Fire! Where was all the water?

[Mark Piepkorn <duckchow@mail2.greenbuilder.com>]

Doing my part to keep the universe in balance, here's a fire story to
complement Sara's and Sarah's water stories. (Now we need air and earth
stories, right? And metal, I guess, with a nod toward the fifth element of
some Oriental traditions. And how about beer hall and cathouse facilities
in the Sedona AZ area?...)

There was a fire in Casa Chica at the Black Range Lodge on January 1st.
(Hopefully Norbert Senf will have something to say about this.) Casa Chica
was/is an exercise in low-tech building, incorporating straw, earth, stone
and wood as its principle materials. No cement (at all), no plastics
(except for the radiant-heat tubing in the earthen floor and the poly bags
used in part of the foundation), no industrially-processed materials
generally (except the Torchdown membrane under the living roof and the
glass in the windows). There's a photo of it at
http://www.strawbalecentral.com/miscellaneous/misc2.html , labeled #20,
which shows the very same corner of which I am about to speak.

After the structure was built (in '96 or so), it was decided that a cob
fireplace would be a dandy thing to have inside it. The fireplace was built
it into a corner at the junction of an earth-plastered bale wall (to the
right on the photo, with the beginnings of a cob addition attached) and a
straw-clay wall (to the left on the photo behind the cob-covered stone
banco, with wattle-and-daub above). The thickness of the earth plaster,
along with the cob constituting the oven, separated the firebox (not brick,
just cob) from the bales with about 4" of unstabilized earth with minimal
straw content.

On New Year's Eve there was a long, hot fire in the fireplace... nothing
that hasn't been done many times before. Next mid-morning, Tony noticed
smoke and investigated - the smoke was coming out of the walls under the
roof overhang.

Pete and Tony and Luciano (now at The Farm with wife Lucia and son Theo
[pronounced "tay-oh"] for a while before their visas expire - they're from
Uruguay... and Joe Kennedy just announced that he, wife Rose, and daughter
Taya [pronounced "tie-ah"] are moving to The Farm to head up the natural
building part of the Ecovillage Training Center at Albert Bate's
invitation... FWIW) took to taking the wall down with a pick, shovel, and
garden hose as Sarah (a different one) and I snapped pictures. Various
people like Catherine, Yo (pronounced "yo"), Tom Watson, and others, looked
occasionally on.

As expected, there were no flames, just smoldering, except when loose
straw ignited - which only happened during the deconstruction of the
affected area, and only happened a few times. The garden hose probably had
something to do with keeping that limited. Deconstruction was sort of
leisurely, given the circumstances, and took a couple hours.

There was (is) a roundwood bearing post in the corner, partially set into
the wall envelope, between the bale and straw-clay sections. It's a big
sucker, about 6", as seen in the photo. It's charred fully halfway through
- that smoldering fire had obviously been going for hours.

All told, (the equivalent of) three rows of bales were removed, floor to
ceiling... from the big corner-log to the doorway cut into the bale wall on
the far side of the cob extension, as seen in the photo. Comparatively
little of the straw had actually charred - perhaps in volume one bale's
worth - but it followed airflows, so wasn't confined to a particular place.
The fire had worked its way in reverse-rivulets upward from near the bottom
of the wall (where the smolder started), fingering upward and outward like
a clump of extroverted and willful Taoists. (Don't ask me to explain that.)

The straw-clay wall, where the sustained heat source was against it,
turned into a sort of flaky charcoal.

What happened? It seems that Watson, before retiring to full-time armchair
practical natural philosophy, had spent a good number of years as a
traditional-southwest-oven-and-fireplace restorationist and recreationist
both as a builder and consultant. He said that:

1. When a sustained heat source (the fire in this instance) creates
combustion or near-combustion temperatures in a cellulosic material (the
straw, with heat via conduction in this instance), the material releases
flammable gasses - sort of the principle behind secondary burn chambers in
contemporary woodstoves, particularly catalytic stoves.

2. A fire will pull air to itself from anywhere it can, from anywhere that
air flows; the hotter the fire, the more this is true.

The theory, based on those points, is that:

1. There was a pinhole or crack leading from the bales through the 4" of
earthen render, and air was drawn through this discontinuity to feed the
fire. This of course means that there were other discontinuities elsewhere
(such as up under the overhang where the smoke was exiting) which fed
replacement air into the wall. (Earth-plastered walls don't "breathe" in
the sense that air moves readily through them; the theory is more along the
lines of "perspiration.")

2. The bales became heated enough to start releasing combustible gases;
these gases were sucked through with the air to the fire, creating a sort
of miniature gas jet - like on a gas stove, but smaller and less steady.
Sometimes in a bonfire or fireplace where there's a big log, they'll
"squirt" fire for a couple seconds. This is the same principle - the inside
of the log isn't on fire, it's releasing combustible gases which are
escaping.

3. An momentary equalization of the air/gas-flow can make the gas jet work
in reverse... the gases ignite in the bales, and the ball gets rolling.

The lessons?

Follow good stove design and construction if you're going to design and
construct a stove. The back-side of the cob firebox was EXTREMELY hot as
the wall was dismantled, and there are areas of it that appear to have
begun to vitrify. Leaving an air space between the stove and wall would
have been a good idea; a couple scraps of corrugated roofing screwed
together in offset to create air channels could easily have been inserted
in front of the wall before the oven was built.

Plastered bale walls don't necessarily need to have a direct source of
flame to combust (though I still don't harbor any illusions that plastered
bale walls will spontaneously combust).

Posted comments and discussion are welcome. I'll upload photos to the
Gallery section of http://www.strawbalecentral.com when I get them
developed and scanned. No promises how soon it will be...



   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Freewheeling autonomous speculation - Think!
    I'm off the clock and on my own time, dig?
         Mark Piepkorn (f.k.a. M J Epko)
        <duckchow@mail2.greenbuilder.com>
               Kingston, New Mexico
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The greatest discovery of my generation is
    that human beings can alter their lives by
    altering their attitudes of mind.
                               - William James