Development of the outdoor personal thermal index (OPTI) for evaluating heat strain risk using personal, observational, geographical, and meteorological data

• Published in: BMC public health Vol. 25; no. 1; pp. 2445 - 15
• Main Authors: Ordudari, Zahra, Yazdanirad, Saeid, Dehghan, Habibollah, Azhdari, Mohammadreza
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 14.07.2025; BioMed Central; BMC
• Subjects: Accuracy; Adult; Age; Body mass index; Body temperature; Consent; Environmental aspects; Environmental conditions; Geographical data; Health aspects; Heart beat; Heart rate; Heart Rate - physiology; Heat; Heat stress; Heat stress disorders; Heat Stress Disorders - diagnosis; Heat stress index; Heat tolerance; Hot Temperature - adverse effects; Humans; Humidity; Insulation; Male; Metabolic rate; Metabolism; Meteorological Concepts; Meteorological data; Middle Aged; Observational data; Occupational health and safety; Outdoors; Parameters; Personal factors; Physical fitness; Physiological aspects; Physiological responses; Physiology; Prevention; Regression analysis; Relative humidity; Risk Assessment - methods; Risk factors; Thermal risk; Thermal strain; Weather; Work environment; Workers; Taiwan; Iran; Observational data; Personal factors; Heat stress index; Meteorological data; AMOS model; Geographical data; Outdoor workplace; Thermal risk
• DOI: 10.1186/s12889-025-23632-0
• ISSN: 1471-2458

Numerous thermal indices have been developed to assess heat stress among workers. This study aimed to develop and validate a new and accurate index for outdoor workplace environments, utilizing personal, observational, meteorological, and geographical parameters as well as eliminating the need for instruments. This study involved 201 men working outdoors, encompassing environments that are both hot and dry, as well as hot and humid. Measurements of tympanic temperature and heart rate were taken both at rest and 90 min after the start of work. Environmental conditions were assessed using suitable instruments, while relevant data were also gathered from meteorological and geographical databases. Estimates were made regarding the metabolic rate and the insulation value of the clothing worn by the subjects, with information on other observational parameters also recorded. The findings revealed that main factors, and personal factors exerted a significant and direct influence on tympanic temperature. Among the main factors, environmental variables displayed the most substantial indirect effects; specifically, globe temperature, dry temperature, and relative humidity. The overall index score was divided into four categories based on established optimal cut-off points of 18.41, 21.44, and 22.61. Linear regression analysis indicated that the OPTI based on instrumental and meteorological data could account for 72% and 63% of the variance in tympanic temperature respectively. The OPTI index, which was developed based on personal, observational, geographical, and meteorological data, proved to be a simple, accurate, and reliable index for predicting thermal strain, demonstrating compatibility with human physiological responses.