Circadian Timing and Heat Stress in Firefighters

Description

Title & Dataset supporting: Circadian modulation of core temperature and thermoregulatory strain during live-fire compartment exposure in firefighters Mauvieux B., Markov A., Besnard S., Touitou Y., Edwards B.J. (2025) Description : This dataset accompanies the manuscript submitted to the Journal of Thermal Biology. It contains anonymized physiological and environmental data recorded during standardized live-fire compartment training conducted at two circadian phases: late morning (09:00 h) and late evening (21:30 h). Twenty-one male professional firefighters completed both sessions on the same day under matched thermal loads. The dataset allows replication of all analyses described in the paper, including core-temperature kinetics, cardiovascular and perceptual strain, hydration indices, and environmental thermal gradients. Data content - The repository includes the following files: Tcore_AM_PM.csv (Continuous core temperature (°C) recorded via ingestible e-Celsius® sensors) Variables: Subject_ID, Condition (AM/PM), Time_min, Tcore_C. HR_RPE_BW.csv Heart-rate data, Borg RPE, body mass and total body water pre/post exposure. Variables: Subject_ID, Condition, HR_mean, HR_max, RPE, BodyMass_pre, BodyMass_post, TBW_pre, TBW_post. Skin_Microclimate.csv Chest and neck skin temperature (°C) and under-PPE humidity (%RH). Variables: Subject_ID, Condition, Tskin_chest, Tskin_neck, Temp_underPPE, RH_underPPE. Environment_Thermocouples.csv Air-temperature recordings (°C) from vertical thermocouple trees at five heights (0.10–2.30 m). Variables: Session_ID, Condition, Height_m, Time_min, Temp_C. Summary_Table1.xlsx Summary statistics (mean ± SD) for all physiological variables, matching Table 1 of the manuscript. Metadata_StudyDesign.pdf Overview of study design, measurement devices, calibration details, and analysis workflow (R v4.x; lme4, afex, emmeans). Units All temperatures are in degrees Celsius (°C). Heart rate: beats per minute (bpm). Body mass: kilograms (kg). Total body water: percentage of body mass (%). Humidity: relative humidity (%RH). Time: minutes relative to exposure start (T = 0 min). Ethics and confidentiality : All participants provided written informed consent. Data are pseudonymized (Subject IDs = random numeric codes) and comply with the GDPR MR-004 framework (CNIL, France). Licensing : This dataset is released under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence, permitting reuse with proper citation. Citation - If you use these data, please cite: Mauvieux B., Markov A., Besnard S., Touitou Y., Edwards B.J. (2025). Circadian modulation of core temperature and thermoregulatory strain during live-fire compartment exposure in firefighters. Dataset available at Mendeley Data . Contact For questions or additional data access, please contact: Benoit Mauvieux – Normandie Univ., UNICAEN, UR 7480 VERTEX, Caen, France Email: benoit.mauvieux@unicaen.fr ORCID: 0000-0003-4862-6531

Steps to reproduce

Steps to reproduce Recruitment and screening Twenty-one healthy male professional firefighters were recruited from the Departmental Fire and Rescue Service of Saône-et-Loire (SDIS 71, France). All participants were medically cleared for active duty and provided written informed consent. Experimental design Each participant completed two identical 40-min live-fire container exposures on the same day: Morning session (AM): 09:00–09:40 h — heat-gain circadian phase Evening session (PM): 21:30–22:10 h — heat-loss circadian phase Environmental conditions were matched using identical 40-ft steel containers and standardized fuel loads (wood pallets and OSB panels). Instrumentation and measurements Core temperature (Tcore): ingestible e-Celsius® capsule (BodyCap, France), 0.033 Hz sampling. Skin temperatures: chest and neck, iButton® DS1922T loggers (0.033 Hz). Under-PPE microclimate: temperature and relative humidity (iButton® DS1923, 0.033 Hz). Heart rate: Polar H10 sensor, beat-to-beat. Body mass / TBW: Tanita MC-780MA-N S bioimpedance, pre- and post-exposure. Perceived exertion: Borg 6–20 scale, 10 min post-exit. Environmental temperatures: Type N thermocouples at 0.10–2.30 m (0.5 Hz). Data synchronization All sensors were synchronized to a single NTP-calibrated clock before each session. Raw data were exported as CSV files and aligned by time stamps (Δt = 30 s or 8-min bins for summary analyses). Data processing and analysis Statistical analyses performed in R (v4.x) using lme4, lmerTest, afex, and emmeans. Mixed-effects models assessed fixed effects of time-of-day (AM vs PM), time, and their interaction, with random intercepts for subjects. Effect sizes computed as Cohen’s dz and partial η². Figures generated with ggplot2 and exported at 600 dpi. Replication guidance Using the provided CSV files, researchers can replicate the main analyses by loading the datasets into R, running the provided linear mixed-effects models, and comparing the ΔTcore slopes, HR, and recovery kinetics between AM and PM sessions.

Institutions

• Normandie Universite

Categories

Funders

• Fondation Adolphe de Rothschild – Thérèse Tremel-Pontremoli Donation
• Fonds National de Prévention (CNRACL)

Licence