Re: Fire and roof tiles

[Michael Perry <mperry@efn.org>]

I've heard the same stories (about buildings exploding in fire storms
and/or burning from inside-out).

Here in the NW, I've seen a firestorm consume a forest. The air becomes
super-heated, and the trees heat up and "explode"... instead of being
ignited by the fire... and you can see the fire racing along the
treetops. I got caught in one of these fires, and it was a near thing.
We were racing down a logging road in a truck, and the fire was keeping
pace, and actually passed us at one point. The heat at our level was not
great (maybe 150 degrees) but it must have been several hundred degrees
"up there".

Ok... then go back to the midwest, with their tornados. There, they say,
much of the damage is caused by sudden drops in pressure, which causes
the house to "explode" outwards. I'm told, when fires are hot enough,
they cause this same event, and can drop pressure rapidly, followed by
"sucking" in air, which brings in fresh oxygen.

Ok, if the fire is hot enough, most of the air is sucked out of the
house, and the structure is "super heated" to above combustion
temperature (I can't recall the exact temp wood will burn at, but paper
burns around 450 degrees F). Windows might be blown outwards. Then, when
the low pressure is at its max, a sudden inflow of air blows the
superheated air into the structure, with the necessary oxygen. The
result, from the movie I watched, is that the house almost explodes
(wood provides fuel, temperature is well above ignition point... all
that's needed is oxygen... which is provided in a sudden inrush).

In these cases, NOTHING will stop the house from burning.

Fortunately, most residential fires don't involve a fire storm of this
magnitude.  Metal, and now plastic, studs in the roof, combined with
inflamable roofing materials help eleviate fires where they can be their
worse... above the ceiling. Reflective materials on the walls... and
possibly shudders on the windows... will reflect much of the heat
outwards (even light colored paint over wood siding helps).

Sealing the roofing materials is another BIG help in reducing the
chances of a fire starting. Having your home in the middle of a closely
space subdivision also helps, because house-to-house fires are more
controllable than a wild fire. Removing all burnables from around the
subdivision also helps a great deal. This means having a close-cropped
"green" zone around the entire area. Brush... and especially trees...
can carry fire into the division. It's thought that a surround of 1/2
mile is necessary to stop all but the worse firestorms.

Actually, building in normal "fire planes"... where fire travels in its
naturaly pattern... is not a good idea. Unfortunately, as developments
continue to spread, none of these areas are "spared" from development.
Perhaps the "best" solution might be to log all burned houses on the
deed. This would be very unpopular, because "burn planes" would tend to
be less insurable, if free-market is allowed to take its course w/o
government intervention. These, eventually, would be VERY expensive to
insure (as would flood planes)... and would make these houses
uninsurable to the normal owner. Of course, as long as there are those
who feel everyone should be insurable, we will all have to continue to
support those who feel it's their Gawd-given right to build whereever
they feel like building.

Hey, if they want to build where it's unsafe to build, let them... but
make it at their own risk... at least that's my 2 cents.

Robin Rierdan wrote:
> 
> In Fine Homebuilding a year or two ago, there was an article about
> protecting homes from fire. It highlighted this  one house, the only one
> standing after a fire took out a bunch of homes near Newport Beach or
> San Clemente. The house was designed by an engineer with fire in mind.
> It showed all of the roof tile courses  plugged with cement at the lower
> edge of the roof to stop embers from traveling up inside the roof. That
> was just one of the tricks that left this house standing when all others
> were burned to the ground. It was a very good article.
> 
>  Amazingly it said that houses in a wildfire burn from the inside out.
> It gets so hot in these fires that the interior combusts and the
> resulting fire takes out the rest of the structure. That whole concept
> sounds so  incredible to me that maybe I got it wrong. But I do  seem to
> remember seeing houses explode before just before the flames got them in
> the great 1969 fire in San Diego. Maybe I imagined that too.
> 
> r2