Development and Validation of an Occupational Heat Risk and Illness Index: An Integrated Tool for Assessing Heat Stress Vulnerability in Outdoor Workers

OBJECTIVE: This study developed and validated a composite Occupational Heat Risk and Illness Index (O-HRII) that integrates exposure to risk factors and self-reported symptoms, benchmarked against urine-specific gravity. METHODS: A cross-sectional study was conducted among 400 outdoor workers in Tamil Nadu, India, during peak summer, combining two components: heat exposure risk score, based on validated risk factors, and heat illness symptom score, derived from clinical frameworks. End-of-shift elevated urine-specific gravity (≥1.020) was used as physiological reference for validation. RESULTS: Heat exposure risk score showed strong validity and reliability, whereas heat illness symptom score effectively identified symptomatic workers. The combined O-HRII aligned well with the physiological marker, classifying most workers under moderate-to-severe risk. Importantly, the tool facilitated evidence-based recommendations for immediate on-site use. CONCLUSIONS: The O-HRII is a validated, field-feasible tool for identifying vulnerable outdoor workers and guiding heat-stress interventions.