Analysis of Safety Distances for Fire Brigade in Response to Confined-Space Hazardous Materials Accidents: A Case Study from South Korea

<title>Abstract</title> <p>Confined-space hazardous-materials incidents generate rapid toxic exposure and secondary harm to firefighters, yet operational safety distances are typically defined qualitatively rather than based on dispersion behavior. This study evaluated firefighter safety distances using a hydrogen sulfide (H₂S) accident in a chemical storage tank in Suncheon, South Korea (2025), where 24 firefighters sustained secondary exposure and three civilians died. A case-based analysis integrated accident investigation data, reconstructed responder locations, concentration-based exposure criteria, and ALOHA dispersion simulation. The H₂S release rate was estimated at 0.25 g/s and modeled under low-wind conditions (1 m/s) using dense-gas dispersion methods. Simulation results showed H₂S remaining near the ground and spreading under limited ventilation. Maximum downwind impact distances were 4.1 m at 100 ppm, 7.4 m at 30 ppm, 30 m at 2 ppm, and 42 m at 1 ppm. Comparison with reconstructed firefighter positions revealed that command and emergency medical personnel without self-contained breathing apparatus could fall within low-concentration exposure zones. These findings demonstrate that conventional hazard-zone settings may underestimate responder exposure in confined-space toxic-gas incidents and support quantitative, concentration-based zone designation for emergency-response safety.</p>