Firefighting is a hazardous profession that involves intermittent but intense exposure to a complex mixture of combustion products containing multiple known or suspected human carcinogens (IARC, 2023). The International Agency for Research on Cancer (IARC) has classified occupational exposure in firefighters as Group 1 (carcinogenic to humans) on the basis of sufficient evidence of increased cancer risk across multiple operational roles and fire settings (IARC, 2023). Among these airborne toxicants, benzene is particularly significant. It is classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen (IARC, 2018), which is consistent with its well-established genotoxicity, hematotoxicity, and epidemiological associations with an increased risk of leukemia (IARC, 2018).

The carcinogenicity of benzene stems from its metabolic activation in the liver, where it is primarily processed by cytochrome P450 2E1 (CYP2E1) to form benzene oxide, an epoxide that can rearrange into phenol or be converted into catechol and hydroquinone (IARC, 2018). These metabolites are further oxidized in the bone marrow into electrophilic species such as benzoquinones and semiquinone radicals, which cause oxidative DNA damage, chromosomal aberrations, and immunosuppression (IARC, 2018). These mechanisms underlie benzene's link to hematopoietic toxicity and the development of acute myeloid leukemia (AML), even at relatively low exposure levels.

Benzene is a volatile organic compound (VOC) formed during the incomplete combustion of organic materials such as biomass, plastics, petroleum products, and synthetic polymers. It has been ubiquitously detected across wildland, prescribed burn, structural, and training fire environments (e.g., Austin et al., 2001a, 2001b; Brandt-Rauf et al., 1988; Romagnoli et al., 2014; Navarro et al., 2021; Bolstad-Johnson et al., 2000; Barboni et al., 2010; Mayer et al., 2022). Given its widespread presence, established mechanistic plausibility, and consistent epidemiological findings, benzene has become a central focus in firefighter health research and occupational exposure assessment. Reflecting heightened concern, the American Conference of Governmental Industrial Hygienists (ACGIH) recently reduced its threshold limit value (TLV) for benzene from 0.5 ppm to 0.02 ppm—a 25-fold decrease (ACGIH, 2024).

Benzene exposure continues through various pathways beyond active fire suppression, including premature removal of self-contained breathing apparatus (SCBA), allowing unfiltered inhalation of residual vapors (Austin et al., 2001b; Brandt-Rauf et al., 1988; Jankovic et al., 1991), vapor ingress into turnout gear (Kirk and Logan, 2019; Kirk et al., 2021; Mayer et al., 2022, 2023), dermal absorption (e.g., Mayer et al., 2022, 2023; Fent et al., 2020), and off-gassing from contaminated equipment (e.g., Fent et al., 2015; Padamsey et al., 2024a; Rogula-Kozłowska et al., 2024), which all contribute to systemic uptake. These pathways are supported by biomonitoring studies that report elevated levels of exhaled benzene and urinary biomarkers following firefighting, even when respiratory protection was reportedly in use (e.g., Mayer et al., 2022, 2023; Fent et al., 2020; Fent et al., 2019b; Fent et al., 2022; Laitinen et al., 2010).

Despite a growing body of exposure studies, a thorough review of the literature did not find any systematic review that has synthesized airborne benzene concentrations across various types of firefighting environments or determined the biological relevance of measured concentrations via mechanistic toxicology. Few studies have assessed how the intensity or duration of exposure is influenced by behavioral practices (e.g., mask removal, gear doffing), fuel type, or sampling design (e.g., Austin et al., 2001b; Brandt-Rauf et al., 1988; Fent et al., 2019a; Horn et al., 2023; Janković et al., 1991; Navarro et al., 2021). Without this integration, efforts to interpret measured concentrations within a toxicological framework have been limited by the lack of understanding of how toxicological mechanisms relate to sampling design, task roles, fuel materials, and operational behaviors.

This review directly addresses these gaps by systematically examining airborne benzene concentrations reported across wildland, prescribed burn, structural, and live-fire training settings. It interprets findings within a toxicological framework that considers how sampling design, task roles, fuel materials, and operational behaviors influence measured concentrations and are related to established biological pathways of benzene toxicity. The findings can inform more effective exposure assessment strategies, biomonitoring protocols, and evidence-based PPE and post-fire decontamination practices for fire service personnel within the context of increasing regulatory scrutiny and increasing awareness of firefighter cancer risk.