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Tuesday
Oct222013

Foam 107 - Application Techniques 

For finished Foam to be effective it must be “applied” to the surface of the hazard properly. Proper application, allows the finished Foam to set-up in a cohesive “blanket” that subsequently smothers, cools, and suppresses vapors emanating from the hazards surface. If this blanket is disrupted by; poor Foam application, personnel, or in-proper equipment, your Foam effectiveness is diminished. The three (3) application techniques used for proper hand-line application are;

1] Bounce Off

2] Bank-In

3] Rain down

Bounce Off

The bounce-off method is useful when dealing with three (3) dimensional fires that afford an object in or behind the spill area. By directing your Foam stream “at” the object, the stream is broken up and falls gently on the fire or hazard area. This also contributes to additional agitation which increases the expansion of the Foam solution when using non-aspirating nozzles. Some of the issues for concern with this method include the temperature of the object inside the spill area and its cool down/application time, heat loss during the pouring down of Foam after object contact, Foam destruction as it passes through fire to reach the object. All of these influence the total time and volume calculations needed during application.

Bank In

When objects are not available to utilize the “bounce off” technique, the bank-in method should be used. This technique involves directing the stream at an area in front of the hazard, allowing the Foam to bank-up in a pile and roll onto the hazard. Two benefits of this method are;

1] No fire or vapor destruction occurs to the Foam passing through flame and,

2] The mechanical agitation that occurs from the Foam stream striking the ground helps to additionally agitate the Foam and increases expansion reducing the Foam’s drain time.

Additionally, the spread factor of squeezing the Foam’s “quantum” removes its alternate linear path, allowing it to equilaterally “spread” rather than follow the straight line of the hose stream. This action increases flow in all directions covering more area over the hazards surface at a faster rate.

Rain Down

            When either of the aforementioned techniques is not practical due to the situation, the alternative is to elevate the stream and allow application to “Rain Down” or fall out on top of the hazard. This method allows gravity to overcome the force of the stream and settles the Foam onto the hazard in a gentle manner much like snow falling. Expanded or “aerated” Foam is preferred as it will fall like a softer snow shower. These expanded streams are a trade-off of effectiveness as while they may be “burned-back” by the fire and thus wasted, they can eventually be more affective as extinguishment and vapor suppression than a heavier “less” expanded stream. Consequently, the reverse also becomes an issue of concern.

Another concern deals with mixed systems common to the fire service. If your system utilizes both class “A” and class “B” application through common piping systems, a recommended “flushing” cycle should be added to the pump operator’s procedure after using these Foams. Class “A” constituent solvents can activate the polymeric membrane in AR-AFFF causing a globular/viscous like formation that may permanently clog lines. The same can be said for the wetting agents with like chemistry.

Lastly; whichever technique is implemented, NEVER plunge a stream line into a hazard. This disrupts the Foam blanket allowing vapors to escape and or possibly re-ignite. This practice is the exact opposite of what you are attempting to achieve. For these same reasons, NEVER direct a water line on top of a blanketed spill as this will dilute the blankets concentration, and sealing ability of the finished Foam blanket. If you must enter the spill area, for a three dimensional fire or product shut-off, every disturbance and foot-print you create must be covered with more finished Foam application. The standard technique is to use the rain-down method on top of your personnel continuously while they are inside the spill area. NEVER drag equipment or hose lines through spills as this causes disturbances to the Foam blanket and increases re-ignition and vaporization danger to your personnel.

Over time, your Foam blanket may appear as “skeletal” in nature. This is the remains of the Foam after the blanket has achieved its “drain-time”. When this occurs, reapplication of additional Foam is required to reaffirm the blankets fire extinguishment and hazard vapor suppression. “Skeletal” remains will allow vaporization and possible re-ignition of your hazard.

                              Haz Mat Mike

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