Numerical simulations for thermal radiation and personnel risk associated with large-scale oil pool fires under unsteady environmental wind conditions

Large-scale oil pool fires release intense thermal radiation, posing significant threats to personnel, equipment, and adjacent facilities. In actual accidents, such fires are often influenced by unsteady environmental wind conditions rather than ideal calm or steady wind. Wind fluctuations alter flame inclination, smoke diffusion, air entrainment, and the spatial distribution of thermal radiation intensity, thereby increasing uncertainty in personnel risk assessment. Existing research has primarily focused on no-wind or steady-wind conditions, leaving the coupled effects of wind speed and turbulence intensity insufficiently understood. This study investigates the thermal radiation and personnel risk associated with large-scale oil pool fires under unsteady environmental wind conditions based on numerical simulations.

A square-shaped diesel oil pool fire model of 50 m² was developed using Fire Dynamics Simulator. Unsteady environmental wind fields were generated by combining the Kaimal spectrum function with the harmonic superposition method, and the resulting wind velocity time histories were incorporated into the numerical simulations. Three wind speeds (5 m/s, 10 m/s, and 15 m/s) and five turbulence intensities (0%, 5%, 10%, 20%, and 30%) were utilized to generate 15 distinct cases. The 0% turbulence intensity case served as the steady-wind reference. Heat flux gauges were positioned at z=1.5 m and on the vertical section to capture the spatial distribution and temporal variation of thermal radiation intensity. The model was validated against full-scale controlled wind tunnel oil pool fire data for wind speeds of 5 m/s and 10 m/s. Representative gauge values at similar distances from the oil pool center were compared with experimental measurements to assess the reliability of the numerical simulations. Following validation, the effects of wind speed, turbulence intensity, and measuring distance on thermal radiation intensity were analyzed. Cumulative probability was introduced to quantify the stochastic fluctuations of thermal radiation intensity, and a logistic model was used to fit the relationship between thermal radiation intensity and cumulative probability. Finally, the thermal radiation intensity threshold model was combined with the simulated distribution to evaluate personnel safety distances under various wind conditions.

The numerical simulations yielded the following results: 1) Compared with full-scale controlled wind tunnel experimental data, the relative errors in the far-field region, critical for personnel risk assessment, ranged from 0.43% to 32.49%, with an average of 16.43%. Notably, 16 of 20 cases had errors within 25%. 2) The validated model showed that unsteady environmental wind increased the complexity of thermal radiation intensity variation. At low turbulence intensity, fluctuations were primarily controlled by flame entrainment and flame turbulence, whereas at high turbulence intensity, ambient wind turbulence was the dominant factor. 3) The relationship between thermal radiation intensity and cumulative probability followed a logistic model. For a given thermal radiation intensity, the cumulative probability decreased with increasing turbulence intensity. 4) Personnel safety distance was jointly influenced by wind speed and turbulence intensity. The downstream safety distance increased with wind speed and decreased with turbulence intensity, whereas the lateral safety distance exhibited the opposite trend. 5) The peak thermal radiation intensity generally occurred within 30 s after ignition, indicating that the early stages of fire development represent the critical period for personnel exposure.

By incorporating unsteady environmental wind into the numerical simulation of large-scale oil pool fires, this study clarified the coupled effects of wind speed and turbulence intensity on thermal radiation intensity, cumulative probability, and personnel safety distance. The logistic model proved effective in characterizing the probabilistic distribution of thermal radiation intensity. The results show that assessments based solely on steady-wind assumptions may underestimate lateral and upwind risks, thus providing a more realistic foundation for hazard-zone determination and emergency evacuation planning.