4/12/2006: Ellsworth AFB foam test

[FireFightingMan]

Originally Posted by xoxoxoBruce

Class B fires keep flaring up because the fumes are reignited by what's still burning? Do they stop flaring once the flames are completely extinguished?
I guess the AFFF would suppress the flammable vapors from reforming while you get the flames beaten down.

First a CORRECTION: AFFF is NOT appropriate for Class C (which makes sense).

On to the question: Please understand that I am not 100% certain on the physics, only about 70% certain. Once you get ANY combustible burning, regardless of its class, there is a certain period of time where the surrounding environment is still hot enough to vaporize the material, which can then oxidize and thus reignite - remember, if it ain't evaporating, it ain't burning...unless it's a class D, but I'm not going to go there. This situation is especially problematic for volatile liquids because they are constantly evaporating, even at room temperature, and typically have flashpoints that are close to their evaporation point. So, once you get a diesel/gas mix burning, you are in deep crap. The gas gets the diesel hot enough to ignite. Then when you put it out, you are still at just below the flash point of the diesel...which is well above the flashpoint of the gasoline. So, it is common for the pan fire to be extinguished, only to reignite two seconds later.

The students who are successful in putting the pan fire out quickly start in the middle, then force the fire into a corner while spraying back and forth across the surface that they have already extinguished. After the fire is "out", they continue to spray back and forth across the entire surface for several seconds longer. This continued spraying 1) displaces the gasoline vapors that are continuing to evaporate so that they cannot reach a density sufficient to combust and 2) cools the surface so that less vapor is released.

In the real world this type of thing does not always happen. If the fire is in an area where the liquid is in a low spot and the sides are raised, without significant air disturbance, then the danger is real. A hangar is a great example of a setup where such reignition would be expected.

[fredengle]

well what if instead of the nozzle i made the hose into a venturi?????

[fredengle]

you can get an aerating nozzle at fireade source .com

[xoxoxoBruce]

Holy crap, 523,000 views on this thread!

Welcome to the Cellar, fredengle.
Fireman?

Another inexpensive way to get a good foam stream is to use a pesticide sprayer with a RoundUp foaming tip.
We used that to get foam to put out small fires when we were burning groves here in FL. Worked great.

[barefoot serpent]

Originally Posted by rkzenrage

We used that to get foam to put out small fires when we were burning groves here in FL. Worked great.

a lost technology

[FireFightingMan]

SMALL.

Here's the skinny on brush fires. 1) Brush fires are relatively hard to extinguish because the are relatively hard to contain, and it's relatively difficult to do overhaul on them because of the magnitude of the task. The reason for that is that since the fire is out in the open with lots of fuel all around, it's difficult to ensure that an area that is burning doesn't continue to burn. Brush fires burn grass, brush, and trees for the most part. Early-ish in the Spring (or at any time in Spring when there is little rainfall) all of the deadfall from the previous Winter is just sitting there waiting to go up. That is one of the reasons why there tend to be more brush fires in the Spring in more places than later in the season, even though the ones later get most of the attention. Trees are just like the studs, joists, etc. in your house, except they're usually farther from the firefighting apparatus, which means that when we're trying to put them out we have to hand-carry the water/foam/whatever, along with the other tools necessary some distance from the rig. The other tools are typically axes and maybe saws. We have to break the wood apart to get at all the fire burning inside the tree, especially in old deadfall trees.

Now some of you might be asking yourself "Why not just let the stuff in the middle burn?" To a large degree we do. However, fire isn't an exact or an absolute thing. Not all of an area that is "burning" is actually burning. Some of it (usually most of it) won't burn at all. There will be swatches through the landscape where there is fire. The problem is that if you just let everything in the interior of the fireground burn, then the ajacent, unburned land is also at risk (since it hasn't burned...yet.

Structure fires are pretty easy - the structure contains the fire for the most part, and if it gets completely out of hand, we just "surround and drown". End of problem. We can park apparatus near the fire. We can overwhelm the fire with water (the usual approach). You can't do any of that with a brush fire.

2) Brush fires don't just burn down houses. Stupid people get thier houses burned down. There was a study done by I believe it was the US Fire Commission or the Forestry Service that stated that of houses lost to brush fires, the most obvious factors are shake roofs or a large combustible load in contact with the house, i.e. bushes that haven't been trimmed so that they don't touch the home. Mulch does not appear to be a significant contributing factor. If you are worried about your house making it through a firestorm, TRIM YOUR BUSHES. Get them off your house. The further away they are, the better. Bushes burning allow the contact time to get your house burning. The further away they are from your house the better. Obviously in the case of a fire approaching the first priority for you and your family is your personal safety, so don't be an idiot and die trying to cut the foliage down. Get the hell out so you dont.

3) If you want your house to still be standing when you get back, make it easy to defend. We aren't driving through neighborhoods looking to save every house. We are looking for the place where we're going to make a stand. Swimming pool with easy access: good. Clearing around the home: good. Not on a hillside: good. Brick or other non-combustible construction: good. Well-manicured property without lots of brush or other crap near the house: good. However, I have to tell you that there is one way to put your house on the "MUST SAVE" list: VOLUNTEER AT YOUR LOCAL FIRE DEPARTMENT. You will learn how to save your own house, and you will get an "in" with the people who have to decide who's house they're going to save.

[xoxoxoBruce]

Is there anything else I can answer for you, Bruce?

No, that's plenty, thanks for the info.

And thanks for doing what you do.

Originally Posted by barefoot serpent

a lost technology

You don't hear about citrus growers starting large fires no matter how much we burn, and we burn a lot.
We are careful and watch our fires full-time.

[Shawnee123]

HUH? Holi Pet, Batman.

[Sundae]

We seem to have lost all but the first photo though.

[capnhowdy]

Welcome to the Cellar, bevoer. Looks like you're off to a nice start.

Hahaha. Off to a nice start? Are you sure?

[classicman]

Caution - Hidden link in above post!

[xoxoxoBruce]

Not anymore.