In Part 2 of this series of articles we dealt with Class A foams and the chemistry of legacy Class B AFFF products manufactured using the Simons process of electrochemical fluorination (ECF). In this part current AFFF formulations using fluorotelomers are discussed, which have been manufactured by manufacturers like DuPont, Dynax, Ciba Geigy, Elf Atochem, Daikin, Asahi Glass, Clariant, etc.

Fluoro-telomerisation:

By contrast with the Simons ECF process which produces a mixture of branched and linear isomers with odd and even carbon chain length, fluoro-telomerisation yields almost exclusively linear even-numbered carbon chains (Vyas et al 2007 [3], determined by the starting telogen, i.e. perfluoroethyl iodide (C2F5I) or perfluorobutyl iodide (C4F9I), that is containing carbon chains N, N+2, N+4, N+6, etc.

Telomerisation involves the free radical addition of tetrafluoroethylene (CF2=CF2), the taxogen, to an alkyl iodide, the telogen, such a perfluorobutyl iodide (C4F9I) as shown below. The perfluorinated chain is then terminated with a dimethylene group, -CH2-CH2-, characteristic of end-product fluorotelomers.

Source: Buck et al (2011)

The starting material is the perfluoroalkyl iodide, whereas the reactive end-product fluorotelomer iodide is used to manufacture a range of end products, e.g., fluorotelomer alcohols, thiols, sulfonic acids and sulfonamides.

Understanding chain length distribution synthesized during telomerisation to yield fluorotelomer iodide is important. Telomerisation produces a homologous series of products with chain lengths consisting of evenly spaced perfluorocarbon units, for example, 4:2, 6:2, 8:2, 10;2, 12:2, 14:2, etc. (N:2 indicates N perfluorinated carbons attached to a non-fluorinated two-carbon unit -(CH2)2-. This is then purified by fractional distillation yielding a fraction containing the shorter chain lengths, i.e., C4-C10 mainly consisting of C6/C8, which has been used mainly for firefighting foams, and longer chain lengths >C8 used for fabric, textile, leather and paper treatments. Other structural variants on the telomer process have occasionally been used by individual manufacturers, including the use of a three carbon spacer, -(CH2)3-, instead of a two carbon unit.

Post the 2010-2015 PFOA Stewardship Program considerable efforts by the fluorochemical industry have managed to reduce the 8:2 fluorotelomer content of the precursor used for firefighting foams to less than 25ppb, as this can act as a precursor for PFOA through breakdown. Early products used to make the fluorosurfactants for formulating firefighting foams were actually a mixture of mainly C6/C8 perfluorinated chain lengths, i.e., 6:2 and 8:2. Modern fluorotelomer foams are now predominantly 6;2 and 4:2 and referred to in the industry as ‘’pure C6’’.

Unfortunately, but predictably, replacement of C6/C8 formulations with ’pure’ C6 fluorotelomers resulted in loss of foam performance which in turn required the use of higher fluorosurfactant concentrations, itself undesirable from an environmental point of view.

Compositions of six foams ~2005-2010. Data from Backe, Day & Field 2013

Fluorotelomer Intermediate Homologue Distributions

Source : DuPont

Perfluoro compounds are used in firefighting foam to lower surface tension enabling film-formation on many hydrocarbon fuels except those shorter than iso-octane such as hexane or pentane; to provide excellent heat and chemical resistance; to increase hydrocarbon repellency and thus to resist to solvent contamination or ‘f’uel pickup’’; to provide effective vapour suppression.
Manufacturers offer a range of perfluorochemicals, most of them being fluorosurfactants. These surfactants are a combination of a hydrophobic and oleophobic perfluorinated tail and a polar head group giving functionality, enabling dispersion or solubilisation of the products in the foam concentrate. One of the most popular and efficient products was probably the C8:2 perfluorinated betaine surfactant together with its C6:2 homologue.

The starting material is the perfluoroalkyl iodide, whereas the reactive end-product fluorotelomer iodide is used to manufacture a range of end products, e.g., fluorotelomer alcohols, thiols, sulfonic acids and sulfonamides.

Class B Fluorine-Free Foams (F3) for liquid hydrocarbons and polar solvents

The development of fluorine-free foams (F3) was started in the late 1990s by Ted Schaefer working for 3M Australia. By the early 2000s the first operational fluorine-free firefighting foam, called RF-3 and RF-6 for Rehealing foam 3% and 6% became available. Queensland Fire Service went fluorine-free as early as 2003. Over the next decade or so fluorine-free foam technology greatly improved to the point that today F3 products are available on the market achieving or even in some cases exceeding AFFF performance, whilst offering better value for money. Early developments included Solberg Scandinavian buying the RF patents from 3M as well as Ted Schaefer’s expertise in 2007, as well as the development of F3 by Thierry Bluteau in 2002, then working for Bio-Ex France. In the late 2000s, Gary McDowall (3F Ltd, UK) also developed F3 products. Later on, 3F Ltd offered new F3 solvent-free, i.e., glycol free, thus greatly reducing the BOD-COD problem by around 40-60%. Other major manufacturers followed suite and today F3 firefighting foams are widely available on the market, with many major organisations in civilian and military aviation, oil and gas and petrochemical industries, as well as large municipal fire departments transitioning from fluorine-containing AFFF to fluorine-free F3 foams.

The transition has taken nearly 10-15 years, mainly due to built-in conservatism in many fire departments, but also because of the costs involved which include modifying or cleaning existing equipment, as well as the proper and expensive disposal of existing legacy stocks of AFFF. Another driving force, especially in the US, has been the increasing financial and legal exposure of continuing to use products which give rise to persistent and widespread environmental contamination.

The environmentally sustainable destruction of legacy AFFF stocks, often involving huge volumes of concentrate running to millions of litres, requires destruction methods that are highly efficient (> 99.999% DRE), capable of handling solid and liquid charges, do not further contaminate the environment, and are financially feasible. Methods that are currently available will be discussed in a further article.

Apart from using fluorocompounds for their exceptional physicochemical properties, firefighting foam contains a range of other chemicals which are necessary to achieve the extinction.

The main components found in firefighting foam with or without fluorosurfactants or fluoropolymers include the following:

Foaming agents:

(a)Some fluorosurfactants like PFOS and PFHxS and their functionalised derivatives, or fluorotelomer compounds such as 1157 (perfluoroalkyl betaine) or 1183 (perfluoroalkyl aminoxide) have been used occasionally to boost foam volume in AFFF foams.
(b)r A large range of hydrocarbon surfactants are widely used by manufacturers in all types of synthetic foams: AFFF, AFFF-AR, High Expansion, Class A and F3.
Synthetic surfactants: are made from hydrocarbon chain precursors (e.g., CH3(CH2)n-produced by the petrochemical industry from mineral oil and/or animal and plant fatty acids, which are then functionalized with a polar head-group to obtain the desired surfactant property, for example, octyl sulfonate, CH3(CH2)7SO3-, or dodecyl sulfate, CH3(CH2)11SO4-.

(c) Protein polymer: obtained from the hydrolysis of slaughterhouse waste ‘‘horn and hoof’’, this old-fashioned and polluting process consists of heating the raw material in highly alkaline media. The keratin is degraded into small protein fragments, followed by neutralisation and stabilisation. The concentrated end-product can be contaminated with haemoglobin from residual blood giving it a very characteristic dark brown colour. Under operational conditions protein foams are characteristically dark brown in colour with a highly distinctive smell especially when applied to a fire.

Foam stabilisers: most of them are glycol ethers. The most used are butyl glycol, butyl carbitol and hexylene glycol, and more recently ethyl or butyl propylene glycols. We can find too lauryl alcohol.

Anti-freeze agents: monoethylene glycol, (CH2OH)2, and mono-propylene glycol, CH2(CH2OH)2, are widely used, but manufacturers also use sodium chloride, urea, etc, in some formulations.

The glycols and glycol ethers present in foam formulations are at relatively high concentrations – typically 10-20% – and are the major contributors to the BOD/COD value.

Other additives: in this category formulators use preservatives, anti-corrosion products, buffers to stabilise foam pH, and chelating agents for ions that would degrade foam performance, all at levels below 1%.

Natural polymers: carbohydrate xanthan gum is a very common natural polymer used to give alcohol-resistance to the foam. Applied to a burning fuel surface, the polymer precipitates and chars forming a barrier which resists and prevents contamination of the foam blanket by fuel – ‘’fuel pickup’’. Other polymers and gums are also used, such as celluloses, alginates, guar, locust bean, or carrageenan.

The tables below summarise the main properties of principal ingredients used in formulations.

Currently, there are at least 12 different types or foam on the market, some of which have declined in the volume used over recent years.

Different users have different hazards associated with specific risks. In selecting the correct foam, it is important to do a suitable and sufficient assessment of these specific risks, ensuring that the foam chosen is ‘fit-for-purpose’, and then go through the following steps during procurement and operational use:

(a) list the equipment: whether this is fixed or mobile, i.e., tank farm, monitors or fire appliances;

(b) check the correct induction rate, e.g., 1%, 3% or 6%, for use;

(c) ensure that the application rate is suitable;

(d) determine the length of time that the foam should be applied, and the foam        blanket stability and when re-application is necessary;

(e) determine the availability of possible support from external sources, i.e,. reinforcement;

(f) be aware of the manufacturer’s warranty and specified operating conditions for the foam;

(g) consider local environmental regulations – both current and any likely

3F is a responsible manufacturer and will be pleased to assist any of its customers in the assessment of risks and selection of an appropriate foam and associated equipment.

To be continued in Part 4.

References

Benskin J.P., De Silva A.O., Martin J.W. (2010) Isomer Profiling of Perfluorinated Substances as a Tool for Source Tracking: A Review of Early Findings and Future Applications. Rev. Environ. Contam. Toxicol.:111-160.

Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., de Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A., and van Leeuwen, S.P.J. (2011) Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins. Integr. Environ. Assess. Manag. 7(4), 513-541.

D’Agostino, L.A, and Mabury, S.A. (2014) Identification of Novel Fluorinated Surfactants in Aqueous Film Forming Foams and Commercial Surfactant Concentrates. Environ. Sci. Technol. 48(1):121-9.

Moe, M.K., Huber, S., Svensen, J., Hagenaars, A,. Pabon, M., Trümper, M., Berger, U., Knapen, D., and Herzke, D. (2012) The structure of the fire fighting foam surfactant Forafac®1157 and its biological and photolytic transformation products. Chemosphere 89(7), 869-875.

Naile, J., Garrison, A.W., Avants, J.K., and Washington, J.W. Isomers/Enatiomers of Perfluorcarboxylic Acids: Method Development and Detection in Environmental Samples. Chemosphere 44, 1722-1728.

Sasaki, T., Egami, A., Yajima, T., Uekusa, H., and Sato, H. (2018) Unusual Molecular and Supramolecular Strcuturs of Chiral Low Molecular Weight Organogelators with Long Perfluoroalkyl Chains. Crystal Growth and Design 18(7) 4200-4205.

In this part we deal with the chemistry involved in formulating Class A foams for carbonaceous fuels, and legacy Class B AFFF foams based on PFOS chemistry for liquid hydrocarbon and polar solvent fires.

In Part 1 of this series of articles we saw that AFFF firefighting foams contain various perfluoroalkyl substances (PFAS); however, firefighting foam is only one of many applications.
PFAS have been used for decades in more than 200 other industrial and domestic applications, such as food packaging, leather and textile treatment, carpet and clothing anti-stain protection, detergents, water-proofing and oil-proofing, paints and varnishes, printing inks, chromium plating, outdoor and protective clothing (PPE) for the emergency services and military. These perfluorinated substances are widely used as they offer a combination of unique properties, including the ability to repel water (hydrophobicity), the ability to repel oils (oleophobicity), the ability to reduce the surface tension of aqueous solutions to less than 20 dyne/cm and with it acting as detergents, emulsifiers, wetting agents, and dispersants.

The OECD (2021) has recently clarified the definition of what constitutes a PFAS, whilst acknowledging that given by Buck et al (2011), as follows:

“PFASs are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it), i.e. with a few noted exceptions, any chemical with at least a perfluorinated methyl group (–CF3) or a perfluorinated methylene group (–CF2–) is a PFAS.”

More than 800 products currently available in the marketplace have been identified, but the true list of PFAS used in commerce and industry is likely to be 10,000 or more; the UN Stockholm Convention has listed 4,700 substances related to PFOA alone. PFAS started to be manufactured in large quantities in the early 50’s. All of them are anthropogenic created by humans using chemical synthesis. They do not exist naturally. Their extremely stable and chemically resistant perfluorinated end-products of breakdown in the environment have long been identified as ‘forever chemicals’, for example by scientists and journalists such as Rebecca Renner [“Growing Concern Over Perfluorinated Chemicals” (2001) Environ. Sci. Technol. 35(7) 154A-160A; “The long and the short of perfluorinated replacements” (2006) Environ. Sci. Technol. 40(1) 12-13] or Sharon Lerner writing in the Intercept [“Toxic Chemicals Discovered in Hundreds of Products” Sharon Lerner (The Intercept December 2020)].

It must be stressed that although still commonly and inaccurately referred to as ‘emerging contaminants’, PFAS have truly emerged as contaminants of concern for at least 10 years and should no longer be described as ‘emerging’. On the other hand, the technology of how to deal with PFAS waste is currently still emerging and developing.

Firefighting foams are classified either as Class A suitable for carbonaceous fuels such as wood, paper or vegetation, acting as wetting agents improving the penetration of water into deep seated fires and do not contain fluorosurfactants, only hydrocarbon surfactants; or, on the other hand, Class B foams are specifically formulated for liquid hydrocarbons such as gasoline and polar solvents such as ethanol. Modern Class B foams may either contain fluorsurfactants and be capable of film-formation at the air-fuel interface (AFFF), or completely fluorine-free, F3 foams, specially formulated containing only hydrocarbon surfactants. Interestingly Class B fluorine-free foams (F3) can be used effectively for both Class A and Class B fires unlike AFFF,

Class A foams for carbonaceous fuels

Class A firefighting foams are used extensively worldwide, especially in Australia, America and Southern Europe, for incidents involving carbonaceous fuels, e.g., structural house fires, plastic and tyre waste, as well as grassland and wildland or bush fires. Ted Schaefer then working for
3M Australia in the late 1980s developed one of the first effective Class A foams, “3M Fire-Brake BFFF”, recognised in 2001 by the Australian Academy of Technological Sciences and Engineering as one of the top 100 Australian inventions of the 20th century.
Class A foams behave very differently to fluorosurfactant-containing AFFFs, as they are specifically formulated to penetrate carbonaceous fuel effectively, such as compacted vegetation, paper or wood, using specialised hydrocarbon surfactants, not unrelated to kitchen washing-up liquid. Fluorosurfactant AFFFs, designed for surface application to liquid hydrocarbon or polar solvent fires, are nowhere nearly as efficient at penetrating such deep-seated fires and claims by some in the industry that their AFFF products can be used as dual Class A / Class B foams is frankly misleading.

Mister H: Penetration by Class A                          Mister F: Failure to penetrate by Class B AFFF

(Bluteau 2007)

Class B AFFF foams for liquid hydrocarbons and polar solvents

The first report of an aqueous film-forming foam (AFFF), called LightWater®, by R.L. Tuve et al of the Naval Research Laboratory and the 3M Company March 1964 of a foam capable of vapour suppression and film forming on the surface with low flash point flammable fuels such as gasoline, showed that it was 1200% more effective than standard protein foams under identical conditions.
The compounds tested in foam formulations were in the general class of perfluorosulfonic acid derivatives, some being quaternary salts, others being alcohols, esters, anionic salts of substituted sulfonamido carboxylic acids, etc. All of these water soluble, high molecular weight fluorocarbons shown dramatic surface tension depression of water to below 20 dynes/cm. In general they are insensitive to electrolytes and show surface activity when dissolved in organic solvents.
The first Patent for an AFFF was granted to Richard Tuve and Edwin Jablonski in June 1966 [1], representing a new era in firefighting foams which was to last for the next 30-40 years until the 3M Company Minnesota withdrew from PFOS-based chemistry altogether in May 2000.

Information from the patent literature gives a fascinating insight into the derivatives used in these early AFFFs. Derivatives of perfluorooctane sulfonamide (PFOSA) and perfluorooctane carboxylic acid (PFOA) were used. As reported in the 1966 patent these early formulations include the quaternary ammonium salts of PFOS and PFOA amido derivatives:

C8F17-SO2NH2-(CH3)3N(CH3)3+I-

C7F15-CONH-(CH3)3N(CH3)3+I-

an amphoteric amino betaine derivative of PFOA

C₇F₁₅-CONH-(CH₂)₃–N⁺(CH₃)₂-CH₂-CH₂-COO^–

and the potassium salt of a PFOS sulphonamide derivative

C₈F₁₇SO₂N(C₂H₅)-CH₂COOK

The potassium salt of PFOS in the form of surfactant FC-95 was also used in early foams.
Interestingly it was some 50 years later that Barzen-Hanson et al in 2017 [2] from Jennifer Field’s group at Oregon State University identified a vast range of other derivatives, or their breakdown products, involving 40 different classes in legacy AFFFs.

Electrochemical Fluorination (ECF) – the Simons Process

The 3M Company announced in May 2000 that it was phasing out fluorosurfactant production based on PFOS chemistry and withdrawing entirely from the fluorinated AFFF firefighting foam market marking an end to the availability of Light Water™ and Light Water™ ATC™ formulations (3M Company (2000)). Other products using PFOS included ScotchGuard™ stain and water repellent treatments. Production of PFOS by the 3M Company is thought to have ceased entirely around 2002, being replaced by the shorter chain compound PFBS, although PFOS and PFHxS production is thought to have continued in China and India.
Until 2000 PFOS had been manufactured using the Simons electrochemical fluorination (ECF) process (3M Company, 1999; Ignat’ev et al , 2009; Sartori and Ignat’ev, 1998). This process involves replacing the hydrogen atoms of octyl sulfonate using hydrogen fluoride electrolytically in order to generate perfluorooctane sulfonyl fluoride, PFOSF.

C₈H₁₇SO₃H + HF ==>> C₈F₁₇(C=O)F

PFOSF is highly reactive acyl fluoride and is the starting material for preparing PFOS derivataives such as the sulfonamide PFOSA or N-ethyl-PFOSA, for example:

C₈F₁₇(C=O)F + C₂H₅NH₂ ==>> C₈F₁₇(C=O)-NH-C₂H₅

PFOSF production using electro-chemical fluorination (ECF) was, and remains, an inherently ‘dirty’ process resulting in a wide range of structural isomers, both straight chain and branched with CF-CF3 and C-(CF3)2 side chains, as well as odd and even chain length homologues such as C4 PFBS, C6 PFHxS and C7 PFHpS. As a result, technical grade PFOS was always and continues to be contaminated with a significant percentage of PFHxS. In addition, the perfluoroalkyl chains of both PFOS and PFHxS can form left- or right-handed helices resulting in pseudo-racemates that have been detected in human sera (Wang et al, 2011; Naile et al , 2016; Sasaki et al , 2018). Quoting from the ECHA (13 June 2019) PFHxS restriction proposal:

“…Sources indicate that when manufacturing perfluorinated compounds, a mixture of compounds of varying chain- length is usually formed, with typical amounts of PFHxS formed when manufacturing PFOS being between 4 and 14% ( from (BiPRO, 2018) citing (Ren, 2016). These numbers are supported by measurements of PFHxS in commercial PFOS-products, namely 3.5%–9.8% in 3M’s FC-95 (from (BiPRO, 2018) citing 3M (2015) and 11.2 % – 14.2% in three products from China (Jiang et al, 2015). BiPRO also note, however, that the amount of the C6-component may be reducedby purification at different stages of the production line….”

The significance of the relatively high levels of the C6 homologue perfluorohexane sulfonic acid, PFHxS, in these AFFF formulations is that PFHxS is more toxic and bioaccumulative than PFOS, has a longer biological half-life in humans, and has also been list in the Annexes of the UN Stockholm Convention for restriction. Unfortunately, some manufacturers especially in Asia have used PFHxS as a ‘regrettable substitution’ for PFOS.

The use of ECF to produce perfluorinated sulfonic and carboxylic acids, such as PFOS and PFOA and their derivatives, has been summarised by Buck et al [2011], as shown below.

source: Buck et al (2011)

To be continued as Part3.

References

Barzen-Hanson, K.A., Roberts, S.C., Choyke, S., Oetjen, K., McAlees, A., Riddell, N., McCrindle, R., Ferguson, P.L., Higgins, C.P., and Field, J.A.. (2017) “Discovery of 40 Classes of Per- and Polyfluoroalkyl Substances in Historical Aqueous Film-Forming Foams (AFFFs) and AFFF-Impacted Groundwater” Environ, Sci. Technol. 51, 2047-2057.

Benskin J.P., De Silva A.O., Martin J.W. (2010) Isomer Profiling of Perfluorinated Substances as a Tool for Source Tracking: A Review of Early Findings and Future Applications. Rev. Environ. Contam. Toxicol.:111-160.

Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., de Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A., and van Leeuwen, S.P.J. (2011)  Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins. Integr. Environ. Assess. Manag. 7(4), 513-541.

Ignat’ev, N.V., Willner, W., and Sartori, P. (2009)  Electrochemical fluorination (Simons process) – A powerful tool for the preparation of new conducting salts, ionic liquids and strong Brǿnsted acids. J. Fluorine Chem. 130(12), 1183-1191.

Naile, J., Garrison, A.W., Avants, J.K., and Washington, J.W. Isomers/Enatiomers of Perfluorcarboxylic Acids: Method Development and Detection in Environmental Samples. Chemosphere 44, 1722-1728.

OECD (2021), Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances:

Recommendations and Practical Guidance, OECD Series on Risk Management, No. 61, OECD

Publishing, Paris.

Sartori, P. and Ignat’ev, N.V. (1988) The actual state of our knowledge about mechanism of electrochemical fluorination in anhydrous hydrogen fluoride. J. Fluorine Chem. 87(2(, 157-162.

Sasaki, T., Egami, A., Yajima, T., Uekusa, H., and Sato, H. (2018) Unusual Molecular and Supramolecular Structures of Chiral Low Molecular Weight Organogelators with Long Perfluoroalkyl Chains. Crystal Growth and Design 18(7) 4200-4205.

Tuve, R.L. amd Jablonksi, E.J. (1966) US 3,258,423 Patent June 28, 1966 “Method Of Extinguishing Liquid Hydrocarbon Fires”, assignors to the United States of America as represented by the Secretary of the Navy. Filed Sept. 4, 1963, Ser. No. 306,665.

Vyas, S.M., Kania-Korwel, I., Lehmler, H.J. (2007) Differences in isomer composition of perfluorooctanoylsulfonyl (PFOS) derivatives. J. Environ. Sci. Health and Toxic Hazard Substance Environ. Eng. 42, 249-255.

Wang,  Y., Beeson, S., Benskin, J.P., De Silva, A.O., Genuis, S.J., and Martin J.W. (2011) Enantiomer Fractions of Chiral Perfluoroctanesulfonate (PFOS) in Human Sera. Environ. Sci. Technol. 45(20) 8907-8914.

Modern chemistry has created many hundreds of thousands of chemical compounds, which we encounter as part of our daily lives. Indeed, it would be very hard to spend a day without being in contact with a class of molecules – perfluoroalkyl substances or PFAS – which have been commercially exploited since the end of WWII over the last 75 years.

Even if we could qualify chemistry as a miracle of science, it is worth knowing that chemistry has been approached by the Egyptian 3000 years BC, and was later on studied by the Ancient Greeks which described the combination of the 5 elements: earth, air, fire, water and ether. This theory was largely accepted for more than 1000 years.

The basis of the modern chemistry, as we now understand it, was established over the last three hundred years. The nature of the atom, the identification of atomic compounds, the first modern synthesis was achieved.

In 1906, Frédéric Henri Moissan (1852-1907), a French chemist working in Paris at the École Supérieure de Pharmacie, isolated for the first-time elemental fluorine gas, F2, a discovery for which he was awarded the Nobel Prize in Chemistry in 1906. Hydrogen fluoride obtained from fluorspar had been identified by the renowned Swedish chemist Karl Wilhelm Scheele some years earlier.

The post war years after WWI In the mid 1930s, were the heyday the German chemical industry, especially as regards new synthetic dyes. Fluorine chemistry started to have a commercial role – a red dye Naphthol AS, used as the official red colour the Nazi flag, and Indanthrene Blue used as a component of ‘Flieger Grau’ or Pilot Grey, the blue-grey colour of Luftwaffe uniforms, both contained a fluorinated methyl group, CF3, which helped prevent fading. Carothers working for DuPont produced the first industrial wholly synthetic fabric, the polymer Nylon. From this point chemists have never stopped to inventing new compounds!

When we think about chemicals, it is important to realise that many, if not most of the synthetic compounds now commercially available are produced by the petrochemical industry. Since the invention of the internal combustion engine, petrol (gasoline) and petroleum products have been become increasingly important around in for many human activities but are associated with a high fire risk.
The nature of this risk highlighted the necessity of addressing these often-catastrophic fires. In the early 40’s, protein foam made from ‘horn and hoof’, a slaughterhouse waste, was developed to control Class B hydrocarbon fires, e.g., those involving oil, gasoline, aircraft fuel and solvents.
In 1949, the 3M Company Minnesota industrialized the Simons electrochemical fluorination (ECF) process for making perfluoro-compounds (PFC) such as perfluorinated amines, carboxylic and sulphonic acids in which the hydrogens of the alkyl carbon chain had been totally replace by fluorine. Joseph Simons had discovered the ECF process whilst working at Pennsylvania State College in the 1930s but was unable to publish his work until after WWII because fluorine chemistry was essential for uranium purification as part of the Manhattan Project.

In 1953 the structure of Scotchgard was accidentally discovered by Patsy Sherman and Sam Smith working for the 3M Company whilst working on a rubber for jet fuel lines. Three years later in 1956, the 3M Company launched Scotchguard on the market. This fabric, textile and leather treatment is based on a PFOS-derivative containing N-ethyl-PFOSA and gives water, oil, and other liquids and stain-protection to the treated fibre.
Interestingly, N-ethyl-PFOSA known as Sulfluramid, was originally developed to kill ants, cockroaches and termites, and is still used to this day as the insecticide sulfluramid against leaf-cutting ants in Brazil. The lithium salt of PFOS was developed to kill wasps and hornets but is highly toxic to honey bees.

PFOS, perfluoro-octane sulphonic acid, and its derivatives subsequently become crucial for the development of Class B aqueous film-forming foams (AFFFs) effective against liquid hydrocarbon and solvent fires.

Figure 1. The structure of PFOS, perfluoro-octane sulphonic acid.

During the 1960s the US Department of the Navy Naval Research Laboratory in collaboration with the 3M Company began developing PFOS-based firefighting foams. A patent for AFFF firefighting foam was awarded in June 1996 for extinguishing liquid hydrocarbon fires.

In the late 60’s, a series of major fuel fires happen on board US Navy ships causing extensive loss of life and damage:
(i) 1966: USS Oriskany – fire kills 44 sailors.
(ii) 1968: USS Forrestal – whilst on active service in the Gulf of Tonkin during the Vietnam War, malfunction and accidental firing of a fighter Zuni rocket on the flight deck of this super-carrier led to a catastrophic aviation fuel fire claiming the lives of 134 crew, injuring many more, destroying nearly 50 aircraft, doing $72 million worth of damage, and leaving the vessel unfit for active service.

(iii) 1969: USS Enterprise – a shipboard fire kills 28 sailors.

These major fires prompt the US Department of the Navy to mandate the use of the recently developed AFFF firefighting foam, which the 3M Company was manufacturing for the US military.

Perfluorocompounds had been successfully used to create AFFF, and 3M’s PFOS-based LightWater® and alcohol-resistant ATC® brands became the staple for liquid hydrocarbon fuel fires from the 1970s until May 2000 when the Company announced that it was phasing out PFOS-based chemistry on environmental grounds. AFFF had indeed conquered the world of firefighting and was seen for decades as the ultimate answer to extinguishing large hydrocarbon (oil and gasoline) fires both for military and civilian use especially by the aviation and petrochemical industries.

In the 70’s, an alternative technology was developed based on the telomerization process. This technology provided an alternative to the ECF process and introduced a new class perfluorochemicals on the market. Whereas the ECF process produced mainly PFOS contaminated with odd and even numbered homologues of PFOS such as PFHxS (~5-8 % w/w), perfluorohexane sulphonic acid, as well as branched chain isomers, telomerisation produced only even number linear alkyl carbon chains. The characteristic of fluorotelomer derivates is a perfluoroalkyl moiety linked by a dimethylene group -CH2-CH2- to a functional group which could be negatively (anionic), positively (cationic) or both negatively and positively charged (amphoteric).

Most modern fluorotelomer-based AFFF firefighting foams, known as ‘pure C6 foams’, are based on derivatives of 6:2 fluororelomer sulphonic acid (6:2FTS), or a thioether analogue, containing a C6 perfluoroakyl chain linked through -(CH2)2- to a charged functional group. 6:2FTS contains a C8 chain and its structure is shown below. Its similarity to PFOS is clear but the CH2 groups cause it to behave very differently in terms of its PBT profile. All perfluoroalkyl moieties or their breakdown products are extremely environmentally persistent (vP), but with differing bioaccumulation or toxic potential.

Figure 2. Structure of 6:2FTS

Early fluorotelomer foams, however, contained both 6:2FTS and often substantial amounts of 8:2FTS derivatives. This was a problem as the 8:2FTS could be degraded to a stable end product perfluoroctanoic acid or PFOA which had substantial toxicity. This problem has now been essentially resolved as a result of the industry PFOA Stewardship Program 2010-2015, with residual PFOA or its precursors reduced to less than 25 parts perbillion (ppb).

Figure 3. 8:2FTS breakdown to PFOA

From the 1970s to the late 1990s, many manufacturers of firefighting foam appeared in the market, developing and offering a wide range of different foams for end-users. These included Class B AFFF, AFFF-AR (alcohol resistant), film-forming-protein (FFFP) and fluoro-protein (FP) foams. Class A foams specifically intended for solid carbonaceous fires such as structural building or wildland (bush) fires were also developed in this period.

On 16 May 2000 the 3M Company abruptly announced the phasing-out of its activity in PFOS-based chemistry for producing fluorochemicals, affecting not only firefighting foams but also a wide range of domestic and commercial products. This announcement was justified on company responsibility for environment, as it was confirmed that the C8 perfluoroalkyl substances (PFAS) made using ECF technology posed a threat to the environment, with pollution that had spread worldwide affecting a wide range of environmental compartments as well as biota including man.
Over the next 2-3 years, the company had stopped all activities involving PFOS-based chemistry, with a total withdrawal from the firefighting foam market, replacing it with mitigated success by a shorter chain PFBS-based (perfluorobutyl sulphonate) chemistry. However, some production of PFOS and PFHxS derivatives using the ECF process did continue in both China and India.
With 3M’s phase-out of PFOS-chemistry and withdrawal from the firefighting foam market, other major manufacturers of PFAS fluorochemicals and firefighting foam stressed that they considered fluorotelomer chemistry was ’safe’ and indeed environmentally friendly as it had nothing to do with ECF chemistry and products could not contain either PFOS or PFOA. The firefighting foam market transitioned to AFFF products based on fluorotelomers over the next few years 2000-2010.

From 2002 onwards a lively and sometimes acrimonious debate took place between manufacturers of PFAS and AFFF – under the auspices of a trade association, the Fire Fighting Foam Coalition (FFFC), funded mainly by the fluorochemical industry – and independent manufacturers especially of nascent fluorine-free foams (F3), regulators and scientific experts from academia. This discussion gave rise to a series of international seminars, conferences as well as hundreds of publications in the peer-reviewed literature about the environmental consequences of substituting fluorotelomers for PFOS-based products. At this time the main international forum for discussing developments in firefighting foam technology turned out to be the Reebok series of foam conferences, held in Manchester and Bolton in the UK, 2002, 2004, 2007, 2009 and 2013.

Starting as early as 2002 a number of the smaller independent foam manufacturers started to offer first generation experimental Class B liquid hydrocarbon fluorine-free foams (F3) as more environmentally sustainable alternatives to PFAS -containing foams. During the following 10 years the debate raged on driven by published scientific studies which concluded that telomer chemistry posed a threat to the environment. Early telomer formulation were mixtures of 6:2 and 8:2 derivatives. The 8:2 material was shown to be a potential precursor for the generation of environmentally extremely persistent PFOA (perfluorooctanoic acid or C8) through breakdown, subsequently associated with long-term health effects. At the time this was vigorously contested by representatives advocating the fluorochemical industry attending Reebok conferences.
However, as a result of pressure from the US EPA many large feedstock manufacturers adopted the PFOA Stewardship Program 2010-2015 aimed at reducing the use of PFOA or its precursors. Improvements in purifying the fluorotelomer derivatives resulted in a reduction of PFOA related material to less than 25 ppb providing so-called ‘pure C6’ fluorotelomer derivatives. The Stewardship Program led to a change in foam formulations formerly containing C6/C8 fluorotelomers to a so-called ‘drop in’ replacement containing predominantly C6 fluorotelomer.
Unfortunately, this change was not as simple as it was supposed to be and foam manufacturers had to reformulate and increase the total fluorochemical content to achieve a similar performance compared with previous C6/C8 formulations. Unfortunately, end-users were not even made aware of this change!

Around the same time, scientific studies accumulated evidence that even hyper-pure C6 was NOT a suitable alternative, but a ‘regrettable substitution’ and the debate went to another level. 2015 marked a sea-change in the PFAS debate. The toxicity of PFOA was no longer denied by the fluorochemical industry or regulators and the issue was brought to the attention of the public by scientific journalists.

A series of public statements signed by scientists worldwide – the Helsingǿr Statement 2014, the Madrid Statement 2014 and the Zürich Statement 2018 – raised concerns about the continuing use of PFAS and as major planetary pollutants and their long-term impact on the environment. A major publication in 2020 raised the issue that all PFAS should be treated as a chemical class because of their common environmental problems rather than individual chemicals.

The United Nations Stockholm Convention and their Persistent Organic Pollutants Review Committee (POPRC) has added PFOS, PFHxS and PFOA to the appropriate Annexes banning or restricting use (2018-2022).

Countries such as Germany and Norway, or individual states such Queensland in Australia, have been at the forefront in regulating the use of PFAS, especially for highly dispersive use such as firefighting foams.

Some countries are not waiting for UN decisions to regulate the use of PFAS. In Europe, PFOS has been prohibited since 2011 and PFOA since 2018; current discussions aim to stop the use of all PFAS with C4 to C20 carbons completely with a deadline of 2025, in anticipation of these restrictions many industries are moving to fluorine-free technology. In the USA, change is being driven mainly by the cost of litigation with thousands of cases against the fluorochemical industry including foam manufacturers in the pipeline.

To be continued in Part 2