## 1 Introduction
In addition to wildfires (spatial aspect), which may follow the so-called external fires, the key issue is internal fire protection, which aims to prevent the development and spread of flames within a given object (such as a building), including beyond the place of its origin (especially firebreak extinguishing), which is possible through the use of sophisticated firefighting techniques, including the acoustic method [18; 19; 20]. In practice, for a fire to occur, according to the so-called triangle of combustion, the simultaneous occurrence of three components is necessary. The first is a fuel (combustible material), the second is an oxidant (such as air with oxygen), and the third is a source ofthermal energy. The reduction of any of these factors affects the combustion process and its elimination influences the extinguishing of flames, which is used in the development of new firefighting techniques. Going back to the beginning of the environmentally friendly acoustic method, its origins can be traced back to military applications (the Instant Fire Suppression program) [21]. In practice, even with an amplified modulated human voice, flames can be extinguished using low-frequency acoustic waves. Tone generators may be useful for this [22; 23; 24]. Moreover, the use of an explosive bomb can extinguish flames, due to the fact that the shock wave pushes out oxygen, which is necessary not only to initiate, but also to sustain a fire [25]. This technique may work well for extinguishing liquids (including oil). In practice, the higher the concentration of oxygen in the atmosphere, the more violent the combustion reaction, while the flame temperature is higher. This is associated with a lower ignition temperature and less energy required to cause the combustion reaction. From a practical point of view, acoustic technology applies low-frequency waves to fight fire [26; 27]. As has been proven, properly amplified and generated acoustic waves (according to the described mechanism) can be effectively applied to extinguish flames [28; 29; 30; 31]. It should be noted that one of the methods of fire prevention is the continuous monitoring and implementation of early detection systems for smoke and fire, which is directly related to reducing the risk and consequences of these dangerous events. Implementing the DNN (Deep Neural Network) module using machine learning algorithms in the acoustic extinguisher can allow, by separating the sounds associated with the fire hazard from the ambient sounds, the extinguisher to be activated quickly as soon as flames are detected (early response systems) [32]. Early detection may also be implemented through visual detection [33; 34; 35; 36; 37]. The benefit of using automated platforms is the speed of data processing (usually time less than 10 ms), which is not achievable in the case of manual operation of devices by humans, which translates into starting the fire extinguishing action without unnecessary time delay (future application of the intelligent acoustic fire extinguisher). However, because of the subject matter of this paper, these issues are only mentioned (some publications are included in the bibliography of this paper). This is important because in the case of using an acoustic fire extinguisher equipped with an artificial intelligence module, in the absence of a human being at the extinguishing site, the risk of adverse effects of acoustic waves on human health (health aspect) does not occur. Most often, dedicated relay modules are applied for this purpose (the 12/24 V control signals). The role of sensors (including vision sensors) is to detect undesirable phenomena and, if necessary, trigger an alarm. Examples are included in the works of [PERSON] and [PERSON] et al., e.g., [38; 39; 40; 41; 42]. The subject of applying acoustic waves to extinguish flames is relatively new, hence few publications have appeared from experimental attempts applying the acoustic field. Analyzing the literature on the subject, [PERSON] et al.