by Joan Leedy, Technical Director

NFPA 11 The Standard for Low-, Medium- and High-Expansion Foam recommends that foam proportioning systems be tested when installed and yearly thereafter.

NFPA 11 Section 12.6.5 states “The foam concentrate induction rate of a proportioner, expressed as a percentage of the foam solution flow (water plus foam concentrate), shall be within minus 0 percent to plus 30 percent of the manufacturer’s listed concentrations, or plus 1 percentage point, whichever is less.”

The table below states the concentration percent requirements for typical firefighting foam:

Manufacturer’s Listed Concentration (%)

Concentrate % in Accordance with NFPA 11







However, because of environmental concerns with the fluorochemical surfactants in firefighting foams, some jurisdictions have banned discharging foam solution while testing the foam system. So how do you make sure a foam system will work effectively in the event of a fire without the ability to run the system annually and verify accurate proportioning? NFPA 11 Section 12.6.4 allows for the use of a listed or approved method that does not require the discharge of foam concentrate. Two methods are described in the Annex of NFPA 11, one being the Surrogate Liquid Test Method and the second being the Water Equivalency Method. 

The viscosity of firefighting foam has always been an important property to monitor as foam ages. But monitoring the viscosity has become even more critical to overall performance now as we transition to testing proportioning systems without discharging foam.

The Surrogate Liquid Test Method and the Water Equivalency Method do not discharge foam during the recommended annual proportioning test. The assumption made is that the viscosity of the foam concentrate has not changed significantly since the acceptance test. But should the viscosity of the foam concentrate increase significantly—which can happen in storage—the foam concentrate will proportion at a lower, possibly ineffective, concentration.

To ensure the system will proportion correctly throughout the life of the foam concentrate, Dyne recommends the viscosity of the new foam concentrate be determined when first installed in the system and then annually thereafter. The viscosity of new foam can either be sampled and tested when installed or the viscosity can also be determined from the manufacturer’s certificate of analysis. The viscosity can then be monitored annually for any changes and trends can be noted and, if necessary, investigated. This is particularly important with alcohol-resistant foam concentrates and some of the new synthetic fluorine-free foam concentrates which have a relatively high viscosity when manufactured.

The viscosity of viscous foams is included in the annual foam concentrate testing service offered by Dyne Fire Protection Labs. For more information, email or call (800) 632-2304.

©Dyne Fire Protection Labs 2021