Evidence and Methodology

Daniels and colleagues (2014) conducted a pooled cohort study of 29,993 career firefighters from San Francisco, Chicago, and Philadelphia, with mortality and cancer incidence followed from 1950 through 2009. The study was led by the National Institute for Occupational Safety and Health (NIOSH).

The authors reported a Standardized Incidence Ratio (SIR) of 2.29 (95% CI 1.60 to 3.19) for malignant mesothelioma in U.S. firefighters, rounded on the homepage to 2.3x. An SIR of 2.29 indicates that U.S. firefighters were diagnosed with mesothelioma at 2.29 times the rate expected in the general population. The result is statistically significant, as the lower bound of the 95% confidence interval (1.60) is above 1.0.

The Daniels cohort consists of career firefighters from three large urban U.S. fire departments. Findings may not generalize identically to volunteer firefighters, wildland firefighters, or more recent firefighter cohorts who benefit from improved protective equipment and decontamination practices.

The 2.3x figure reflects cancer incidence (new diagnoses). The same study reported a Standardized Mortality Ratio of 2.00 (95% CI 1.03 to 3.49) for mesothelioma, indicating U.S. firefighters also die of mesothelioma at approximately twice the expected rate.

Dobraca and colleagues (2015) conducted a biomonitoring study of 101 Southern California firefighters as part of the California Department of Public Health's Biomonitoring California program, in collaboration with UC Irvine and the California Environmental Protection Agency. The study measured 12 serum perfluorinated chemicals in firefighter blood samples and compared results to National Health and Nutrition Examination Survey (NHANES) adult male reference data.

The authors reported that perfluorodecanoic acid (PFDA) serum concentrations in this firefighter cohort were approximately three times higher than in NHANES adult males. PFDA is one of a broader class of chemicals known as per- and polyfluoroalkyl substances (PFAS), commonly referred to as "forever chemicals" due to their environmental persistence and long biological half-lives in humans. PFAS exposure among firefighters has been linked to turnout gear, aqueous film-forming foams used to suppress fuel fires, and dust contamination in fire stations.

The Dobraca cohort consists of Southern California firefighters sampled in 2010-2011. Regional variation in PFAS exposure exists across U.S. firefighter populations, reflecting differences in local AFFF use history, drinking water contamination, and department-level protective equipment practices. PFDA was the specific PFAS compound with the most elevated levels in this cohort; most other PFAS compounds measured showed concentrations similar to or within range of NHANES adult male reference values. The 3x figure applies specifically to PFDA, not to the broader PFAS class as a whole.

Lewis-Schroeder and colleagues (2018) published a peer-reviewed review article in the Harvard Review of Psychiatry synthesizing the literature on PTSD prevalence among first responders. The authors, affiliated with Harvard Medical School and McLean Hospital, reported firefighter PTSD prevalence ranges from 17 to 32 percent across multiple peer-reviewed studies, compared with a U.S. general population PTSD prevalence of 7 to 12 percent.

The upper-end firefighter figure (32 percent) and the general population range (7 to 12 percent) are both reported directly in this source, with no derived calculation involved.

Prevalence estimates for firefighter PTSD vary considerably across studies, reflecting differences in sample populations (urban vs. wildland, career vs. volunteer, U.S. vs. international), measurement instruments (self-report vs. structured clinical interview), and exposure contexts (routine vs. large-scale disaster). The 17 to 32 percent range captures this variability. Lower-end estimates from other reviews have reported figures as low as 7 percent, which is consistent with systematic reviews that include international firefighter populations with less routine exposure than the U.S. career firefighter cohort.

Stanley and colleagues (2015) conducted a nationwide cross-sectional survey of 1,027 current and retired U.S. firefighters and reported a career prevalence of suicidal ideation of 46.8 percent.

Nock and colleagues (2008) reported U.S.-specific lifetime prevalence of suicidal ideation at 15.6 percent. This figure is drawn from the USA row of Table 2a in the published paper, which reports country-by-country lifetime prevalence data. The U.S. figure comes from the National Comorbidity Survey Replication, which served as the U.S. component of the WHO World Mental Health Survey Initiative.

The ratio of 46.8 percent to 15.6 percent equals approximately 3.0, a rounded relative-risk comparison between U.S. firefighters and the U.S. general population reported as 3x.

Career prevalence and lifetime prevalence are not identical measures. Career prevalence captures suicidal ideation occurring at any point during an individual's firefighting service. Lifetime prevalence captures suicidal ideation occurring at any point in an individual's life. Because firefighting is an adult occupation and the Stanley cohort had a mean age of 38.5 years with a substantial proportion of retired respondents, career prevalence in this population reasonably approximates adult-lifetime prevalence.

The Stanley (2015) figure is based on a convenience sample of firefighters who self-selected into a web-based survey, which introduces the possibility of participation bias. The 46.8 percent figure remains the most widely cited primary estimate of firefighter career suicidal ideation in the peer-reviewed literature, and subsequent systematic reviews have continued to use it as the reference estimate for this population.

Earlier versions of this comparison in the literature have produced multiplier ranges as wide as 3 to 8 times by comparing the firefighter figure to cross-national or pooled high-income-country baselines. The 3x figure reported here reflects the U.S.-specific comparison, using U.S.-only data on both sides of the ratio.