Effect of relative humidity on the emission height and reaction force of single-tube fireworks.

In this study, aerial fireworks commonly used for celebrations in Taiwan were analyzed. These fireworks have propellant components, which are stored under varying humidity and temperature conditions. Differential scanning calorimetry (DSC) and the Vent Sizing Package 2 (VSP2) were used to assess the relationship between microscale heat transfer and temperature as well as thermal runaway in an adiabatic environment. Thermodynamic methods, namely the Friedman, Flynn–Wall–Ozawa, and ASTM E698, were used to analyze the safety and latent thermal hazards of aerial fireworks. DSC experiments confirmed the high solubility of potassium nitrate (KNO3), which enables it to readily dissolve in K+ and NO 3 - . Increasing the relative humidity and exposure time caused the surface of the oxidizer to dissolve, resulting in the reduction of the second exothermic peak and, in turn, incomplete combustion and launch failure. The results obtained using the ASTM E698 method revealed that when the samples were soaked in deionized (DI) water, their apparent activation energy increased considerably from 45.78 to 153.68 kJ mol−1, reflecting a decrease in the temperature sensitivity of the gunpowder in the fireworks. To reduce the reactivity of the gunpowder and minimize the thermal hazard associated with fireworks, a large amount of water must be added. However, the experiment performed using VSP2 showed that when the humidity increased, the adiabatic exothermic onset temperature was delayed. The maximum temperature of the original sample was the highest. The maximum reaction rate of the samples stored at a relative humidity of 40% was shorter than that of other samples, and that of the samples soaked in DI water was the longest. Regarding the relationship between pressure rise rate and temperature, (dP/dt)max can be used to determine whether the propulsion capacity of a firework during ignition is sufficient. When DI water was added, the propulsion capacity decreased, and fireworks could not be ignited. The samples stored at a relative humidity of 40% had higher pressure than did the original sample. The samples soaked in DI water had lower pressure than did the original sample. These results indicate that increasing humidity affects temperature and pressure. [ABSTRACT FROM AUTHOR]