Analysis on the Substitution of Perfluoro-Octane Sulphonates in Foam-Based Extinguishing Agents in China

Abstract

In this comprehensive study, we examined an extensive array of 1396 production certifications, which encompassed 136 foam-based extinguishing agent manufacturers in China. Our investigation focused on the production, application, and composition of various foam-based extinguishing agents utilized in recent years. Notably, a significant proportion of the domestic market, i.e., 64.1% of the total, consisted of fluorocarbon surfactants devoid of perfluorooctane sulfonates (PFOS). These manufacturers predominantly operated in the economically thriving eastern coastal region of China. Our research delved into the correlation between diverse parameters of foam-based extinguishing agents and their performance indices. It was observed that foam-based extinguishing agents with resistance to seawater exhibited superior performance to conventional agents in cold environments. Additionally, we synthesized the findings of PFOS-free products, which serve as promising alternatives to foam-based extinguishing agents in China. This study furnishes statistical evidence and establishes a theoretical foundation to facilitate future control measures for PFOS foam-based extinguishing agents, while promoting nationwide research and development of alternative solutions.

1. Introduction

As the major component of fluorosurfactants (FS) used in the manufacturing of aqueous film-forming foam (AFFF), perfluoro-octane sulfonates (PFOS) used to be one of the most common and best-performing foam-based extinguishing agents [1]. PFOS consists of amphiphilic molecules, is less volatile at ordinary temperature, and has strong persistence, which makes it suitable for high temperatures, as well as strong acidic and alkaline environments [2]. Due to the long carbon chain-based structure of perfluoride, PFOS has the characteristics of both grease and water resistance. The aqueous solution of AFFF can quickly spread on the oil film, forming a water film and foam layers, which isolate the air and heat. AFFF improves the anti-combustion ability of fire extinguishing foam and achieves rapid and effective fire control while having a long storage time [3,4]. AFFF has long dominated the global market for dealing with fires, especially Class B fires [5], which refer to liquid or meltable solid material fires, such as fires involving methanol, ethanol, kerosene, diesel, crude oil, asphalt, paraffin, plastic, etc. [6]. Due to its excellent performance, it is difficult to replace AFFF in a short time period. The production and application of AFFF may cause higher concentrations of PFOS in air, soil, surface water, and even drinking water [7], as it is the main source of PFOS contamination in the environment [8,9,10].

PFOS is a typical Persistent Organic Pollutant (POPs)-based method with priority control, as it is highly toxic and has the ability to bioaccumulate and transfer over a long distance. A study conducted on blood tests and toxicokinetic factors by Post et al. revealed that PFOS levels in drinking water were far below 100 ng/L, while PFOS levels in the serum of adults increased, on average, by more than 100 times the drinking water concentration [11]. Humans exposed to PFOS are at higher risk of cancer, reduced immune function, etc. [12,13,14]; therefore, PFOS is listed as a reference indicator for drinking water quality standards [15,16,17,18]. Martin et al. detected fluorinated contaminants in the Diporeia hoyi of Lake Ontario, which ranged from <0.5 to 90 ng/g. They studied the PFOS concentrations found in organisms found in Lake Ontario, which revealed that PFOS concentrations are positively correlated with nutrient levels. This finding shows that PFOS has a significant biomagnifying effect on the main pelagic food web [17].

PFOS was added to the list of POPs in Annex B of the Stockholm Convention in 2009, which was approved by China in 2014. The production, distribution, application, import, and export of PFOS has been banned globally since 2019, except for use for some acceptable purposes, e.g., metal plating in closed-loop systems (hard metal plating) and extinguishing Class B fires in installed systems [19]. Since the implementation of the GEF project called “Priority industry cutting and elimination project of PFOS in China” in 2016, the Chinese Government has taken serious action against the industries involved in PFOS production, and it stopped PFOS production by the end of 2021. PFOS was added to the List of New Pollutants for Priority Control (2023 Final Version) in December 2022 by the Ministry of Ecological Environment, which clarified that the exemption period for the use of PFOS for the production of fire-extinguishing foam agents will end no later than 31 December 2023.

Furthermore, as the production and use of foam-based extinguishing agents in China is not yet fully understood, lack of knowledge will be an obstacle to our compliance with the POPs Convention. Therefore, in this study, we investigated the total certifications and information of products used by domestic enterprises in foam-based fire-extinguishing agents. Statistical classification and analytical predictions related to the application of PFOS contained agents are conducted. The main purpose of this study was to understand the production, use, and substitution process of PFOS in the Chinese firefighting industry, further promoting the production and promotion of safe, environmentally friendly, and sustainable substitutes of PFOS, as well as to provide support for the management of new pollutants in China.

2. Materials and Methods

A total of 136 domestic foam-based extinguishing agent manufacturers were investigated in China in September 2022. The product types and certification information of all the foam manufacturers were surveyed systematically. Manufacturers information regarding the product category, certificate, model, foam-based extinguishing agent performance test report, and surfactant manufacturer were categorized and counted according to the list of certifications belonging to foam-based extinguishing agent and surfactant manufacturers. There were 1396 types of foam-based extinguishing agents with fire product certification. Among them, 952 kinds of surfactants were classified in the certification. Specifically, 815 types of certificates were found that were related to surfactants users and manufacturers.

ArcMap 10.8 was used for the presentation of the spatial distribution characteristics and the number of manufacturers using PFOS in fluorocarbon surfactants. Correlation analysis was performed to explore the relationship between different categories of foam-based extinguishing agents. The manufacturers’ product types and certification information were classified and counted, and the future developments and time trends were analyzed and predicted regarding foam-based fire-extinguishing agents containing PFOS.

3. Results and Discussion

3.1. Foam-Based Extinguishing Agent Certification in the Last Four Years in China

The foam-based extinguishing agent certifications reflect the typed of products produced by each enterprise, which, in turn, reflects the production and use of PFOS in China. The certifications of foam-based fire-extinguishing agents were investigated between 2019 and 2022 in China (Figure 1). The total number of certifications for foam-based extinguishing agents continues to decline, falling from 613 in 2019 to 184 in 2022. A clear difference was found in the number of product certifications between 2019 and 2020, which dropped sharply from 613 to 282. The adoption of amendments to the PFOS Convention by the Ninth Meeting of the Parties in 2019, which further restricted and banned the production and use of PFOS, resulted in a further reduction in the number of PFOS-containing foam-based fire-extinguishing agent certifications from 155 to 64 (a reduction of almost 59%). As can be seen in the pie charts in Figure 1, even though the number of certified foam-based extinguishing agent products was declining, domestically produced foam-based extinguishing agents containing PFOS still occupy a large proportion of the market, i.e., 25%, 35%, 24%, and 35%, respectively, for the years 2019 to 2022. Since 2019, the proportion of surfactants with PFOS-free ingredients in foam-based extinguishing agents has also gradually increased, rising from 32% in 2019 to 49% in 2020, before rising to 46% in 2021 and, finally, 49% in 2022. This trend shows that China is continuing to replace the foam-based extinguishing agents containing PFOS class. Domestic enterprises have also shifted focus onto novel environment friendly and efficient alternatives to foam-based fire-extinguishing agents.

3.2. Foam-Based Extinguishing Agent Manufacturers

Based on the data published by China Fire Product Information Network, we investigated the status of foam-based extinguishing agent enterprises in China. There were 136 enterprises producing foam-based extinguishing agents, with a total of 1396 certificates, in September 2022. Among all enterprises, the top 10% of the certified types of foam-based extinguishing agents in China are shown in Figure 2. These enterprises produce 21–60 types of foam-based extinguishing agents, with five enterprises producing more than 30 types. SuoL. Fire Technology Co. was the largest firm, producing 60 types, while the second largest enterprise was LangC. Fire Technology Co., which produced 45 types. The types of foam-based extinguishing agents produced by these two enterprises accounted for 24.6% of the top 10%. These leading enterprises also represented whole industries nationwide. Finding more detailed information about these enterprises might be useful to help us to further understand the production and use of foam-based extinguishing agents, which will become priority means of fire control in the future.

3.3. The Types of Surfactants Used in Foam-Based Extinguishing Agents

Surfactants are a key component involved in determining whether or not a foam-based fire-extinguishing agent contains PFOS. Based on the surfactant, foam-based extinguishing agents can be categorized into fluorinated and non-fluorinated agents. Due to environmental protection concerns, non-fluorinated foam-based fire-extinguishing agents have been developed in recent years. However, fluorinated foam-based extinguishing agents still occupy a large share of the market due to their excellent fire-extinguishing performance. Its composition will affect the characteristics of water-based film and determine the performance of fire-extinguishing foam. In the process of extinguishing fires using a foam-based extinguishing agent, the water-based film is located between the fuel and foam to cool the fuel surface. It acts as a vapor barrier to support the diffusion of foam onto fuel and enhance the self-recovery of the affected foam layer.

The main types of fluorinated foam-based extinguishing agents are surfactants, and some domestic manufacturers that use them in China are shown in

Table 1. Main types of fluorocarbon foam-based extinguishing agents and some domestic manufacturers.

Main Types of Fluorinated Foam-Based Extinguishing Agent	Surfactant Brand	Foam-Based Extinguishing Agent Manufacturer	Manufacturer Location
Aqueous film-forming foam (AFFF)	SF-852	SuoL. Fire Technology Co.	Jiangsu, China
	YF-138, F1212, F1440	LangC. Fire Technology Co.	Henan, China
	VF-570, VF-9129	HongT. Fire Materials Co.	Guangdong, China
	1157	AnG. Fire Technology Co.	Fujian, China
	F1470	HaiS. Fire Equipment Co.	Hebei, China
Alcohol-resistant aqueous film-forming foam (AR-AFFF)	SF-852	SuoL. Fire Technology Co.	Jiangsu, China
	YF-138, F1212	LangC. Fire Technology Co.	Henan, China
	SF-852, SF-182	HongT. Fire Materials Co.	Guangdong, China
	JF1127	XiangH. Fire Agent Co.	Henan, China
Film-forming fluoroprotein foam (FFFP)	F1440	ShiY. Fire Equipment Co.	Hubei, China
Alcohol-resistant film-forming fluoroprotein foam (AR-FFFP)	-	SuoL. Fire Technology Co.	Jiangsu, China
Fluoroprotein foam (FP)	YM-316	YunL. Fire Equipment Co.	Guangdong, China
	KF402A, C810	XiaoD. Fire Technology Co.	Jiangsu, China
	F1440	TingA. Fire-fighting Materials Co.	Jiangsu, China
Alcohol-resistant fluoroprotein foam (AR-FP)	YF-138	LangC. Fire Technology Co.	Henan, China
	VF-6116, VF-9129	XinX. Fire Safety Equipment Co.	Henan, China
	1157	SuoL. Fire Technology Co.	Jiangsu, China

. The common types of surfactants currently available are SF-852, YF-138, F1212, etc., for AFFF; YF-138, F1212, etc., for AR-AFFF; F1440 for FFFP; YM-316, KF402A, etc., for FP; and YF-138, KF402A, etc., for AR-FP. Among them, YF-138, VF-570, JF1127, and some other surfactants contain PFOS components; the certification of these foam-based extinguishing agents is still in effect, though with the implementation of domestic control policies, these kinds of foam-based extinguishing agents will be gradually replaced. At the same time, new fluorocarbon surfactants without PFOS are being developed, such as SF-852, VF-9129, F1470, etc. However, it is necessary to investigate whether the new fluorocarbon surfactants are environmentally friendly or contain any potential perfluorocarbon and sulfonate precursors [13].

3.4. Surfactant Manufacturers

To understand the current production structure of companies, data regarding the types of surfactants are presented in Figure 3. According to the statistical data, currently, surfactant types without PFOS produced by KeM. Chemical Co. are widely used in China. Moreover, DuPont USA Ltd.-, HuiP. Chemical Co.-, and SuoL. Fire Technology Co.-produced fluorocarbon surfactants do not contain PFOS substances. However, YaF. Chemical Co., YaK. Technology Co. and ChengS Technology Co. are currently producing surfactants that contain almost all PFOS, and these companies need to be effectively monitored and controlled. Among the different types of surfactants produced by JingCTC. Technology Development Co., the types containing PFOS account for 64% of the total, while the rest are based on new non-fluorocarbon compounds used as raw materials in surfactant production. In recent years, all enterprises will have to pay more attention to the environmental effects of new foam-based extinguishing agent products that are put into use and production. It is expected that the safe and environmentally friendly replacement of PFOS in foam-based extinguishing agent products will be fully achieved in the future.

There are 983 kinds of certification possessed by all surfactant manufacturers. Among them, 630 surfactant components do not contain PFOS substances, with these certifications accounting for 64.1% of the total proportion. Currently, the domestic market is paying close attention to the development and use of new environment-friendly surfactants, and the types of surfactants without PFOS substances have the greatest market share. The environmentally friendly non-fluorocarbon surfactants, which lack PFOS components, account for 9.87% of the market. Although PFOS-free fluorinated surfactants are becoming more common in the market, the production and application of the PFOS containing surfactants is still at large scale, which means that they remain the main products used in China [20].

3.5. Distribution of Foam-Based Extinguishing Agent Manufacturers

Identifying the distribution of manufacturers’ locations can be used as a primary source and potential signature for PFOS in relevant samples. According to the data presented in Figure 4, enterprises producing foam-based extinguishing agents are mainly distributed in the middle-eastern and southeastern regions of China. This increased distribution of the enterprises might be due to rapid economic development, the large demand for foreign import and exports, and the dense distribution of population and enterprises in the coastal areas. Moreover, the coastal areas are probably influenced by the large number of urban buildings and the high probability of fire in such buildings. Starting these enterprises in coastal areas could also reduce the costs of transporting products to other regions [21]. The number of foam-based extinguishing agent manufacturing enterprises in the central region ranges from one to four, while Sichuan Province has seven enterprises, a higher number than other provinces. It is worth noting that the western and south-western regions of China, as well as Jilin Province, have no foam-based extinguishing agent manufacturers, and they mostly import products from other provinces, which need to be properly stored and sealed to prevent the leakage during transportation. Products containing PFOS are widely used and disposed of in other industries, including the fire protection industry, as well as carpet, leather, textile industries; the production of these products is mainly located in coastal areas. Therefore, via comparison with other regions of China, the PFOS level in the eastern coastal areas is shown to have increased. PFOS concentration in the Pearl River (Guangdong) and Taihu Lake (Jiangsu) has exceeded the water quality standards. Researchers are keenly observing the environmental health risks posed by PFOS [22].

3.6. Relationship between Foam-Based Extinguishing Agent Manufacturers and Certified Product Types

The number of foam-based extinguishing agent manufacturers and certified product types in different provinces of China were analyzed (Figure 5); these data included 21 provinces, 124 manufacturers, and 1320 foam-based extinguishing agent certifications. Jiangsu, Henan, and Shandong provinces are the largest of foam-based extinguishing agent-producing provinces, with the number of enterprises ranked in the top three in their industry being 16, 16, and 22 for each province, while each province has 286, 223, and 170 foam-based extinguishing agent certifications, respectively. These three provinces accounted for more than half of the country’s certifications, accounting for 53.9% in total, while Jiangsu and Henan province together accounted for 40.1%. The number of certifications possessed by foam-based extinguishing agent manufacturers is greater than 100 in four provinces: Jiangsu, Henan, Shandong, and Zhejiang. As can be seen in Figure 5, the cumulative number of certifications in 8 provinces and 93 enterprises reached 80% in China. A total of 11 provinces and 105 enterprises are included, and the cumulative number of certifications covers 90% of the country, which shows that the main areas of national production of foam-based extinguishing agents are found in the first 11 provinces shown (Figure 5).

Based on the certification type, enterprises in these areas will produce a part of an AFFF-based extinguishing agent containing PFOS. The number of manufacturing enterprises can also represent PFOS sources driven by population. The emissions of PFOS-related chemicals that enter the environment are uniformly converted into PFOS-equivalent emissions through their respective formation factors. The most populous and economically developed regions in China, i.e., the Beijing–Tianjin region, the Pearl River Delta, and the Yangtze River Delta, have significantly higher PFOS-equivalent emission densities [23]. It is necessary to strengthen the monitoring and control of pollution growth around these major production areas.

3.7. Correlation Analysis of the Characteristics of Foam-Based extinguishing Agent Types

The correlation between different parameters of foam-based extinguishing agents and their characteristics was explored. According to the nature of surfactants, regardless of whether they belong to fluorocarbon surfactant or there is the presence or absence of per- and poly-fluoroalkyl substances (PFAS) in the formulation, regulations classify the product into either the PFAS or the non-PFAS category. The PFAS category includes fluorocarbon surfactants containing PFOS and without PFOS. The non-PFAS category mainly includes hydrocarbon or protein-based surfactants. We normalized the data and performed correlation analysis yields, as shown in Figure 6.

AFFF and AR-AFFF were positively correlated with PFAS, and their correlation coefficients were 0.08 and 0.07, respectively. These two types of foam-based extinguishing agents contain a small amount of fluorinated surfactants in their main components [24], which showed high correlation with PFAS compounds. Most PFOS-containing foam-based extinguishing agents use a foam concentration ratio of 6% and are often used in fresh water situations; their correlation coefficients were 0.07 and 0.14. The non-PFOS fluorocarbon foam-based extinguishing agent correlation coefficients with seawater and cold resistance were 0.16 and 0.09, respectively. The seawater and cold resistance characteristics of the non-PFOS fluorocarbon foam-based extinguishing agent make it one of the leading foam-based extinguishing agents available on the market. New hydrocarbon- or protein-based foam-based extinguishing agents showed a positive correlation, having a correlation coefficient of 0.08 and a concentration ratio of 1% or 100%, respectively. According to the correlation analysis, foam-based extinguishing agents with seawater-resistant properties showed a positive correlation with 0−15 °C, the coefficient was 0.28, the foam-based extinguishing agents suitable for fresh water showed a positive correlation with −16−30 °C and <−30 °C, and the coefficients were all 0.23, which proved that the foam-based extinguishing agents with seawater resistance are superior to the normal agents in terms of cold resistance.

3.8. Analysis of Foam-Based Extinguishing Agent Types in the Future

According to the analysis of foam-based extinguishing agents’ certification information in the period 2024–2027, the number of foam-based fire-extinguishing agent certifications is on the decline, as shown in Figure 7. The total number of foam-based extinguishing agent certifications in the period 2024–2027 are predicted to be 832, 230, 212 and 82 per year, respectively, with an overall decrease of 90.1% after four years. Foam-based extinguishing agents containing PFOS will fall by 87.5%, from 208 to 26, and as the quantity decreased, the proportion of surfactants with PFOS-free ingredients in foam-based extinguishing agents gradually increased, rising from 30 to 50%, before growing to 59% and, finally, 60%. The production and use of PFOS containing fire-extinguishing foam-based agents will be prohibited from 2024 onward, and PFOS containing foam-based extinguishing agents will gradually be replaced by environmentally friendly foam-based extinguishing agents.

In China, the alternatives to foam-based extinguishing agents are mainly divided into two categories: fluorinated non-perfluoro-octane sulfonate foam-based extinguishing agents and fluorine-free foam-based extinguishing agents. Surfactant constituents in fluorous non-PFOS foam-based fire-extinguishing agents mainly select chemicals containing short heterochain components [25], such as alternative FS products made in 2018. The new surfactants developed in some parts of China for export to foreign markets have received international standard approval [1]. Due to the surface activity, as well as the chemical and other properties, of Fluorine-free foam-based extinguishing agents, the performance of alternative products has not yet stabilized and fully developed; thus, the application of this type of foam-based extinguishing agent is relatively limited. In addition, some of the short chain-based substitutes are easily degraded into perfluorohexanoic acid and perfluoro-octanoic acid through biodegradation [26]. It is necessary to consider the probable environmental risks posed by the substitutes during the period of their development.

4. Conclusions

Analysis of the certification information related to foam-based extinguishing agent manufacturing enterprises showed that the foam extinguishers containing PFOS are still being used in China, and they will continue to be used until the end of 2023. However, the number of PFOS-free fluorocarbon surfactant species is the major constituent of the domestic market. Active research and development of environmentally friendly foam-based extinguishers are needed. Alternatives should be found to completely replace foam-based extinguishers containing PFOS [27]. China is currently intensifying the pace of management of new pollutants, and the management policies and standards for PFOS are becoming more rigorous. According to the present study, the measures of control for PFOS in China are still insufficient, and there are still certain gaps compared to the performance requirements of the latest conventions on POPs. Currently, due to the insufficient development of alternatives to PFOS, as well as lack of research and development and weak performance testing and environmental risk assessment, the domestic alternatives have not yet been achieved full commercialization. Each enterprise is in the stage of self-development, lacking the formation of industry chain upstream and downstream alternative product cooperation. The performances of the developed alternatives are not satisfactory; therefore, enterprises needs to invest in the development of efficient alternatives to PFOS. The acceleration of the pace of full-scale production of alternatives can be facilitated by enhancing market incentives to encourage the development and application of substitutes and alternate technologies.