Fireballs of liquid organic peroxides differ from those of liquid hydrocarbon fuels. Modified equations for predicting the fireball diameter, height, surface emissive power and the duration in dependence of the fuel mass are presented for di-tert-butyl peroxide. They base on 13 steel drum tests with fuel masses from 10 kg to 168 kg. Moreover, computational fluid dynamics simulations are performed using the laminar flamelet approach and a statistically turbulence treatment. Fireballs involving peroxide from 10 kg to 80 kg were simulated and their properties compared to the experimentally developed models. The deviations of each property are partially compensating each other leading to an adequate prediction of thermal safety distances for both, a time-independent and a time-averaged treatment. Simulations prove to be a good tool for predicting thermal radiation hazards of fireball scenarios.
Single and multiple fireballs of di-tert-butyl peroxide are numerically investigated using ANSYS CFX. Calculations contain varying inlet conditions, scale-adaptive shear stress turbulence modeling and one-step combustion reaction on a three-dimensional hexahedral mesh. Time-resolved flame temperatures, sizes and thermal radiation are compared to experimental results. There, fireballs were generated by fire engulfment of steel drums containing 200 l substance. After a vigorous burning, the remaining peroxide forms single and multiple fireballs involving 10 % to 20 % of the initial amount. The comparison of all simulations and two selected experiments show the special numerical treatment required for organic peroxides. Finally, the numerical predictions of irradiance in 30 m distance to the fire show a good agreement for both experiments. This proves the use of CFD as an appropriate method for thermal hazard assessment and the prediction of safety distances for organic peroxide fireballs.
To simulate a full fire engulfment during transportation or storage a closed removable head steel drum filled with 200 l Di-tert-butyl peroxide (DTBP) is subjected to a wood fire. Due to the enormous heat flux and the exothermic self-decomposition large flames arise and finally multiple fireballs occur. The fireballs consume up to 20 % of the total mass (20 % equals to 31 kg). They are characterized by high surface emissive power and large flames associated with high thermal radiation causing spontaneous ignition of objects in the surrounding. The measured sizes of the DTBP fireballs are smaller compared to the results of the general equations for hydrocarbon fireballs. Because these equations are recommended by the Health and Safety Executive (UK) to be applicable for organic peroxides explicit comparisons of DTBP with LPG, diesel and gasoline concerning the characteristics of fireballs are carried out. Also the burning time is compared and confirms a faster combustion of the peroxide. Moreover, the development of size and emissive power for DTBP and diesel fireballs are compared in a normalized graph. The results provide the assumption that new empirical models are required to be developed for hazard assessment of organic peroxide fireballs.
Das Abbrandverhalten und die thermische Strahlung von Poolfeuern organischer Peroxide (OP) wurden bereits in der Vergangenheit ausführlich untersucht. Dabei ergaben sich zum Teil erhebliche Unterschiede hinsichtlich der Abbrandraten, Temperaturen, Strahlungsintensitäten und Flammenlängen im Vergleich zu flüssigen Kohlenwasserstoffen. Das größere Gefahrenpotenzial von OP führt zu strikteren Sicherheitsbestimmungen für Lagerung und Transport. Da das Gefahrenpotenzial maßgeblich von den tatsächlich auftretenden Szenarien abhängt, ist eine Bewertung solcher Ereignisse unumgänglich um nachhaltig die Gesundheit von Mensch und Umgebung zu sichern. Ein Metallfass, gefüllt mit 200 Litern DTBP (Di-tertiär-butylperoxid), wurde auf dem Testgelände Technische Sicherheit der BAM einem Außenfeuer ausgesetzt. Durch den starken Wärmeeintrag erhöht sich die Massenabbrandrate des Peroxids um ein Vielfaches und das Fass entleert sich schließlich unter Ausbildung mehrerer Feuerbälle. Die Flammengröße, Flammentemperatur und damit die thermische Strahlung überschreiten die der gewöhnlichen OP-Poolfeuer. Die resultierenden höheren Sicherheitsabstände sind abschließend berechnet.