Comparison of Existing Empirical Equations for Blast Peak Positive Overpressure from Spherical Free Air and Hemispherical Surface Bursts

The blast-induced impulsive loads due to unabated accidental and man-made explosions on structures are receiving attention from structural designers. Recent devastating Beirut ammonium nitrate explosion and very recent blast at a chemical factory on the outskirts of Bangkok are examples of the accidental explosions. Such loading applies a high-intensity pressure over a very short duration (microsecond to the millisecond), is generally more damaging than quasi-static and other less intense dynamic loadings induced by wind, wave, or earthquake. The positive phase of the blast load is generally considered in the analysis neglecting the negative phase being less impulsive to cause significant damage to the structure. A number of available empirical relations predict blast wave parameters and each relation validates its experimental results, however, the proposed relations had not been vetted with different available experimental data. In this paper, several existing empirical equations proposed by various researchers for blast peak positive overpressure of spherical free-air and hemispherical surface-bursts, the arrival time of air-blast shockwave, and positive phase duration of the blast are presented and compared with the available experimental results and predictions of blast design manuals UFC 3-340-02(2008) and IS 4991:1968 for a span of scaled distances. The phenomenon of the blast is explained and a list of technical documents and required accessories to measure the experimental response is provided. The limitations of the empirical relationships are explored. This study is useful to structural engineers and researchers for the blast-resistant design of structures.