Preparation and characterization of typical potassium salt dry water and its fire extinguishing performance

Abstract

To develop an efficient and environmentally friendly fire extinguishing agent, hydrophobic SiO₂ and deionized water were dispersed in a high-speed disperser for a period to form dry water. Cold-curing resin and potassium salts were then added to modify it. The microstructure was characterized using SEM, TEM, XRD, and EDS. The fire extinguishing efficiency of different dry waters on wood pile fires was tested using thermocouples and infrared thermal imaging cameras. Results indicate that cold-set resin colloids interconnect to form a network structure, enhancing the dry water’s structural strength and improving its pressure resistance. Thermocouple tests on wood pile fires revealed all four dry water formulations effectively extinguished flames, with CH₃COOK dry water demonstrating optimal performance. This suggests multiple extinguishing mechanisms: external SiO₂ isolates oxygen, internal solution evaporation absorbs heat, and KOH decomposition products react with flame radicals. CH₃COOK dry water holds promise as an efficient, eco-friendly fire suppressant.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-35477-7.

Introduction

As urban development accelerates and population density continues to rise, the frequency and danger of fires have increased, posing a threat to the safety of individuals and public property^1,2. Equipping efficient fire suppression agents and firefighting devices is crucial for controlling fires and protecting lives and property. Halon fire extinguishing agents are widely used due to their high efficiency, but the halogens they contain cause lasting damage to the ozone layer^3–6. Dry powder extinguishers and fine water mist extinguishers are also commonly used due to their low cost and high effectiveness^7–9, but dry powder extinguishers have poor moisture resistance and tend to clump, posing dust hazards; fine water mist extinguishers are less effective at extinguishing smoldering fires. Scientists have been exploring efficient and environmentally friendly fire suppression agents^10–13.

Dry water materials have gained significant attention since 1990. Composed of hydrophobic SiO2 and an aqueous solution with over 90% water content, dry water exhibits excellent flowability and dispersion properties^14–16, making it widely applicable in fire suppression^17,18 and gas storage^19,20. The external SiO2 can block the fire source, while the internal aqueous solution evaporates and absorbs heat, combining the advantages of both dry powder and fine water mist extinguishing agents to achieve a dual suppression effect^21,22. Chen Xianfeng’s research group has prepared calcium alginate gel dry water²³ and SiO₂ gel dry water²⁴, finding improvements in flowability, pressure resistance, water retention, and stability. Wang Yang²⁵ tested the fire suppression efficiency of dry water at different pressures, concluding that the efficiency is optimal between 0.6 and 0.7 MPa. Class A fires are more complex than Class B fires, consisting of homogeneous and heterogeneous combustion²⁶. Homogeneous combustion refers to the pyrolysis of wood piles generating combustible volatiles that ignite with oxygen at high temperatures, while heterogeneous combustion involves the carbon layer on the surface of the wood pile coming into contact with oxygen in the air, leading to smoldering. Zhang²⁷ discovered that alkali metal salts enhance the fire suppression efficiency of pure water. At high temperatures, alkali metal solutions generate gaseous KOH, which participates in chain termination reactions within flames to achieve chemical fire suppression effects. This paper explores the suppression effects of different potassium salt dry waters on Class A fires by modifying dry water with potassium salt solutions and cold gel.

Experimental procedure

Experimental reagents

The reagents used in the experiment include: KCl from Xilong Scientific Co., Ltd., AR 99%; CH₃COOK from Xilong Scientific Co., Ltd., AR 99%; KH₂PO₄ from Xilong Scientific Co., Ltd., AR; hydrophobic SiO₂ from Hubei Huifu Nano Materials Co., Ltd (Particle size: 7 nm); deionized water, prepared in the laboratory; and n-heptane from Shandong Xuchen Chemical Technology Co., Ltd., AR 99%.

Sample preparation

Hydrophobic SiO₂ and deionised water in the ratio of 1:10 by mass were used as the experimental raw materials, and the effect of different rotational speeds on the preparation of dry water was explored by changing the rotational speed of the dispersing machine (5000 r/min, 6000 r/min, 7000 r/min, 8000 r/min) at 60 s, and the micrographs of the observations are shown in Fig. 1.

Fig. 1.

Microscopic view of dry water at different speeds. (a) 5000 r/min, (b) 6000 r/min, (c) 7000 r/min, (d) 8000 r/min.

From the figure, it can be seen that the morphology of dry water varies greatly under different speeds at the same time, and the high speed disperser stirred at 7000r/min for 60 s has a better effect of SiO₂ coating on the solution. It shows that the liquid phase can be sheared into small particles with uniform particle size at this rotational speed, and the dry water is quickly coated by SiO₂. When the rotational speed is small, the shear force is small, the liquid is not well dispersed, and the SiO₂ agglomerates with each other, resulting in part of the liquid not being coated as shown in the shadows of Fig. 1a, b, and the stability of the dry water prepared at this rotational speed is poor. Higher rotational speed produces higher shear force, resulting in part of the well-coated dry water being destroyed and solid-liquid separation occurs as shown in Fig. 1d, and the particle size of the dry water prepared at this rotational speed is not uniform.

Hydrophobic SiO₂ and deionised water in the ratio of 1:10 by mass were used as the experimental raw materials, and the effects of different times (30s, 60 s and 90 s) on the preparation of dry water were explored under a high-speed disperser at 7000 r/min, and the microscopic observation diagrams are shown in Fig. 2.

Fig. 2.

Microscopic diagram of dry water at different times. (a) 30 s, (b) 60 s, (c) 90s.

From the figure, it can be seen that the morphology of dry water under the same rotational speed with different time has a large difference, and the high speed disperser was stirred at 7000 r/min for 60 s, and SiO₂ had a better effect on the solution coating. At stirring time 30 s, the large dry water was not dispersed into small particles, and the prepared dry water had a larger particle size, as shown in Fig. 2a. At stirring time 90 s, the morphology of dry water particles was similar to that of dry water at 60 s, and a small number of larger and irregular particles appeared, as shown in Fig. 2c, which was due to the fact that some of the particles were mixed with each other for too long a stirring time, and large irregular dry water particles appeared.

Preparation of Dry Water: Deionized water and SiO₂ were mixed at a mass ratio of 10:1 and stirred in a high-speed mixer at 7000 rpm for 1 min to obtain dry water.

Preparation of Potassium Salt Dry Water: A certain amount of CH₃COOK, KCl, and KH₂PO₄ was added to deionized water to prepare solutions with a concentration of 5%. These solutions were then mixed with SiO₂ at a mass ratio of 10:1 and stirred in a high-speed disperser at 7000 rpm for 1 min to obtain CH₃COOK dry water, KCl dry water, and KH₂PO₄ dry water.

Preparation of Gelrite gellan gum Potassium Salt Dry Water: Deionized water was heated to boiling. To ensure gel formation while considering the moisture content and cost of the extinguishing agent, 0.3% Ggg was added and stirred until completely dissolved. A certain amount of CH₃COOK, KCl, and KH₂PO₄ was then added to prepare solutions with a concentration of 5%. These solutions were mixed with SiO₂ at a mass ratio of 10:1 and stirred in a high-speed disperser at 7000 rpm for 1 min to obtain Ggg CH₃COOK dry water, Ggg KCl dry water, and Ggg KH₂PO₄ dry water. The experimental flow chart and mechanism diagram are shown in Fig. 3.

Fig. 3.

Flow diagram and mechanism diagram of dry water preparation. (a) Flow Chart for Dry Water Preparation, (b) Mechanism Diagram for Dry Water Preparation.

Dry water characterization

Scanning electron microscopy (SEM) was used to observe the microstructure of the four types of dry water. Optical microscopy was employed to examine the compression behavior of the dry water samples at 0.6 MPa. The particle size of the dry water was measured using the MS2000 laser particle size analyzer from Malvern Instruments, UK. The flowability of the dry water was assessed using the static angle method. Thermal stability tests of the dry water were conducted using a differential scanning calorimeter (DSC) from Mettler-Toledo, Switzerland.

Dry water spray fire extinguishing experiment

This experiment investigated the fire suppression performance of different potassium salt dry waters on wood stack fires. The fire extinguishing platform was equipped with a temperature collection device, a video recorder, a thermal imager, and five armored thermocouples, as shown in Fig. 4. The wood stack was made of pine, measuring 2 cm × 2 cm × 20 cm, and arranged in a 4 × 5 configuration. The first armored thermocouple is placed at the center of the wood stack, The remaining thermocouples should be placed starting 10 cm from the surface of the wood stack, with one thermocouple positioned every 10 cm from bottom to top, labeled T1, T2, T3, T4, and T5. The nozzle was directed towards the center of the wood stack, positioned 80 cm above it. The experiment indicated that this arrangement could improve the efficiency of powder utilization²⁸.

Fig. 4.

Spray fire extinguishing test apparatus.

A total of 500 g of dry water was placed in the fire extinguishing tube, and its mass was recorded as W. Nitrogen gas (N₂) was introduced until the pressure gauge read 0.6 MPa²⁶. The temperature measurement system was activated, and temperature changes were recorded. n-Heptane was ignited to start the wood stack fire, and once the n-heptane was consumed and the wood stack fire stabilized, dry water was sprayed until the flames were extinguished. The remaining mass was recorded as W1, and the actual mass discharged was calculated as W2 = W - W1. This process was repeated three times, and the average amount of fire extinguishing agent used was calculated.

Results and discussion

Characteristics of dry water features

The morphology of the four types of dry water was examined using scanning electron microscopy (SEM), as illustrated in Fig. 5. The images show that the dry water particles are uniformly distributed and exhibit a spherical or near-spherical shape, with an external “bumpy” texture resulting from the encapsulating SiO₂. Comparative analysis indicates that the dry water containing Gelrite gellan gum has a larger particle size than that without type. This can be attributed to the resin’s effect on increasing the surface tension and concentration of the solution, which makes it more challenging for the liquid to fragment into smaller droplets during high-speed dispersion²⁹. As a result, the SiO₂ encapsulation leads to larger dry water particles.

Fig. 5.

Microscopic diagram of different dry waters. (a) Pure Dry Water, (b) CH3COOK Dry Water, (c) KH2PO4 Dry Water, (d) KCl Dry Water, (e) Ggg Pure Dry Water, (f) Ggg CH3COOK Dry Wate, (g) Ggg KH2PO4 Dry Water, (h) Ggg KCl Dry Water.

To assess the pressure resistance of the fire suppression materials, Eight separate samples of 0.6 g dry water were placed in a high-temperature, high-pressure reactor at 0.6 MPa and left to stand for 30 min. The morphology of the dry water after standing was observed under an optical microscope, as shown in Fig. 6.

Fig. 6.

Morphology of different dry waters at different pressures. (a) Dry water morphology at 0.1 MPa, (b) CH3COOK Dry water morphology at 0.1 MPa, (c) KH2PO4 Dry water morphology at 0.1 MPa, (d) KCl Dry water morphology at 0.1 MPa, (e) Dry water morphology at 0.6 MPa, (f) CH3COOK Dry water morphology at 0.6 MPa, (g) KH2PO4 Dry water morphology at 0.6 MPa, (h) KCl Dry water morphology at 0.6 MPa, (i) Ggg Dry water morphology at 0.1 MPa, (g) Ggg CH3COOK Dry water morphology at 0.1 MPa, (k) Ggg KH2PO4 Dry water morphology at 0.1 MPa, (l) Ggg KCl Dry water morphology at 0.1 MPa, (m) Ggg Dry water morphology at 0.6 MPa, (n) Ggg CH3COOK Dry water morphology at 0.6 MPa, (o) Ggg KH2PO4 Dry water morphology at 0.6 MPa, (p) Ggg KCl Dry water morphology at 0.6 MPa.

The figure shows that dry water without Gelrite gellan gum was expelled as liquid at 0.6 MPa, while the dry water with Ggg compressed into smaller particles. This suggests that the Ggg enhances the pressure resistance of the dry water. The primary structure of dry water consists of flowing powder, which is susceptible to crushing, diminishing its effectiveness. Ggg, a microbial exopolysaccharide, promotes interactions among colloidal particles or polymers in the solution, creating a spatial network structure that strengthens the integrity of the dry water fire suppressant. Moreover, the resin increases the viscosity of the internal liquid core, further enhancing structural strength and pressure resistance. Conversely, the dry water without resin sustained structural damage at 0.6 MPa, adversely affecting its fire suppression performance. Figure 3 reveals gaps between SiO₂ particles, which may lead to moisture evaporation during long-term storage and transport, thereby reducing fire suppression efficiency. The spatial network created by the Ggg helps inhibit this moisture loss.

The particle size of dry water influences its spray range, Using the MS2000 laser particle size analyzer (dry method), the particle sizes of four different potassium salt dry water samples were analyzed, and the particle size distribution curves are shown in Fig. 7.

Fig. 7.

Particle size distribution of different dry waters.

The figure demonstrates that the particle size distribution of the four types of dry water displays a unimodal structure, indicating uniformity achieved through high-speed stirring and dispersion. Notably, the Ggg pure water dry water has a particle size distribution from 0 to 65 μm, with the smallest span coefficient, reflecting the most consistent particle size. In contrast, the Ggg KH₂PO₄ dry water ranges from 0 to 80 μm, exhibiting the largest span coefficient, which suggests greater variability. This unevenness may result from the KH₂PO₄ altering the solution’s surface tension and the internal network structure’s insufficient strength. Additionally, ultrasonic vibrations from the laser particle size analyzer might have caused some dry water particles to fracture, increasing the span coefficient.

The repose angle method is employed to assess powder flowability. The repose angle is the angle formed by a material that freely falls and accumulates on a flat surface without external forces. A smaller repose angle indicates better flowability. The experimental setup consists of a funnel, iron stand, and base (r = 3 cm). The angle of repose was used to measure the fluidity of dry water. The weighed 100 g of dry water was poured into the funnel which the bottom was blocked by hand. It should be noted that the entire hole at the bottom of the funnel must be filled with the dry water. The funnel hole was opened to let the dry water flow freely through the hole into the chassis until the chassis was completely filled and the dry water overflowed. The height of the cone was measured after standing for 2 min. A total of three samples of each solid-liquid ratio prepared were tested and averaged. The repose angle testing apparatus is illustrated in Fig. 8. The results, calculated using the formula ​, are presented in Table 1.

Fig. 8.

Angle of repose tester and test results.

Table 1.

Angle of repose for different dry waters.

Dry water type	Ggg pure water dry water	Ggg CH3COOK dry water	Ggg KCl dry water	Ggg KH2PO4 dry water
Angle of rest ()	31.5°	32.3°	33.5°	35.2°
Standard deviation (°)	0.15	0.21	0.25	0.34

The analysis of the charts reveals that the Ggg pure water dry water has the smallest repose angle, indicating superior flowability due to its uniform particle size distribution and low span coefficient. In contrast, Ggg KH₂PO₄ exhibits the poorest dry powder flowability. This is attributed to its larger particle size, resulting in an uneven overall particle size distribution with a high span coefficient. Powder flowability is influenced by surface friction and electrostatic forces. Powders with a large span coefficient increase surface friction, thereby impairing flowability.

Thermal stability analysis

The endothermic capacity is a vital parameter for assessing the fire suppression efficiency of dry water. In this experiment, DSC was employed to measure the endothermic properties of various dry water samples, as shown in Fig. 9. The results indicate that the endothermic peaks for all samples are below 200 °C, which is lower than the combustion temperature of wood pile fires. This suggests that these dry waters can effectively suppress wood combustion through evaporation and heat absorption.

Fig. 9.

DSC for different dry waters. (a) Thermal analysis of KCl dry water. (b) Thermal analysis of dry water. (c) Thermal analysis of KH₂PO₄ dry water. (d) Thermal analysis of CH₃COOK dry water.

The results show that as the temperature increases, the Ggg pure water dry water experiences the highest weight loss rate at 85 °C, concluding at 120 °C. The Ggg CH₃COOK dry water peaks in weight loss at 100 °C and ends at 160 °C. The addition of potassium salt delays the peak of endothermic heat evaporation, indicating improved moisture retention. Both Ggg KCl and KH₂PO₄ dry waters exhibit exothermic peaks at 300 °C, while the Ggg CH₃COOK shows an endothermic peak between 280 °C and 310 °C, which corresponds to the melting process of CH₃COOK. Additionally, an exothermic peak appears between 380 °C and 450 °C, indicating the crystallization of CH₃COOK products, followed by another exothermic peak from 450 °C to 670 °C, related to the further melting and pyrolysis of CH₃COOK products.

Suppression of class A fires with different dry waters

Dry water spray fire suppression process

Ignite the heptane to set the wood pile ablaze. Once the wood pile is fully engulfed in flames (200 s), spray different potassium salts with dry water to conduct fire extinguishing experiments. Thermal imaging was used to record the burning patterns and suppression effects of different dry waters, as shown in Fig. 10. Left is Dry chemical fire extinguishing image Right is Thermal imaging camera image of dry chemical fire extinguishing. Initially, the flame plume is formed by the simultaneous combustion of n-heptane and the woodpile. As n-heptane burns, the flame plume height increases, diminishing once the n-heptane is exhausted, leading to the independent combustion of the woodpile. The infrared thermal imaging shows that when the woodpile appears fully red, it indicates complete combustion. Once the flame height stabilizes(200s), dry water is sprayed. The images reveal that at the moment of spraying, the external flame plume is suppressed, while a faint internal flame persists, indicating that most of the dry water initially targets the outer flame, with a smaller portion penetrating to affect the interior. As spraying continues, the thermal imaging shows the woodpile transitioning to a yellow low-temperature state, indicating smoldering; further spraying results in the entire woodpile appearing blue, with internal yellow spots representing smoldering. The surface water on the wood pile was collected and divided into dry and wet samples for SEM morphological observation, as shown in Fig. 11. Figure 11a depicts the wet water, while Fig. 11b shows the dry water after the reaction. The unreacted dry water particles appear plump and are surrounded by a dense layer of SiO₂. This outer SiO₂ layer features a large specific surface area and a porous structure, enabling better adsorption of flame free radicals. In contrast, the reacted dry water particles appear shriveled and exhibit a “bumpy” surface, indicating that under high temperatures, the dry water ruptures. This causes the internal solution to vaporize and absorb heat, while the outer SiO₂ isolates oxygen, with its large specific surface area and porous structure facilitating the adsorption of flame free radicals.

Fig. 10.

Wood crib flame change diagram. (Left) Dry chemical fire extinguishing image (Right) Thermal imaging camera image of dry chemical fire extinguishing.

Fig. 11.

SEM image of dry water before and after the reaction. (a) Dry water before reaction. (b) Dry water after reaction.

Temperature-time curves of flame suppression with different dry waters

Through experiments on extinguishing dry water by spraying different substances, the optimal dry water extinguishing medium was investigated. The temperature-time curve recorded by the thermocouple is shown in Fig. 12. Figure 12a depicts the temperature curve recorded by the thermocouple for pure water dry water extinguishing; Fig. 12b depicts the temperature curve recorded by the thermocouple for KH₂PO₄ dry water extinguishing; Fig. 12c depicts the temperature curve recorded by the thermocouple for CH₃COOK dry water extinguishing; Fig. 12d depicts the temperature curve recorded by the thermocouple for KCl dry water extinguishing. Investigating the suppression effects of different dry water on Class A Fires. The temperature trends are consistent across all conditions, featuring an ignition phase, a stable combustion phase, and a decline during the release of dry water. In the ignition phase, the temperature rises sharply as n-heptane ignites. Once the n-heptane is consumed, the woodpile burns freely. During the stable combustion phase, temperature fluctuations occur due to flame turbulence. In the dry water release phase, interactions between the dry water and flames lead to a rapid temperature drop to 400 °C at the thermocouple above the woodpile. This is followed by a slower temperature decrease due to the smoldering of the woodpile. Within two minutes of spraying the four types of dry water, temperatures drop below 100 °C in all cases, confirming the effectiveness of the experiments.

Fig. 12.

Temperature-time curve of wood crib fire extinguished by different dry water. (a) Ggg pure dry water, (b) Ggg KH₂PO₄ dry water, (c) Ggg CH₃COOK dry water, (d) Ggg KCl dry water.

From the figure, it can be seen that several groups of dry water extinguishing the end of the stack surface are piled up dry water to prevent re-ignition. Due to the presence of wood stack fire negative combustion phenomenon, so the calculation of different dry water injection 20 s and dry water release 60 s thermocouple cooling rate as shown in Tables 2 and 3, the temperature drop rate of different dry water are first increased and then decreased, the internal and above of the wood stacks (T1, T2) cooling rate is larger, the wood stacks above the (T3-T5) cooling rate is smaller, indicating that the dry water can be penetrated through the flame, diffuse into the interior of the wood stacks. Thermocouple T2 is located in 10 cm above the wood stack, measured as the temperature at the heart of the wood stack flame, calculate the cooling rate of the release of dry water for 20 s, that is, to explore the inhibition effect of different dry water on the flaming fire, the cooling rate of the Ggg pure water dry water is 33.145 ℃/s, the cooling rate of the Ggg KH₂PO₄ dry water and the Ggg KCl dry water is 17.405 ℃/s and 27.49 ℃/s, the efficiency of the fire extinguishing decreased by 47.5% and 17.1%. The cooling rate of the Ggg CH₃COOK dry water was 38.605 °C/s, and the fire extinguishing efficiency increased by 16.5%. Thermocouple T1 is located inside the wood pallet fire, measured as the temperature of the wood pallet fire at the shadow ignition, calculate the cooling rate of 60 s after the release of dry water, that is, to explore the inhibition effect of different dry water on the shadow ignition of the fire, compared and found that the best inhibition effect of Ggg CH₃COOK dry water on the shadow ignition of the fire, the superior fire extinguishing efficiency of CH₃COOK dry chemical compared to pure water dry chemical primarily stems from chemical inhibition. As evident from the formula (1–2), the decomposition of CH₃COOK solution exhibits multistage endothermic reactions.

1

2

Table 2.

Cooling efficiency of different dry water for spraying 20s.

Type	Pure water dry water	KH2PO4 dry water	CH3COOK dry water	KCl dry water
△T1/△t	22.39 ℃/s	13.275 ℃/s	22.64 ℃/s	15.045 ℃/s
△T2/△t	33.145 ℃/s	17.405 ℃/s	38.605 ℃/s	27.49 ℃/s
△T3/△t	10.825 ℃/s	12.1 ℃/s	14.635 ℃/s	13.99 ℃/s
△T4/△t	8.97 ℃/s	11.49 ℃/s	9.37 ℃/s	9.06 ℃/s
△T5/△t	4.96 ℃/s	7.005 ℃/s	5.395 ℃/s	4.48 ℃/s

Table 3.

Different dry water cooling rates at 60 s after injection.

Type	Pure water dry water	KH2PO4 dry water	CH3COOK dry water	KCl dry water
△T1/△t	3.05 ℃/s	2.85 ℃/s	3.11 ℃/s	2.99 ℃/s
△T2/△t	3.16 ℃/s	2.91 ℃/s	3.25 ℃/s	3.05 ℃/s
△T3/△t	2.75 ℃/s	2.56 ℃/s	2.81 ℃/s	2.65 ℃/s
△T4/△t	2.63 ℃/s	2.31 ℃/s	2.71 ℃/s	2.40 ℃/s
△T5/△t	2.01 ℃/s	1.75 ℃/s	2.12 ℃/s	1.85 ℃/s

From Fig. 14, it can be seen that after spraying the Ggg KH₂PO₄ dry water, there is a ‘hanging wall’ foam on the outside of the stacks, that is, the Ggg KH₂PO₄ dry water is broken during the spraying process, which indicates that the effect of the Ggg KH₂PO₄ dry water is not good, because the H₂PO₄ in the KH₂PO₄ will form a hydrogen bond with the H₂O³¹, which will grab water molecules from SiO₂³², resulting in the poor effect of SiO₂ covering the KH₂PO₄ solution. SiO₂ to grab water molecules³², resulting in poor SiO₂ encapsulation of KH₂PO₄ solution, which was crushed and broken by the jet nozzle extrusion at the injection instant, destroying the unstable structure of the Ggg KH₂PO₄ dry water, the stable dry water structure protects the internal aqueous solution from evaporation during spraying. If the dry water structure is disrupted, the internal aqueous solution will evaporate during spraying. The external SiO₂ particles, being lighter in mass, will disperse into the air, reducing extinguishing efficiency.and therefore, the Ggg KH₂PO₄ had the worst fire extinguishing efficiency. Thermocouple T1 is located inside the wood stack to detect the wood stack fire cathodic combustion temperature.

Fig. 14.

Diagram of the reaction mechanism.

Table 4 shows the amount of different dry water extinguishing agents used to extinguish wood pallet fire, Ggg CH₃COOK dry water used at least 106.06 g, because of the existence of physical and chemical inhibition of CH₃COOK dry water, extinguishing efficiency is good and the amount used is small. Ggg KH₂PO₄ dry water usage was 159.67 g at most, because the structure of Ggg KH₂PO₄ dry water was broken in the process of spraying, the fire extinguishing efficiency was poor and the dry water usage was more, which was consistent with the above conclusion.

Table 4.

Amounts of different dry water sprayed.

Type	Usage/g	Average value/g
CH3COOK dry water	107.8, 105.9, 104.5	106.06
Pure water dry water	123.5, 124.6, 126.5	124.87
KCl dry water	124.6, 125.6, 124.5	124.90
KH2PO4 dry water	160.8, 158.7, 159.5	159.67

Analysis of the extinguishing mechanism of CH₃COOK dry water

The core temperature of the woodpile flame exceeds 700℃, which is higher than the decomposition temperature of CH₃COOK. The residual Ggg CH₃COOK from the woodpile and the CH₃COOK heated to 800℃ in a muffle furnace were analyzed using XRD, as shown in Fig. 13.

Fig. 13.

XRD curve of CH₃COOK dry water.

The figure clearly shows that the characteristic diffraction peak of CH₃COOK dry water at 800 °C corresponds to the standard PDF color chart, indicating that KOH is produced from the thermal decomposition of CH₃COOK dry water at 800 °C. However, the characteristic diffraction peak of KOH in the dry water on the wood pile surface is weaker, suggesting that the KOH generated from the thermal decomposition of CH₃COOK dry water reacts with flame radicals at high temperatures. The reaction mechanisms of KOH with flame radicals H, O, and HO are illustrated in formulas (3–9)³³.

3

4

5

6

7

8

9

The suppression process of dry water on Class A fires involves two main stages: extinguishing open flames and addressing smoldering fires. Open flame suppression mechanisms include cooling, smothering, isolation, and chemical suppression. When dry water is sprayed onto the heat source, N₂ enhances airflow, diluting oxygen and removing heat. Some unstable dry water ruptures at the nozzle, creating a mist that rapidly evaporates and absorbs heat. The stable spray covers the heat source with SiO₂, preventing oxygen from reacting with flame radicals. SiO₂’s porous structure effectively adsorbs these radicals.

The ruptured liquid evaporates quickly, cooling the fire source significantly. Vaporized water and inert gases from the extinguishing bottle dilute the oxygen concentration in the fire area, achieving smothering suppression. The SiO₂ layer isolates the woodpile from oxygen, while chemical suppression occurs when gaseous products react with flame radicals, capturing them and terminating combustion.

Once open flames are extinguished, smoldering may continue. If smoldering heat exceeds dissipation and reaches a certain temperature, combustion can resume. Dry water extinguishing agents are especially effective against smoldering fires due to their smaller particle size, allowing penetration into the woodpile. The internal cold gel resin adheres to smoldering materials, isolating them from air. The vaporization of the internal liquid and the thermal degradation of the agent absorb heat, while gaseous products react with flame radicals, capturing them and effectively ending combustion. This process achieves both physical cooling and chemical suppression, as illustrated in Fig. 14.

Conclusions

Four types of dry water—pure water, KH₂PO₄, KCl, and CH₃COOK—were synthesized using high-speed stirring, with modifications involving Ggg. Scanning electron microscopy showed that the dry water containing Ggg had larger particle sizes. Pressure tests indicated that this formulation exhibited superior pressure resistance, attributed to changes in liquid viscosity and surface tension, which allowed for a network structure among colloidal particles, enhancing overall structural strength.

Extinguishing experiments were conducted by spraying pure water dry powder, KH₂PO₄ dry powder, KCl dry powder, and CH₃COOK dry powder onto a wood pile fire. Results showed that all four dry powders effectively extinguished the fire, with CH₃COOK dry powder demonstrating the highest extinguishing efficiency. This is because CH₃COOK dry powder combines both physical and chemical suppression mechanisms: Internal water solution vaporization absorbs heat; water vapor produced by water vaporization, inert gas ejected from fire extinguishing cylinders achieving suffocation inhibition. Chemical suppression: KOH produced by the decomposition of CH3COOK solution undergoes chain reactions with flame radicals H, O, and OH groups, thereby disrupting the flame’s chain reaction. CH₃COOK dry water fire extinguishing agents are clean and environmentally friendly materials, rendering them materials with extensive research prospects.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

YANG Yaoyong wrote the main manuscript text, WANG Quan reviewed the entire article and suggested revisions, YAOYingkang prepared figures, XU Jianshe and FENG Dingyu draws and optimizes the charts. Manuscripts were reviewed by all authors.

Data availability

The authors state that the data supporting the findings of the study are available in the article and supplementary materials.

Declarations

Competing interests

The authors declare no competing interests.