In the paper, the author proposes the concept that fire extinguishment is composed of flame extinction phenomena and extinguishing strategy. The extinguishing strategy is the methodology of how the extinguishing agent is transported to the fire area and delivered to the flames and is important for firefighting. In order to demonstrate the value of discussing extinguishing strategies to achieve the fire extinguishment, two different experimental studies conducted by the author are explained in this paper. One is the extinguishing experiment of a gaseous fuel diffusion flame with a sweeping CO₂ jet. The other is blast extinguishment of linearly arranged jet burner flames with a micro explosive.

This paper introduces recent developments in new and innovative fire extinguishing methods that use sound to extinguish fires. There are examples of relatively low frequency sound acting as a traveling wave against the fire extinguish­ing target. Many studies have been conducted on pool flames because they are designed for normal fires. The flow created by the sound pushes and bends the flame, triggering it to be extinguished. Recently, fire extinguishing methods have been proposed that use higher frequency sound as a traveling or standing wave. In this case, the nonlinear effects of high frequencies are utilized to successfully extinguish the fire. Both methods are limited in the extent to which they can extinguish a fire at one time. If a larger area is desired to be extinguished, a “Extinguishing strategy” that effectively moves the firefighting area is needed.

There is a need to develop innovative firefighting methods against large-scale, simultaneous and widespread forest fires. It is difficult to transport the fire extinguishing agent to the target position accurately in the general fire extinguishing method using water from the air because it is strongly affected by natural convection and wind. In addition, in fire extinguishing using water, the adhesion to combustible surfaces is poor, and there is also a problem in reignition suppression performance. In recent years, methods using high-viscosity fluids and gels have been investigated as a solution to this problem. In this paper, we outline the case studies of fire extinguishing methods using high-viscosity fluids and gels, and furthermore, describe our approach to a fire extinguishing method that uses a blast to transport high-viscosity fluids (“Hydro-Gel Blasting (HGB) fire extinguishing method”).

In this study, we investigated the impact of fluorine compounds added to foam used in petroleum tank fires on the extinguishment performance if the use of fluorine compounds were to be banned in the near future. In addition, the study examined ways to improve the efficiency of extinguishing petroleum tank fires with fluorine-free foams. As a result, it was found that the addition of fluorine compounds is extremely important to ensure the extinguishment performance of the foam. Although under limited conditions, the optimum foam properties (Expansion ratio and Drainage rate) and foam application rate were shown for foam extinguishment in petroleum tank fires. However, it is known that foam extinguishment performance is greatly affected by tank size and oil type, as well as by the foam application method. Therefore, it is necessary to further study the extinguishment performance of foam against these parameters.

This article aims to explain the relationship of ammonium phosphate content and extinguishing ability. The fire extinguisher, dry chemical, certification system, fire extinguishing mechanism and verification methods are explained, and experiment results are discussed. The fire extinguishing time of the high-performance fire extinguisher with high ammonium phosphate content is less than half that of conventional fire extinguisher in the B-7 model. Furthermore, the fire extinguisher with high ammonium phosphate content can extinguish the B-14 model in 7.5 seconds. However, the conventional fire extinguisher fails to extinguish the B-14 test. It is suggested that increasing the content of ammonium phosphate in the power extinguishing agent greatly improved its fire extinguishing effect.

A new fire extinguishing agent that can generate fire-fighting smoke was proposed. The ultra-fine particles in the smoke can float in air for a long period, which makes the smoke behaves as gas. The potassium compounds in the particles exhibits fire extinguishing performance base on negative catalyst effect. New fire extinguishing equipment and systems were designed based upon the examined fire extinguishing property of the new agent. The volumetric agent concentration was determined by the fire-extinguishing time and the reignite prevention examined in laboratory scale experiment. Real scale extinguishing experiments of Class A, Class B and vehicle fire were also carried out. The new agent can be manufactured into sheet, block and liquid, which give it a variety of applications, such as protection for industrial machinery and batteries, and also fire extinguishing building materials.

In order to bridge the gap between droplet combustion and spray combustion, “Group Combustion” experiments were conducted aboard the Japanese Experiment Module “Kibo” on the ISS. The complete title of “Group Combustion” is “Elucidation of Flame Spread and Group Combustion Excitation Mechanism of Randomly Distributed Droplet Clouds.” The local flame-spread rules were studied using droplet-cloud elements, etc., and the group-combustion-excitation limit was identified using randomly distributed droplet clouds. This paper describes the background of “Group Combustion”, such as droplet combustion, flame spread over droplets, and percolation models for group-combustion excitation through flame spread and some recent accomplishments from the “Group Combustion” experiments with randomly distributed droplet clouds to study the group-combustion-excitation limit. Anomalous combustion phenomena observed near the group-combustion-excitation limit and cool-flame appearance are also reported.

Cool flame occurs in a certain temperature and a pressure range from a hydrocarbon fuel mixtures as a result of low temperature reaction before hot flame occurrence, and plays a key role in control of ignition timing. This article introduces the mechanism of the spontaneous ignition of the cool flame. As curious behavior, cool flame shows oscillatory behavior under a certain condition. For the analysis of this dynamics which is driven under coupling with transport and chemical reactions, accompanying with cyclic domination switching between chain branching reaction and chain propagation reaction, we also introduce the projection method of the dynamic system expressed in a higher-order manifold to a low dimensional space by using Variational Auto-Encoder which consists of a deep neural network. This technique was successfully able to distinguish the state during cool flame oscillation for single droplet and droplet pair.