The National Fire Protection Association (NFPA) “Standard for Low-, Medium- and High-Expansion Foam”, Current Edition 2021, recognizes foams manufactured without per- and polyfluoroalkyl substances (PFAS) and has defined them as synthetic fluorine free foam (SFFF). Yes, I know, yet another acronym!
Section 3.3.12.8 of NFPA 11 reads as follows:
Synthetic Fluorine Free Foam (SFFF). Foam concentrate based on a mixture of hydrocarbon
surface active agents that is not formulated to contain per- or poly-fluoroalkyl substances (PFAS).
There are several listed or approved SFFF concentrates commercially available today and many foam users are considering switching from an aqueous film forming foam (AFFF) to an SFFF to avoid the negative environmental properties associated with foams containing PFAS. NFPA 11 recommends all foam, whether it’s AFFF or SFFF, be tested annually as stated in section 13.2.6.1 and 13.2.6.2:
At least annually, an inspection shall be made of foam concentrate and their tanks or
storage containers for evidence of excessive sludging or deterioration.
Samples of concentrates shall be sent to the manufacturer or qualified laboratory for quality condition testing.
So how are SFFF concentrates tested compared to AFFFs?
1) Like AFFFs, the physical properties of the SFFF foam concentrate are tested and compared to the manufacturer’s specification. The typical physical properties are:
a. Appearance – a significant change in appearance can be a sign of degradation i.e., if the manufacturer defines the appearance as “viscous yellow liquid” and the sample is rust-colored, this can be a sign of corrosion or contamination.
b. pH – generally foam concentrates have a neutral pH of approximately 6 to 9. If the pH is well outside of this range, it is a sign of degradation which breaks down the hydrocarbon surfactants and can reduce expansion and ultimately extinguishing performance.
c. Density or specific gravity – typically the density or specific gravity of foam concentrate is higher than the density or specific gravity of water. A change in the density or specific gravity can be an indication of contamination with another substance i.e., water or another foam concentrate.
d. Viscosity – a decrease in viscosity often indicates dilution, an increase in viscosity can indicate unfavorable storage conditions. A significant increase in viscosity can render the foam ineffective as it will not proportion at a sufficient concentration.
2) The performance properties are also critical when testing SFFF and AFFF.
a. However, unlike AFFFs, SFFFs do not form an aqueous film on hydrocarbon liquids. Because SFFFs are not able to form a film, when testing SFFF, it is not necessary to test for film formation or spreading coefficient.
b. SFFF foam solutions require a sufficient foam expansion to perform effectively therefore testing the expansion is recommended and critical to the performance. The expansion is the ratio of the volume of the expanded foam to the foam solution. Typically values range from 4:1 to 10:1. While AFFFs were often applied using non-air aspirating nozzles, it is recommended that SFFFs be used through air-aspirating nozzles.
Section H.1.2 Item 4 of NFPA 11 reads as follows:
SFFFs presently available appear to work much better on extinguishing
Class B fire when applied using an air-aspirated nozzle…..
It is also required that SFFF expand at a higher rate when used through the same equipment. The recently released Mil-PRF-32725 performance specification for Fire Extinguishing Agent, Fluorine-free Foam Liquid Concentrate - Table I on Page 4 - requires a minimum expansion of 7.0, while the corresponding specification for AFFF, MIL-PRF-24385F required a minimum expansion of 5.0.
c. The 25% drain time is the time for 25% of the expanded foam to drain into a foam solution. This property is also tested on SFFFs.
d. If the type of foam is undocumented but it is being used to protect polar solvent liquids, a polar solvent burnback test can be conducted to ensure performance on these types of flammable liquids.
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at lab@dyneusa.com or (800)632-2304.