By Emily Maranell, Quality Technician I
Verifying that a firefighting foam system accurately proportions is critical to system effectiveness in the event of a fire. If a foam solution is too lean, it may not have the necessary fire suppression capabilities to effectively extinguish the fire. If it’s too rich, the system may consume its foam concentrate supply too quickly before the fire is fully extinguished. Proper proportioning testing is essential to maintaining the intended performance of a firefighting foam system and confirming the correct concentration of foam solution is delivered when needed.
Standard
NFPA 25, 2026 Edition, Section 11.3.2.5.7, provides the acceptable tolerance for foam proportioning:
“The foam agent concentrate induction rate, expressed as a percentage of the foam solution flow(I.e., water plus foam concentrate), shall be within minus 0 percent to plus 30 percent of the manufacturer’s listed concentration or plus 1 percentage point, whichever is less.”
Testing
NFPA 11, 2024 Edition, Annex D, recognizes two primary methods for determining the concentration of firefighting foam solutions: refractive index and conductivity. Both methods utilize known foam solution concentrations to establish a calibration curve, which is then compared to an unknown foam solution to determine its concentration.
To obtain accurate and reliable results, several factors should be considered:
1. The standard solutions must be accurately measured and mixed.
2. The water and foam concentrate used to prepare the standard solutions should be representative of those in the proportioning system.
3. The refractometer or conductivity meter must be properly calibrated and accurate.
4. The foam solution should be generated at flow rates representative of the system’s intended operation conditions.
Proportioning verification is often performed in the field, allowing immediate feedback. However, laboratory testing provides a more controlled environment, helping minimize variables that may affect test accuracy. Dyne Fire Protection Labs utilizes a calibrated balance and benchtop refractometer that measures to the 5th decimal to accurately prepare and measure standard solutions.
Sampling
To accurately evaluate proportioning performance through laboratory testing, three representative samples must be collected: foam concentrate, system water, and foam solution.
1. A foam concentrate sample is required to prepare the known standard solutions used during testing. These standards establish a calibration curve used to determine the concentration of the unknown produced foam solution. The sample can be collected directly from the foam concentrate storage tank or from an appropriate sampling connection.
2. The system water sample is used to prepare the standard solutions and establish a baseline for refractive index measurements. When collecting a water sample, allow the water to run until it is representative of the system’s water supply.
3. The foam solution sample is used to evaluate the proportioning accuracy of the system. This sample should be collected from the designated test connection on the proportioner or directly from an appropriate discharge device. Before collecting the sample, allow the system to reach a stable operating flow rate.
Allowed Alternative Test Methods
Note that alternative proportioning test methods may be used when permitted by the applicable standard, consistent with the system and foam manufacturer's instructions, and accepted by the authority having jurisdiction (AHJ). Depending on the system design, these methods may use water or an approved surrogate in place of concentrate. These approaches can verify proportioner performance while reducing or avoiding the discharge of finished foam solution.
Results
When Dyne issues laboratory reports for proportioning samples, the results include physical properties along with the calculated foam concentrate percentage. Understanding what these results represent can help identify potential issues with the foam solution or proportioning system and determine what corrective action may be necessary to bring the system to meet the required standards.
1. Appearance: An observation of color, consistency, and the visible presence of sediment. Significant changes in appearance from previous testing may indicate that further investigation of the foam concentrate or storage conditions is necessary.
2. Refractive Index and Density: Both measurements provide additional information about the composition of the sample. If these measurements are like those of pure water, it may indicate that little or no foam concentrate is present in the sample.
3. pH: This measurement indicates how acidic or alkaline a sample is. Acidic (below 4) or alkaline (above 10) readings may indicate changes in the chemical condition of the foam solution and warrant further investigation.
4. Estimated Concentration: If the measured concentration falls outside the acceptable range, the system may not deliver the intended fire suppression performance.
Reasons for Failure
1. An incorrect foam to water ratio can result in an under or overconcentrated solution. This can occur when a system operates outside its manufacturer’s listed flow rate range, preventing the proportioner from accurately mixing the solution.
2. Improper sample collection can produce inaccurate results. Collecting samples from stagnant piping containing rust or sediment, or incorrectly identifying samples from a bladder tank, can lead to false failures. Providing the laboratory within correct product information can also result in inaccurate testing.
3. Proportioning systems require sufficient operating time to reach a stable flow condition. Collecting samples too early can result in diluted solutions due to standing water in the piping, producing inaccurate concentration readings.
What to do after a failed test
A failed proportioning test does not necessarily mean the foam concentrate is unusable, or the entire system needs a replacement.
1. Verify sample information: Confirm that the correct foam concentrate, system water, and foam solution samples were collected and properly identified.
2. Inspect the system: Investigate potential mechanical issues, incorrect settings, obstructions, or flow rate issues.
3. Make necessary corrections: Complete the required adjustments, repairs, or maintenance according to the manufacturer’s recommendations.
4. Perform follow-up testing: Collect a new representative foam solution sample and submit it for testing to verify that the issue has been corrected.
Proper investigation, corrective maintenance, and follow-up testing helps confirm the system can deliver the intended performance when needed during an emergency. Testing isn’t simply about passing or failing. It’s about identifying problems before the system is needed in an emergency. Should you ever have questions about proportioning testing, Dyne’s customer service team and quality technicians are here to help at 800-632-2304 or dyne.lab@nfpaglobal.com.
©Dyne Fire Protection Labs 2026.
