Impact of firefighters’ work schedule on cardiovascular disease risk, wellbeing and safety in firefighters: protocol for the SWIFT study, a multidisciplinary prospective and cross-sectional study

Abstract

Introduction

Firefighters face frequent physical and psychosocial stressors, increasing their risk for hypertension. Rising call volumes with a stable workforce have heightened occupational burdens. To meet their occupational demands while increasing time off-duty, fire departments across the country have switched from a 24 hours on 48 hours off (termed ‘24/48’) work schedule to one that increases the number of consecutive days off (eg, 1 day on, 3 days off, 2 days on, 3 days off (termed ‘1/3/2/3’) or 48 hours on 96 hours off (termed ‘48/96’)). However, these schedule changes come at the expense of increasing time on-duty, which may have negative health and safety consequences. This paper provides the framework and methods to investigate how these schedules (24/48, 1/3/2/3 and 48/96) impact hypertension risk, well-being and safety among firefighters.

Methods and analysis

This quasi-experimental study assesses hypertension risk (primary outcome) markers, including 48-hour ambulatory blood pressure and safety (secondary outcome) using the psychomotor vigilance test and incidence of injuries. The study encompasses a cross-sectional analysis that examines three distinct schedules (24/48, 1/3/2/3 and 48/96) and a prospective analysis, capitalising on a pre-planned schedule transition from a 24/48 to a 1/3/2/3, as a natural experiment without any intervention from the study team. Additionally, the mediating role of sleep (assessed objectively using actigraphy and subjectively using questionnaires) and daily stress in the relationship between work schedule and hypertension risk or sustained attention is investigated to inform both mechanisms and general considerations for developing and promoting a healthy work design for firefighters. The feasibility and acceptability of the three schedules are assessed using validated surveys and qualitative interviews.

Ethics and dissemination

The study received approval from the institutional review boards of Oregon Health & Science University (IRB# 20553) and the University of Utah (IRB#165866) and engages fire departments in the Pacific Northwest and Utah. It leverages community engagement with these fire departments, offering an exceptional opportunity to examine the physical and mental impacts of firefighters’ work schedules. Aggregate findings will be disseminated through practical resources, benefiting both regional and national firefighting communities.

WHAT IS ALREADY KNOWN ON THIS TOPIC

• The need for 24-hour emergency response results in reduced and disrupted sleep opportunity for firefighters when on-duty.

• Impaired sleep, among other occupational hazards, increases firefighter’s risk for cardiovascular disease and mortality.

• An increased number of fire departments across the country have moved to schedules that afford firefighters greater consecutive days off-duty (≥72 hours) but often at the cost of increased consecutive time (≥48 hours) on-duty.

WHAT THIS STUDY ADDS

• This study also provides an example of community engagement to develop both protocol aims and means to appropriately disseminate findings.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• This study will provide a rigorous comparison of emerging firefighter work schedules, offering objective evidence on their impacts on hypertension risk, safety and well-being, while identifying sleep and stress as key mechanisms to inform behavioural interventions.

Introduction

Firefighters have an elevated risk of hypertension,^{1 2} attributed to physical, environmental and psychosocial stressors, such as smoke, heat, noise, traumatic events and irregular physical exertion.3,6 Shiftwork-related sleep disruption is another critical factor, with nocturnal calls fragmenting and reducing sleep opportunities. Short sleep (<7 hours) and reduced sleep quality are strongly linked to hypertension and related morbidity.7,9 Fire departments often operate on a 24-hour shift schedule (eg, 24 hours work on and 48 hours off: termed ‘24/48’). This shift schedule can allow for rest during quiet periods. However, increased emergency call volumes—up nearly 50% in recent years¹⁰—coupled with population growth and static firefighter numbers,¹¹ may further diminish a firefighter’s ability to obtain rest.¹²

Recovery from heightened psychological or physiological arousal, such as during emergencies or while awaiting alarms, is essential for promoting cardiovascular resilience.^{13 14} Sleep, particularly through naps or extended sleep opportunities, has been shown to reduce sleepiness, blood pressure and cortisol, while improving vigilance and mood.15,22 However, the specific restorative role of sleep, such as the amount of sleep needed after fire suppression or extended work shift, and the impact on cardiovascular resilience among firefighters, remains unclear. Sleep is also just one aspect of recovery. Strategies such as psychological detachment from work, exercise and recreational activities during downtime can alleviate stress.^{23 24}

Firefighters face unique barriers to recovery including high workloads, unpredictable calls and limited control over recovery opportunities at work.^{25 26} Consequently, off-duty recovery becomes crucial, but this can strain family relationships, as extended shifts (≥24 hours) and the need for naps at home may heighten stress for partners and lead to family conflicts.27,29 Increased time between shifts has been suggested as a solution, offering firefighters more time for recovery while reducing work-family conflicts.³⁰

To provide more consecutive days off-duty while meeting growing demands, over 300 fire departments nationally (up from 65 in 2015) have adopted schedules that include a 48-hour work shift, such as a 48/96 or 24/72/48/72. The latter is more commonly referred to as a 1/3/2/3 (day on/days off/days on/days off) by firefighters and will be the notation used herein. An illustration of these work schedules is depicted in figure 1. These schedules have been increasingly adopted under the premise that they increase recovery and morale, though evidence is limited.31,33 Initial station reports and one published study suggest the 48/96 schedule reduces commuting and increases time with family and friends,³³ potentially improving recovery. However, the effects of consecutive days on-duty on cardiovascular resilience and specifically hypertension risk, as well as safety, remain unclear, highlighting the need for systematic research.

Figure 1. Distribution of 24-hour work shifts on the 24/48, 1/3/2/3 and 48/96 work schedules over 14 days.

This Shiftwork in Firefighters (SWIFT) study is informed by the conceptual model of cardiovascular resilience, which posits that physiological and behavioural responses to occupational stressors influence long-term cardiovascular health outcomes.^{13 14 34} Cardiovascular resilience refers to the ability to maintain stable cardiovascular function despite repeated stress exposures, which is particularly relevant for firefighters given their exposure to high-intensity physical exertion, sleep disruption and psychosocial stressors. This framework considers how shifts in autonomic regulation, neuroendocrine function and sleep patterns contribute to hypertension risk or, conversely, provide an opportunity for recovery and adaptation when off-duty.³⁵ Under the guise of this conceptual framework, we aim to test the hypothesis that a 1/3/2/3 or 48/96 schedule, with longer consecutive days off improves recovery from sleep loss (enhancing safety, vigilance and mood) and stress (reducing blood pressure and cortisol). We will also test the hypothesis that increased consecutive days on-duty negatively impact daily measures of blood pressure regulation and safety. To address the hypotheses, we will conduct (1) a prospective natural experiment tracking a shift from 24/48 to 1/3/2/3 schedules in Pacific Northwest fire departments; and (2) a cross-sectional study comparing 24/48, 1/3/2/3 and 48/96 schedules from firefighters across the Pacific Northwest and Utah. This Total Worker Health (TWH) study integrates organisational policies and practices to address both work-related risks and overall well-being, encompassing life at work and home.³⁶ Using the TWH framework, which has shown greater effectiveness than traditional methods,^{37 38} the project aligns with National Institute for Occupational Safety and Health (NIOSH) priorities for the ‘Future of Work’ and ‘Healthy Work Design and Well-Being.’³⁹

Methods and analysis

This study combines cross-sectional and prospective data from full-time firefighters to examine how work schedules, specifically consecutive days on-duty and off-duty, affect hypertension risk, wellness and safety. The prospective component leverages a natural experiment involving a planned transition (study investigators were not involved in schedule decisions) from a 24/48 to a 1/3/2/3 schedule, enabling within-subject comparisons of health and safety outcomes.

The prospective study collects baseline and follow-up data over three 2-week intervals within a year (figure 2). The cross-sectional study uses baseline data from the 24/48 group and a single 2-week data collection from departments operating on a 1/3/2/3 schedule or a 48/96 schedule for more than a year. This design helps distinguish schedule-related changes from external factors (eg, seasons, pandemics). Robust effects are indicated by consistent findings across both prospective and cross-sectional studies.

Figure 2. Prospective study timeline.

The primary aim of this study is to evaluate hypertensive risk (primary outcome), including 48-hour ambulatory blood pressure, adiposity and sympathetic tone, and safety outcomes (secondary outcome), including vigilance and safety incidents across work schedules (24/48, 1/3/2/3, 48/96). Additionally, the study aims to assess how work schedules impact these outcomes by examining the role of recovery strategies, including sleep (objectively measured using actigraphy and self-reported) and stress exposure (daily events and work-life conflict).

Patient and public involvement

The prospective study builds on 5 years of community engagement in the Pacific Northwest, initiated by the Portland Fire Association, which sought guidance from Oregon Health & Science University (OHSU) on optimal scheduling alternatives to the 24/48. In the time since, the OHSU team conducted needs assessments, focus groups and a pilot study with Portland Fire and Rescue to refine surveys, the utility of collecting biological samples and the practicality of using wearable devices for this larger study.²⁹ Findings related to attrition, response rate and participants’ perspectives on the burden of daily tasks and degree of comfort of the study devices were shared with department and union leadership as well as the membership at large via infographics, the departments’ wellness show, a podcast recorded with the union, and a podcast recorded by the Oregon Institute of Occupational Health Sciences’ study team’s podcast: What’s Work Got to Do with It?. Thus, when the union and department agreed on a trial period of the 1/3/2/3, the study team was able to implement previously tested and feasible methods to assess before and after the transition to the 1/3/2/3. Similar levels of engagement are continuing with departments across the Pacific Northwest for prospective and cross-sectional data collection.

The University of Utah’s (UU) Rocky Mountain Center for Occupational and Environmental Health (RMCOEH) has cultivated longstanding partnerships with numerous fire departments across the state of Utah. This collaboration spans various health initiatives, including research to identify and mitigate health hazards, providing pre-placement and annual NFPA 1582 physical exams for firefighters, and managing work-related injuries. Academic programmes such as the Master of Occupational Health maintain ongoing research projects with interested fire departments to address specific concerns related to firefighters’ health and well-being. As part of these continued initiatives, our team reached out to the main fire departments in Salt Lake Valley, namely Unified Fire Authority, Salt Lake City Fire Department and West Jordan Fire Department (WJFD), to discuss their potential participation in the study. The contacted fire departments were open to exploring the study details in preparation for their participation. We started with WJFD, given its relatively small size compared with the other two departments, as a pilot department in Utah. They facilitated in-person recruitment sessions between our team and their crews to discuss the study details and answer any questions that firefighters may have before participation. Our experience in recruiting firefighters from WJFD has been promising and encouraging so far. We intend to proceed as planned with the other two fire departments until reaching the study sample size goal. This study is another example of the deep trust and collaboration built over years between RMCOEH and Utah’s fire departments.

Ethics and dissemination

In collaboration with participants and working partners/interested parties, aggregate findings will be disseminated as practical resources (eg, flyers, website) with national audiences.

Study start and end dates

Data collection for the Oregon arm of the study began in January 2022. All methods described in this manuscript were finalised prior to the start of data collection for the Utah arm of the study, which commenced in May 2024 and is expected to be completed by December 2025.

General procedures

All full-time firefighters (inclusive of gender and age), including station captains, shift lieutenants and mainline firefighters (including paramedics that work both positions, responsible for attending all emergency/community events and participation in training), and their domestic partners are eligible to participate. All participants will provide written informed consent for study participation and can withdraw from the study at any time.

Each data collection interval (summarised in table 1) is scheduled to take place over a 2-week time period in order to capture at least one 48-hour work shift and subsequent off days on the 1/3/2/3 and 48/96 schedules (figure 1). Additionally, the International Classification of Sleep Disorders recommends sleep diaries and actigraphy be performed for 14 days.⁴⁰ On day 1 of the 2-week assessment, participants will be texted a one-time survey battery estimated to take approximately 1 hour to assess subjective sleep quality, workplace safety incidents and potentially informative covariates. Each subsequent morning (days 2–15), participants will be prompted via text to complete (1) a sleep diary (~3 min), which indicates the quality of sleep and indicates the time and duration of any daytime naps the prior day, and (2) the 3 min psychomotor vigilance test. Each evening (days 1–14), participants will also be prompted via text to complete (1) a survey on daily substance consumption (ie, caffeine, alcohol), stress and work events, recovery and work-life conflict (~10 min for all measures); (2) 3 min psychomotor vigilance test and (3) indication of work/non-work day. Domestic partners of firefighters will be texted a simplified baseline questionnaire on day 1 and the work-family questionnaire each evening (~3 min). All surveys will be conducted on a personal smartphone (iTouches are also available to loan) and provided using Twilio, a Health Insurance Portability and Accountability Act (HIPAA)-compliant cloud communication platform, and Research Electronic Data Capture, a clinical and translational research application for building and managing HIPAA-compliant and IRB-compliant online surveys and databases.

Table 1. Study outcomes^*.

Measure	Data collection interval 1	Data collection interval 2	Data collection interval 3
Demographics	X
Physiological measures
Sleep (actigraphy and sleep journal, 14 days)	X	X	X
Physical activity (actigraphy, 14 days)	X	X	X
Cardiovascular reactivity and monitoring (heart rate/heart rate variability, 48-hour ABPM and ECG on off days, 14 days)	X	X	X
Sympathetic nervous system and HPA axis (24-hour urine)	X	X	X
Perceived health
Objective measures of mental/physical health, life satisfaction, emotional distress, life satisfaction, and diet (PROMIS scales, BRFSS scales, PEAT, CCQ-R and Bond & Lader VAS)	X	X	X
Alertness
Sustained vigilance (mobile 3 min psychomotor vigilance task)	X	X	X
Recovery
Recovery experience (Recovery Experience Questionnaire and daily diaries)	X	X	X
Work-family interference
Work-family conflict (14-day daily diaries)	X	X	X
Safety
Self-reported workplace injuries and close-calls (NIOSH Quality of Work Life)	X		X
Qualitative evaluation			X

^*Cross-sectional study completes Data Collection Interval one only.

ABPM, ambulatory blood pressure monitoring; Bond & Lader VAS, Bond & Lader Visual Analogue Scales; BRFSS, Behavioral Risk Factor Surveillance System; CCQ-R, Caffeine Consumption Questionnaire-Revised; ECG, electrocardiography; HPA, hypothalamic-pituitary-adrenal; NIOSH, National Institute for Occupational Safety and Health; PEAT, Pittsburgh Enjoyable Activities Test; PROMIS, Patient-Reported Outcomes Measurement Information System.

Primary outcomes: hypertension risk

In addition to blood pressure itself, we will assess a range of non-invasive factors that regulate blood pressure and thus can contribute to hypertension risk.

Ambulatory blood pressure will be measured for 48-h off-duty using standard methods (Spacelabs Healthcare, Washington) for each 2-week sampling interval.⁴¹ Ambulatory monitoring, which correlates more strongly with morbidity risk,^{42 43} will be used to assess 48-h mean systolic and diastolic blood pressure (primary outcome) and mean awake/asleep values (secondary outcomes).

Continuous heart rate will be obtained using Polar H7 (Polar Electro Inc.) chest straps worn throughout the 14-day collection interval. The primary outcome will be 24-hour mean heart rate and secondary outcomes will assess mean awake and sleep heart rate. Parasympathetic activity will be estimated via respiratory sinus arrhythmia, derived from the high-frequency power of the heart rate variability power spectrum^{44 45} using Kubios HRV V.3.3.⁴⁶ The primary outcome will assess the 24-hour mean, with a secondary outcome examining mean awake and sleep heart rate variability.

To assess sympathetic activity, participants will provide their urine over 24 hours. Urine collections (100% of urine produced over 24 hours) will be used to measure cortisol (sympathetic potentiating hormone), epinephrine (adrenal cortex contribution) and norepinephrine (sympathetic nerve activity). Study staff will provide containers for urine collection as well as a thermally insulated cooler with ice to keep urine samples cool until the completion of the 24-hour collection. Participants will keep their normal diet while providing their urine samples. However, daily information on substance use will be recorded (see below). While caffeine, for example, can stimulate the release of catecholamines (epinephrine and norepinephrine),^{47 48} abstinence can also result in withdrawal symptoms. Furthermore, given that caffeine consumption is nearly universal among firefighters and that each individual is in their own control for the prospective study, a massive influence of stimulating beverages is unlikely. Following sample pickup by research staff, urine volume will be recorded, and aliquots will be removed and stored at −80° until analyses. Only participants with complete 24-hour urinary collections (determined by measurements of urinary creatinine) will be included in the analysis. Samples will be collected on shift to obtain levels during peak stress exposure.

Finally, once during each 2-week data collection interval, anthropometric measures, including measured height and weight, will be collected to calculate body mass index, body fat and fat-free mass (Tanita Corp., Tokyo, Japan).

Secondary outcomes

The primary outcome for safety will be the median reaction time and the number of lapses on the psychomotor vigilance task (PVT). The PVT is traditionally a 10 min reaction time test that assesses sustained vigilance⁴⁹ but has been validated to work for durations of <10 min.⁵⁰ As firefighters may have limited time, at each test interval, a 3 min PVT task adapted to work on mobile devices developed by the National Aeronautics and Space Administration(NASA PVT+: validated mobile touchscreen app freely available to the public) will be used.⁵¹ Firefighters will complete twice-daily (upon awakening and before sleep each day) 3 min PVT on their personal iOS device or else a study-provided iTouch. Additionally, a modified survey from the NIOSH Quality of Work Life Questionnaire⁵² will be used on day 1 to measure self-reported workplace injuries during the last 6 months, and a version of that item will be used to capture close calls.

To determine the extent to which daily stress changes with respect to work schedule and impacts hypertension risk and safety, firefighters will complete the Daily Inventory of Life Events.⁵³ To assess specific occupational stressors experienced while on-duty, firefighters will complete a 13-item checklist (‘Yes’/‘No’ response options) based on research with emergency medical service providers and feedback provided by our study partners.^{54 55} Checklist items include routine work challenges (eg, ‘high call volume shift’), infrequent yet potentially high impact incidents (eg, ‘violence/threat to crew safety’) and an ‘other problem’ option with a free text box for a brief description. Items will be summed to yield a total score. Stressor checklists represent one of the most common methods for assessing stress and are suitable for daily assessment given the low response burden they impose.⁵⁶

Work-family conflict will be measured using the Work-Family Conflict Scale adapted for a daily time frame;^{57 58} two of the questions focus on work-to-family interference and two on family-to-work interference. To capture both the effects of bidirectional crossover and within-individual work-family conflict,^{59 60} participating partners/spouses will complete this daily survey for themselves as well in reference to their firefighter’s work situation.

Measures of recovery will be collected using both objective and subjective measures. Objective measures of sleep duration and efficiency will be assessed by actigraphy (ActiGraph wGT3X-BT, ActiGraph) worn on the non-dominant wrist for the complete duration of each 2-week study interval. Participants will also be sent a survey to complete each morning to document sleep/wake times, nocturnal awakenings and naps taken the previous day. Sleep questions are similar to those used for the consensus sleep diary⁶¹ and are used to confirm actigraphy measurements. Activity counts will be collected in 60 s epochs and will be analysed using ActiLife 6 software (ActiGraph). Subjective measures of sleep quality and sleep satisfaction will be assessed (day 1 survey battery) using the Patient-Reported Outcomes Measurement Information System (PROMIS) short forms for sleep disturbance and sleep-related impairment.^{62 63} For non-sleep recovery activities, firefighters will complete the Recovery Experience Questionnaire⁶⁴ and a 10-item checklist (‘Yes’/‘No’ response options) based on the Pittsburgh Enjoyable Activities Test.⁶⁵ Items will be summed to yield a total score.

A mixed-methods approach will be used to identify barriers, conflicts and attitudes around transitioning to a 1/3/2/3 schedule that can be brought to key study partners for feedback. Barrier assessments are a critical component for the translation of research and the sustainability of an intervention.⁶⁶ Thus, at each assessment, firefighters and their domestic partners will be asked to complete components of the Acceptability of Intervention Measure, the Intervention Appropriateness Measure and the Feasibility of Intervention Measure.⁶⁷

To capture potential benefits or challenges related to schedule change not captured in quantitative assessments, qualitative interviews will be conducted (interviews will only be conducted once firefighters are on a 1/3/2/3 schedule). Interviews (30 min to 1 hour in length) will roughly follow an interview guide. Questions will include the pros and cons of the new schedule; how the new schedule has impacted dynamics at work (eg, interactions with coworkers, job satisfaction); a description of current family dynamics when at home and when at work; perceived changes to their personal long-term health as a result of schedule change; and how the schedule change impacted their perception of their preferred work schedule. Interviews will be recorded and outsourced for transcription. Transcription coding (NVivo 12 plus) and analysis will be determined using thematic analysis and reported using the Consolidated Criteria for Reporting Qualitative Research 32-item checklist.⁶⁸

Covariables

Person-level covariates, including demographic variables (age, gender, tenure of the job, marital status, number of dependent children, smoking status—inclusive of vaping, chewing tobacco or nicotine pouch) will be measured as part of the day 1 data collection. Additionally, as part of the day 1 survey battery, mental health is measured using PROMIS short forms for anxiety, depression, general life satisfaction and levels of emotional support (four to five items on a5-point Likert scale). Workload/call volume will also be assessed using administrative logs.

As part of daily surveys, substance use is measured using a modified version of the Behavioral Risk Factor Surveillance System (BRFSS, a national US survey that collects data on health-related behaviours) scale. A daily comment box will be provided to indicate the use of medications. Daily caffeine consumption will be measured using the Caffeine Consumption Questionnaire – Revised.⁶⁹ For physical activity, participants’ daily levels of vigorous, moderate and sedentary activity will be assessed using actigraphy. To determine if a firefighter works a second job on days off from firefighting, we will ask, “Did you work another job today?” (‘Yes’/‘No’ response option). Finally, given the periodic surges of COVID-19, on the last morning (day 15) of the daily surveys, participants will be asked if they were exposed to COVID-19 and required to quarantine, tested positive for COVID-19 and required to quarantine; and if they tested positive, what was the severity of their symptoms.

Sample size and power analysis

Power analyses were conducted using G*Power 3 and were based on our primary hypertension risk factor measures. Prior research has identified the following minimal clinically important differences (MCIDs) for factors associated with hypertension or a cardiac event: changes of 2 mm Hg in blood pressure, changes of 5% in body mass index and changes of 5 beats per minute in resting heart rate.70,74 Preliminary data from our pilot study showed that these MCIDs are smaller than the mean differences observed between firefighters under the 24/48 and 1/3/2/3 shift schedules. For sufficient power (0.80), to compare the three work schedules (24/48, 1/3/2/3 and 48/96), a total of 291 (97/schedule type) firefighters are needed for the cross-sectional study to detect the MCID for blood pressure, the most conservative estimate based on the three primary factors. Based on this estimate, and in anticipation of 15% attrition over the 2-week measurement sampling interval, a sample size of 342 (114 from each department) is planned to be recruited. To achieve sufficient power for the prospective study, a total of 55 firefighters are needed to detect the MCID for blood pressure. Based on our 6-month pilot study, we expect a retention rate of 80% from baseline to the final follow-up (figure 3). Therefore, the 114 participants recruited for the cross-sectional study (baseline for the prospective study) from Portland Fire and Rescue will provide sufficient power even in the light of additional participant loss due to the need to quarantine for COVID-19 for themselves or the care of children. Individual interviews for the qualitative portion of the study will be conducted until theme saturation is reached.⁷⁵ The inclusion of ~30 participants (20 firefighters, 10 partners) based on previous qualitative studies with this population is anticipated.²⁹

Figure 3. Recruitment targets for prospective and cross-sectional studies’ data collection for the three work schedules (24/48, 1/3/2/3 and 48/96). *The study will include the DP for those 65 FF included in the cross-sectional study. DP, domestic partners; FF, firefighters.

Statistical analysis

Descriptive analyses will be reported. A linear mixed model approach will be used for both the longitudinal and cross-sectional studies.

In the prospective study, daily observations are nested within participants for each assessment period to evaluate mean within-participant changes over the study period. Given the relatively small number, stations will be treated as a fixed effect to account for variations due to differences across stations (eg, call volume, crew captain). Participants within stations will be treated as random. Assessment time (pre-schedule, 2-month, and 10-month to 12-month post-schedule change) will be modelled as a fixed effect. Mean changes in outcome variables over time will be tested in separate models. Daily measures will also be assessed for the effect of work/non-workday (or consecutive days on-duty or off-duty). A Bonferroni correction will be used for post hoc analyses to identify which days are significantly different. Sensitivity analyses will be conducted to explore whether accounting for time-varying and time-invariant confounding variables alters model conclusions.

In the cross-sectional study, daily observations during the 2-week assessment period are nested within participants to analyse mean differences between work schedules while accounting for confounding individual-level and station-level effects. Stations will be treated as a fixed effect and participants within stations will be treated as random.

To next assess the extent to which stress and/or recovery contributes to the differences in outcomes of blood pressure (and related regulators) as well as safety by work schedule, measures of stress (eg, daily events, work-life conflict), recovery (eg, sleep, recovery strategies) and relevant confounding variables will be introduced to the linear mixed models in a stepwise approach.

Summary

The SWIFT study will make use of a mixed method approach including the use of wearable devices, surveys, urine biomarker analysis and interviews to assess how firefighters’ work schedules affect cardiovascular health, safety, well-being, sleep, stress and work-life conflict. By comparing 24/48, 1/3/2/3 and 48/96 schedules, the study aims to inform decisions about optimal scheduling for firefighter health, specifically cardiovascular resilience. Findings will also provide insights into the effects of consecutive shifts and time off, potentially shaping policies on overtime and rest periods.

Data availability statement

Data are available upon reasonable request.