Dilution with water is the most common reason why fire-fighting foam fails. If the tank is not properly isolated, water can inadvertently get into a tank and dilute the foam concentrate. A properly designed system has isolation valves and backflow prevention valves to prevent inadvertent dilution. When fire-fighting foam becomes diluted, it will not work effectively in the event of a fire.
Manufacturers will typically warrant their foam products for a time period which can range for as little as a week for some premixed foam solutions to 5 years for protein-based foam to 20 years for some synthetic foams. However, foam products will degrade over time and at some point the solutions and or concentrate may no longer work effectively. So the age of the foam can also be a reason for failure.
NFPA 11 recommends that different types or brands of firefighting foam should not be mixed in storage. This is especially true for alcohol-resistant foams. For example, if an alcohol-resistant concentrate is mixed with a freeze protected concentrate, there is possibility of the polymer dropping out of solution. Not only will this diminish the firefighting capabilities of the foam, it can plug the proportioning orifice and prevent the foam concentrate from mixing with the water supply.
Putting the wrong type of fire-fighting foam concentrate into a tank can cause a foam to fail. Standard AFFF foam is designed to extinguish only non-polar or hydrocarbon solvents and is not effective in protecting polar solvents such as ethanol or isopropanol. It is critical to match the foam concentrate to the specific hazard to ensure effective fire protection. By using the wrong type of firefighting foam, the tank may be filled with the incorrect concentration of foam. For example, if a system is designed to proportion 3% foam, but it filled with 6% foam, the solution will not effectively extinguish a fire.
Improper sampling technique is another reason that firefighting foam fails. Many times bladder water is sampled for testing instead of firefighting foam. This will immediately cause the “concentrate” to fail. Another example of this is not taking a representative sample of the tank. Depending on a system, more than one sample may need to be taken and/or tested to ensure that the tank is being represented. Proper training and understanding of a system will ensure that proper sampling techniques are being followed.
These are just the most common reasons a firefighting foam sample can fail its annual inspection. By testing a system annually, as recommended by NFPA, these failures can be identified and fixed so your systems will operate effectively when needed.
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