This post is the one that I wish someone else had written that I could have read before yesterday.
The first thing you need to know about brush fires is that it's all about the wind. If the wind is blowing, you're screwed. There is nothing you can do but pack your stuff and the hell out of Dodge. I learned this from an acquaintance who lost his house in another fire a few years ago. He's a volunteer firefighter, so he has all the right training and equipment. He did all the right things. He had pumps and hoses and a chainsaw to cut away the wooden deck outside his house. The fire came to with a few yards of his house and then stopped. He thought he was safe, since there was now a wide zone between him and the fire that was depleted of fuel. The same brush can't burn twice, right?
Wrong. The wind shifted, and what had previously burned as a relatively controlled slow-moving fire, now re-ignited as if it was a blast furnace. His house pretty much just went "poof", and he was lucky to escape with his life. The heat from the fire blew out the back window of his truck and lit him on fire as he was heading down the hill. Fortunately, there were firefighters at the bottom who were able to extinguish him before turning their attention to their own truck, which had also caught fire. And yes, I saw photos. He documented everything quite meticulously.
Miraculously, although the weather has been unseasonably hot and dry (and that's saying something in August in Southern California) we have had virtually no wind. That's been horrible for air quality, but it's almost certainly the only reason more houses haven't been lost.
So last year I decided to get better prepared for the fire that I knew would inevitably come (though I wasn't expecting my timing to be quite this good). I explored various options, including a roof sprinkler, and a gas-fired pump that draws water from the pool. After consulting with a local fireman we decided to go with the pump. We also got a supply of foam and Barricade Gel. Yesterday I was able to put all that stuff to the test.
In retrospect I think we got it exactly backwards. If I had it to do over again I'd go with the roof sprinkler and forego the pump. The problem is that you have to be there to man it, and you have to be there when the fire arrives. And, as we found out the hard way yesterday, the same fire can arrive more than once.
The gel and foam turn out to be pretty useless also. The foam in particular just seemed to dissolve on contact with whatever it landed on. Five minutes after being applied there was no hint it had ever been there. The Barricade Gel, on the other hand, works as advertised. It leaves everything covered with a 1/4-inch thick layer of slimy goo. Word to the wise: wear leather work gloves when you apply this stuff, not because you need the protection, but because it's incredibly slippery, and if it gets on your hands you can't grip anything any more.
The trouble with the gel is it only lasts for an hour or two, so your timing still has to be pretty much dead-nuts on. It also leaves a horrible mess behind. Our house is now covered with a slimy film of residual gel, and I have no idea how we're going to get it off.
A roof sprinkler system has its own problems, of course. If you have eaves it won't do anything to protect the sides of the house. Of course, you can install sprinklers all around the eaves as well, but that starts to get expensive and/or unsightly. PVC will melt in a fire, so you need to use copper or galvanized steel for the plumbing. But the nice thing about it is that it's fire-and-forget (so to speak). You turn it on, evacuate, and whenever the fire arrives everything will be nice and soggy. It won't protect against a wind-driven fire (nothing will) but it will help prevent flying embers from igniting your house, which is pretty much all you can do. If mother nature decides she wants your house she will take it. The only way to be absolutely safe is to build out of concrete (and even then the radiant heat from a really hot fire can penetrate the windows and light the interior on fire).
One last thing to keep in mind if you decide to go with gel: it's seriously hard work to apply. You can do it with a garden hose, but that's very slow. We used the gas-fired pump, and let me tell you, wrangling a 100PSI fire hose make you feel very manly, but it is seriously hard work. By the time I was done applying the gel I was at the limits of my physical endurance in my upper body. Granted, I'm not in great shape. Most of the exercise I get above the waist is from typing. But I think I'm not alone in this. Oh, also, buy four times as much gel as you think you need.
There are two more drawbacks to the gel: its expensive, and it has a limited shelf life. You have to shake the containers every six months, and even then it only lasts a couple of years.
Of course, the best way to prepare for a brush fire is to buy a house far away from brush.