structural equation modeling application to determine validity of the structure of a thermal strain screening method

background: heat stress is one of the most important consequences of occupational heat exposure worldwide. current heat stress indexes are not suitable for heat strain screening in developing countries due to their inherent and applied limitations. a new observation and subjective screening method is required that needs no instrument. in this study, a scale is developed based on the most important known risk factors (environmental, occupational, personal, and physiological). the aim of this study was to develop and validate the “heat strain score index (hssi) in iran’s climatic conditions.   methods: the cross-sectional experiment was conducted on 122 workers selected from national petrochemical company (asalouyeh) and esfahan steel company between july and september 2010. in the stage of item generation, the initial 45 samples were selected. content validity was conducted by health professionals and the items internal consistencies were investigated by chronbach's alpha coefficients. exploratory factor analysis was used to reduce the number of items.   findings: in content validity evaluation 5 items were considered as invalid and removed. also in correlation analysis 24 items, which had correlation less than 0.3, were omitted. internal consistency of the 17 remained items was obtained at 0.92 (0.71–0.85). exploratory factor analysis indicated three subscales: subjective judgment, protective clothes and physical activity which explained 67.7% of the variance. the internal consistency was high in three subscales (α = 0.73–0.91).   conclusion: exploratory factor analysis revealed that there are three vital factors with high internal consistency in hssi. structural validity and reliability indicated that hssi is a valid and suitable method for screening heat strain in iran.     key word: heat strain score index, validation, heat strain, iran