Analysis of a Large Balloon Explosion Incident

On December 19, 2017, a large balloon containing about 22 thousand cubic meters of hydrogen was deliberately torn open to initiate deflation at the completion of a filling test. An inadvertent ignition occurred after about two seconds and caused an explosion that produced extensive light damage to a large building near the balloon test pad. The analysis described here includes an estimate of the buoyancy induced mixing into the torn balloon, and the blast wave produced by assumed constant flame speed combustion of the 55% to 65% hydrogen-in-air mixture. Comparisons of calculated blast wave pressures are consistent with estimates of the pressure needed to cause the observed building damage for flame speeds in the range 85 m/s to about 100 m/s.