## 4 Results and Discussion
### Using Laboratory Results to Predict Parameters Found for Field Tests (at 250% Scale)
#### 4.4.2 Comparing Experimental Values between Field and Laboratory Tests
While the TNT equivalence for PE-4 of 1.2 is well-documented [27], the combination of scaling up to 250% and using TNT equivalence could have influenced the arrival time of the overpressure wave. This is because the two explosives, PE-4 and TNT, would have different detonation velocities. Figure 14: Overpressure\(-\)time histories and cumulative specific impulse at gauges A and B2 for the 250% (black) with predicted 75% (**a**) and 100% (**b**) laboratory-scaled tests. Additionally, the weather conditions measured onsite were 20 \({}^{\circ}\)C with 58% humidity, whereas the temperature and humidity when the laboratory experiments took place were closer to 25 \({}^{\circ}\)C and 30%, respectively. These weather factors would not only affect gauge A but also the B gauges as they influenced the wave propagation in ambient air. Along with this, the surrounding environment and structure (a flat steel base plate with a smooth steel structure versus grasslands with a concrete structure) would influence the behaviour of the wave propagation. **B (1,2,3) Gauges**: As a reminder, less data was available for the B gauges. Hence, the range given in [11] is not indicative of the full set of tests where A was measured. Despite this, the incident overpressure and time of arrival for the B gauges were well predicted compared to gauge A. Large variations were observed for the positive phase duration and, consequently, the cumulative impulse. Upon further observation of the curves for B1 (see Figure 16), where the largest percentage difference of \(-44\) and \(-45\)% for the 100% and 75% scales were found, initially the three curves tended to align with one another. However, at 2.8 ms, a rise in pressure occurs in the field trial measurements. This rise was likely a reflective pressure wave from the surroundings and appeared to extend the duration when compared to the scaled lab experiments. This also occurred for B2 at 4.7 ms where a slight rise in  
Figure 15: Overpressure\(-\)time histories and cumulative specific impulse at gauges A and B3 for the 250% (black) with predicted 75% (**a**) and 100% (**b**) laboratory-scaled tests. pressure was observed in the field trial data. The converse was true for B3 where the predicted durations were longer than the field trial values (due to the half symmetry model implemented in the laboratory tests). As shown in the numerical models, B3 was influenced by the blast wave propagating through the rear of the corner structure (considered on the symmetric plane of field trials [11]). This caused a pressure rise as the initial blast wave decayed, extending the duration. In general, blast parameters at the B gauges were well predicted, especially within the initial forward blast wave propagating past the corner. The surrounding environment and details of the structure (including symmetry) would have had an effect as the pressure decayed. Further testing is recommended in the future to determine the extent of these influences, which can be built upon the existing laboratory set-up as a basis, moving towards quantifying the distinct aspects of the surrounding environment and structure and decomposing the complexities found in field tests.