by Joan Leedy
At Dyne, we are often asked “What is the shelf life of my firefighting foam concentrate?” And the answer is – that depends. There are many factors that can affect shelf life. I will discuss the major ones here.
The Brand and Model of Foam – Though there are some similarities among the foams produced today, none are identical and some formulations will have longer shelf lives than others. Check with the manufacturer of your foam to obtain a shelf life estimate. Manufacturers typically run accelerated aging studies to predict the shelf life of a formulation.
Materials of Construction – The foam manufacturer should be able to provide acceptable materials of construction for storing their respective foam concentrate in order to maximize shelf life. This will include the tank, piping materials, valves, pumps and other surfaces that come in contact with the foam concentrate.
The 2016 edition of the National Fire Protection Association Standard 11 - High, Medium and Low, Expansion Foam also provides recommendations on the materials of construction in contact with firefighting foam concentrate. NFPA 11 recommends that foam concentrate piping and fittings be constructed of brass (red or naval), bronze, stainless steel (304 or 316) or “other material, in accordance with the foam concentrate manufacturer’s certification of compatibility with the foam concentrate and as approved by the AHJ”. Carbon steel piping or fittings is not recommended for use with foam concentrate. See NFPA 11 Section 4.7.
An additional concern with materials of construction can be galvanic corrosion when using dissimilar metals. Dielectric components are recommended to insulate dissimilar metals – see NFPA 11 section 220.127.116.11.
Evaporation – Foam concentrates are typically made up of 60 to 80 percent water and 10 to 30 percent solvent such as ethylene glycol monobutyl ether. If left open to the atmosphere, the water and solvent in the foam concentrate can evaporate over time. If extensive evaporation occurs, the concentrate can become ineffective. The 2016 edition of NFPA 11 addresses this issue in Section 18.104.22.168: “The storage tank shall be designed to minimize evaporation.”
Contamination – By far the most likely reason for a field foam to no longer perform is due to dilution with water. The system is connected to a water source by design and if the water inadvertently enters the foam concentrate tank, it can dilute the foam to the point where it will not perform effectively.
Mixing of Incompatible Foam Concentrates – Often times a foam concentrate tank must be topped off with additional foam after system testing or after a fire incident. Prior to adding foam concentrate to a tank, make sure the foam you are adding to the tank is compatible with the foam in the tank. The 2016 edition of NFPA 11 does not recommend that different types of foam concentrate be mixed in storage – for example do not mix an AFFF with a fluoroprotein foam. However, NFPA 11 does allow the mixing of the same type of foam concentrate as indicated in section 22.214.171.124 “Different brands of the same type of concentrate shall not be mixed unless data are provided by the manufacturer and accepted by the AHJ to prove they are compatible.”
Storage Temperature – Foam concentrates are designed to be stored at a particular temperature range – the most common being between 35- and 120-degrees Fahrenheit. If stored below 35-degrees F, there is a risk of freezing. Typically freezing does not affect the shelf life of a foam concentrate though it can stratify with several freeze-thaw cycles which may require mixing prior to use. If stored above 120-degrees F, the shelf life can be decreased. In general, the higher the storage temperature, the shorter the shelf life of a foam concentrate. The 2016 edition of NFPA 11 section 126.96.36.199.2 states “Foam concentrates shall be stored within the listed temperature limitations.”
Shelf Life of Foam Solutions – In general, once foam is mixed with water at its nominal concentration – say a 3% foam concentrate has be put into a storage tank with 3 parts concentrate and 97 parts water – it may have a significant reduction in shelf life. Again, the manufacturer of the foam should be consulted to determine the shelf life of a foam solution.
Summary – The shelf life of a foam concentrate can vary from type to type and from manufacturer to manufacturer. Additionally, many storage factors may affect the shelf life of a foam. This is why annually testing of foam concentrate is recommended.
If you have any questions regarding this article or would like more information, please contact Dyne Fire Protection Labs at firstname.lastname@example.org or (800) 632-2304.
©Dyne Fire Protection Labs 2019