## 4 Conclusions
Analyzing the data obtained for experimental attempts using higher harmonics, it can be seen that they have an impact on the extinguishing of the flames, as can be seen both in the case of the power that had to be delivered to the sound source to observe the phenomenon of complete extinguishing of the flames and the sound pressure level capable of extinguishing them. The successful extinguishing experiments carried out allow one to conclude that the sound pressure at which the extinguishing effect was noted is in the approximate range of 120 to 130 dB, depending on the frequency and the order of harmonics. At such sound pressure levels, flame turbulence sufficient to extinguish the flame was recorded because of the emission of acoustic waves. In turn, the observed power that had to be delivered to the sound source to extinguish the flames ranged from less than 100 to 900 W, depending on the frequency and the order of harmonics. Determined values by experimental means can serve as a reference for extinguishing flames in real fires, while it is important to note the specific sound pressure level at the extinguishing site. In the future, it is planned to analyze other fundamental frequencies than those included in this research and the influence of other harmonics on extinguishing flames. Due to their wavelength, low-frequency acoustic waves are difficult to attenuate. Since they pass through both solids, liquids, and gases, this is an unquestionable advantage, which in turn translates into practical applicability. It is assumed that the presented technology can be used in industrial halls, warehouses, and equipment racks, for the purpose of extinguishing flames in tanks with flammable liquids, gases, and even in the space segment, where the amount of and access to traditional fire protection measures are severely limited. At the site of a fire, there are different concentrations of substances in the ambient air, such as O\({}_{2}\), CO\({}_{2}\), NOx, smoke particles, etc. In practice, it is easier to extinguish flames in an enclosed space than in an open space. High-power acoustic extinguishers can be a primary or supporting mobile or stationary (permanently installed) component in the foundations, walls of buildings, or means of mass transportation (e.g., airplanes, trains, ships) so that their dimensions do not hinder installation. However, in order for this to happen, further work and analysis are needed aimed at testing the strength of materials (including, i.e., room furnishings due to resonant vibrations) subjected to continuous exposure to low-frequency acoustic waves, as well as, in the case of human participation in firefighting actions, testing their impact on health. To reduce or exclude this adverse effect, automated platforms can be applied, as previously indicated [38; 39; 40; 41; 42; 53; 54; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67]. This is important because this technique works well to extinguish firebreaks and can successfully prevent the spread of fire in the initial phase (by cutting off the oxygen that supports combustion processes). The research was carried out under the 'Inkubator Innovacyinosci+' program funded by the Ministry of Science and Higher Education (grant no. 3/2017). Not applicable. Data Availability Statement: Data are contained within the article. The author would like to thank the companies 'Ekohigiena Aparaturra Ryszard Putyra' and 'PHT SUPON' their support shown in the realization of scientific research. The authors declare no conflicts of interest.