AFF Mixing?

[Martin-123]

Hello,

I'm doing research for novel firefighting equipment and can't be too specific about the application, I'm sorry.

My issue is the weight of the hose, and its contents, when in use. I need it to be as light as possible. 

I understand AFF is a mixture of chemicals and water, and that there are low, medium and high expansion foams.

Can anyone please advise...

Is the expansion due to a chemical reaction (if so, what's the gas released?) or just due to the mechanical effects of being mixed and then jettisoned from a nozzle?

 

Where does the 'mixing' between chemicals & water, and crucially, where does the 'expansion' take place? I see three possibilities for the mixing...

1. Is AFF stored ready-mixed, in a tank? In which case, when/where does the expansion take place? Is it stored, expanded, in the tank? ... does it expand in the hose after release from the tank? ... does it expand on release from the nozzle? 
2. Are the water and chemicals stored separately and mixed just prior to entering the hose, where the expansion takes place ... or (again) on release from the nozzle?
3. Are the water and chemicals fed in separate hoses and mixed in the nozzle?

 

Very grateful for any contributions.

Martin

[AnthonyB]

Chemical Foam used to be predominant in the early to mid 20th century but was rapidly replaced as the century as mechanical foam was developed in the 20's & 30's and gained favour.

Foam is stored as a bulk concentrate and depending on the type of foam and application is usually proportioned with water at 1% , 3% or 6%.

Most foam solution has been traditionally aspirated through a branch pipe designed to use the venturi effect to agitate the solution and aerate it to create low or medium expansion finished foam, but in more recent times, particularly in portable extinguishers, with synthetic foams such as AFFF non aspirated spray has been used to good effect. 

Foam solution can be stored premixed, such as in most extinguishers, fixed extinguishing systems and some rapid intervention fire fighting vehicles or can be added by an inline inductor to the water supply at any point up to and including the actual branchpipe.

Hi expansion foam usually uses large water pressure driven fans and a fabric tube to create.
You could really do with a copy of the Angus Foam Handbook, sadly that isn't on their website and I'm not sure they have print copies left.