The Discussion with Jersey went very well and covered a couple of other items outside Foam. The foam portion that we discussed talked about the events that took place leading up to the the moment the engineer cavitated the pump on foam. We talked a little theory as to what could have led up to that point and way to mitigate the situation(s).
Class A foam was being introduced into the tank. the Tank was, 2000 Gallon and mixed about a full 5 gallons of Foam into the tank. This Mix Ratio now would be the equivalent of .25% (move the decimal two place to the left for the conversion to decimal from percent and you have .0025. Take the 2000 Gallons and multiply by .0025 = 5.00 gal jug of foam).
Then it was stated that the engineer was NOT completely filling the tank with water after the first round, so each time he is putting in less and less water which can lead to NOT Enough of the foam solution being washed out of the tank and thereby not being mixed properly in the right proportion. This also leads to the production of more and more bubbles being generated.
Doing a quick check with the Waterous Company, they have NEVER had an issue with cavitation with foam use so long as you have ENOUGH water to have a solid flow to the impeller. I concur! Several issues are at play here though that I believe can exacerbate the situation of cavitation with the introduction of foam. Those are: large pumps, small intake plumbing, back flow prevention butterfly gates in the water way, any intake plumbing leaks that introduce air, high impeller RPM’s, high vacuum pressure and now a surfactant that incredibly reduces surface tension will all play into the ease of cavitation of an impeller.
It is my own personal suggestion that if you want to batch mix, take your tank capacity, subtract 10% of the volume then multiply by the .001 for a .1% solution. For Example, in an Engine with an 850 Gal tank, take 850 x .1 = 765, Then take the 765 multiply by .001 = .765 Gallons of Foam or 3/4. This would work for SEATS as well folks. you could physically add .85Gal of foam concentrate to an 850 gallon hopper for the same effect. You will still have enough of the concentrate to allow the solution to mix into the fuels, but it produces slightly less bubbles that can generate a bit less of a mess on your truck.
If working with Helicopters and dip tanks and you want foam? NO PROBLEM, if you have a 5,000 gallon dip tank, take the full 5,000 and multiply by .001. You add 5 gallons of foam concentrate to the batch, when the seat or helicopter drop their water, the solution will mix on the way down!
We also talked about what seems like a foreign concept to have water tenders supplying a city with water during fire suppression operations in the urban setting as well as the aspect that most of the firefighters do not have that much skill nor are taught the skill of drafting, i.e. draft to fire operations like in wildland.
The discussion took place Jan 21, 2020 at 6:30PM.