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Foam Concepts

I recently received a question via my website regarding Foam and specific gravity.

This month, we shall look at the relationship between specific gravity values and the behavior of Foam products.

The important concept to understand when discussing specific gravity as it relates to Foam is “1/4 drain time.” This value is the time length that is 25% of the total time required to drain a properly aspirated and applied Foam blanket to the surface of a flammable liquid or hazardous material. At 100% the Foam becomes totally formed back into its original liquid, sinks below the surface of the hazard and no longer extinguishes or protects against evolving vaporization. The goal is to determine “¼ drain time” and at this point begin re-application before the protective blanket reduces to the above statement. This gives the responder a unit of measure for monitoring the re-application time table to maximize success at the incident site.

Liquid concentrate Foam, when mixed with water such as in a hand-line or Master Stream device, becomes Foam Solution. This mixture when properly aspirated either by compressed air or an appropriate air aspirating nozzle, creates the Foams bubble. This is mass produced by continuing operation forming the Finished Foam Blanket that suppresses vapors and extinguishes fires. The unique relationship between the specific gravity and the Foam Bubble constituents determines the blankets ¼ drain time. This essentially is the bubble breakdown time BEFORE the blanket bubbles begin to reform into solution and then by its weight, begin sinking through the liquid hazardous material or flammable fuel towards the container bottom. Aspiration rates during formulation do not change, but depending on the ¼ drain time of your chosen Foam, blanket security, vapor suppression, and extinguishment may. Realize that this function is important when choosing the “type” of Foam for your operations. An inappropriate choice could very well cause fast use of your Foam reserves sometimes resulting in exhaustion before extinguishment or complete vapor suppression.

As stated above, the long term creation of these resulting blankets to accomplish extinguishment and vapor suppression is the ultimate goal. ¼ drain times that do not last sufficiently to accomplish this goal cause’s increased use of your total Foam concentrate reserve. If like most facilities, you have less than an endless supply of Foam concentrate, you will soon exceed your reserves before your goal is accomplished. In this case, the result will be subsequent “burn-back” resulting in the loss of your suppression blanket, a full surface fire, and the resulting vapors generating. In other words failure to extinguish/suppress the incident scene. Choose ¼ drain time carefully!

Most Foam concentrate sold today is of the AFFF type, usually with some degree of environmental “green” component for easy clean-up. Older composite or “rubberized” Foam concentrates that yield a solid blanket that needs separate remediation after an incident no longer exist. These are such a problem that using them for training is usually just too much trouble for organizations to deal with. The best solution for these types is to contact your vendor of Foam concentrate and see if he/she will afford you some sort of re-bate for disposal and possibly cost deferment towards the “green” Foam concentrates that you will need to safeguard your response options. Long ago, these solid blankets were mechanically removed after the incident and land-filled as environmental remediation of these products was not an issue. One product that I have used extensively and stand by is the National Foam “Universal Gold”. If you are researching different types, take a close look at this product. I think you will find it a superior product.

Finally; extinguishment and post vapor suppression serves you well in two (2) important steps.

1] This limits more extensive damage to your facility and minimizes vapor contamination to the surrounding environment.

2] Post fire/Haz Mat vapor security provides a safe and toxin free zone for your contractors or plant personnel to operate in. During post-incident operations is a time when exposure to vapors can cause extreme exposures. To minimize exposure to employees while preventing minimal negative health effects is the optimum way to provide an efficient remediation on your response site or property.

                                              Haz Mat Mike


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