by Grant Lobdell
According to the current, 2016 edition of National Fire Protection Association (NFPA) 11 Standard for Low-, Medium, and High-Expansion Foam, samples of foam concentrates are to be sent to a laboratory for quality conditioning testing at least annually. Not much is given, however, as to how this sample is to be obtained. As a result, we have put together a few things to consider when taking your foam concentrate sample.
Top and Bottom Sample
Most people take just one foam concentrate sample from each of their tanks, drawn from wherever it is easiest to obtain a sample on their system, to send in for the quality conditioning testing. I ask that you consider your tank may not be homogenous throughout, especially those tanks that hold several hundreds to thousands of gallons of foam concentrate. The top of the tank may be very different from the bottom. Often, any dilution, whether that be due to human error or unavoidable condensation, typically settles at the top of the tank. Furthermore, if you’ve topped off your tank at some point, it is very likely that the foam concentrate at the top will be slightly different than the foam concentrate at the bottom even if they are from the same lot to begin with. This is simply due to differing storage conditions throughout their life. Finally, also note that it is possible for some ingredients in the foam concentrate to settle out of solution. This typically occurs when the product is stored outside of the manufacturer’s recommended storage conditions. If this has occurred, ingredients less dense than water will settle on the top of the tank and the ingredients denser than water will settle at the bottom.
By only taking one sample isolated from either the top or bottom, you may not be getting the whole picture. The sample may not be representative of the whole tank. To get a better picture of the tank as whole, consider taking both a top and bottom sample.
Drain Some Foam Concentrate Before Sampling
Most often, people drain and collect as little foam concentrate as possible when taking a sample of their foam concentrate from a bladder system. This does reduce waste, but it also may not give you the most representative sample. Consider that the foam stored in metal trim pipe, which has been exposed to that metal pipe for quite some time, may be quite a bit different from the foam stored in an elastomeric bladder. Also consider the condition of the metal of the trim piping itself where applicable. Often times it can be corroded and is depositing those corrosion byproducts into the foam concentrate. Lastly, understand that small volumes of a foam concentrate, like that found in the trim piping, are more susceptible to adverse storage conditions than larger volumes, like that found in the bladder. To understand this phenomenon, consider how much easier it is to boil 1 cup of water vs 1 gallon.
To take a representative sample from metal trim piping, it is advised that you first drain out the foam concentrate that has been sitting in the trim piping since the last sampling. To figure out how much foam concentrate to drain, consider both the length and diameter of the pipe connecting to the bladder. Collecting and properly disposing of the drained foam concentrate is advised.
Avoiding Mineral Oil
Mineral oil may be found at the top of some atmospheric tanks to prevent solvent from evaporating out of the foam concentrate. The mineral oil is a good barrier to prevent this evaporation from happening, but it can have an adverse effect on foam concentrate performance. Mineral oil is not designed to expand and extinguish fires. As such, it is recommended that the top sample of foam concentrate drawn from tanks with mineral oil be drawn well below the mineral oil layer.
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at firstname.lastname@example.org or (800) 632-2304.
©Dyne Fire Protection Labs 2020