Abstract Introduction Given the dearth of prospective research on shift-work exposures and objective sleep in firefighters, this study aimed to characterize sleep characteristics of firefighters and their associations with nightly call volumes during 24-hour shifts. Methods Actigraphy(Philips Spectrum Plus)-assessed sleep and nightly call volume from daily diaries were completed by thirty-two firefighters (across six stations), each followed twenty-one days. Generalized estimating equations linear regressions estimated unadjusted and adjusted associations between on-duty nightly call volume (after 10pm; categorized as no/low0-2 (reference), average3-4, high≥5), and actigraphically-assessed longest on-duty sleep period measures- sleep latency(SL), total sleep time(TST), wake after sleep onset(WASO), and sleep efficiency(SE). Robust Poisson regression models estimated unadjusted and adjusted relative risks (RR) for SL 8min (vs.≥8min), TST≤134min (25th percentile vs.134min), WASO24.5min (75th percentile vs.≤24.5), and SE≤80%(vs.80%) for average and high nightly call volumes versus no/low. Regression models were adjusted for age and station. Results 245 on-duty person-days (of 657 person-days) of actigraphic and diary data from February-May 2025 were analyzed. Cohort was 91% male; median age was 43.5 years (IQR=15), with mean 9.34 (SD=2.39) work-days per participant. On-duty sleep measure prevalences (95% CI) were: SL 8min(49.4% 43.1-55.7%), TST≤134min(26.2%20.6-31.7%), WASO24.5min (21.6%16.4-26.8%), and SE≤80%(33.5%27.5-39.4%). High nightly call volume, versus no/low, was significantly associated with decreased mean TST (β =-64.9, p=0.0090), WASO (β=-5.1, p=0.0090), and SE (β=-7.7, p=0.0354) after age and station adjustments, but not continuous SL. High nightly call volume, versus no/low, was significantly associated with TST≤134min (vs.134min) (RR=3.42, p 0.0001). Conclusion Firefighters working 24-hour shifts are expected to sleep on duty, yet high nightly call volume during 24-hour shifts increased risks for TST≤134min(vs.134) by over 3-fold, suggesting this shift-work exposure be recognized as a risk for short on-duty sleep. Advancing prospective research on objective sleep in on-duty firefighters may help inform sleep health promotion interventions in this population. Support (if any) This research was supported by grants from the U.S. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health to the Johns Hopkins Education and Research Center for Occupational Safety and Health (award No. T42 OH0008428) and the Johns Hopkins P.O.E. Total Worker Health Center in Mental Health (POE Center, award No. U19OH012297).
Szklo‐Coxe et al. (2026) studied this question.