###### Abstract
An advantage of using acoustic extinguishers equipped with a flame detection module that uses deep neural networks is the ability to detect and extinguish fires in real time. The advantage of the solution proposed by combining both techniques is that there is no need for human involvement during the extinguishing action. By the term infrasound, one means acoustic waves whose frequency is too low to be heard by humans. It should be noted that the most common side effects for people are fatigue, headaches, mood swings, and vibroacoustic disease [34]. The lower limit of audible frequencies, at the same time the upper limit of infrasound, is conventionally considered to be 20 Hz. However, it should be noted that the audible range is an individual matter. Under laboratory conditions, when a sine wave is played at a very high volume, the human sense of hearing can identify  
Figure 1: UL-94 flame-retardant tests. low sounds (as low as 12 Hz). Certain people (such as opera singers) may have a sense of hearing that allows them to hear sounds at lower frequencies relative to the assumed values [35]. Therefore, it is assumed that a person should not be exposed to infrasound or sound pressure levels higher than the pain threshold of the human ear (110 dB). So, there is no risk if a person is not present when the fire is extinguished. Another issue is the need for research on the effects of low-frequency and high-sound-pressure acoustic waves on building structures. This is particularly relevant for waves of very low frequency and very high sound pressure. These aspects require further research. Another potential application of acoustic waves is to reduce the intensity of smoke and harmful substances in the ambient air, the presence of which is the result of fires, and also the use of scientific and technological advances (i.e., polluting engines). Due to the subject matter of this article, these issues have been omitted. If flames are detected, the fire extinguishing system can be activated automatically (without human involvement). Artificial intelligence may be applied for visual flame detection. A low-cost smart module that allows this (as one of the optional components of an acoustic extinguisher) has been developed in collaboration with researchers in Bulgaria, i.e., [36]. Furthermore, in the event of a fire, data can be captured and transmitted wirelessly to relevant services [37; 38], in the case of inaccessible locations, using satellite links. The acoustic technique for extinguishing flames is relatively new, so little work has been carried out in this area (some examples are [39; 40; 41; 42; 43; 44; 45]). In recent years, authors have conducted research to develop new technology that will allow flames to be extinguished with low-frequency acoustic waves generated by a high-power sound source [46; 47; 43; 36; 48; 4]. For this purpose, different frequencies and waveforms have been analyzed. This is because the technique has not yet been fully discovered. According to experiments that have already been conducted, unmodulated and modulated waves can be used to extinguish flames. The benefit of using an acoustic extinguisher is that it can be universally tuned for a specific flame source, so that the extinguisher may be as effective as possible in extinguishing flames originating from the combustion of a specific material. In this regard, Class B and C fires are indicated, i.e., flammable liquid and gas fires. In the case of solid fires, there is a difficulty in taking heat away from the interior of the material. However, this method can be used supportively. Due to the limitations in the volume of this article, information on this topic (as an extension of knowledge) can be found in other articles by the authors included in the bibliography of this article [46; 47; 48; 31; 36; 4]. Therefore, more research is needed for other frequencies and waveforms. Going back into history, it is worth noting that documented attempts to extinguish flames using acoustic waves have been conducted in the US.