When sending in foam concentrate samples to a laboratory to determine its continued performance for inspection, testing and maintenance purposes, it is important that the sample is representative of the tank to ensure safety, receive quick and accurate results, and to limit future retesting expenses. It is also important to realize that a foam concentrate tank is not always uniform throughout so it can be beneficial to take a sample from two different areas of the tank, specifically the top and bottom of the tank.
The best outcome is that both samples pass and both have the same physical properties and level of performance. This indicates the foam is fairly uniform in that tank and you can expect the same performance from the initial trip of the system all the way through the tank supply. However, even when both samples pass the annual testing, the results may differ slightly. Most often, the top sample can have lower physical property values and performance, particularly in a bladder tank. Result differences could also come from a tank being topped off with different foam than what is already in the tank.
The most beneficial reason to taking a top and bottom sample when sending in foam concentrates comes when one of the two fails. Let’s say there is some water at the top of a tank that has diluted the concentrate enough to where the foam there no longer performs but the bottom, which may be unaffected by the dilution, still performs. If only a top sample was taken, one might assume the whole tank must be replaced. However, that dilution may only be affecting a small percent of the tank and removing the diluted foam and salvaging the performing foam may be allowed. Had a bottom sample been taken along with the top in that situation, it would have indicated some foam might be salvageable, sparking further investigation, and thus saving thousands in replacement costs. On the flip side, if only the bottom sample had been taken, one might assume the whole tank is performing. This could be very dangerous as a portion of that tank might not be performing. While not as likely, it is also possible the bottom sample is underperforming while the top is just fine. This can be a result of polymer separation, metal ions from the bottom piping or the result of different foams being used when topping the tank off.
Should both the top and bottom fail, you can feel more confident that the whole tank must be replaced. Should the results indicate dilution for both samples, you could be looking at a bladder rip, missing isolation valve, or other storage issues.
While it costs more to test the additional sample, it can give you a much better picture of the tank. The cost spent up front taking multiple samples may one day be recouped and then some if it saves full foam replacement. If you are looking to determine what happened to the foam to possibly prevent future issues, the savings are also immense. However, some people do choose to get the best of both worlds by taking a top and bottom sample then combining them into one test sample. The thought is that the composite sample is more representative of the tank while still only requiring one sample to be tested. While allowed, it does mean the benefits of seeing the difference between the top and bottom performance are now lost. If we take our diluted top and performing bottom example again, it could be that the top is diluted enough to still produce a failing result even when mixed with the performing bottom. It could also be that the performing bottom is good enough to mask the dilution at the top. Both results could be costly.
If you have questions and would like to speak with a chemist at Dyne Fire Protection Labs contact us at lab@dyneusa.com or (800) 632-2304.