there's a couple (at least) different classes of foam.
one isn't really recommended for fuel spills, etc, as footsteps, etc, thru it will violate the integrity of your oxygen barrier---but if you hose it a little more, sposed to be fine.
it's nasty to run thru your apparatus---we got a couple rigged up with kinda backpacks for the foam itself, mixes right at the nozzle thru kinda a venturii setup.
then there's 'slime'---this is pretty neat stuff! we got about 50 structures on the forest that have been threatened by approaching fires a couple times, and they're in a canyon bottem with very limited egress and safety zones, slow, basically one lane out---you can put this stuff on and it's supposed to last up to an hour, and you can rehydrate it once or twice---but it's a real hassle to get it off afterwards----our theory here was to slime it, get the heck outa the way and come back in after main fire had burnt by
foam setups are really pushed at you when you buy a new truck---don't remember the acronym---quite expensive, somewhat complicated --and the foam is spendy also--but it's a real water saver. we got one first response brush truck rigged up with it---but it's kinda a hassle---prefer the backpack deal, you strap it on, switch nozzles and are ready to go in a couple minutes. Had one 4,000 acre fire this spring---and another dandy in really rough country----other than that, with the large amount of last yrs grass and extreme drought--we've had maybe 3" total precip in last 12 mos---we've been extremely lucky.
we used to use "forestry nozzles" on our brush trucks----generally obtained by liberating them from above agency when interacting--and designed with water conservation in mind---since then we've got wheels under several thousand gallons of water, have switched to way higher volumen nozzles and are able to attack lots more aggresively---being on f.d. is something you can do for community that's really kinda neat---and lots of vol f.d.'s are shorthanded---