Workstation-worker geometric mismatch and breathing-zone exposure in local exhaust ventilation: a structured narrative review

Local exhaust ventilation (LEV) is a principal engineering control for capturing contaminants at the source, yet its performance is conventionally judged by face velocity, capture velocity, sash height, and exhaust flow rate, parameters mostly verified in routine practice under static, worker-free conditions that do not reliably predict breathing-zone concentrations. This structured narrative review introduces workstation-worker geometric mismatch-the spatial misalignment among contaminant source, hood opening, work surface, worker body, and breathing zone-as a unifying exposure-control construct. Because the evidence spans tracer-gas, wind-tunnel, flow-visualization, computational fluid dynamics, and methodological studies, no pooled effect size was estimated; instead, 40 publications (31 primary experimental or numerical investigations and 9 review or methodological papers) were synthesized according to five mechanistic pathways: worker wake and reverse flow; source-breathing-zone distance; sash and hood-opening geometry; posture, orientation, and movement; and the human thermal plume. Nominal velocity repeatedly failed to guarantee breathing-zone protection, and human presence, proximity, movement, and body heat could overwhelm apparently adequate static designs, although evidence directness differs across mechanisms. The worker should therefore be treated not as an external user of LEV but as an active aerodynamic and thermal component within it, supporting worker-centred, geometry-aware evaluation, certification, and training.