Foam concentrate 3% or 6%

[airfield17]

I know we have different percentage mixes for foam concentrate, and they relate to the type of fuel involved in fire, hydrocarbon at 3% and 6% for polar fuels, but could someone give me some examples of these? petrols, kerosenes, alcohols, which groups do these come under? Our inline inductor has 3%, 3%AR, 6% and 6%AR. What does the AR stand for (Alcohol resistant??) and what does the AR setting do?

Also we are told to use 65mm hose (two lengths foam the foam proportioner, be it from the vehicle pump or inline inductor) when using foam but on airfields they use 45mm. Can anyone shed some light?

Regards.

[John Webb]

Petrol, kerosene and diesel are 'non-polar' fuels, that is, the molecule has no specific electrical distribution. Alchohols and other fuels have a molecule which is negative one end and positive the other. This is, I believe, why alcohols will dissolve in water (or water in it) which is also polar. Hence the foam mix needs to be stonger to tackle polar liquids - they tend to remove the water from the foam thus destroying it.

Alcohol Resistant (AR) foams have additives which form a layer between the fuel and foam to protect the foam, this makes them more viscous and therefore the inductor needs to be adjusted to ensure the right mix.

Cannot answer for certain re 65mm versus 45mm - larger hose minimises back pressure on the inductor, but is less easy to move, 45mm gives more flexibility for quick changes as may be needed at an aircraft incident - also takes less water/foam to fill.

[John Webb]

Managed to dig up my Fire Service Manual, Volume 2 FS Operations, Fire Fighting Foam. (My copy published by HMSO in 1998). This deals with the use of the different foams in different scenarios.

Polar solvents also include things like acetones, ketones and a lot of other things besides alcohols.

The equipment is described in one of the parts of Volume 1 of the Manual which I do not have. So I cannot say anything further about the inductors etc..

[The Reiver]

Dug up some examples for ya !!

<-----Loves Wikipedia and copy / pasting

Non-Polar Solvents:
Hexane    
Benzene    
Toluene    
Diethyl ether    
Chloroform    
Ethyl acetate

Polar Aprotic Solvents:
1,4-Dioxane    
Tetrahydrofuran (THF)
Dichloromethane (DCM)
Acetone    
Acetonitrile (MeCN)    
Dimethylformamide (DMF)    
Dimethyl sulfoxide

Polar Protic Solvents:
Acetic acid    
n-Butanol    
Isopropanol (IPA)    
n-Propanol    
Ethanol    
Methanol    
Formic acid
And believe it or not.........Water

Kerosene is in the hydrocarbon (non-polar solvent) bracket as it's a distillation of petroleum.

The AR setting on your inductor switches the output to AR foam concentrate. So I guess there will be a tee piece and switching valve somewhere. One for the AR and one for the FFFP, FP, AFFF, Protein, High Expansion, PFOS Free, F3 or whatever else you're loaded up with.

What materials are you covering ?

[kurnal]

The settings also relate to the type of foam concentrate you are using, some of the older flouroprotein foam concentrates were designed to be inducted at 6% whereas some of the more modern concentrates were more efficient and were designed to be used at 3%.

The number of lengths between inductor and branch is all about maintaining the accurate induction rate. The inductor works by venturi principle - there needs to be a pressure difference between input and output across the inductor for the venturi to work. If you try and induce against a head the efficiency will reduce- pumping uphill or against too many lengths of hose will do this. The settings are calculated against the flow rate through the nozzle in the foam branch and a typical two lengths. It will work with different equipment but you will have to run at higher settings on the control to achieve the same standard of finished foam.