Creation of a retrospective job-exposure matrix using surrogate measures of exposure for a cohort of US career firefighters from San Francisco, Chicago and Philadelphia

Abstract

Objectives: To construct a cohort-specific job-exposure matrix (JEM) using surrogate metrics of exposure for a cancer study on career firefighters from the Chicago, Philadelphia and San Francisco Fire Departments.

Methods: Departmental work history records, along with data on historical annual fire-runs and hours, were collected from 1950 to 2009 and coded into separate databases. These data were used to create a JEM based on standardised job titles and fire apparatus assignments using several surrogate exposure metrics to estimate firefighters' exposure to the combustion byproducts of fire. The metrics included duration of exposure (cumulative time with a standardised exposed job title and assignment), fire-runs (cumulative events of potential fire exposure) and time at fire (cumulative hours of potential fire exposure).

Results: The JEM consisted of 2298 unique job titles alongside 16,174 fire apparatus assignments from the three departments, which were collapsed into 15 standardised job titles and 15 standardised job assignments. Correlations were found between fire-runs and time at fires (Pearson coefficient=0.92), duration of exposure and time at fires (Pearson coefficient=0.85), and duration of exposure and fire-runs (Pearson coefficient=0.82). Total misclassification rates were found to be between 16-30% when using duration of employment as an exposure surrogate, which has been traditionally used in most epidemiological studies, compared with using the duration of exposure surrogate metric.

Conclusions: The constructed JEM successfully differentiated firefighters based on gradient levels of potential exposure to the combustion byproducts of fire using multiple surrogate exposure metrics.

Keywords: Dose-Response; Firefighters; Job-Exposure Matrix.

Figure 1

Development of the job-exposure matrix based on standardised job titles and assignments (EMS, emergency medical services; HAZMAT, hazardous materials).

Figure 2

(A) Philadelphia Fire Department fire-runs by engine (adjusted and unadjusted) and truck with the annual greater alarms. (B) Chicago Fire Department fire-runs by engine and truck with the annual greater alarms. (C) Chicago Fire Department time at fire (fire hours) by engine and truck with the annual greater alarms.

Figure 3

Distribution of the various cumulative exposure metrics. (A) Duration of employment (all departments), (B) duration of exposure (all departments), (C) fire-runs (Chicago and Philadelphia Fire Departments) and (D) time at fire (Chicago Fire department).

Figure 4

Correlation plots of the four possible exposure metrics. (A) Duration of employment versus duration of exposure. (B) Duration of employment versus fire-runs. (C) Duration of employment versus time at fire. (D) Duration of exposure versus fire-runs. (E) Duration of exposure versus time at fire. (F) Fire-runs versus time at fire.