Combined effects of thermal and acoustic stress on human psychophysiology and performance wearing firefighting protective clothing

Purpose This study investigates combined thermal and acoustic impacts on individuals wearing firefighting protective equipment. It also illuminates the intricate relationships between multi-factor and single-factor responses. Design/methodology/approach Ten healthy males were employed to participate in the experiment, wearing standardized firefighting PPE. The experimental protocol tested independent effects of temperature and noise and their combined effects. Single-factor trials tested ambient temperatures from 25°C to 40°C and noise levels from 65 dB to 90 dB. Four combined conditions (25°C/65 dB, 25°C/90 dB, 40°C/65 dB, 40°C/90 dB) were examined to evaluate potential effects. Physiological parameters, subjective perceptions and performance were measured. Significance analyses and correlation analyses were employed for independent effect, while regression analyses were for combined effect. Findings Thermal stress triggered physiological responses concurrent with psychological distress, while acoustic stress impaired auditory processing. Thermal and acoustic stress delayed reaction times. Heart rate, thermal sensation and thermal comfort responded to both stressors, while acoustic sensation and acoustic comfort were merely positively correlated to acoustic stress. Regression models confirmed thermal stress's dominant impact. These findings demonstrate that contemporary safety standards should integrate the multifaceted interactions of operational stressors. Prioritizing thermal stress protection is imperative, while work intensity requires strategic modulation to mitigate excessive metabolic heat production. To optimize thermoregulation, active cooling interventions should be implemented to reduce the skin temperature. Originality/value The existing studies pay less focus on the combined effect of thermal and acoustic stressors on firefighters, and there are fewer studies on the association between combined and independent effects. This study systematically explored the combined effects of thermal and acoustic stress on human psychophysiology and performance. The findings clarify physiological mechanisms and provide objective performance assessments, establishing a quantitative basis for improving protective equipment standards and firefighter safety.