by Types of Firefighting Foam
There are several different types of firefighting foam that are used to extinguish fires. Each type is designed to be effective against certain types of fires.
AFFF Foam
The most common type of foam used by fire departments is aqueous film-forming foam, also known as AFFF. This type of foam works by creating a thin film over the surface of the fuel, separating the fuel from oxygen. This causes the fire to be starved of oxygen and be extinguished. AFFF foam works on Class B hydrocarbon fuel fires, such as those involving gasoline, oil, grease, and other flammable liquids. It is effective at quickly knocking down large vapor fuel fires.
AR-AFFF Foam
Alcohol-resistant AFFF foam, or AR-AFFF, is similar to standard AFFF but contains additional surfactants that make it more effective in fighting fires involving alcohols or polar solvent fuels. These types of fuels can break down the film created by standard AFFF foam, so the extra surfactants in AR-AFFF help it maintain a film over alcohol or polar solvent fires.
Different types of Firefighting Foams have been developed for their effectiveness against various fuel and material types.
FFFP Foam
Film-forming fluoroprotein foam, also called FFFP foam, works in a similar way to AFFF by creating an extinguishing film over a fire. However, FFFP foam contains no fluorochemicals and is considered more environmentally friendly. It can be used on Class B hydrocarbon fuel fires but is generally not as effective as AFFF.
Wet Water
Wet water, as the name implies, is just water. It has limited application in firefighting foam as it does not work well on liquid fuel fires since the water does not spread evenly over the fuel surface. However, wet water can be used to extinguish certain Class A fires involving ordinary combustibles such as wood, paper, and textiles. It performs best when applied as a fine water mist.
Dry Chemical
Dry chemical fire extinguishers use a powder extinguishing agent that works by interrupting the chemical chain reaction in a fire. Common dry chemical agents include sodium bicarbonate or potassium bicarbonate. Dry chemical extinguishers are effective against Class B flammable liquid and gas fires, as well as some Class A fires involving ordinary combustibles. They leave a powdery mess but can quickly extinguish smaller fires.
Wet Chemical
Wet chemical extinguishers are pressurized with a dry powder chemical along with a liquefied gas propellant. When discharged, the chemical changes to a wet foam barrier. They are used in commercial kitchens to fight grease and flammable liquid cooking fires. Wet chemicals leave less of a powder mess compared to dry chemicals.
AFFF Foam Application Techniques
There are different application techniques firefighters use depending on the type and size of the fire:
Direct Application
For small pool or pan fires, firefighters can use a direct stream application of AFFF foam aimed directly into the burning fuel. The foam smothers the fire by separating it from oxygen.
Induced Flow Application
For larger pool fires, firefighters induce the foam to flow across and over the surface of the burning liquid by initially directing the foam discharge off to the side of the fuel source, not directly into it. As more foam builds up, it is guided over the fire to completely blanket it.
Dam and Dike Applications
On very large, flammable liquid spills or bodies of fire, firefighters will construct dams or dikes of AFFF foam to contain the fire area. They then fill the contained area with foam to extinguish the fire. This technique works to prevent the fire from spreading.
Foam Quality and Application Rate
For AFFF foam to work properly, it needs to have the correct expansion ratio anddrainage time properties. expansion ratio refers to how much the foam concentrates increase in volume when mixed with water; common ratios are between 3:1 and 500:1. Drainage time dictates how long the foam blanket maintains integrity before collapsing; most AFFFs are specified to maintain coverage for at least 10 minutes. Application rate also plays a role in delivering the right amount of foam over the fire source in the proper time frame. Too little foam or an application rate that is too slow will not effectively smother the fire. Following manufacturers’ specifications ensures good foam quality for effective firefighting.
Environmental and Health Impacts
While foam concentrates are highly effective at extinguishing liquid fuel fires, many older fluorinated foam formulas contained per- and polyfluoroalkyl substances (PFAS) that are now recognized as bioaccumulative toxins. PFAS can contaminate soil and groundwater if foam runoff is not contained and treated after a fire response. Many fire departments are moving away from PFAS-based foams to newer fluorine-free or PFAS-free formulations that have less impact on the environment and public health. However, non-fluorinated foams may have reduced performance compared to AFFF. Overall, foam application techniques need to focus on containment to prevent groundwater contamination. Firefighter exposure to decomposing foam fumes also needs to be minimized throughthe use of proper protective equipment.
Applying the proper foam using correct techniques is crucial to smothering flames and preventing fire spread. As awareness grows of foam contaminants, less environmentally hazardous formulas are increasingly available, though performance tradeoffs still exist.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
