Bladder tank proportioning foam systems require no external power other than adequate water supply and pressure. A bladder tank consists of a carbon steel tank with an inner elastomeric bladder (diaphragm bag). Foam is stored inside this bladder while water is directed through piping to the area between the steel tank and the internal bladder. The resulting pressure forces the foam out of the bladder and into a controller which mixes foam and water at the prescribed concentration, typically 1 to 6 percent.

Most foam users are aware that the National Fire Protection Association Standard 25, “Testing and Maintenance of Water-Based Fire Protection Systems”, recommends that the foam concentrate in the bladder tank be sent to a laboratory for testing at least annually.

“ Foam concentrate testing shall be conducted annually. Samples of foam concentrates
shall be sent to the manufacturer or an approved testing laboratory for quality condition testing.”

In addition, NFPA 25 recommends foam bladder systems be inspected at least annually. Furthermore, NFPA 25 states the inspection shall include an inspection for the presence of foam in the water surrounding the bladder.

“ Where bladder tanks are used, an inspection for the presence of foam in
 the water surrounding the bladder tank shall be conducted annually.”

Foam concentrates in the water surrounding the bladder can be an indication of several potential problems:

  1. A tear in the bladder – foam concentrate can leak through the tear into the water surrounding the bladder. Even a small tear in the bladder can render the system inoperable.
  2.  A missing isolation valve or an isolation valve that was not closed. The foam isolation valve prevents foam concentrate from siphoning through the controller and into the shell area.
  3. Improperly filling the bladder tank by filling the shell area with foam instead of the bladder tank.

Dyne offers bladder water testing and samples can be sent to our laboratory using our standard foam test kits. Dyne will verify the concentration of foam concentrate in the bladder water samples by running the following tests.

  1. Refractive index – the refractive index is often used to measure the concentration of foam concentrate in water and can be measured in the field. In a bladder system however, substances other than foam can contribute to the refractive index value – such as oils used to lubricate the bladder.
  2. Density – the density value along with the refractive index can be a better indicator of the presence or absence of foam. Generally, an elevated refractive index yet a density value similar to water indicates no foam but the presence of lubricating oils while an elevated refractive index and density is more likely to indicate foam concentrate.
  3. Expansion, Film Formation and Surface Tension – If the refractive index and density are both elevated, Dyne goes a step further to determine if this elevation is being caused by foam or some other substance. By testing a typical property of foam such as expansion and determining the solution is expanding when agitated, we can be assured the sample contains foam.
  4. Concentration – by considering the results from the tests listed above, Dyne provides an estimate of the concentration of foam in the bladder or shell water. If the concentration is significant, the system can be further tested to determine why foam concentrate is getting into the shell water.

These tests are run to identify a significant concentration of foam in the bladder water which would indicate deficiencies with the foam system. If the testing is being completed to determine how to dispose of the bladder water, consider more sophisticated analytical methods with lower detection limits.

If you are interested in sending bladder or shell water to Dyne for testing, or have additional questions, please give us a call at (800) 632-2304 or e-mail

©Dyne Fire Protection Labs 2023

If you have any questions regarding this article, please contact Dyne Fire Protection Labs at or (800)632-2304.