Search Past Articles
Explore Past Articles
Haz Mat "Specialist Course"
« Foam 103 - Foam Properties | Main | Foam 101 - What is Foam? »
Thursday
Aug012013

Foam 102 - Tetrahedrons & Terminology

            Intimate knowledge of the Foam tetrahedron as well as Foam terminology is the basis for truly mastering Foam operations at fire scenes and hazardous material incidents. The geometric shape of the form “tetrahedron” is used to demonstrate the interrelated properties of this science. It is especially useful because this “Pyramid” shape shows the “faces” of interconnectivity between all three sides of its constituent triangles. Each elements edge interfaces with the remaining three elements. This demonstrates the connectivity of proper “combinations” of these elements to produce a quality “Finished Foam” blanket. If any of the four (4) elements necessary below are NOT combined properly, or MISSING, the end result will be poor quality Foam, or no Foam at all. This of course will result in no suppression of the fire, and no suppression of hazardous vapors. The four elements of Foam Operations that must combine properly are;

1] Foam Concentrate

2] Water

3] Air Aspiration (via an air aspiring nozzle or system device)

4] Mechanical Agitation (or aeration via an induction mechanism)

Foam Terminology seems to be one of the most problematic areas facing firefighting Foam Operations and hazardous materials Teams today. Environmental Teams usually do not struggle with these issues as often. The reason is firefighters have multiple sources and uses for Foam applications. Environmental Teams are generally restricted to a single point of use, vaporization reduction. On many fire incidents, the use of incorrect Foam Terminology can confuse and send opposing messages to those in a position of responsibility for the incident stabilization. Many times I have seen operations retarded and crippled because of incorrect terminology. When using Foam terminology take care to be sure YOU are using the correct definitions when referring to Foam practices. Do not confuse the responders in your charge by using inappropriate terminology. This one practice has defeated many a Teams’ Foam operations. The following terms MUST ALWAYS be followed and interpreted, and defined in the following manner to reduce operational confusion;

1] Foam Concentrate: product purchased from the manufacturer in its original container

2] Foam Solution: the solution AFTER the concentrate has been proportioned into water

3] Finished Foam: the resulting blanket deployed AFTER air aspiration

Depending on the context in which these terms are confused can easily send an incorrect message to the IC, pump-operator, or Entry Team/firefighter. All three (3) of these, when translated improperly can cause a poor decision to be reached which then increases risk to the Team members.

The production of Finished Foam also has corresponding terminology that requires the same clarity of understanding. Conceptually, Foam concentrate is mixed with water, mixed again with air, and exits the discharge appliance onto the hazard as Finished Foam forming a blanket of bubbles (see article “Beneath the Blanket How Foam Works”). The discharge device is set-up with an “Eductor” within the discharge side of the system “educting” (or vacuuming Foam Concentrate into the discharge water supply). The proper terminology is as follows;

1] Foam solution: the mixture of water and Foam concentrate inside the discharge line.

2] Aspirating device: a nozzle where exterior air is drawn into the tip of the nozzle.

3] Finished Foam Applied: the discharged aggregate of enlarged bubbles as a Foam blanket.

Foam properties are not only due to the effectiveness of “HOW” they are produced by the above method, but the “characteristics” of the Foam concentrate chosen. Foam concentrate has followed a logical progression of development towards the type of hazard they were designed to protect. The design of a Foam concentrate excelling in one area may become a trade-off in performance characteristics in another area. Terminology is also critical in Foam concentrate properties and are;

1] Knockdown: the (speed) of extinguishment and vapor suppression

2] Heat Resistance: the length of time the bubble will maintain integrity in fire conditions

3] Fuel Tolerance: the resistance of bubble breakdown from hazard contact

4] Vapor Suppression: elimination of vapors from the hazard to the atmosphere

5] Cooling: temperature reduction of the hazard surface

Let us take a closer look into each one of these factors to better explain their “role” in the consideration process.

KNOCKDOWN, is simply the speed at which a fire or hazard can be controlled by the Finished Foams’ ability to spread rapidly across the surface of the fuel. This is achieved by producing a Foam concentrate that exhibits a relatively fast “drain time” or (drainage, bubbles that pop quickly) allowing the solution contained inside the bubbles to rapidly spread across the surface of the fuel.

HEAT RESISTANCE is the ability of the Foam bubble structure to withstand direct flame impingement or contact with elevated temperature surfaces, with little or no destruction of the Finished Foam blanket. This blanket must be stable and slow to drain to withstand this heat. The more rigid and stable the Foam bubble, the better the heat resistance of the Finished Foam blanket. The measure of this resistance when testing for UL (Underwriters Laboratory) certification is referred to as “Burn-back Resistance.” This gives the user a unit measure in time of how long the blanket will remain intact before it begins to dissolve, allow re-ignition of the hazard, and burn the remaining blanket back to the original state before Finished Foam application began.

FUEL TOLERANCE is the ability of the Foam bubbles to pass “through” a hazard (such as in a sub-surface injection system), and float to the hazards surface without picking up the fuel or hazard “in” the structure of the bubble while also being able to shed the fuel from its exterior bubble surface.

VAPOR SUPPRESSION is the ability of the Finished Foam blanket to suppress hazardous or flammable vapor evolution from the hazards surface.

These concepts are critical towards the mitigation of both hazards. Vapor suppression accomplishes two (2) goals.

1] Flammable vapors are extinguished and

2] Hazardous Materials vapors are kept from affecting the surrounding area, eliminating the need for mass evacuations and all their ancillary issues.

  The proper combination of these “Foam Science” elements, along with the knowledge of proper Foam Terminology is crucial towards successful Foam Operations and deployment to mitigate flammable liquid fires and hazardous materials incidents. Next month, Foam 103-Foam Properties.

                                               Haz Mat Mike

PrintView Printer Friendly Version

EmailEmail Article to Friend