Foam Training

With the Essentials classes on break for a week, I got to go to our training night last night, and was really glad I did. The main focus of the evening was on foam.

A little background: there are different classes of fire. Class A is wood, rubber, "normal" fires, Class B is liquid fuels fires (in the past, this included cooking grease fires, although that's becoming Class K these days), Class C is electrical fires (which usually, when you cut the power, become Class A fires), and Class D is combustible metals (which are often nasty and require really weird stuff to put out).

More background: the fire tetrahedron. Four things are needed for fire: heat, fuel, oxygen and the chemical reaction of fire itself. With Class A fires, you spray them with water, which most times cools things down enough that you've removed the necessary heat, and the fire goes out. Class C I mentioned above; you cut the power, and they become Class A. Class D fires often require removal of the oxygen or fuel, or messes chemically with the reaction necessary for fire (although honestly, I don't know much about metals fires, so don't rely on what I say about them just yet).

That leaves Class B/K fires. I'll have to dig up a link to a YouTube video I saw, where they poured a cup (i.e. 8 oz) of water on a grease fire in a pan on a stove. The thing positively exploded. Here's why: water is heavier than oil. Pour water on a grease fire, and it sinks, then heats, turns to steam, and expands. Violently. Spraying lit fuel everywhere. But more importantly, atomizing it, allowing it to mix with available oxygen, and burn much MUCH more rapidly. Hence the explosion.

Class B CO2 extinguishers work nicely in this case (if I understand things right), as they remove both heat and oxygen, causing the fire to go out. Simply covering the flaming pan (i.e. with a lid or damp towel) cuts off the oxygen as well (although it's very easy for such a fire to reignite when you remove the lid, as you're just reintroducing oxygen, and the needed heat is still there; it's very important to then turn off the stove and allow the pan to cool before doing anything else, like moving it). But not all liquid fuel fires are small enough to be put out with an extinguisher.

That's where foam comes in. Imagine soap suds. Apparently it's more high-tech than that, but that's what it smells and feels like (well, unscented soap suds, anyway; nothing lemony fresh about what we did last night...). There's the foam stuff (liquid? gel?) in a container, with a venturi tube that comes up to the hose. Water flows through the hose, pulls up the gel, mixes with it, and comes out foam.

For Class B fires, foam is good in a couple of ways. First, as with Class A fires, (and perhaps even FOR Class A fires, as it supposedly uses less water), it cools things down, hopefully below the heat of combustion. Second, with the air mixed in, it remains lighter than the fuel, and sits on top of it, rather than doing the sink-and-explode thing that plain water does.

We've got 2 or 3 ways to flow foam: a foam extinguisher, a ProPak kit, (which holds a couple of nozzles and a smallish quantity of gel), and an eduction appliance (which fits in between 2.5" hose and a 1.25"/1.5" handline, with a tube that goes into a stand-alone bucket of gel).

We tested out the necessary water pressure needed to get the eductor to work, and found it to be pretty close to 200psi (whereas normal pressure for those lines, IIRC, was 100psi or less). We also got a chance to flow foam both from a handline and from the ProPak, and see how each of the nozzles work.

We talked about situations how and where you'd apply foam. As mentioned above, it is very useful for Class B fires. Also, if you have a fuel spill (unignited), you might cover it with foam to make sure it doesn't ignite. Applying it also has its fine points. If you spray it directly onto the spill or fire, you're likely to push the fuel around, perhaps making a bad situation worse. OTOH, you can aim the nozzle at the ground between yourself and the fuel, allowing the foam to build up in front of you, then use pressure to push that foam over the fuel. Alternatively, you can aim high and let the foam rain down, or aim for a nearby wall and let it flow down off of that.

One thing to be careful about is, once you've put a layer of foam over a spill or fire, not to walk through the foam. Apart from the fact that the fuel is still down there, walking through it breaks the vapor barrier that the foam creates, making it much less useful (and making the situation once again much more hazardous).

Anyway, the evening was quite interesting, and probably the coolest part was that I got to flow something (foam, in this case) from a nozzle. I've certainly got lots more to learn, but it was quite exciting.