# A Review of Blast Loading in the Urban Environment
## 2 Current Knowledge
### Large Magnitude Urban Blast  
On 4 August 2020, one of the largest non-nuclear explosions in history occurred in the Port of Beirut, Lebanon. Approximately 2750 tons of ammonium nitrate, which hadbeen held in storage since 2014 [56], detonated shortly after 18:07 local time following a fire in the warehouse where it was being stored. The explosion injured over 7000 people and resulted in more than 200 casualties and over $15 billion in infrastructure damage [57]. Broken glass and debris were observed at distances up to 3 km away, encompassing an area with more than 750,000 inhabitants [58].  
[PERSON] et al. [4] estimated the yield of the explosion using video footage uploaded to social media shortly after the event. In total, 38 individual data points were identified, and a mixture of fireball, audio and visual data was collected. By searching through the videos on a frame-by-frame basis, the time of detonation and the time of arrival could be determined. By identifying a video's recording location, the distance to the blast origin could be approximately determined (\(\pm\)10 m) through Google Earth.  
The authors derived a simplified polylogarithmic function based on the Kingery and Bulmash [59] semi-empirical relationships for the time of arrival as a function of scaled distance. A \"best fit\" yield range was determined to be 0.50-1.12 kt of TNT, as shown in Figure 6. It should be noted that the best estimate was 0.50 kt TNT; the upper limit of 1.12 kt of TNT was given to account for the significant uncertainties in the raw data. [PERSON] et al. [60] adopted a similar approach to [PERSON] et al. [4], albeit with a smaller number of datapoints, and estimated the yield to be \(\sim\)400-960 tonnes TNT equivalent. This suggests that, for large-magnitude explosions, time and distance data are sufficient to obtain a reasonable and rapid estimate of the yield--even when the dataset is relatively coarse.  
Other approaches, e.g., dimensional analysis of the detonation product fireball [61; 62; 63], the Locking [64] power index method [65], analysis of seismological, hydroacoustic, infrastonic and radar remote sensing data [66], observed damage to structures [67; 68; 69], crater size [70], and debris/mushroom cloud height [71], generally agree that the yield of the Beirut explosion was in the range of 200-1400 tonnes TNT equivalent.  
The events in Beirut are not unprecedented; there have been many recent large scale industrial explosions (\(\gg\)10 tonnes TNT equivalent) in built-up areas [56], including Tianjin, China (2015; 173 deaths), and Buncefield, UK (2005; 43 injuries). Accordingly, the structural response to long-duration blast loading is an ongoing topic of interest, particularly for structures sensitive to such loads, e.g., bare steel sections [72; 73], partially-clad steel frames [74], cylindrical shell structures [75; 76], ISO containers [77], and bridges [78]. Accurately simulating long-duration blasts and their interaction with structural components several times smaller than the blast wavelength is highly challenging and requires considerable computational expense [79; 80].  
Figure 6: Best fit yield of the Beirut explosion with an upper yield, adapted from [PERSON] et al. [4].