Experimental research on the thermal decomposition of pentafluoroethane (HFC-125) extinguishing agent with n-heptane/air pool fire in confined space

Abstract

To discuss the production law of hazardous gases (e.g. hydrogen fluoride) during the interaction between a pentafluoroethane extinguishing agent and an n-heptane flame, we designed a simulation of experimental total flooding conditions that is highly similar to the actual total flooding automatic extinguishing conditions. In this study, a qualitative and quantitative analysis on the thermolysis gaseous products was performed through GC-MS and ion chromatography (IC) by studying the thermal decomposition characteristics of the interaction between a pentafluoroethane extinguishing agent and an n-heptane flame in a 1 m³ fire-smothering room under different fire sizes and interaction times. Research results demonstrated that the thermolysis gaseous products of the pentafluoroethane extinguishing agent and n-heptane flame include hydrogen fluoride (HF) and other organic gases, such as CF₃CH=CF₂ and CF₃CH₂CF₃. The HF output was proportional to the fire size and interaction time. When the interaction time was controlled within 10 s, production of hazardous gases could be effectively reduced.

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1. Introduction

In firefighting scenes, rescue workers, escapees and other living bodies may come in direct contact with the tail gases generated from the interaction between an extinguishing agent and flames.^1–4 Therefore, understanding the formation, composition and toxicity features of these gases is important to provide significant guidance to avoid similar smoke damage in further applications.^1,5,6 Existing reports on the characteristics of tail gases generated during the firing of a new fluorine-containing extinguishing agent mainly focus on trifluoromethane,^7,8 heptafluoropropane,^9,10 C6-fluoroketone,¹¹ and pentafluoroethane (HFC-125),¹² especially when the extinguishing agents come in close contact with the common flame (B-class)/air conditions.

HFC-125, mainly used as a refrigerant for a long time, has been chosen as a new extinguishing agent to replace halon in the developed countries like Europe and America because of its characteristics of being colourless, almost tasteless, non-conductivity, corrosion resistance, easy storage and having a high extinguishing efficiency.^12–14 Moreover, as zero value for ozone-depletion potential (ODP) and no residue after fire extinguishing, HFC-125 has captured wide attention with its ODP, fire extinguishing convenience and being economical, high clean class after fire extinguishing in the field of aircraft fire protection.^15,16 Its basic physical and chemical properties, extinguishing efficiency, and engineering applications has been well studied in the previous reports.^17–19 However, only few research studies on the tail gases generating from the interaction between HFC-125 and a B-class flame have been reported to date. Correspondingly, there are a few research studies that have discussed the composition of tail gas generating from the combustion of HFC-125. Daniel et al.²⁰ studied a HFC-125 extinguishing agent to inhibit a CH₄–O₂–air low-pressure premixed flame and detected a series of combustion components by tunable diode laser absorption spectroscopy (TDLAS). Andersson et al.²¹ analyzed the thermolysis products of the interaction between HFC-125 and the dimethylmethane diffusion flame by using Fourier transform infrared spectroscopy (FT-IR) and ion chromatography (IC), detecting the production of HF and fluorophosgene. Under a low material supply rate, almost all fluorine elements were converted into HF. The fluorophosgene output was positively correlated with the material supply rate, whereas the HF output was negatively correlated. Recently, Linteris et al.¹² estimated HF production by equilibrium calculations when using pentafluoroethane to inhibit the methane–air flame and conducted the extinguishing experiments using different scales of a cup-shaped burner. Other well published studies^22,23 also presented the influences of HFC 125 with bromide on the extinguishing process and gave the primary formulation of tail gases.

To summarize, in the existing reports, the researchers have detected toxicants (e.g. fluorophosgene and CO) in the tail gas after the combustion of HFC-125 besides HF as well as the relationship between the production of these toxicants and reaction conditions. However, almost all of this work is mainly based on cup-like burner experiments and basically a constant flame intensity, which is regarded as significantly different from the actual firefighting under total flooding conditions. Because the flame intensity in a cup-like burner is relatively low, the flame intensity in an actual fire scene gradually declines due to the inhibition by the extinguishing agents. In actual firefighting, the extinguishing agents may repeatedly interact with flames.

In this study, to solve this problem, we first designed a relatively sealed fire-smothering room, which ensured sufficient interaction between HFC-125 and the flame in a confined space. Since gases easily diffuse in open experimental systems, extinguishing agents in previous cup-like extinguishment experiments were carried away by the airflow after they interacted with the flame, which could not ensure a sufficient interaction time and effect. This was similar to the extinguishing conditions by gaseous extinguishing agents under the total flooding conditions and closer to the actual firefighting situations. Moreover, we also carefully designed the experimental conditions close to those in the actual situations. For offering a high flame intensity, we made an oil pool (n-heptane) on spontaneous combustion in a confined room under different working conditions without using any extinguishing agent. Even for a given HFC-125 concentration, the flame intensity on the oil pool weakened and the specific fuel consumption slowed down together with a gradual decrease in oxygen in the fire-smothering room. However, previous experiments involved igniting the fuels, and then spraying the extinguishing agent, making it difficult to maintain the appropriate concentration of the fire extinguishing agent. A high concentration of HFC-125 will cause strong flame inhibition, resulting in an inadequate interaction time and low concentration leading to a strong flame with insufficient interaction and weak signals. Therefore, to study the toxicity features of these gases, the HFC-125 concentration in the fire-smothering room was set to 50% of the extinguishment concentration to ensure that the interaction time between HFC-125 and n-heptane flames was adequately maintained to guarantee the full interaction between the extinguishing agent and the flame.

The objective of this study was to investigate the effects of the actual interaction between the HFC-125 and the flame under different fire sizes and interaction times. Moreover, we tried to analyze the possible tail gases (e.g. HF) by using ion chromatography and GC-MS. It could provide an effective benchmarking study on the thermolysis of gases in the thermal decomposition of HFC-125 and an n-heptane/air flame. Also, it might be useful for the real application of the extinguishing agent and for reducing the risk of unintended accidental losses in the firefighting scenes.

2. Experimental section

2.1 Materials and chemicals

Pentafluoroethane (C₂F₅H, purity > 99.7%) was obtained from SINOCHEM LAMTIAN Inc. The combustible fuel was n-heptane. The oil pool was designed by our own laboratory. The flame model of the oil pool was of three sizes: (1) 5.0 cm × 5.0 cm × 8.0 cm, (2) 7.5 cm × 7.5 cm × 8.0 cm and (3) 10.0 cm × 10.0 cm × 8.0 cm. The loaded 3.0 mm thick n-heptane liquid level was 5.0 mm below the oil pool opening and the oil pool bottom was paved with clean water. Glass rotameter (LZB-6) was purchased from Shanghai Tianchuan instrument and meter plant. A soap film flowmeter (LZM-1) was purchased from Shanghai Hongyu Institute of environmental protection application.

2.2 Experimental preparation

2.2.1 Experimental apparatus. The experimental system (Fig. 1) mainly consisted of three parts, including (1) the device for HFC-125, a gas cylinder containing the extinguishing agent that can be tuned by a matching flowmeter, (2) a sealed fire-smothering room, consisting of an n-heptane room (1.0 × 1.0 × 1.0 m³) that was made of a 1.3 mm thick stainless steel plate and an ignition device. The flame in the oil pool could be extinguished by pulling the outside push–pull rod to cover the oil pool loaded with n-heptane and was 45 cm off the ground and below a metal cover. The third part (3) was the tail gas collector, which was composed of an organic gas collector and HF collector. The tail gas was collected by the corrosion-resistant air pump with a smoke filter at the front end of the pump, which can keep the smoke particles out of the gas collection paths and ensure a stable collection of the gaseous products. The collection speed of the thermolysis gaseous products was adjusted by the throttle needle valve and the three-way valve was used to control the switch between the organic gas collection paths and the HF collection channel. The organic gaseous products were washed with water to eliminate HF, which was then dried and stored in a gas collection bag for GC-MS analysis. The HF gas was absorbed for 30 min by three series-wound aspirator bottles with 300 mL deionized water, which was used for ion chromatography to test the HF content.

Fig. 1 Schematic of the experimental apparatus.

2.2.2 Experimental steps. The experimental steps are as follows: (1) open the door of the fire-smothering room for full ventilation and prepare oil pools with n-heptane and put on the covers. Close the door of the fire-smothering room and ventilation openings at the two sides to tightly close the fire-smothering room, (2) pump designed dosage of HFC-125 into the fire-smothering room and open the fan for 10 min. Next, pull the push–pull rod to open the oil pool and ignite n-heptane in the oil pool. When the combustion time reaches a certain time (10 s, 15 s, 20 s and 30 s), quickly push the push–pull rod to extinguish the fire in the oil pool. Open the fan quickly for 10 min and then close it for gas collection, (3) adjust the needle valve to control the gas flow at 300 L h⁻¹. Then, rotate the three-way valve to the organic gas collection channel. The organic gas products are stored into the gas collection bag. Next, the three-way valve is rotated to HF collection channel. HF gas is absorbed for 30 min by three series-wound aspirator bottles with 300 mL of deionized water. Cover the bottles and carry them back to the laboratory for further analysis. Then, (4) open the fire-smothering room and ventilation openings at the two sides. Blow the gasous product in the fire-smothering room by the fan for about 30 min and end the experiment. Repeat the experiment under the same experimental conditions for more than three times, and then take an average of the test results to be included in the final statistics.

2.3 Experimental characterization

2.3.1 Ion chromatography (IC). IC was performed using an ion chromatograph (ICS-90, DIONEX CHINA LIMITED, China), IonPac AS19 (4 × 250 mm) separation column, IonPac AG19 (4 × 50 mm) protection column, 20 mM KOH leacheate, 1.0 mL min⁻¹ flow rate and 10 μL sample size.

2.3.2 Gas chromatography-mass spectrum (GC-MS). A GC-MS instrument was used for the gas chromatography/mass spectrometry analyses (Agilent 5975, Agilent Technologies Inc. United States). A GS-Gas Pro capillary-column (30 m × 0.32 mm) was used as the chromatographic column and the initial column chamber temperature was set at 60 °C. Subsequently, the temperature was increased to 240 °C at a rate of 10 °C min⁻¹. Helium (He) was used as the carrier gas and was loaded at 1 mL min⁻¹. The split ratio and sample size were 10 : 1 and 100 μL, respectively. The MS conditions include EI ionization way, 70 eV electron multiplier pressure, 230 °C ion source temperature and a m/z 10–650 scan range.

3. Results and discussion

3.1 Oil pool fire flame test

For a typical class B flame, various types and theoretical models of n-heptane flames have been studied for more than thirty years.^24–26 Although some studies exist in the literature²⁷ that have investigated the relationship between the structure of the n-heptane flames and certain extinguishing agents, it is still necessary for us (1) to precisely determine the rate of heat released from the pool-fire flames and (2) eliminate the self-inhibition effect caused by the decrease in the oxygen concentration in a confined space with different oil pool sizes (5, 7.5, 10 cm) by weighing the mass of the given n-heptane. Fig. 2 gives the relationships between the burning time and the oil mass (gram) of n-heptane in an oil pool with different pool sizes (Fig. 2a). The results show that the oil mass of n-heptane gradually decreased with an increase in the burning time and the burning time was longer than 200 s, which indicates that the free flame of the pool fire cannot be inhibited by a decrease in the oxygen concertation at a certain period of time, and the durations of burning are as short as 273 s (Fig. 2b, 5 cm), 267 s (Fig. 2c, 7.5 cm) and 223 s (Fig. 2d, 10 cm). Note that as the concentration of oxygen decreases in a confined space, the burning time decreases to 249.5 s, 213.6 s and 196.9 s with an increase in the pool size. And all three oil pan do not be lighted again.

Fig. 2 Burning time of the oil pool fire with different pool sizes (5, 7.5, and 10 cm) in a confined space.

After customization of the rate of heat released from the flames and calibration of the HFC-125 concentration, the interaction time is the key step for studying the interaction between HFC-125 and the n-heptane/air pool fire in the confined fire-smothering room. The rate of the heat released can obtained by the following formula,

Q = χ × m × ΔH (1)

where Q is the rate of heat release (kW), χ is the combustion efficiency, m is the mass burning rate of combustion (g s⁻¹), which can calculated from Fig. 2b–d, and ΔH is the enthalpy of combustion (4806.6 kJ mol⁻¹ for n-heptane). The Q values obtained for the three different pool sizes (5, 7.5, and 10 cm) are 0.90 kW, 2.49 kW, and 4.79 kW, respectively.

3.2 Concentration calibration of HFC-125

For researching the flame interaction of the HFC-125 extinguishing agent of n-heptane/air pool fire in a confined space, in addition to the rate of heat released, we should also determine the concentration of HFC-125. Table 1 shows the details of the actual value of HFC-125 repeated three times for the precise determinations. Furthermore, we also fit the curve of the actual value of HFC-125 to adjust the amount of the extinguishing agent as a linear fit mode by the Origin 8.0 software according to the following equation:

y = 0.6148x + 32.2 (2)

where x is the measurement time (s) and y is the actual value (L) of HFC-125.

Table 1 The comparison of set value and actual value of HFC-125

Set value (L h^−1)	Cv^a (mL)	Measuring time^b (s)			Average value (s)	Actual value (L h^−1)
		1	2	3
a Cv (calibration volume), is set according to a set value of HFC-125 concentration.b Measuring time can be determined as a single soap film flowing through a 1000 mL volume in the soap membrane flowmeter via a stopwatch.
100	1000	38.77	38.80	38.80	38.79	92.80
200	1000	23.12	23.13	23.12	23.12	155.71
300	1000	16.49	16.50	16.51	16.50	218.18
400	1000	13.31	13.30	13.30	13.30	270.68

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In principle, we can obtain the amount of HFC-125 at any time. For maintaining an adequate interaction time to guarantee a full interaction between HFC-125 and the flame, the HFC-125 concentration in the fire-smothering room was set to 50% of the extinguishment concentration to ensure an adequate interaction time between HFC-125 and the n-heptane/air flames. The extinguishment concentration of HFC-125 was 9.3% according to ISO14520-8,²⁸ and thus the 50% value of its extinguishment concentration was 4.65%. Therefore, for a given volume of the fire-smothering room (1000 L here), it required 46.5 L (or 248.2 g) of HFC-125 under standard conditions. In this experiment, 50% (corresponds to n-heptane fuel) of HFC-125 should be injected into the fire-smothering room first, and then the n-heptane fuel was ignited to ensure an adequate interaction time.

3.3 Determining the interaction time of HFC-125

When the HFC-125 concentration was 50% of its extinguishment concentration, the flame intensity on the oil pool weakened and the specific fuel consumption slowed down, which would surely prolong the spontaneous firing. This result agrees well with that of an another reported study.²⁸ The flame intensity gradually weakened since oxygen in the fire-smothering room was gradually consumed. Therefore, the smoke that was generated in the first 30 s was collected for tail gas analysis. Specifically, the interaction time between HFC-125 and the n-heptane flames was after the inhibition of the fire by HFC-125 controlled within 30 s. It was speculated that during the interaction of HFC-125 and the n-heptane/air flame, the power of the flame at early times slightly changed. This means that the interaction time between HFC-125 and the n-heptane flames was controlled within 30 s.

3.4 HF content test

HF is a highly toxic substance and it has strong stimulus and corrosion effects on the respiratory mucous membranes and skin.²⁹ Inhalation of high concentrations of HF will cause pneumonia, tracheitis, toxic effects to the whole body and even fluorosis of bone.³⁰ Therefore, determining the HF content in the thermolysis gaseous products after the interaction between HFC-125 and an n-heptane flame is conducive to determine the toxicity of the products. A pH paper test showed that the water solution of thermolysis gaseous products is strongly acidic, indicating the possibility of HF generation. It can also be inferred from the related studies that the gaseous products from the thermolysis of the reaction between HFC-125 and the flame may include HF.³¹ Herein, the HF content was measured by a three-way valve. Before the test, 1000 mg L⁻¹ of fluorine ion mother liquor was prepared using NaF, and then it was diluted to 5, 10, 15, 20 and 25 mg L⁻¹ of fluorine ion standard liquids using aspirator bottles filled with 300 mL deionized water to absorb the thermolysis gases for 30 min.

3.4.1 Quantitative analysis of HF under different fire sizes. Further analysis of the thermolysis gaseous products, generated as a result of the interaction between HFC-125 and an n-heptane/air flame, was performed by an IC-based quantitative analysis of the water solution of HF gaseous products desorbed by the deionized water (three samples) under different sizes of the oil poor fires. For a better comparison, we calculated the HF mass in a 1 m³ fire-smothering room by controlling the flow rate during gas collection (Table 2 and Fig. 3) within 30 s, which is the interaction time of HFC-125 abovementioned in Section 3.3.

Table 2 Details of the interaction time of HF contents (time = 30 s)

Oil pool size (cm)	Soap film volume (L)	Actual value (L min^−1)	Time (min)	Gas volume (L)	Sample 1 (mg L^−1)	Sample 2 (mg L^−1)	Sample 3 (mg L^−1)	Total (mg L^−1)	Sum of HF (mg)	HF of 1 m^3 (mg)
5 × 5	0.8	3.78	15	56.69	22.22	1.09	0	23.31	6.99	123.37
7.5 × 7.5	1	3.85	15	57.69	20.71	5.57	0	26.28	7.88	136.67
10 × 10	1	5.51	10	55.10	65.06	12.98	0	78.04	23.41	424.89

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Fig. 3 Influence of the oil pool fire size on the HF content (interaction time = 30 s).

The relationship between the oil poor fire size and HF content in the thermolysis gaseous products when the interaction time is fixed at 30 s is shown in Fig. 3. It is clear from Fig. 3 that for a given interaction time, HF is also detected in the flame interaction of HFC-125 and the n-heptane/air pool fire in a confined space. The HF content increases as the pool size increases. The HF content reaches to 123.3 mg m⁻³, when the fire size is 0.90 kW (5 × 5 cm). HF production slightly increased within 2.5 kW (7.5 × 7.5 cm) and increased to the highest of 424.9 mg m⁻³ as the fire size increased to 4.79 kW (10 × 10 cm). In this situation, due to the existing 50% concentration of HFC-125, the strong flame intensity is regarded as a full interaction with the flame until we pushed the push–pull rod off. This means that the experimental apparatus designed in this study can be considered to be the real situation in firefighting scenes by overcoming the weak fire flame intensity and gradually decreasing the flame intensity. Of course, in the real situation, HF can be diffused during this time period. As a result, we can determine the highest content of HF, which is a key for application and formulation of Material Safety Data Sheets (MSDS).

3.4.2 Quantitative analysis of HF under different interaction times. The second part is the GS-MS-based qualitative analysis of thermolysis gaseous products that have been washed with water to eliminate HF under a fire size 4.79 kW (10 × 10 cm) at different interaction times (Fig. 4). The relationship between the interaction time and the HF content is shown in Fig. 4 and Table 3. The interaction time can be significantly influenced by the HF content in thermolysis gaseous products. As the interaction continues, HF content slowly increases and then quickly increases. Before the first 20 s, especially in the first 10 s, HF content slowly increases as the interaction continues. However, when the interaction time exceeds 20 s, HF content quickly increases from 115.5 mg m⁻³ to the peak, reaching 424.9 mg m⁻³. Water produced from n-heptane fuel combustion would condense on the inner wall of the fire-smothering room, which would dissolve some HF when the sampling time is long. Therefore, the tested HF content may be lower than the actual content when the sampling time is long. Exposure to 400–430 mg m⁻³ of HF will cause acute-poisoning deaths. People can endure 100 mg m⁻³ of HF for one minute.³² When the interaction time is 10 s, HF content is 54.4 mg m⁻³, which is lower than 100 mg m⁻³. However, it exceeds 100 mg m⁻³ if the interaction continues. It reaches the peak value (424.9 mg m⁻³) when the interaction time increases to 30 s, falling within the concentration range of acute poisoning deaths. Therefore, the interaction time between HFC-125 and the flame shall be strictly controlled within 10 s to reduce the HF content and ensure safe usage of HFC-125.

Fig. 4 Influence of the interaction time on the HF content (fire size = 4.79 kW).

Table 3 Details of the interaction time of HF contents (time = 30 s)

Time (s)	Flowing time (s)	Actual value (L min^−1)	Measuring time (min)	Gas volume (L)	Sample 1 (mg L^−1)	Sample 2 (mg L^−1)	Sample 3 (mg L^−1)	Total (mg L^−1)	Sum of HF (mg)	HF of 1 m^3 (mg)
10	12.9	4.65	15	70.56	11.38	1.42	0	12.80	3.84	54.43
15	12.7	4.72	15	70.87	23.42	2.24	0	25.68	7.70	108.65
20	16.2	3.70	15	55.56	20.51	0.88	0	21.39	6.42	115.48
30	9.8	5.51	10	55.10	65.06	12.98	0	78.04	23.41	424.89

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3.5 Analysis of other organic ingredients of tail gas

A qualitative analysis of the tail gas composition was implemented and the organic gases produced after the interaction between HFC-125 and the flame under these conditions were collected for the GC-MS analysis (Fig. 5). For an accurate analysis, the parameters of the typical interaction were chosen as the highest flame intensity (4.79 kW) under the longest interaction time (30 s) and as abovementioned in Section 3.4.2, the maximum content. Contrary to the previously reported results, besides HF and the n-heptane fuel (Fig. 5a), the tail gas also includes some organic gases, such as CF₃CH=CF₂ (Fig. 5b) and CF₃CH₂CF₃ (Fig. 5c), as shown in Table 4.

Fig. 5 GC-MS analysis results of the organic ingredients of the tail gas generated due to the interaction between HFC-125 and the n-heptane flame: (a) C₇H₁₆, (b) CF₃CHCF₂ and (c) CF₃CH₂CF₃.

Table 4 MS analysis results of gaseous products

Time (min)	Mass-to-charge ratio (m/z)	Products
2.974	CF2CHCF2+(113), CFCCF2+(93), CF3CH+(82), CF3+(69), CF2CH+(63), CF+(31)	CF3CH=CF2
4.886	CF2CH2CF3+(133), CFCHCF3+(113), CF3CH+(82), CF3+(69), CF+(31)	CF3CH2CF3

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Both CF₃CH=CF₂ and CF₃CH₂CF₃ are irritating gases.³³ CF₃CH=CF₂ irritates the eyes, respiratory system and skin, whereas short-time exposure to CF₃CH₂CF₃ will cause headache, debilitation, dizziness, nausea, vomiting, dyspnea and pricking, and even cardiac arrhythmia, hyperspermia, coma and asphyxia.³⁴ Although their contents are far lower than those of the inorganic gaseous products of HF, they also can cause certain damage to the human body. It is speculated that pentafluoropropene and hexafluoropropane are produced by flame interference in relatively closed total flooding conditions, repeated reaction of the extinguishing agent and flame, as well as the chemical reaction of the extinguishing agent with the intermediate products and combustion products in the flame region.

These results also indicate that the possible reaction of HF formulation is as follows

CF₃CH₂CF₃ → CF₃CH=CF₂ + HF↑

This possible pathway is also in agreement with that reported in a former study.³⁵ However, compared with the thermal decomposition reaction pathway of FEC-125,³¹ the interaction of HFC-125 and the flame is more complex and needs to be studied in the future.

4. Conclusions

In summary, we studied the thermolysis decomposition characteristics of the interaction between HFC-125 and n-heptane in a confined space under different fire sizes (0.90 kW, 2.49 kW and 4.79 kW) and the interaction times (10 s, 15 s, 20 s and 30 s) using an ideal oil pool fire. A qualitative and quantitative analysis on the thermolysis gaseous products by combining an IC and GC-MS analytical method was performed. It was concluded that:

(1) HF production from the interaction between HFC-125 and n-heptane/air flames was influenced by the fire size. With an increase in fire size, the HF content slowly increased, and then significantly accelerated. At the minimum fire size (0.90 kW), the interaction between HFC-125 and the n-heptane flames was fierce and the HF content was very high, reaching a value of 123.3 mg m⁻³.

(2) The interaction time can also be influenced by HF production from the interaction between HFC-125 and the n-heptane flames. As the interaction time increases, HF production slowly increases in the first 10 s of combustion, and then significantly accelerates. After 20 s of combustion, the HF content quickly increases from 115.5 mg m⁻³ to 424.9 mg m⁻³, which is the maximum content.

(3) Given a 4.79 kW fire size and 30 s interaction time, HF production reached its peak (424.9 mg m⁻³). The organic gaseous products from the interaction between HFC-125 and the n-heptane flames include CF₃CH=CF₂ and CF₃CH₂CF₃, which are irritants and may cause certain damage to the person at the site of the fire.

Smoke from the combustion of HFC-125 contains toxic and harmful substances (e.g. HF). Production of these toxic and harmful substances is positively related to the fire size and interaction time. Since it is difficult to control the fire size in actual firefighting, the interaction time between HFC-125 and the flame shall be strictly controlled within 10 s to inhibit the production of HF and other harmful gases. This could effectively control the potential risks related with the use of HFC-125.

Acknowledgements

The work was supported by the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 13KJD620001), the project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and the collaborative Innovation Centre of Social Safety Science and Technology.

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