Non-invasive attempts to extinguish flames with the use of high-power acoustic extinguisher - De Gruyter
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Open Eng. 2021; 11:349–355
Research Article
Paweł Stawczyk* and Jacek Wilk-Jakubowski
Non-invasive attempts to extinguish flames with
the use of high-power acoustic extinguisher
https://doi.org/10.1515/eng-2021-0037 contemporary achievements in signal analysis with the use
Received Jun 19, 2020; accepted Jan 03, 2021 of computer methods and fire extinguishing using drones
seem to be interesting [12–15]. The extinguishing technol-
Abstract: This paper presents an innovative method of ex-
ogy described in the article can also be used in automation
tinguishing of flames using a high-power acoustic extin-
systems to extinguish flames in case of fire, also in the free
guisher. This method allows for effective and non-invasive
space. Currently, many scientific centres are working on the
extinguishing of the flames. Experimental results showing
use of robots in the event of natural disasters or detection
the effectiveness of the fire extinguisher for different dis-
of flames [16, 17].
tances from the flame source and different frequencies of
In 2007, the popular science program “Myth busters”
the acoustic wave are discussed. The paper ends with the
verified the effectiveness of flame extinguishing using
description of the advantages, disadvantages, and limita-
acoustic waves. It was found that this can be done be-
tions of the proposed fire extinguishing method.
cause the sound waves disrupt the air enough to snuff out
Keywords: Acoustic extinguisher; fire detection; fire retar- the flame [18]. In 2008, American Defense Advanced Re-
dation; fire suppression; resonant frequency; non-invasive search Projects Agency (DARPA), launched the Instant Fire
extinguishing of the flames Suppression (IFS) research programme aimed at a better
understanding of the nature of sound waves in terms of
their potential application in military applications. In 2012,
the research team arranged two speakers opposite each
1 Introduction
other, to demonstrate the effectiveness of the extinguish
process depending on the sound parameters of the acoustic
For many years, effective methods of fire extinguishing
wave [19]. As research has shown, effective extinguish tests
have been sought. Traditional methods of fire extinguish
were carried out using low frequency acoustic waves [20].
are based on cutting off the oxygen supply from a burning
It is related to that effectiveness of the extinguish process
surface. These include powder extinguishers, traditional
depends on the amplitude of the air vibrations. Another
water-extinguishers, and CO2 fire extinguishers [1, 2]. De-
parameter that determines the effectiveness of the extin-
spite their proven effectiveness in the fight against fire, they
guishing process is the acoustic power.
pose a real thread of serious damage equipment installed
in the rooms. For this reason, contemporary fire-fighters are
looking for new methods to reduce the damage caused by
fire-fighting incidents [3–8]. It is possible to extinguish the 2 Assumptions and theoretical
flames using an acoustic wave [9]. The operational principle
of this type of the fire extinguisher depends on disturbing
basics
of the flames crown. Air turbulence resulting from variable
The main assumption was to build a fire extinguisher that
acoustic pressure breaks the continuity of the flame and
would produce a directional acoustic stream capable of
leads to its extinguish [10, 11]. Against this background,
extinguishing flames. This is essential for improving the
effectiveness of the extinguish process by improving the
range of extinguishing and reducing the required acoustic
*Corresponding Author: Paweł Stawczyk: Department of In- power. For this reason, a proper acoustic system is needed.
dustrial Electrical Engineering, Kielce University of Technology, 7 The simplest examples of this are a closed end tube and
Tysiąclecia Państwa Polskiego. Ave, Kielce 25-314 Kielce, Poland;
an open tube with a circular cross-section called a waveg-
Email: pstawczyk@tu.kielce.pl
Jacek Wilk-Jakubowski: Department of Information Systems, uide [21]. The principle of the waveguide is to strengthen
Kielce University of Technology, 7 Tysiąclecia Państwa Polskiego. the acoustic wave as a result of acoustic resonance. This res-
Ave, Kielce 25-314 Kielce, Poland; Email: j.wilk@tu.kielce.pl
Open Access. © 2021 P. Stawczyk and J. Wilk-Jakubowski, published by De Gruyter. This work is licensed under the Creative
Commons Attribution 4.0 License
350 | P. Stawczyk and J. Wilk-Jakubowski
onance occurs due to reflecting of the acoustic wave inside
the waveguide. At certain frequency (called resonance fre-
3 Test station
quency) a standing wave occurs. The standing wave arises
Investigations of the influence of acoustic wave parameters
as a result of the interference of two same waves, moving in
on the efficiency of flames extinguishing were carried out
the same direction, but having opposite turns. Distribution
on a test station shown in Figure 2.
of standing waves in the closed end tube and open tube is
shown in Figure 1.
(a)
Figure 2: Experimental set-up diagram 1) signal generator, 2) power
amplifier, 3) waveguide, 4) loudspeaker, 5) sound level meter, 6)
source of fire
The measuring station consists of Rigol DG4102 func-
(b) tion/arbitrary waveform generator, Proel HPX2800 power
amplifier, SVAN 979 sound level meter, and an acoustic ex-
Figure 1: Distribution of standing wave in the waveguide for the first tinguisher. To clearly determine the influence of the acous-
f1 and second f2 resonant frequency a) closed end tube, b) open
tic wave parameters on the extinguishing process, a burn-
tube
ing candle was used. Unlike a diffuse fire source which can
be obtained by using a gas fire-pit pan, the use of a burning
The minimum wavelengths required for the resonance candle allowed to clearly identify the extinction process. In
phenomenon are different. It will be respectively: the experiments carried out by using a gas fire-pit pan, it
could be observed that when the diffuse flames were not
V
λ1 = (1) fully extinguished, they were re-ignited. For this reason,
4f
it was decided that a point source of fire in the form of
V a burning candle will be more suitable for experimental
λ2 = (2)
2f researches. The flame height was about 2 cm.
where λ1 – the length of the closed end tube, λ2 – the length The acoustic extinguisher was made in the form of
of the open tube, V – air velocity, f – sound frequency. a folded tapered, closed end waveguide with a rectangular
It can be noticed that the required length of the waveg- cross-section of 4.28 m in length – this type of waveguide
uide is two times smaller in the closed end tube [22, 23]. was used in all experiments. The B&C 21DS115 loudspeaker
This is especially important for practical reasons – for low with a nominal power of 1700 W was installed at the begin-
frequencies a significant waveguide length is required. The ning of the waveguide.
generation of a 20 Hz sound wave requires, for example: λ1
= 4.28 m for the closed end tube, and λ2 = 8.57 m for the
open tube.
For this reason, previous attempts to fire extinguish
4 Experimental results
with acoustic waves have been carried out with a closed
Experimental researches have been divided into two main
end tube. However, these tests were carried out only with
parts: determination of basic fire extinguisher parameters
the use of low power and low range of acoustic extinguish-
and extinguishing model fire source.
ers [24, 25]. These devices had a small extinguishing range
and included a small working area – for this reason it was
necessary to build an innovative high power and high range
fire extinguisher, to get the potential possibilities of this
extinguishing method [26–30].
Non-invasive attempts to extinguish flames with the use of high-power acoustic extinguisher | 351
4.1 Identification of fire extinguisher
parameters
Determining the parameters of an acoustic extinguisher
is important to ensure the most effective operation of the
device in the event of fire. The following parameters were
determined: an impedance curve, a sound pressure level
curve, and the directional characteristics of the device.
a) Impedance curve
The impedance curve was measured in the range of 10–90
Hz. On the basis of the impedance curve, the operating
frequency was specified.
Figure 4: Sound pressure level curve of the extinguisher
Taking into account Figure 3, the frequency was set at
17.25 Hz. The minimum impedance (Zmin = 11.4Ω) of the fire
extinguisher was measured at the indicated frequency. At can be noticed that this frequency, previously defined as
this frequency, the speaker cone was the most acoustically the operating frequency, is the optimum value for both the
stressed, which significantly reduced its vibration ampli- maximum mechanical load on the speaker cone and the
tude. That allows for more efficiency use of the speaker’s acoustic efficiency.
power capabilities.
c) Directional characteristics
During designing devices for acoustic fire extinguishing, it
is necessary to determine their directional characteristics.
These characteristics allow for the optimal positioning of
the extinguisher relative to the source of the fire (concen-
tration of the acoustic beam allows to reduce the required
acoustic power and dimensions of the extinguishing device)
[31, 32]. The measuring station is shown in Figure 5.
Figure 3: Impedance curve of the extinguisher
b) Sound pressure level curve
The impedance curve was measured in the range of 10–90
Hz in the waveguide axis. The accuracy of measurement
was 1 Hz. The distance of the sound level meter from the
waveguide output was 1 m. The extinguisher was powered
by a sinusoidal voltage of 13 V RMS value.
Considering Figure 4, we can observe that the maxi- Figure 5: Test station 1) waveguide output, 2) sound level meter
mum sound pressure level 103.1 dB occurred at 17 Hz. It
352 | P. Stawczyk and J. Wilk-Jakubowski
Measurement conditions
The measurements were carried out in an open air for three
different distances of the sound level meter: R = 2 m, R =
2.5 m and R = 3 m. The accuracy of measurements was ∆
= 22.5∘ . The intensity of the acoustic background during
the measurement was 64.7 dB. The measurements were Figure 7: Test station 1) waveguide output, 2) fire source
taken at the working frequency of 17.25 Hz and 150 W of
power supplied to the speaker.
Figure 6 shows the directional characteristics for three Measurement conditions
different distances of the sound level meter: R = 2 m, R = 2.5 Investigations were carried out under wind-free conditions
m, R = 3 m. It can be seen that the fire extinguisher emits in the open air. Attempts to extinguish the fire were made in
the sound omnidirectionally, however the main acoustic the axis of the waveguide output. The accuracy of measure-
stream is emitted in the waveguide axis. Obtaining a one- ment was 0.1 m. The intensity of the acoustic background
way emission would require building a waveguide of a during the measurement was 64.7 dB.
length equal to the wavelength.
a) Influence of distance between fire source
and waveguide output on extinguishing effect
The measurements were made with the use of three fre-
quencies: 14 Hz, working frequency 17.25 Hz, and 20 Hz of
sine wave.
Considering Figure 8, it can be observed that the most
efficiency frequency of the extinguishing wave is the op-
erating frequency. The maximum extinguishing range ob-
tained during the measurement was 1.2 m. The power de-
livered to the fire extinguisher was 1000 W. More powerful
tests were not performed due to the power limitation of the
loudspeaker and amplifier, which nominal parameters are
given according to the guidelines for musical signals (AES
standards). Another limitation that appeared during extin-
guishing attempts was the significant vibration amplitude
Figure 6: Directional characteristics for three different distances of
the sound level meter: R = 2 m, R = 2.5 m, R = 3 m
4.2 Extinguishing a model fire source
The main goal of this study was to investigate the influence
of acoustic wave parameters on extinguishing efficiency.
The measuring station is shown in Figure 7.
Figure 8: Minimum electrical power delivered to the extinguisher
causing extinguishing effect in the function of the distance from the
waveguide outputNon-invasive attempts to extinguish flames with the use of high-power acoustic extinguisher | 353
of the speaker’s diaphragm, which appeared (especially) at • Measurement of the influence of acoustic wave fre-
14 Hz. This can be observed both in Figure 8 and Figure 9 quency on the minimum extinguishing power
(blue curves) as a limited range of extinguishing – at 50 • Measurement of the influence of acoustic wave fre-
cm a significant amplitude vibration of the speaker’s di- quency on the minimum sound pressure causing ex-
aphragm was observed. Higher vibration amplitude was tinguishing effect
also observed at 22 Hz. The vibration amplitude was lower
The results show that acoustic wave frequencies be-
than it was for 14 Hz.
tween 14–21 Hz are capable of extinguishing flames.
It can be seen that with the increase in the frequency of
the acoustic wave, the required electrical power supplied to
the fire extinguisher also increases as is shown in Figure 10.
The lowest extinguishing power of 125 W was measured at
14 Hz and the highest of 350 W at 20 Hz.
The minimum extinguishing sound pressure increases
from 116 dB for 14 Hz to 125 dB for 20 Hz as is shown in
Figure 11. It can be seen that both the power and the sound
Figure 9: Sound pressure level causing extinguishing effect in the
function of the distance from the waveguide output
Considering Figure 9, it can be concluded that the
sound pressure capable of extinguishing effect was in the
range of 120–130 dB. The decrease of sound pressure level
observed with increasing distance between the flame and
the waveguide output is caused by the overlapping of phase
incompatible reverberant waves (reflected from the limiting Figure 10: Minimum electrical power delivered to the extinguisher
surfaces of the measuring area) and waves directly emitted causing extinguishing effect in the function of sound frequency
by the extinguisher. This resulted in sound pressure fluctu-
ations which increased with increasing distance from the
waveguide output. At 17.25 Hz and a distance of 110 cm from
the waveguide output, the sound pressure level increased
unexpectedly. It may result from a temporary change in
atmospheric conditions.
b) Influence of sound frequency on extinguish effect
Investigations of the influence of sound frequency on the ex-
tinguishing efficiency were carried out for frequencies in
the range of 14–21 Hz of sine wave. The accuracy of the mea-
surements was 1 Hz. The distance of the fire source from
the waveguide output was 0.5 m.
Experimental research has been divided into two parts: Figure 11: Minimum sound pressure causing extinguishing effect in
the function of sound frequency354 | P. Stawczyk and J. Wilk-Jakubowski
pressure curves have a local maximum that may be mea- extinguishing efficiency (1.2 m) was measured at operating
sured near the operating frequency. frequency 17.25 Hz.
It can also be seen that the power and sound pressure Significant size of extinguishing devices made with
curves are similar in shape. This is due to the fact that boththis technology and the unaffected impact of infrasound of
of these values were measured in the same extinguishing such a high intensity on the health of rescuers and injured
attempts. Moreover, the sound pressure level is logarithmi- persons limit the scope of potential applications. For this
cally dependent on the power supplied to the speaker. reason, the fire-fighting technology with the use of acoustic
waves could become element supporting the safety of server
rooms or industrial halls as stationary fire extinguishing
systems.
5 Conclusions The device can be used for extinguishing fires of dif-
ferent classes, as the acoustic waves penetrate both solids,
Experimental researches confirmed the effectiveness of the
liquids, and gases. Nowadays it can be used in the case of
innovative acoustic extinguisher in the fight against fire.
fires of classes B and C, when gases or liquids are burning.
The main assumption that variable sound pressure can
However, it is unlikely to be as effective in the case of solid
cause turbulence to disturb the flame front, leading to its
flames, as the flame may re-ignite due to the lack of heat
extension, has been confirmed. The use of higher frequency
absorption from the interior of the material.
acoustic waves resulted in an increased electrical power
To answer for all possible questions about the use of
supplied to the extinguisher causing the extinguishing ef-
acoustic extinguishing technology, it is necessary to carry
fect. Acoustic waves of lower frequencies are more suitable
out tests on devices with much higher power and different
because they cause a higher amplitude of flame vibrations
operating frequencies – not only for one, 17.25 Hz, as it was
and thus have a higher extinguishing efficiency. During
shown in this paper. This will allow to define the limits
the extinguishing tests the lowest of the tested frequencies,
of the range of operation both in the context of possible
14 Hz, showed the highest extinguishing efficiency. Then
applications and to determine the impact of low-frequency
the necessary electrical power delivered to the fire extin-
acoustic waves on the human body. The second important
guisher was the lowest. Therefore, it seems reasonable to
issue is to determine the impact of such low-frequency
build acoustic extinguishing devices with the lowest pos-
waves on building structures. The risk that occurs here and
sible operating frequencies. However, generating a wave
which must be verified – how the resonance vibrations of
with a frequency of several Hertz requires the use of a much
walls or windows may contribute to damage or destruction
longer waveguide, which results in difficulties in practical
of the building? – at this moment it has not been conducted.
implementation. The limit frequency of the acoustic wave
above which it was difficult to observe the phenomenon
Acknowledgement: The authors would like to thank the
of extinguishing flames, was 22 Hz. The use of higher fre-
company “Ekohigiena Aparatura Ryszard Putyra Sp.J.”,
quency acoustic waves brings some benefits. One of them
19 Strzelecka St., 55-300 Sroda Śląska, Poland very much
is the greater concentration of the acoustic beam, which
for support in the realization of the research.
appears as the frequency of the acoustic waves increases.
The sound emission then becomes more directional, which
directly improves the effective range of extinguishing. The
second one is the limitation of the size of the extinguisher, References
which is particularly important in the context of mobile
applications. Moreover, experimental research has shown [1] G. Jensen, COW1 AS. Manual Fire Extinguishing Equipment for
Protection of Heritage. The Norwegian Directorate for Cultural
that acoustic waves of higher frequencies, despite their
Heritage and Queen’s Printer for Scotland, Oslo 2006, Norway.
advantages, require more electric power supplied to the ex-
[2] V. Loboichenko, V. Strelets, M. Gurbanova, A. Morozov, P. Ko-
tinguisher. A correlation between the increasing required valov, R. Shevchenko, T. Kovalova, R. Ponomarenko. Review
power supplied to the loudspeaker increases with the fre- of the Environmental Characteristics of Fire Extinguishing Sub-
quency was observed – it can be seen in Figure 8. stances of Different Composition used for Fires Extinguishing of
Experimental research has also shown that a fire ex- Various Classes. Journal of Engineering and Applied Sciences,
14(16), pp. 5925–5941. DOI: 10.36478/jeasci.2019.5925.5941.
tinguisher emits sound omnidirectionally, however, the
[3] K. Radwan, J. Rakowska. Analiza skuteczności zastosowania
main acoustic stream is located in the axis of the waveg- wodnych roztworów mieszanin koncentratów pianotwórczych do
uide. The dispersion of the acoustic beam limits the range gaszenia pożarów cieczy palnych.(Analysis of the effectiveness
of effective firefighting. The maximum distance with full of application of aqueous solutions of foam-forming concen-Non-invasive attempts to extinguish flames with the use of high-power acoustic extinguisher | 355
trates to extinguish fires of flammable liquids, PL), Przemysł [20] G. Mason. Two Engineering Students Invent A Sonic Fire
chemiczny, vol. 90 (12), pp. 2118-2121 (2011). Extinguisher. University in Virginia (2017), https://interestingen
[4] Twardochleb, A. Jaszkiewicz, I. Szwach, K. Prochaska. Aktywność gineering.com/two-engineering-students-invent-a-sonic-fire-e
powierzchniowa, pianotwórczość oraz biodegradowalność sur- xtinguisher.
faktantów stosowanych w pianotwórczych środkach gaśniczych. [21] A. Noga. Przegląd obecnego stanu wiedzy z zakresu techniki
(Surface activity, foaming activity and biodegradability of sur- infradźwiękowej i możliwości wykorzystania fal akustycznych do
factants used in extinguishing foaming agents, PL), Przemysł oczyszczania urządzeń energetycznych.(Review of the current
chemiczny, vol. 90 (10), pp. 1802–1807 (2011). state of the art in the field of infrasound technology and the
[5] W. Wnęk, P. Kubica, M. Basiak. Standardy projektowania possibility of using acoustic waves to purify power equipment,
urządzeń gaśniczych tryskaczowych – porównanie głównych PL), Zeszyty Energetyczne, vol. 1, pp. 225–234 (2014).
parametrów. (Design standards for extinguishing systems – com- [22] A. Jędrusyna, A. Noga. Wykorzystanie generatora fal in-
parison of main parameters, PL), Bezpieczeństwo I Technika fradźwiękowych dużej mocy do oczyszczania z osadów
Pożarnicza, vol. 27 (3), pp. 83–96, (2012). powierzchni grzewczych kotłów energetycznych. (Use of a high-
[6] J. Rakowska, Z. Ślosorz. Korozja instalacji gaśniczych i armatury power infrasound wave generator to clean the heating surfaces
pożarniczej. (Corrosion of firefighting systems and fittings, PL), of power boilers from sediments, PL), Piece Przemysłowe&Kotły,
Bezpieczeństwo I Technika Pożarnicza, vol. 4, pp. 113–120 (2011). vol. 11-12, pp. 30–37 (2012).
[7] R. T. Sai, G. Sharma. Sonic Fire Extinguisher. Pramana Research [23] F. Hausdorf. Podręcznik budowy zestawów głośnikowych. (Guide
Journal, vol.8, pp. 337–346 (2017). to loudspeaker system design, PL), VISATON, Poznań (1996).
[8] A. N. Friedman, J. Hughes, P. I. Danis, G. J. Fiola, C. A. Barnes, [24] A. S. Sharan, S. Akanksh, R.K. Mohan Ram, H.R. Uttunga.
S. I. Stoliarov. Acoustically Enhanced Water Mist Suppression Development of portable fire extinguisher using acoustic
of Heptane Fueled Flames. Fire Technology, 54, pp. 1829–1840. waves. project No.39_BE_1977, http://www.kscst.iisc.ernet.in/
DOI: 10.1007/s10694-018-0777-0. spp/39_series/SPP39S/02_Exhibition_Projects/196_39S_BE_1
[9] P. Niegodajew, K. Gruszka, R. Gnatowska, M. Šofer. Application of 977.pdf.
acoustic oscillations in flame extinction in a presence of obstacle. [25] K. Bong-Young, B. Myung-Jin, B. Seong-Geon. A study on Suitabil-
XXIII Fluid Mechanics Conference (KKMP 2018), IOP Conf. Series ity of Sound Fire Extinguisher in Duct Environment. International
Journal of Physics (Conf. Series 1101/2018). DOI: 10.1088/1742- Journal of Applied Engineering Research, ISSN 0973-4562, vol.
6596/1101/1/012023. 12 (24), pp. 15796–15800 (2017).
[10] T. Węsierski, S. Wilczkowski, H. Radomiak. Wygaszanie pro- [26] S.Ivanov, S.Stankov, J. Wilk-Jakubowski, P. Stawczyk. The us-
cesu spalania przy pomocy fal akustycznych. (Extinguishing ing of Deep Neural Networks and acoustic waves modulated by
the combustion process by means of acoustic waves, PL), Bez- triangular waveform for extinguishing fires. International Work-
pieczeństwo i Technika Pożarnicza, vol. 30 (2), pp. 59–64 (2013). shop on New Approaches for Multidimensional Signal Processing
[11] H. Radomiak, M. Mazur, M. Zajemska, D. Musiał. Gaszenie NAMSP 2020, Technical University of Sofia, Sofia, Bulgaria, July
płomienia dyfuzyjnego przy pomocy fal akustycznych. (Extin- 09-11, 2020.
guishing a diffusion flame by means of acoustic waves, PL), Bez- [27] J. Wilk-Jakubowski, P. Stawczyk, S. Ivanov, S.Stankov. Control of
pieczeństwo i Technika Pożarnicza, vol. 40 (4), pp. 29–38, (2015). acoustic extinguisher with Deep Neural Networks for fire detec-
[12] B. Raghothaman, D. A. Linebarger, D. Begušić. Anew method for tion. Submitted for publication in: Elektronika i Elektrotechnika,
low-rank transform domain adaptive filtering. IEEE Transactions 2020/2021.
on Signal Processing , vol. 48 (4) (2000). [28] J. Wilk-Jakubowski, P. Stawczyk, S. Ivanov, S. Stankov.High-
[13] M. Mihelj, D. Novak, S. Beguš. Virtual Reality Technology and power acoustic fire extinguisher with artificial intelligence plat-
Applications, Part of the Intelligent Systems, Control and Au- form. Submitted for publication in: International Journal of Com-
tomation: Science and Engineering book series. ISCA, vol. 68. putational Vision and Robotics, 2020/2021.
DOI: 10.1007/978-94-007-6910-6. [29] J. Wilk-Jakubowski, P. Stawczyk, S. Ivanov, S. Stankov. The using
[14] N. Nedev, Z. Nenova, S. Ivanov. Virtual instruments for humidity of Deep Neural Networks and natural mechanisms of acoustic
and temperature measurements. 2014 Information Technology waves propagation for extinguishing flames. Submitted for pub-
Based Higher Educationand Training. lication in: International Journal of Computational Vision and
[15] P. Miklavčič, M. Vidmar, B. Batagelj. Patch-monopole monopulse Robotics, 2020/2021.
feed for deep reflectors, Electronics Letters. vol. 54 (24), pp. [30] J. Wilk-Jakubowski. Flame extinguishing with the use of low fre-
1364–1366 (2018). quency sinusoidal acoustic waves and frequency sweep tech-
[16] L. Šerić, D. Stipanicev, D. Krstinić. ML/AI in Intelligent Forest Fire nique – Analysis of selected cases. Submitted for publication
Observer Network. Conference 3rd EAI International Conference in: Journal of Electrical Engineering – Elektrotechnický časopis,
on Management of Manufacturing Systems. 2020/21.
[17] M. Ivanova, S. Ivanov, G. Wilk-Jakubowski, R. Harabin. Progress [31] K. Myung-Sook, B. Myung-Jin. A study on a Fire Extinguisher
on robotics in crisis management: a review of the literature. Eu- with Sound Focus. International Information Institute, ISSN 1343-
ropean Journal of Tourism Research, 2020/2021. 4500, vol. 20 (6A), pp. 4055–4062 (2017).
[18] Myth Busters. Voice Flame Extinguisher. Episode 76 (2007). [32] Y. Eun-Young, B. Myung-Jin. A study on the Directionality of Sound
[19] Defense Advanced Research Projects Agency. DARPA sound Fire Extinguisher in Electric Fire. Convergence Research Letter
based fire extinguisher. https://www.extremetech.com/extre of Multimedia Services Convergent with Art, Humanities, and
me/132859-darpa-creates-sound-based-fire-extinguisher. Sociology, ISSN 2384-0870, vol. 3 (4), pp.1449–1452 (2017).You can also read
