AFFF

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AFFF or A3F is the abbreviation for Aqueous Film Forming Foam (German for 'water film forming foam '), a synthetic foam compound that is added to the water to generate foam, especially to extinguish liquid fires.

Light water is often used as a synonym , but it is a brand name of the 3M company . Under this name, 3M was the first manufacturer to develop an AFFF foam concentrate in the 1960s and was able to market it successfully worldwide. Light water is also sometimes incorrectly used as a general term for mains water .

Mode of action

The specialty of the AFFF compared to, for example, the more common multi-range foaming agents, is the ability of the fluorinated surfactants it contains to form a water-containing film between foam and flammable liquid. This property is made possible by the perfluorosurfactants contained in the AFFF: these molecules are hydrophilic at one end (attracting water), but at the other end they are hydrophobic and lipophobic . They “dock” to water molecules on one side, but the free end does not mix with either oily or aqueous substances. This repulsion is so great that the aqueous surfactant film cannot sink under the lighter, non-polar fuel (such as a mineral oil product), but instead forms a film on the surface. This film is vapor-tight and enables faster spreading of the foam carpet on the liquid surface due to its better sliding properties .

commitment

Standard AFFF, like most other common foam concentrates, are only suitable for fighting fires involving non-polar liquids (oil, fuel, many petroleum products).

If larger amounts of polar liquids such as alcohols or ketones catch fire, special alcohol-resistant foaming agents are required. The suitability for polar liquids is indicated with appended abbreviations such as AR (Alcohol Resistant), ARC (Alcohol Resistant Concentrate) or ATC (Alcohol Type Concentrate). For example, the abbreviation “AFFF-AR” would stand for an alcohol-resistant, water-film-forming foam concentrate. No water film forms on polar liquids. If a film is required there, polymer film-forming foaming agents are used. Most AFFF-AR are water (for non-polar liquids) and polymer film-forming (for polar liquids) at the same time. Such “all-rounders” can usually be recognized by their highly viscous, almost gel-like consistency.

More and more public fire brigades are realizing that stocking up on alcohol-resistant AFFFs can make sense, as certain locations, which are also conceivable in the event of transport accidents, can only be managed with alcohol-resistant foam. Modern “normal” fuels also contain a significant proportion of polar additives. For example, gasoline with a normal winter mix can contain MTBE in a double-digit percentage. A plant fire brigade from the chemical or petrochemical industry that AFFF-AR can provide quickly and adequately is not always nearby.

The proportioning rate of the AFFF depends on the product, it is between 1% and 6%. It is also possible that two admixing rates are specified for a product, then it is an alcohol-resistant AFFF, the higher admixing rate only being necessary for polar liquids, such as alcohols.

Most AFFF foaming agents can be used to produce heavy and medium foam .

Environmental and health aspects

Fluorosurfactants ( perfluorinated surfactants , PFT) and their degradation substances have properties that make the use of fluorinated foaming agents (AFFF, FP, FFFP) well worth considering. Released PFTs are persistent and at least partially bioaccumulating . The residence time in the body is very long (half-life about five years). Organic perfluorocompounds, including the perfluorosurfactants (or their degradation products) used in fluorinated foaming agents, can now be found all over the world. In this regard, perfluorooctanesulfonate (PFOS), which was previously contained in many fluorinated foam concentrates, has attracted particular attention in the past . However, part of the fluorosurfactant load is also caused by other areas of industrial products such as non-stick coatings or impregnating agents .

Because of these negative properties, today's AFFF foam concentrates instead of PFOS contain so-called C 6 telomers such as perfluoroalkyl betaines (e.g. Capstone Fluorosurfactant 1183 or Capstone Product B ), which are also persistent in the environment and also more mobile. By inserting a C 2 H 4 unit between the perfluorinated chain and the polar group, the telomer is broken down into telomer sulfonates.

See also

Individual evidence

  1. ↑ LW Yeung, SA Mabury: Bioconcentration of wässrige Film-forming foam (AFFF) in juvenile rainbow trout (Oncorhynchus mykiss). In: Environmental Science & Technology . Volume 47, Number 21, November 2013, pp. 12505-12513, doi : 10.1021 / es403170f , PMID 24060050 .
  2. ↑ T. Kishi, M. Arai: Study on the generation of perfluorooctane sulfonate from the aqueous film-forming foam. In: Journal of Hazardous Materials . Volume 159, number 1, November 2008, pp. 81-86, ISSN  0304-3894 , doi : 10.1016 / j.jhazmat.2007.09.122 , PMID 18060693 .
  3. ↑ A. Hagenaars, IJ Meyer, D. Herzke, BG Pardo, P. Martinez, M. Pabon, W. De Coen, D. Knapen: The search for alternative aqueous film forming foams (AFFF) with a low environmental impact: physiological and transcriptomic effects of two Forafac (®) fluorosurfactants in turbot. In: Aquatic Toxicology . Volume 104, number 3-4, August 2011, pp. 168-176, doi : 10.1016 / j.aquatox.2011.04.012 , PMID 21627958 .
  4. ↑ AFFF at KVFR.org ( Memento from October 28, 2014 in the Internet Archive ). Retrieved October 27, 2014.
  5. ↑ IPEN: Fluorine-Free Firefighting Foams (3F): Viable Alternatives to Fluorinated Aqueous Film-Forming Foams (AFFF) , 2018, p. 51.