by Joan Leedy, Technical Director, Dyne Fire Protection Labs

Why is viscosity a critical measurement to ensure foam performance?

If you’ve received a firefighting foam test report from Dyne, you will often notice that we have tested the viscosity of the foam concentrate. This is an important property to ensure performance.

Manufacturers add polymers to foam concentrates to improve performance. Historically with AFFF and FFFP formulations, polymers were added to enable the concentrate to extinguish polar solvents such as acetone, isopropanol and ethanol. Standard AFFF, for use strictly on hydrocarbons, do not have a significant viscosity and have flow characteristics like water. With the new SFFF (Synthetic Fluorine-Free Foam) concentrates, polymers are added to most of the formulations – including products for use on hydrocarbons only - to improve performance by lengthening the drain time. These polymers increase the viscosity of the foam concentrates.

Monitoring the viscosity of foam concentrates as they age will ensure they maintain performance and proportion accurately. Should the viscosity of a foam concentrate change significantly in storage, it may not proportion properly. For example, if the foam concentrate is designed to be used at 3% and it proportions well below 3%, the fire may not extinguish. Conversely, if the viscosity of the foam concentrate is well below the specification, the foam will proportion above the nominal concentration and the quantity of foam will be insufficient to operate for the required time frame.

Dyne determines the required viscosity from the manufacturers published datasheets. As with all testing, it is critical to correctly identify the brand and type of foam concentrate in order to accurately test to the correct viscosity requirement. The following is a typical example taken directly from a datasheet:

Viscosity: 5000 - 8000 cPs*

*Brookfield Viscometer Spindle #4, Speed 30 rpm

Note the asterisk defines the conditions and equipment used to run the test. Another important condition is the temperature. In the Dyne laboratory, testing is always completed at room temperature of 20 to 24 degrees Celsius. Note this temperature applies to the room, equipment, and foam concentrate.

Changes in viscosity can be caused by aging, equipment incompatibility, concentrate mixing, contamination, temperature extremes, evaporation, and other storage issues. NFPA 11 recommends foam concentrate be sent to a laboratory for “quality condition testing” at least annually.

If you have any questions regarding this article, please contact Dyne Fire Protection Labs at or (800)632-2304.

©Dyne Fire Protection Labs 2024