Brief Introduction on Advances in Fire Suppression

1. Introduction

As society rapidly evolves and urbanization accelerates, fire safety has become an increasingly pressing concern. Fire-extinguishing technology serves as a vital tool for the prevention and control of fires, capable of averting casualties and mitigating severe damage to the environment. The performance of extinguishing agents, a central component of fire-extinguishing technology, is pivotal to both the effectiveness of fire suppression and its environmental repercussions. Notably, technologies utilizing extinguishing agents such as water, dry powder, gas, and foam have demonstrated significant utility across a variety of application scenarios [1,2,3,4]. In light of the recent advancements in efficient fire-extinguishing technologies, access to timely research findings and profound insights is imperative for expanding the knowledge base in this domain. This Special Issue compiles 11 papers that tackle emerging issues and challenges in various fire suppression technologies, offering the necessary insights for effective fire mitigation.

2. Descriptions

The research scope of this Special Issue encompasses the development of fire-extinguishing agents, the design of fire-extinguishing systems, the transport dynamics of agents, dispersion kinetics, and simulation studies. These areas of research lay a robust foundation for the evolution of fire-extinguishing technology and its practical application. As environmental consciousness grows and demands for fire-extinguishing efficiency escalate, the innovation of novel extinguishing agents has emerged as a prevalent field of study. Notably, water-based fire-extinguishing agents, which leverage water as their primary component, have seen enhancements in their fire-suppression capabilities through the incorporation of chemical additives or the modification of water’s physical properties. Among these, fine water mist systems, recognized for their cleanliness and efficacy, have garnered considerable interest [1]. According to the national standard of China for “Water mist extinguishing equipment” [5], fine water mist is characterized by droplets with a flow-weighted cumulative volume distribution of less than 200 μm (D_v0.50) and 400 μm (D_v0.99) under the minimum design operating pressure. Systems are categorized based on operating pressure into high pressure (p ≥ 3.50 MPa), medium pressure (1.20 MPa ≤ p < 3.50 MPa), and low pressure (p < 1.20 MPa), where P denotes the pressure of the medium within the distribution network. The fire-extinguishing mechanisms are illustrated in Figure 1.

Fine-water-mist firefighting technology markedly enhances both the efficiency and versatility of firefighting applications through the incorporation of physical and chemical additives. Physical additives, such as surfactants, bolster cooling and suffocation effects, work by diminishing the surface tension of water, augmenting the diffusivity and wettability of the water mist, and promoting the amalgamation of water with fuel. Surfactants may be hydrocarbon-based or fluorinated [6]. While fluorinated surfactants offer superior hydrophobicity and the capacity to create aerosolized water films, they may also exert adverse environmental effects due to their persistence and potential for bioaccumulation in natural ecosystems [7,8,9]. Chemical additives, including alkalis, transition metals, and their hydroxides and salts, contribute to fire suppression by engaging in chemical reactions and physical processes. For instance, sodium and potassium compounds slow flame propagation and create a foam blanket to smother the fire source [10], whereas metal hydroxides quench combustion through neutralization reactions and by sequestering free radicals [11]. Furthermore, ultrafine water mist, engineered via high-pressure atomization, exhibits exceptional heat transfer efficiency and swift evaporation traits. This technology can precipitously lower the temperature of the fire source, offering a novel and efficient direction for environmentally friendly firefighting techniques.

Gaseous extinguishing agents are a class of fire suppression media that inhibit or extinguish fires through physical or chemical actions, playing a significant role in the field of fire extinguishing. Perfluorohexanone, as a new generation of gaseous fire-extinguishing agents, has garnered widespread attention in the international firefighting community due to its highly efficient fire suppression capabilities and excellent environmental characteristics [3]. This agent features an exceptionally low extinguishing concentration of 4.2%, rapid extinguishing speed, and the ability to effectively prevent fire re-ignition, with an extinguishing efficiency that significantly surpasses that of the traditional halon 1301 agent [12]. Perfluorohexanone has an Ozone Depletion Potential (ODP) value of zero, indicating no harm to the atmospheric ozone layer, and it possesses a relatively low Global Warming Potential (GWP), with an atmospheric lifetime of merely 0.014 years, thereby exerting a negligible impact on global climate change [13]. During the fire-extinguishing process, perfluorohexanone does not generate harmful corrosive gases and exhibits good compatibility with metals and polymeric materials, along with excellent electrical insulation properties. It leaves minimal residue post-extinguishing, reducing environmental pollution and post-fire cleanup efforts. Its excellent long-term storage stability also minimizes the maintenance costs associated with fire suppression systems. Amidst the global focus on environmental protection and sustainable development, the market demand and application prospects for perfluorohexanone are expanding. It is anticipated to play an increasingly prominent role in the realm of fire-extinguishing agents, contributing significantly to the protection of human life, property safety, and the environment.

Foam extinguishing agents are employed to extinguish fires through their mixture with water, resulting in the formation of foam. These agents are categorized into the following two primary types: protein-based and synthetic. Protein-based foam agents incorporate a range of reinforcing agents into their animal protein base liquid. Notably, fluoroprotein types enhance fire-extinguishing efficiency by incorporating fluorocarbon compounds [14]. On the other hand, synthetic foam agents exhibit a spectrum of characteristics. For instance, aqueous film-forming foam (AFFF) can create a protective film on the surface of combustible materials, as depicted in Figure 2. This protective film bolsters the fire-extinguishing process and the material’s resistance to re-ignition [15].

Dry powder extinguishing agents are a class of efficient, economical, and environmentally benign fire suppressants that integrate the functions of chemical extinguishing with physical suppression. Their fire-extinguishing efficacy can be several times greater than that of halon, leading to their widespread adoption across various applications [2]. A derivative of dry powder, dry water extinguishers, leverage the combined benefits of dry powder and water mist technologies, making them exceptionally suitable for extinguishing lithium-ion battery fires [16]. In their preparation, water and hydrophobic silica are blended via high-speed agitation, yielding a core–shell structured powder extinguishing agent (as illustrated in Figure 3). The extinguishing mechanisms of this agent encompass physical cooling, chemical inhibition, thermal radiation blocking, and free radical trapping [17]. During the firefighting process, the substantial volume of water discharged by the dry water extinguisher rapidly evaporates, drawing heat away from the fire source. Concurrently, the hydrophobic silica particles produced create a barrier over the fuel surface, sequestering the fuel from external heat exchange and oxygen, thereby effectively interrupting the combustion chain reaction. Moreover, dry water extinguishers exert minimal environmental impact post-use, aligning with contemporary requirements for green and efficient firefighting technologies.

Recent scholarly research underscores the pivotal role of piping design in the transport and dispersion dynamics of extinguishing agents, which is essential for enhancing fire prevention and suppression strategies. An optimized piping design enhances the flow characteristics and spatial dispersion efficiency of extinguishing agents by considering critical fluid dynamics parameters, including flow velocity, pressure loss, and turbulence [18]. By meticulously designing the pipe diameter, length, elbows, and branches, the system’s pressure loss can be minimized, thereby augmenting the delivery efficiency of the extinguishing agents. The utilization of simulation technology further refines piping design, facilitating the virtual simulation of extinguishing agent flow. This enables pre-assessment and refinement of the design scheme in a controlled environment, ensuring the high efficiency and reliability of the fire suppression system prior to its actual deployment [19].

3. Future Research Direction

The evolution of big data and artificial intelligence technologies is propelling fire suppression research to unprecedented heights. The integration of sophisticated AI algorithms with fire suppression technologies is poised to expand into broader application domains. Concurrently, the exploration of multimodal fire suppression technologies that integrate physical and chemical suppression mechanisms is underway to accommodate a wider array of fire scenarios. Furthermore, innovation in pipeline design, coupled with the application of simulation and modeling technologies, should be further advanced. These advancements should be integrated with transport and dispersion models within actual fire contexts to optimize the distribution efficiency of extinguishing agents. This optimization is essential to ensure the high efficiency and effectiveness of firefighting operations.