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

ABSTRACT 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 (USG). Methods A cross-sectional study was conducted among 400 outdoor workers in Tamil Nadu, India, during peak summer, combining two components: Heat Exposure Risk (HER) score, based on validated risk factors, and Heat Illness Symptom (HIS) score, derived from clinical frameworks. End-of-shift USG (≥1.020) was used as physiological reference for validation. Results HER score showed strong validity and reliability, while HIS score effectively identified symptomatic workers. The combined O-HRII aligned well with physiological marker, classifying most workers as moderate-to-severe risk. Importantly, the tool facilitated evidence-based recommendations for immediate on-site use. Conclusions O-HRII is a validated, field-feasible tool for identifying vulnerable outdoor workers and guiding heat-stress interventions.