Study on aqueous film-forming foam extinguishing agent based on fluorocarbon cationic–hydrocarbon anionic surfactants mixture system

Fluorocarbon surfactants were the main components of aqueous film-forming foam extinguishing agents (AFFF). Unfortunately, the widely used fluorocarbon surfactant perfluorooctane sulfonate (PFOS) was limited due to its toxicity, bioaccumulation and biodegradability. In this paper, an environmentally friendly quaternary ammonium cationic fluorocarbon surfactant with high surface activity and simple synthesis route was reported. The surface performance and aggregation behavior of the mixed solution of this fluorocarbon surfactant and sodium n-octyl sulfate were studied by means of surface tension meter and transmission electron microscope (TEM). The results showed that the synergistic effect of sodium n-octyl sulfate and this fluorocarbon surfactant was significant, and many vesicles could be observed in the mixed solution with the concentration of 0.1 mol/L under TEM. Subsequently, three environmental friendly AFFF formulations (F-1, F-2, F-3) were designed with the mixture of the fluorocarbon surfactant, sodium n-octyl sulfate and lauryl betaine BS-12 as foaming agent. Through its foam performance test, it could be seen that F-3 showed relatively excellent foam performance. The initial foam height h₀ was 70 mm, the 25% drainage time was 315 s, the extinguishing time was 28 s, and the burn-back time was 720 s. This kind of fire extinguishing agent had the potential of fire protection application.     

Preserving Shipboard AFFF Fire Protection System Performance While Preventing Hydrogen Sulfide Formation

There is a very serious problem aboard US Navy ships from generation of toxic hydrogen sulfide (H₂S) in Aqueous Film-Forming Foam (AFFF) solutions used for shipboard fire protection. This is the result of the action of sulfate reducing bacteria (SRB) in mixtures of seawater and AFFF, which remain stagnant for significant time periods in shipboard fire protection system piping. Similar to microbial generation of H₂S in sewage, over time microbes present in seawater consume organic materials in the AFFF mixture and can deplete the dissolved oxygen. If the reduction-oxidation potential falls low enough, anaerobic action of the SRB on the sulfate present in seawater can then result in H₂S generation, reaching dangerous levels. The recommended ceiling for exposure to H₂S is only 10 ppm. If the microbes causing oxygen depletion and/or the SRB can be eliminated (or sufficiently minimized), the dangerous generation of H₂S would not occur. The Navy Technology Center for Safety and Survivability is participating in a research project for the Naval Sea Systems Command (NAVSEA) to evaluate several treatment modalities for their ability to inhibit H₂S formation in AFFF/seawater mixtures and for possible deleterious effects on AFFF performance. Various approaches have been considered employing laboratory evaluations (dynamic surface tension and Ross-Miles foamability), and 28 ft² (2.6 m²) pool fire extinguishment and burnback protection field tests (Military Standard MIL-F-24385F). The protocol selected for NAVSEA shipboard H₂S generation mitigation testing is a combination of a commercial broad-spectrum biocide with a molybdenum compound which is a specific inhibitor of SRB.     

Foam concentration measurement techniques

Three types of foam concentration measurement techniques are examined: total fluorine content, optical absorption, and specific conductivity. Specific conductivity was found to be the most useful for field measurements and was therefore compared with the traditional refractive index approach. It was found that electrical conductance provides a more accurate method of estimating the concentration of AFFF solution than does the refractive index technique described in NFPA 11.     

Aspirating vs. nonaspirating nozzles for making fire fighting foams — Evaluation of a nonaspirating nozzle

The use of nonaspirating nozzles for effective application of aqueous film-forming foam is almost a controversial topic. Fire tests on gasoline compared several commercial nozzles (aspirating and nonaspirating), revealing significant difference in the extinguishment of large fires. A new variable stream nonaspirating nozzle was tested, and by comparison found to be marginally acceptable. Consequences of choosing the wrong equipment for use with various foams and their use on a variety of flammable liquids are discussed. Mobil Research and Development Corporation Reference: L. R. DiMaio, R. F. Lange, and F. J. Cone, “Aspirating vs. Nonaspirating Nozzles for Making Fire Fighting Foams — Evaluation of a Nonaspirating Nozzle,” Fire Technology, Vol. 20, No. 1, February 1984, p. 5.     

The effect of aqueous surfactant films on the ignitability of aviation kerosene

The unexpected ability of some aqueous films to increase the ignitability of kerosene has been investigated by the authors. They tested a series of hypotheses and put forward their view of the most likely explanation of the phenomenon. The results of these investigations and their implications for fire fighting and hydrocarbon spill security are reported here.     

Sealability Properties of Fluorine-Free Fire-Fighting Foams (FfreeF)

This contribution compares the sealability performance of recently developed three synthetic foam formulations (that do not contain fluorosurfactants or fluoropolymers) with that of an aqueous film forming foam (AFFF). We apply the sealability methodology outlined in the Australian Defence Force Specification, DEF(AUST)5706. This methodology specifies a 0.28 m² small-scale indoor fire pan. The pan is first filled with 10 L of water and then 5 L of AVGAS (aviation gasoline, flash point of −50°C) or heptane (flash point of −4°C) is placed on top of the water. Foams were generated from a pressurised extinguisher with a foam nozzle as described in the standard’s specification, set to create foams with expansion of 4:1. The foam spread across the fuel until the entire fuel surface was covered with foam. At 5 min intervals, a lit taper was introduced into the space above the pan area by passing it twice around the surface of the foam in a circular motion at a height of approximately 15 mm from the surface of the foam. The results demonstrate differences in the sealability performance between AFFF and fluorine-free foams (FfreeF). Under laboratory conditions, with a foam blanket 1–2 cm deep, best-performing FfreeF formulation (RF6) provides about 30% of the durability of an AFFF for protection against evaporation of low-flashpoint flammable liquids. We also note in the results the significant differences among FfreeF with almost no sealability of AVGAS vapours offered by the two other formulations. Presented at the Suppression and Detection Research and Applications—A Technical Working Conference (SUPDET 2007); Wyndham Orlando Resort, March 5–8, 2007, Orlando, FL, USA.     

Study on the generation of perfluorooctane sulfonate from the aqueous film-forming foam

Perfluorooctane sulfonate (C(8)HF(17)SO(3)) and perfluorooctane acid (C(8)HF(15)O(2)) are artificial chemicals and have been used all over the world, mainly as water repellent agents, fluorochemical surfactants, coating agents, etc. However, perfluorooctane sulfonate and perfluorooctane acid are environmental contaminants because of their stability, bio-accumulativeness, and long-term persistence in the ecological environment. At the present day, they are diffused all over the world. Lately, this diffusion is viewed with suspicion and there is a movement towards their restriction, even if the environmental fate of them is still under investigation. Fluorochemical surfactants are key compounds in the aqueous film-forming foam (AFFF) formulations. AFFFs are used for massive conflagration such as industrial fire and petroleum fire because of their efficient fire control. On the other hand, a lot of AFFFs are used in case of massive conflagration and most of them enter ocean and groundwater. Actually, perfluorooctane sulfonate and perfluorooctane sulfonate related substances were detected from the fire-fighting facility of US forces. Therefore, there is the possibility of generating perfluorooctane sulfonate and perfluorooctane sulfonate related substances from fluorochemical surfactants in the AFFFs. In this study, activated sludge added AFFF were analyzed for perfluorooctane sulfonate and perfluorooctane acid with time. And the perfluorooctane sulfonate was directly detected after 2 days using LC-MS. This shows that AFFF can be decomposed perfluorooctane sulfonate by microorganisms easily. However, perfluorooctane sulfonate would not decompose at all. Additionally, activated sludge added N-polyoxyethylene-N-propyl perfluorooctane sulfonamide which is one of the fluorochemical surfactants used in the AFFF was analyzed for perfluorooctane sulfonate and perfluorooctane acid with time and the perfluorooctane sulfonate was detected too.     

An Analytically Defined Fire‐Suppressing Foam Formulation for Evaluation of Fluorosurfactant Replacement

A 4‐component, analytically defined, reference fluorosurfactant formulation (Ref‐aqueous film forming foam [AFFF]) composed of 0.3% fluorocarbon‐surfactant concentrate (Capstone 1157), 0.2% hydrocarbon‐surfactant concentrate (Glucopon 215 UP), and 0.5% diethylene glycol mono butyl ether by volume in distilled water was found to have rapid fire extinction comparable to a commercial AFFF in tests conducted on a bench scale and a large scale (28 ft², part of US Military Specification, MIL‐F‐24385F). The Ref‐AFFF was analytically characterized to provide the identity and quantity of the chemical structures of the surfactant molecules that were lacking for commercial AFFF formulations. To arrive at an acceptable Ref‐AFFF formulation, 3 candidate formulations containing different hydrocarbon surfactants in varying amounts were evaluated and ranked relative to a commercial AFFF using a bench‐scale fire‐extinction apparatus; varying the hydrocarbon surfactant was found to affect the fire‐extinction time. The ranking was confirmed by the large‐scale tests suggesting that the bench‐scale apparatus is a reasonable research tool for identifying surfactants likely to succeed in the large‐scale test. In the future, replacing the fluorocarbon surfactant with an alternative surfactant in the Ref‐AFFF enables a direct comparison of fire extinction and environmental impact to identify an acceptable fluorine‐free formulation.     

新型氟碳表面活性剂在轻水泡沫灭火剂中的应用研究

研究一种新型非离子氟碳表面活性剂Interchem-1的溶液性能,最低表面张力可达16.8 mN/m,临界胶束浓度为5×10-4~1×10-3,同时具有良好的发泡性及泡抹稳定性。以Intechem-1氟碳表面活性剂为主剂的轻水泡沫灭火剂,显示出优异的灭火效果。     

Fluorescein and Poly(Ethylene Oxide) Hose Stream Additives for Improved Firefighting Effectiveness

A novel technique has been developed to accurately monitor levels of hose stream additives by adding a fluorescein tracer. A fluorescent agent system is proposed to control and monitor additives into hose streams. Fluorescent water streams also have the advantage of improved nighttime and low-light visibility.Poly(ethylene oxide) (PEO) was shown in the 1960s to be very effective in fire hose streams, providing dramatic increases in hose stream pressure, reach, and volume. As is discussed in this paper, however, PEO fell into disrepute for firefighting operations. A reexamination strongly indicates the inaccuracy of previous misperceptions and indicates that PEO deserves reconsideration as being potentially powerful for greatly enhanced petroleum, ordnance, high-rise and impeded access firefighting, in which increased stand-off distances are desirable.