0389 Nighttime Smartphone Use is Associated with Worse Sleep Among Firefighters: A Pilot Study

Abstract Introduction Firefighters provide around-the-clock emergency responses under demanding schedules. Firefighters may engage with personal devices after responding to nighttime emergency calls to maintain alertness or to decompress, including scrolling social media, watching videos, or playing video games. We hypothesized that greater smartphone use, especially overnight, would be associated with worse sleep that night. Methods Across two weeks, 17 firefighters (24% women; 71% 18-34 years old) from Missouri (N=11) and Utah (N=6) completed daily surveys, wore a wGT3X-BT actigraph for sleep/wake demarcation, and provided daily screenshots of the Screen Time (iOS 16.1-18.5; N=10) or StayFree (Android 12-15; N=7) application on their smartphone. Hourly smartphone use was extracted from Screen Time screenshots using a custom Python script with optical character recognition and from StayFree screenshots via manual data entry. Hourly smartphone use was summed across the 24h calendar day, experienced day (actigraphic waketime-to-waketime), evening (18:00-00:00), and overnight (00:00-06:00). Separate multilevel models with random intercepts for firefighters and person-mean-centered smartphone use predictors were estimated for each actigraphic sleep outcome (sleep timing, duration, and efficiency; mean=10.1 nights/firefighter). All models were adjusted for age, state of employment, type of smartphone, on-/off-duty, and daily naps. Results On average, firefighters used their smartphone for 4.7±2.0h per calendar day, 4.2±2.1h per experienced day, 1.6±0.6h per evening, and 0.4±0.7h (00:00-06:00) after midnight. Within-person results showed that each additional hour of evening smartphone use more than usual was associated with 15.9±5.8 minutes earlier sleep onset (p=0.007) and 16.8±6.5 minutes longer sleep duration (p=0.010) that night. Conversely, sleep onset was 31.7±7.8 minutes later (p< 0.001), sleep duration was 30.0±8.7 minutes shorter (p< 0.001), and sleep efficiency was 2.1±1.0% lower (p=0.033) for each additional hour of smartphone use than usual after midnight. Daily smartphone use was not associated with worse sleep that night. Conclusion Overnight smartphone use was associated with worse sleep that night among firefighters in this pilot study, even after adjusting for on-duty nights, whereas evening smartphone use predicted earlier and longer sleep. Overnight use of personal devices may exacerbate the sleep disruption firefighters routinely experience when responding to emergencies, further compromising firefighters’ sleep and overall health. Support (if any) T32HL166128, R35HL155681, U19OH010154, ORS 656.630