By Jonathan M. Hinson
Firefighting foam has been around for many years, from the powder foam to protein foam to the synthetic foam in use today.
Originally designed to extinguish simple hydrocarbon-based fuel fires, today’s foams can be used on Class A fires and alcohol-based fuel fires and, of course, foam is still used for hydrocarbon fuel fires. Technology has advanced to make foam operations more effective, simplistic, and cost-effective. Flammable and combustible liquids are everywhere and being transported through all modes of transportation. Hopefully, all fire departments have enough foam resources readily available to effect a rescue from a flammable liquid incident. Some communities may have a higher risk or threat, so more foam resources are needed. Whether a department has an eductor and three buckets of foam or thousands of gallons of foam with master stream devices, there are still some basic principles and tips that can apply to both situations that will facilitate a successful foam operation.
Foam 101
Foam has been a source of frustration for many firefighters over the years, as making an effective finished foam blanket can be a challenge. Most foam equipment is very simple in operation, but there are complex systems on apparatus that require in-depth knowledge for operation. Regardless of the system being used, making finished foam without failure requires knowledge of basic principles and the equipment and supplies being used. The foam must also be properly applied to ensure complete extinguishment and prevent reignition.
As taught in most basic firefighting classes, four components are required to make finished Class B foam. Foam concentrate is the first component needed, which is commercially manufactured by both domestic and international companies. The foam concentrate is then introduced into water to form a foam solution. Next, the foam solution is mixed with air either by expelling it into the air through a standard nozzle or while passing through an air-aspirating foam nozzle. The foam must also be agitated, which can occur in a foam nozzle or on contact with a surface after leaving the nozzle. When these four components come together, the result is finished foam that can be used to extinguish flammable/combustible liquid fires or prevent ignition of flammable vapors. If any of these four components are missing, the Class B foam operation will not be effective and possibly fail completely.
There are two common types of foam, Class A and Class B, that equate to the types of fires they are effective on. Class B foams create a film or membrane over the surface of a fuel to prevent vapor production. The higher the expansion rate of the foam application, the longer the blanket will last, and also less foam concentrate will be used during reapplications during longer term incidents. Class A foams break down the surface tension of a fuel, allowing the water to penetrate quicker and deeper. Making a thick foam blanket is not required with Class A foam because the bubbles have nothing to do with the effectiveness of the foam.
Using the wrong type of foam can cause an ineffective firefight, leading to someone getting hurt. Class A foam cannot be used on a Class B fire. Class A foams do not make the needed film to smother the fire and prevent the production of vapors needed for combustion. Class A foam could slow the fire down and even extinguish a small flammable liquid fire somewhat, but even the small fire is going to quickly degrade the foam and allow the fire to reignite. The sudden and often unexpected reignition can injure the firefighters on scene who have possibly let their guard down after seeing extinguishment.
Applying Class B foam to a Class A fire is not as dangerous but can be ineffective. Some br