Evaluation of Conductivity Meters for Firefighting Foams

FAA Technical Note 02-115 "Evaluation of Conductivity Meters for Firefighting Foams

This evaluation was conducted to comparatively test various conductivity meters and refractometers for use in testing airport rescue and firefighting (ARFF) vehicle foam-proportioning systems. The amount of foam concentrate fed to the foam proportioner of a firefighting system is critical, not only in the making of foam with the proper expansion and drainage rate, but also in making a fire-resistant foam. Therefore, it is essential that correct proportioning is maintained and that the concentration meets the required level. During the annual certification inspection of an airport fire department, refractometer and conductivity meter tests are conducted to test the foam concentrate and foam-proportioning systems of the ARFF apparatus.

Historically, refractive index has been used to determine the proportioning of foam-generating systems. Recently, the accuracies of the refractometer tests are questionable. The refractometer gives readings with an accuracy of ±0.3%, whereas conductivity meters can give readings with an accuracy greater than 0.05%. Therefore, the National Fire Protection Association (NFPA) now requires the use of conductivity meters in NFPA 412, Standard for Evaluating Aircraft Rescue and Firefighting Foam Equipment, 1998 edition.

Five conductivity meters were evaluated against the standard refractometer. There were some variations to the operation and calibration of the conductivity meters that made some meters slightly better than others. It was determined, however, that all five conductivity meters were more accurate and easier to use for conducting tests on foam-proportioning systems than the refractometer.

Mr. Keith Bagot
FAA Technical Center
ARFF Research Program
Airport R&D, Bldg. 296
Atlantic City International Airport, New Jersey, 08405

Contact Project Lead: Keith Bagot, ATO-P (formerly AAR-411)

Last Update: 05/18/09