## 1 Introduction
The explosive-pressure-dynamic parameter-calculation program that we developed accurately describes the explosive-load generation process in premises with no protective structures (PS), as well as in EVS-equipped premises. The data in Figure 2 illustrate this. Mathematical description of the explosive-load dynamics registered in a room with an EVS-equipped opening is based on the solution of simultaneous differential equations, which link together explosive pressure and EVS kinematics. A general overview of the simultaneous equations will be provided below. For now, let us focus on the influence of premises dimensions and the mixture type on explosive-load levels. Analysis of the simultaneous equations (see Equations (3) and (5) below), presented in a non-dimensional form (Formulas (1) and (2)):  
\[G_{\text{EVS}}=G\cdot B^{2} \tag{1}\]  
\[(G=\frac{\rho_{1}\cdot g\cdot h}{2}\cdot\frac{1}{\Delta P_{resp}},B=\sqrt{ \frac{P_{atm}}{\rho_{1}\cdot(\epsilon\cdot L_{n})^{2}}}), \tag{2}\]  
where \(B\) is the key parameter defining the pressure surge caused by an EVS. It represents a non-dimensional acceleration of the EVS movement under the pressure forces emerging from an explosion of a certain mixture type, non-dimensional parameter \(B\) being its characteristic. The physical significance of parameter \(G\) is as follows: the greater the linear dimensions of the building, the lower rate of increase explosive pressure as the overall duration of the explosion extends [34; 35; 36; 37; 38]. Therefore, the impulse of the pressure force grows in direct proportion with building dimensions. This, in turn, leads to a larger impulse transferred by the pressure forces to the EVS. On the other hand, the longer the delay of the EVS, the lower the speed at which the EVS moves (for a given impulse). Therefore, as the dimensions of the building (premises) grow, non-dimensional acceleration increases, and vice-versa. Figure 2: A math waveform of pressure following an explosion of a propane-air mixture in a cubic chamber (\(h=305\) mm): (**a**) uncovered openings; (**b**,**c**) openings covered with EVS-simulating panels. Dimensionless parameter \(B\) is characteristic of the type and the quality of the burning mixture. The physical significance of parameter \(B\) lies in the fact that with a growing flame-propagation rate, the emission rate of combustion products increases. In dimensionless terminology, it affects how efficiently the mixture is discharged to the atmosphere through relief openings. The capacity of combustion products drops as long as parameter \(B\) decreases or the visible flame-propagation rate increases. While pressure surges (in a situation with an EVS-equipped opening), the flame front represents a sphere that significantly simplifies the calculation task. Acceleration of explosive combustion at this point can be provided only by initial turbulization of the mixture, which would depend on the actual accident scenario. Combustion-process intensification related to the presence of various obstacles along the flame path plays a subordinate role at the initial stage of the explosion because the visible flame-propagation rate is minimal. Figure 3, which contains instant photos of a deflagration explosion inside a room with a hinged window, illustrates a statement about the spherical nature of the flame front at the moment of EVS opening. Photos 1 and 2 of Figure 3 show that the flame front has an almost spherical shape at the initial stage of the explosion and even at the moment when the EVS panel starts to open. It is only when the flame breaks out into the atmosphere, which corresponds to the first pressure surge (photo 3 Figure 3), when the flame front loses its spherical shape. The influence of the EVS response rate on the explosive pressure is shown in Figure 4, which shows explosive-pressure waveforms for an enclosure equipped with an EVS a with varying response rate.