike the special assignment parameter, it may not have functioned as a good indicator of actual fire scene exposure, for there was not a significant association between fire scene years and increased cancer risk. The number of fire scene days is likely the most unreliably reported work parameter due to recall bias and employee retrospective estimation of days spent on fire scenes, especially for work predating the institution of the work history questionnaire in 2003. In addition, for the OR analysis of bladder cancer risk associated with reported fire scene days, as six of the seven cases were diagnosed prior to initiation of the work history form, the number of accrued days on fire scenes at the time of diagnosis was retrospectively calculated for these six cases through a systematic approach which applied the assumption that total accrued days were evenly distributed over the years worked on fire scenes with ATF. Inaccuracies in reported number of fire scene days and calculation assumptions could account for the lack of association between this work parameter and increased risk of bladder cancer and for the apparent protective effect of working 1–199 days on fire scenes versus zero days, as noted in Section
To conclude, in this nested case-control study on the ATF medical surveillance population, white males with work histories of holding special assignments associated with post-fire/post-blast investigation had statistically significant elevated risk of bladder cancer compared to white males with no work histories of holding these special assignments. The CFI special assignment was associated with the greatest increased risk in bladder cancer. The other work parameters, days spent and years spent working fire scenes, were not associated with statistically significant increased risk for bladder cancer compared to no days spent and no years spent working fire scenes, respectively.
The authors thank ATF for funding the epidemiologic study and paper preparation; FOH for providing support for the study, including but not limited to advocating for the medical surveillance program for ATF that discovered the reported bladder cancer cases, performing the examinations and ancillary tests on the employees participating in the program, and providing the Occupational Health Information Management System (OHIMS) for management of program data; and Bruce Higgins, database manager of OHIMS, for managing the database of the medical surveillance program and assisting with preparation of data for analysis. The opinions in this paper are the authors’ and do not necessarily represent the opinions of ATF or of FOH. S. R. Davis, X. Tao, E. J. Bernacki, A. S. Alfriend, and M. E. Delowery received funding for this study from the Bureau of Alcohol, Tobacco, Firearms and Explosives, United States Department of Justice, Washington, DC, USA.