The reliability and validity of questionnaire for preliminary assessment of heat stress at workplace

Heat stress is one of the most important consequences of occupational heat exposure in worldwide. Current heat stress indices are not suitable for heat strain screening in developing countries due to their inherent and applied limitations. The Aim of this study was design, validity and reliability of a questionnaire method entitled "Heat Strain Score Index" or HSSI for preliminary assessment of heat stress at workplace. This cross-sectional study was conducted during 2009-2010. This research included seven stages (i) Item generation (ii) Evaluation of content validity by 9 subjects of occupational health specialists and 30 occupational health providers (iii) Reliability analysis was performed on 98 workers (iv) Structure validity was conducted on 150 workers (v) Test of the measurement model (vi) Criteria validity on 122 worker and (vii) classification of level thermal risk with ROC curves. Data were analyzed with SPSS-18 and AMOS-16 software. In stage of item generation; 40 items were identified. In Content Validity evaluation in the level of occupational health specialists, 27 items modified, 3 items were removed and 3 items added; in evaluation by occupational health providers, 19 items modified. Internal consistency (α) of items was 0.91. Exploratory factor analysis on items HSSI scale identified four subscales which explained 71.6% of the variance. Confirmatory factor analysis provides evidence of model fits (GFI=0.991, RMSEA=0.036). Correlation between the HSSI score with aural temperature was 0.73.Cut-off point, sensitivity and specificity for upper green zone (no thermal strain) were 13.5, 91% and 50%.whereas Cut-off point, sensitivity and specificity for lower red zone (thermal strain) were 18, 86% and 73%. This study revealed HSSI scale includes 18 of measurable variables that high overlapped with WBGT index and others questionnaires. This scale demonstrated high reliability and validity; sensitivity and specificity of cut-off point in scale were suitable. Therefore HSSI scale for primary evaluation heat stress is suitable.