Quantification of the Blast-Loading Parameters of Large-Scale Explosions

A field trial involving the surface detonation of the equivalent of 5,000 kg of trinitrotoluene (TNT) was carried out in Woomera, South Australia. The overpressures, impulses, and related information obtained from this trial were analyzed and compared against available predictive procedures and previously published data sets. A predictive procedure that is adopted in the widely used Unified Facilities Criteria (UFC) 3-340-02 is based on equations that are established through a small data set, in which issues such as afterburning, increased pressure as a result of the chemical reaction zone, and blast wave asymmetricality were not addressed. The data set contains data from mid and far-field explosions, in which the pressure data in the data set were not directly measured, but were inferred through the arrival-time data. This leads to a significant level of uncertainty in the UFC 3-340-02 procedure, especially for closed-in explosions. Differences between the field measurements and the predictions made when using the blast-parameter charts in UFC 3-340-02 and a computational fluid dynamics code are identified and analyzed in this paper. The findings of the analysis imply that the current predictive approach will neither capture the variabilities of blast parameters in an actual event, as it does not account for the shape of the charge, nor capture the uncertain behavior of the blast wave at a close standoff distance. This may lead to an overly conservative prediction of the impulse or an underestimation of the peak overpressure. The findings of the analysis show that in an uncontrolled blast event, the reliability of the empirical charts provided in the UFC 3-340-02 is questionable.