Heat-health warning systems for outdoor workers: recent advances, implementation gaps, and future priorities

Heat-health warning systems (HHWSs) are moving from population-level alerts toward occupationally relevant forecasts, task-adjusted thresholds, digital guidance, and warning-linked workplace controls. Outdoor workers nevertheless remain under-protected because regional forecasts may not represent job-level exposure and because alert receipt does not ensure that work is modified. This Mini Review critically synthesizes evidence across an occupational warning-to-action pathway: hazard forecasting, task-level risk translation, warning reach and comprehension, workplace action, and health, safety, and equity outcomes. A structured narrative search and source audit were conducted using literature available through July 2026. All cited sources were characterized by design, occupational directness, outcome proximity, implementation reporting, major bias concerns, transferability, and confidence for the specific claim supported. Recent progress includes WBGT forecasting, task and clothing adjustments, on-site verification, physiological prediction, internet of things (IoT)-enabled early warning, and warning-linked multifaceted interventions. Confidence is higher for the occupational heat burden and moderate for field action packages that reduce physiological strain or dehydration; evidence for policy-linked injury reductions is low-to-moderate because of residual confounding, and evidence that digital personalization reduces illness or injury remains low. Key controversies concern standardized vs. adjusted thresholds, advisory vs. mandatory controls, and digital personalization vs. validation, privacy, surveillance, and unequal access. The preventive value of occupational HHWSs therefore depends not only on forecast accuracy but also on decision authority, resources, enforcement, wage protection, worker trust, and the capacity to act.