Sand barrier effect on n-heptane continuous spill fires: an investigation based on fuel evaporation analysis

Sand is subject to various national standards for storage in chemical parks and energy storage companies, and it is widely recognized as an effective measure for preventing and controlling accidental spill fires. This study investigates the propagation process of spill fires on sand barriers through experimental tests and evaporation analysis. The findings from these experiments reveal two distinct phenomena. In scenarios involving thin, finegrained sand layers, both the flame and the fuel seep through the sand layer simultaneously (Type I). In cases with thicker, coarser sand layers, the flame is blocked by the sand while un-ignited fuel gradually flows out (Type II). The difference in blocking effects is primarily governed by the fuel preheating duration. When the preheating duration is shorter than the seepage duration (time for fuel to penetrate the sand layer), Type I occurs. Conversely, Type II emerges when the preheating duration exceeds the seepage duration. Temperature data in the sand layer confirms that the preheating process is mainly driven by flame radiation. To further investigate the characteristics of the preheating duration with various sand layer configurations, a numerical model was developed to predict the evaporation rate during the preheating process. It was found that the distance between the fuel level and the sand layer surface, as well as the thickness of the sand layer, are positively correlated with the preheating duration. In contrast, the grain size is negatively correlated with the preheating duration. Among these factors, the distance between the fuel level and the top of the sand layer plays the predominant role in controlling the preheating process. By comparing the experimental seepage duration with the simulated preheating duration, the model was validated for predicting transitions between fire-blocking modes. These findings provide critical insights for optimizing sand barrier designs, mitigating thermal hazards, and refining industrial safety standards.