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Friday
Jan172014

Foam - 113 "Foam Fini"

We complete our Foam journey with a look at some important concepts learned thus far. Whether your task is firefighting or hazardous materials vapor suppression, the most important concept to retain from the study of “Foam Concentrates” is that there are two (2) opposing forms of physics and chemistry going on here. As we have studied these elements, we can now say with precision that ONE single Wetting Agent/Foam Concentrate cannot be successfully used on both, class “A” and class “B” materials. When your organization is approached by elements representing the economic community of these products, concern of intentions and safety should be paramount for your organization. Again, the desired end result is not only to mitigate these hazards, but for all responders and “affected” civilians to survive the incident.

The culmination of this series has had the focus of two (2) concepts;

1] The extinguishing process and

2] The vapor suppression of Hazardous Materials releases.

The ability to use this one “tool” on 50% of our “type” responses realizes the value of a properly coordinated Foam program integral to the Fire and Emergency Response field. We have seen the facts regarding these theories and now look at the implementation of the extinguishment process. The four (4) basic ideologies for effective extinguishment and vapor suppression are;

1] Isolation of the Fuel

2] Temperature Reduction

3] Separation of the Oxygen Supply

4] Chemically Terminate the Chain Reaction

Each one of these demonstrates the principle of opposing forms of chemistry and physics and why the NFPA has separated the Foam Classes. Each one triggers a separate discussion unique unto itself. Each one gives you data to make a correct decision towards a safe and successful outcome.

Isolating the Fuel

Isolation of fuel sources are unique to the type of fuel you are mitigating. Class “A” Wetting Agents soaks into class “A” fuel reducing temperature, absorbing heat, and begins the extinguishing affect by the absorption of flame into steam. This functions quite well for ALL substances that are WATER MISCIBLE. The encapsulation theory is temporary in nature and does not SECURE these fuels for post-fire operations. Therefore by definition it is unsafe and little more than selected dilution to isolate small volumes of a class “B” fuel source. If, enough dilution has occurred for extinguishment the resulting fuel source or release becomes much larger in size, maximizing the spill area and contaminating the environment much more than the original spill volume.

Class “B” Foam concentrates is designed to have limited solubility or, be more IMMISCIBLE with class “B” fuels. This is the property that allows finished Foam blankets to flow across the surface of class “B” fuels rather than mix into them. This finished Foam blanket permanently “isolates” the class “B” fuel from oxygen, thus smothering the fire while additionally suppressing the evolution of hazardous vapors rising from the materials surface. This “isolation” of the fuel source eliminates/minimizes re-ignition, evacuation, toxic migration, and affected personnel or civilians throughout the hazard area or nearby off-site exposures.

 

Temperature Reduction

In class “A” fuels water “cools” the surface by heat absorption thus “drawing” the heat from the surface of the fuel turning the water into steam. In order for this reaction to go to “completion” each and every water droplet needs to turn into vapor. The surface tension of water particles resists this spreading across the surface of class “A” fuels. Waters’ natural surface tension prevents water droplets from entering small nooks and spaces in class “A” materials, causing these droplets to run off before they have turned into vapor. The common method to decrease this effect is to attack class “A” materials with variable fog nozzle hand lines. These form water into smaller droplets with greater contact area, allowing for longer contact with a burning class “A” surface. This increased area and contact time afford more droplets to vaporize thus cooling and extinguishing through temperature reduction. To create an even more efficient extinguishing agent, class “A” wetting agents change the physical properties of water by “reducing” the water’s surface tension. The above is accomplished even further by the addition of “Class A Wetting Agents” concentrate to water creating a wetting solution that is applied and more thoroughly reacting with the fuel source.

Blanket forming class “B” finished Foam does not “soak” into class “B” fuels as this would continue the process of vaporization and not secure the fuels hazard. Class “B” Foam combats this process by reducing surface tension, but only in a very slight or limited way. Class “B” Foam will drain into the liquid fuel but ONLY with “limited solubility.” It is this physical and chemically opposite property from wetting agents that afford class “B” Foam the ability to flow across a fuels surface, cooling the temperature from the water contact within the Foam, thus reducing the fuels surface temperature below its flashpoint. This of course, results in extinguishment. Maintaining a secure, intact Foam blanket with class “B” finished Foam DOES secure the fuels vaporization creating a safe situation out of mayhem. Class “B” materials vaporization can only be secured by a properly aspirated finished Foam blanket.

Separation of Oxygen Supply

            Class “A” wetting agents separate the oxygen supply by replacing the flame with steam from absorption of the water medium. Effectiveness comes by decreasing the surface tension of water thereby making your volume of water more effective and more completely penetrating into the class “A” fuel.

            Class “B” properly aspirated finished Foam actually forms a barrier in the form of a “blanket” that separates and excludes oxygen from coming in contact with the fuel source. This in turn “smothers” or excludes the oxygen source eliminating the fire or, “extinguishment.” It is the water enclosed in this blanket that cools the class “B” fuels surface making re-ignition more difficult. In addition, hazardous vaporization is halted which precludes the need for evacuation and exposure to the fuels toxic constituents. Re-ignition is maintained when this finished Foam blanket is replenished as needed over the “Drain-Time” period of the finished Foam/hazard ratio.

Chemical Termination of the Chain Reaction  

            As seen in the Foam/Fire tetrahedron, removal of any of the adjacent sides accomplishes termination of the chain reaction. When using wetting agents in class “A” fuels, this is accomplished by making the effectiveness of water greater. Water is still the extinguishing agent, it just responds in a more effective manner. This action minimizes water damage through extending sometimes questionable water supplies.

In the case of class “B” fuels, finished Foam creates a tangible barrier using water that remains in place (when maintained) that permanently terminates this chain reaction. The benefit of class “B” finished Foam must be realized for maximized use with class “B” materials. It is for this reason that when wetting agents are used on class “B” materials, only dilution is realized. This illusion yields a false sense of security, placing your scene, civilians, personnel, and equipment at great risk.

In the end, the Foam concept can be summarized in these four words; interstitial interface limited solubility. If you master this concept you can master “Foam.” Class “B” finished Foam is the most valuable and underused tool in the firefighters/hazardous material responders toolbox. When responding to future hazardous materials incidents consider the usage of Class “B” Foam concentrate. It will quickly and safely manage your emergency to a successful conclusion. It is my sincere hope that this series has demonstrated the frequent “use” value of class “B” Foams for hazardous materials responses. If you have any concerns over YOUR program, and would like creative feedback please do not hesitate to contact me.

                                Haz Mat Mike   

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