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Originally Posted by xoxoxoBruce
If I do the net recipe and stick it in my water extinguisher, what makes it foam when it comes out, just being forced through the nozzle at speed?
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Hey, Bruce. You will get some foaming action on contact just by the force of the straight stream. However, I prefer to shake my can several times (usually while running to whatever I'm trying to put out) to ensure that I have some bubbles already in the mix.
Two things on this point: 1) You don't have an aerating nozzle on a water can. You have a straight-tip nozzle. Therefore you are not going to get the same quality foam you would if you were able to introduce air to the system as you go (the system that Pierce recommends, called CAFS introduces compressed air to the mix in your truck as it comes out of your pump, meaning that you already have foam started in the hand line, even though you might have a conventional straight-tip or combination nozzle instead of a foam nozzle). You can improve your foam by modifying your straight tip on your can to be a venturi,
although I don't recommend that. 2) Just for illustration on how effective just adding soap and/or surfactant can be
without modifying the nozzle, most Essentials classes (the first firefighting class someone takes) include a session where a class B fire is started in a large pan (about 6x6), and the firefighter is given a water can and ordered to extinguish the fire. Most people can extinguish the fire with one or two cans with just water (although keeping the fire from flaring up is difficult, and some trainees take three or four cans to keep the fire out). HOWEVER, with the addition of a foaming agent (AFFF, or insert your home brew here), almost all trainees are able to extinguish the fire with ONE can, AND the mix becomes extremely difficult to reignite for the next trainee.
So the REALLY long answer to your question is...you might not get "good" foam, but it appears to be good enough, and considering how cheap it is to obtain an "old" can from a fire extinguisher dealer (everyone who I know that has asked has been given one for free), fill and pressurize it (you can do it yourself since you have all the ingredients and a water can is charged with an average air hose), and the volume of agent that you can put in a can compared to your average dry chem extinguisher it's a great way to go, at least for the people I know who have seen a fire or two.