Wow, this is a long thread indeed! OK, I have to get my two cents in as well.... I use a TFT combi nozzle because I have to; the folks in the ivory tower make the rules and I have to go with it, even though I prefer a smooth bore for its' superior reach and penetration. With that said, I'm not going deep into the science of it, I'm just going to stay on the practical side of things.
Using a fog stream creates steam.Steam puts out fires in containers, which is what any fire room is. If you have a one room fire, go ahead, steam it up all ya want - but if it's a one room fire, why not apply your straight stream on the burning material and be done with it?
However: houses are not just one room, they are a bunch of interconnected rooms. You don't want to create that kind of steam in a room you intend on occupying, and occupy it you must, to get to the next room. If there is material burning in the room then put as straight of a stream you can get from your combi nozzle directly on the material that is burning. Swing the nozzle around a bit to cool the superheated gases collected at the ceiling. Move on.
Right about now is where I expect someone to say, "but you'll disrupt the thermal layer." Right. Exactly what I want to do. "Deep in" is a falsity. It implies that we have left unchecked fire behind us, which is something we don't want to do. In a building of interconnected rooms you have almost no control of that thermal layer. The only realistic way to control that thermal layer is to have your truckies properly venting the structure ahead of the advancing line.
So, now we are talking about flashover and near flashover. Near flashover? I have a pretty good idea of what near flashover looks like, the problem is, I don't ever know to any degree how near Near is. When the banking smoke is sooty black and you can see, here and there, tongues of orange flames dancing around in it, yeah, it's near but I can't say how near. I think putting water up there can forestall it, but not droplets, they will make steam, which is good for putting fire out, but not so good for anyone trying to occupy that space. If I'm lucky, I can forestall or even avoid a flashover altogether.
But I'm not counting on lady luck. And neither should you.
I recall the advice of... let's see, I think it was Tom Brennan, or possibly it was Vincent Dunn, who said (OK, I'm not going to try to quote here, I'll just get as close as I can remember) If a room is in what looks like near flashover conditions, never get any farther into the room than your bodys length. Always be within a bodys length of the doorway or a window.
Why? Because you can't survive the atmosphere of a flashover for more than a few seconds or so. The only way to survive it is to get out of it. Trying to use a fog stream to protect yourself is no more effective than a water curtain is for protecting an exposure, only in this case you are the exposure.
I had an officer, a guy who I revered for his fire smarts, who always called the line to a stop in those type conditions near a way out. He would say, "Hit it from here and hit it good before we move up. We might have to leave in a hurry."
I always tell the guys in my company, keep that nozzle pattern in as straight a pattern as possible. The only time I want to see it in a fog pattern is when we've checked the fire and are using it as a hydraulic vent out the window.
OK, I got my two cents in. Carry on. TJP