Field experiments of hydrogen-air deflagrations to evaluate appropriate mixture volumes by scaling law

In connection with the recent developments of hydrogen stations for fuel-cell vehiles, deflagrative explosions in hydrogen-air mixtures were studied in field experiments. Latex balloons of 0.15 and 1.4 m³ were used for testing gas mixtures of equivalence ratios 0.7, 1.0, 1.8, 2.0, and 3.0. The flame propagation was recorded by a high-speed camera, and the blast pressures were measured at several locations from the explosion center. A spherical flame expansion inside the balloon induces an increase in the balloon volume, and the flame front ruptures the balloon when it reaches the balloon surface. Typical fireball phenomena were observed for fuel rich mixtures. The overpressures and the positive impulses of the mixtures of equivalence ratios 1.0 and 1.8 were the highest for the gas mixtures tested. Sachs's scaling law was used to compare the obtained overpressures with the results of larger scale experiments of up to about 2 000 m³ reported by other research groups. The scaled overpressure vs. distance plot of the present experimental data agrees well with the data of larger scale experiments. The comparison confirms that the vapor cloud volumes of the present experiments are enough to predict the blast damages on the basis of the blast scaling law.