Wet foam, dry foam

Replies to This Discussion

Permalink Reply by Michael J. Anderson on March 16, 2010 at 9:33am

Claudio,

In the recent years, there has been an effort to teach and explain the uses of "wet" foam and "dry" foam streams in CAFS operations. There is still many different opinions in this concept and may different theoretical numbers to the stream definitions.

Elkhart brass designed a nozzle that could be used with CAFS streams that changes between a "wet" foam and "dry" foam with a change by the nozzle operator instead of changed being made by the pump operator. We don't use this nozzle, but my understanding is the adjustment changes the discharge orifice size to allow for more air to flow uninterupted with the stream.

Hope this helps a little. I hope all is well for you and your family following the earthquakes.

...Michael Anderson, Lieutenant
Station 2 - "C-Shift"
Pflugerville FD, Texas

Permalink Reply by Claudio Cisternas Alvarez on March 16, 2010 at 10:14am

Thanks for the answer and your wishes, fortunately, we had any trouble with that terrible earthquake, I live in the middle of the country where the earthquake wasn't so strong, and I work in the north of Chile, the worse was in the south.

So the difference between wet foam and dry foam may be the "consistency" accordign to the amount of air in mixture ???

Permalink Reply by Michael J. Anderson on March 17, 2010 at 9:25am

The textbook answer to the difference between "wet & dry" has more to do with the ratio of air to water (simplified). Here is what we use as our definitions:CAFS Foam Types according to NFPA 1145:

• WET- High water content. Can range from an expansion ratio of 1:1 (no expansion) to ≤5:1. Wet CAFS can be generated with all types of nozzles. Best described as a watery mass of large and small bubbles that lack body. Best use is for interior firefighting. 25% Drain time of ≤30 seconds.
• Fluid (balanced)- Optimal mixture of air, water, and foam concentrate. Looks like watery shaving lather, with expansion ratios of 5:1 to 10:1. Can be used for direct and indirect attack. Nozzle type not listed, but typically done with CAFS systems. 25% Drain time of ≤90 seconds.
• Dry- Low water content. Looks like shaving lather with expansion ratios of 10:1 or greater. Use only for exposure protection and limited wildland firefighting. Used with a ball valve nozzle. 25% Drain time that is greater than fluid.




as far as the Elkhart nozzle:

IN MY OPINION: (once again never used it, only looked at and read about it)

The difference for the nozzle would be (IMO) the consistency. I believe that by changing the setting, thereby the orifice size, that you would be reducing the "scrubbing" of bubbles through the smaller orifice opening.

Once again, my opinion. There are many more people on here that probably know more. I will have my CAFS "Guru" chime in on here.

BE SAFE !!!



Claudio Cisternas Alvarez said:

Thanks for the answer and your wishes, fortunately, we had any trouble with that terrible earthquake, I live in the middle of the country where the earthquake wasn't so strong, and I work in the north of Chile, the worse was in the south.

So the difference between wet foam and dry foam may be the "consistency" accordign to the amount of air in mixture ???