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Monday
Jul012013

Foam 101 - What is Foam?

            The NFPA (National Fire Protection Agency) under NFPA 11 Foam Operational Procedures establishes the guidelines and tactics for the mitigation of incidents requiring the application of class “B” flammable liquid Foam concentrate. Understanding the definition of what we are actually working with affords understanding how Foam functions, and how it should also be delivered to the surface of a hazardous material. The NFPA defines “Foam” as;

“Firefighting Foam being an aggregate of air-filled bubbles formed from aqueous solutions that are lower in density than flammable liquids. It is used to form a cohesive floating blanket on top of flammable and hazardous liquids by preventing and extinguishing fire through smothering and the cooling of these hazardous materials. It also prevents reigniting by the suppression of flammable vapors. Foam also exhibits the property of adhering to surfaces, which provides exposure protection from adjacent fires.”

The above definition has been clarified for writing purposes. We shall begin our concentration on class “B” fuels which are defined as flammable liquid fuels. They are divided into two (2) categories;

1] Hydrocarbons

2] Polar Solvents

Many hydrocarbon fuels are the by-product of refining or catalytic cracking (a refinery process) or have been extracted from vegetable fiber to create fuel for motorized equipment. Hydrocarbons generally DO NOT blend through solubility with water, as they are generally lighter than water so floatation on water bodies is commonly seen and mitigated as such. This one fact is critical to the understanding of how Foam is used to mitigate hazardous situations.

Polar Solvents are products of distillation or synthetically produced for use in the fabrication of separate products for consumption. Polar Solvents DO mix with water and have a varying attraction for water commonly referred to as “miscibility.” This deals primarily with the “degree” of solubility for example; Acetone has a stronger miscibility for water than does rubbing alcohol. This means that acetone is likely to mix faster and more thoroughly with water into a solution. This “degree of miscibility” determines the final state of the contaminated mixture, and the processes that are needed for remediation. Generally the more homogenous or greater “miscibility” the polar solution has, the more involved the remediation process becomes. This generally equates to greater manpower, increased time at the site, additional equipment, and usually larger recycling costs to separate these two compounds back into the original state before mixing began. In many cases polar mixtures are destructive to hydrocarbon Foams and require specially prepared Foam types to provide alcohol or “polar” resistance.

Why should we use Foam? A properly applied finished Foam Blanket can not only suppress pooled substances from evaporating but also provide protection for un-ignited spills such as in the case of a motor vehicle accident. This feature affords the responder and the victim additional protection during rescues. Another feature is that vapor suppression through the use of Foam prevents vapors from finding an ignition source and re-igniting after the initial extinguishment. Post fire security is increased through the visible “proof” of blanketed security.

What is Foam not effective on? Until recently developments restricted the use of Foam for class “D” or flammable metals, only being extinguished by the shoveling action from a solid extinguishing agent. This is obviously not effective for large scale application. Today, enter in the new generation of “Green Foams.” These Foams are not only biodegradable, but have been scientifically proved affective on class “D” fires. This in itself is quite a feather in the cap of Foam producers as now they have a response tool that is useful for industrial water-reactive metal type fires. Because class “C” fires are electrically energized and Foam consists of 97% water, use of finished Foam with class “C” fires is to be avoided. The best tactic is to de-energize the electrical system and treat the fire as a class “B” fire, in this theater; finished Foam will safely function and reduce the vaporization of burnt by-products. In some cases Foam may conduct electricity “better” than water therefore it is not recommended for use on class C “energized” fires.

Three dimensional fires present another challenge to Foam firefighting and vapor suppression. Here, finished Foam is used in tandem with a dry chemical device for effective extinguishment and vapor suppression. The general tactics are as follows;

1] First, halt vaporization and suppress fire on the pooled material.

2] Second, attack the non-pooled areas with an ABC Dry Chemical extinguisher.

3] Third, once the fire is extinguished, continue cooling the fire area with the same Foam attack system being used to maintain Foam blanket security. This aids in vapor suppression, continuing cooling to hot metal surfaces and reduces the likelihood of re-ignition.

Pressurized gases are another medium of use not effective for Foam applications. Because the vapor pressure of many pressurized gasses is too high to allow them to float atop liquid water, finished Foam will not suppress these vapors. The use of cooling water for the upper portions of the pressurized tank is the proper tactic. This minimizes BLEVE (Boiling Liquid Expanding Vapor Explosion) conditions. For Foam blankets to suppress vaporization there must be a “pool” of liquid material present for the bubbles to float on top of. Finished Foam can be successfully implemented whenever there is a class B, de-energized C class fire or liquid surface vaporization suppression of hazardous materials. Albeit, the above class “D” example, has not yet been certified by UL (Underwriters Laboratories) for Finished Foam use on these types of fires. This is in the works and will likely be completed soon.

                                  Haz Mat Mike                                                                                     

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