By Grant Lobdell, General Manager
The current, 2021 edition of NFPA 11 Standard for Low-, Medium, and High-Expansion Foam defines a balanced pressure bladder tank as “a foam concentrate tank fitted with an internal bladder that uses waterflow through a modified venturi-type proportioner to control the foam concentrate injection rate by displacing the foam concentrate within the bladder with water outside the bladder.” While most are familiar with the inspection testing, and/or maintenance (ITM) of the foam concentrate, proportioner, and tank, people often wonder why Dyne Fire Protection Labs offers analysis of the bladder water itself. Ultimately, bladder water analysis is designed to help building owners and/or their designated representatives determine if the bladder water has been contaminated with foam concentrate. If foam concentrate is found in the bladder water, the building owner and/or their designated representative can then consider both how it got there, including but not limited to additional testing to investigate the bladder integrity, and what to do about it (i.e., how to properly dispose of the bladder water if draining is required).
NFPA 11 requires this testing be completed annually. Section 13.3.2.5.5.2, titled Bladder Tank Proportioner, states “The inspection shall include the following…3) An inspection for the presence of foam in the water surrounding the bladder (annual).”
For bladder water samples, Dyne Fire Protection Labs can determine and report the following:
Physical Properties
· Refractive index
A measure of how light is bent, or refracted, when passing through a sample. This is a commonly reported property for foam concentrates which typically range from 1.3400 to 1.3900 depending on the product. For reference, tap water typically has refractive index of 1.3330. In most cases, the more foam concentrate in the water, the higher the refractive index.
· Density
A measure of how much sample (mass) is in a given volume (density = mass/volume). This is a commonly reported property for foam concentrates which typically range from 1.000 to 1.100 g/mL depending on the product. For reference, tap water typically has a density of 0.998 g/mL. In most cases, the more foam concentrate in the water, the higher the density.
· pH
A measure of how acidic/basic the sample is (with a pH of 7 being considered neutral). This is a commonly reported property for foam concentrates which typically range from 6.0 to 9.5 depending on the product. While not a direct reflection of the amount of foam concentrate in a bladder water sample, the pH can give some sense as to how corrosive the bladder water might be to the tank.
Chemical Composition
· Estimated % Concentration
A rough estimation of how much (%) foam concentrate might be in the sample based on the refractive index or density of the sample compared to the refractive index or density of the foam concentrate and system water (which must also be provided). A sample with a high refractive index and/or density can indicate foam concentrate may be present. However, the refractive index and/or density could be higher than expected due to other sources of contamination, including but not limited to the lubricant used during the bladder install. As a result, before assuming the refractive index and/or density increase is directly the result of foam concentrate contamination, Dyne Fire Protection Labs will also evaluate the bladder water sample’s expansion ratio and film formation (if applicable). After all, if foam concentrate is present, the bladder water should have some performance similar to foam solution.
· Total Organic Fluorine (TOF) – additional test available upon request, additional fee applies
A measure of how much organic fluorine, which is the fluorine found in organic molecules such as per- and polyfluorinated substances (PFAS), is in the sample. For reference, most fluorinated foam concentrates such as aqueous film forming foams (AFFF) typically contain 5,000 to 20,000 ppm TOF whereas most synthetic fluorine free foams (SFFF) contain < 1 ppm TOF. Assessing the amount of PFAS via TOF can be useful when working with local waste treatment plants and environmental protection agencies to determine if the bladder water can be dumped down the drain or if it must be contained and disposed of by other means.
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at lab@dyneusa.com or (800) 632-2304.
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