Firefighters preparing to engage in a basic foam operation must have a working knowledge of the basics. There is some vocabulary that if used incorrectly, can lead to confusion.
Foam concentrate typically comes in 5-gallon pails, or for more major types of operations can be found in 55-gallon drums and even larger storage capacities such as storage containers, called totes, that hold up to 250 gallons of concentrate or more. Foam concentrate must be added into the water stream in the proper ratio.
All of our members, regardless of the facility or community they protect should be thoroughly familiar with the concentrates in use by their department. Consult the web sites for each of the major manufacturers for specific details. See the references at the end of the first part of this series for many high-quality information sources.
For the more typical foam concentrates used on Class B fires, we find manufacturers making concentrates designed to be mixed with water at a 1%, 3%, or 6% ratio. In other words, depending on the type of foam, or the type of fuel, foam concentrate is designed to be mixed with 99 parts water to 1 part concentrate (1 % foam concentrate), 97 parts water to 3 parts (3% foam concentrate), or 94 parts water to 6 parts concentrate (6% foam concentrate).
Foam Solution is the mixing in the correct ratio of water to foam concentrate. After the water and the foam concentrate have been mixed together, the liquid in the hoseline is no longer water alone, nor is it foam concentrate. Rather, we have what is called a foam solution that is only missing one final ingredient.
Finished Foam is the mixing of air (aspiration) to the foam solution in the hoseline. The air being injected into the discharge stream creates the bubbles and “suds” that give foam its finished appearance. This “aeration” gives foam a power to remain in place for a period of time. For example, a thick blanket of foam that may be several inches thick will continue to provide protection and prevent the release of flammable vapors.
Finished foam has great properties in its ability to prevent the release of flammable vapors from mixing with air due to foam’s ability to float on top of a spill and present a barrier between the air and the fuel source. Nevertheless, this foam blanket will not last forever and eventually begins to degrade, especially if affected by fire or residual heat. A foam blanket’s “drain time” is discussed below.
A critical point to be aware of is finished foam’s compatibility with other types of extinguishing agents. As an example, finished foams such as Aqueous Film Forming Foam (AFFF) and Film Forming Fluoroprotein (FFFP) are compatible with dry chemical, and a coordinated attack can be achieved. Always check with the manufacturer regarding the foam concentrate your department uses to see if it is compatible with agents such as dry chemical.
Finished foam can be compatible with various types of extinguishing agents but, ironically, a plain water stream used near a foam stream will only wash away and dilute the finished foam. Therefore, coordination of hoselines is a requirement prior to any application. Even after the finished foam blanket has been applied and is doing its job to prevent the release of vapors, any application of water can destroy this blanket, so use caution near it!
Drain time is how long it takes for a foam blanket to break down. Finished foam can potentially deliver a thick, rich blanket to cover a spill or fire. As time passes, the finished foam blanket begins to degrade. The drainage rate is based on how long 25% of the foam blanket takes to break down. Eventually, a reapplication will be required or the danger of flammable vapors will resurface. If the fuel is hot or the surroundings that contain the fuel are hot, the foam blanket will degrade even more quickly.