By Grant Lobdell, General Manager
While it is important to verify foam concentrate quality periodically, it is equally important to inspect and test the proportioning equipment used in conjunction with that concentrate. Even the best foam concentrate can be rendered ineffective if not proportioned at its designed percent.
NFPA 11 Requirements
NFPA 11 Standard for Low-, Medium-, and High-Expansion Foam requires foam-producing equipment to be inspected and tested for correct operation annually. As part of this inspection, the proportioning equipment needs to be flow tested to ensure the amount of foam concentrate in the produced solution is between its listed concentration and up to +30% past its listed concentration or one full percentage point, whichever is less. For example, a foam concentrate listed for use at 3% would be required to proportion anywhere from 3% to 3.9%. On the other hand, a 6% foam concentrate would be required to proportion anywhere from 6% to 7% given one full percentage point is less than +30% of the listed concentration.
Collecting Proportioned Solution
While NFPA 11 does offer some general guidance on proportioning systems, it is always best to consult the manufacturer for more detailed instructions for your specific proportioning equipment. Before running the system, ensure proportioning equipment is listed for use with your specific foam concentrate. When it comes time to collect the proportioned solution, ensure the system is run as designed and for a sufficient amount of time before collecting your sample.
There are certainly situations where flowing foam concentrate is not possible or recommended. For this reason, NFPA 11 does state that alternative methods shall be permitted where approved by the authority having jurisdiction (AHJ). This includes listed or approved methods that do not even require the discharge of foam concentrate at all. Annex D Tests for Foam Systems in NFPA 11 has two of these alternative methods outlined. For the surrogate liquid method, a more environmentally friendly chemical designed with the same flow characteristics as your foam concentrate is used. For the water equivalency method, only the water flow rate through the proportioning equipment is assessed periodically. Note that with the water equivalency method foam concentrate will still need to be flowed during the initial acceptance test to establish the requirements.
Detailed procedures for determining the concentration of foam concentrate in a foam solution can also be found in Annex D of NFPA 11. The refractive index or conductivity of the foam solution produced from the proportioning equipment is to be compared to the refractive index or conductivity of solutions of known concentration made by hand. The relationship between the percent concentration and refractive index or conductivity is linear. When making your solutions of known concentration by hand, ensure the foam concentrate and water being used are representative of the foam concentrate and water used by the proportioning system at the time of testing.
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at email@example.com or (800) 632-2304.