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Re: GSBN:Re: Fire-Resistant Straw Bale and Fighting a SB fire
- To: GSBN@...
- Subject: Re: GSBN:Re: Fire-Resistant Straw Bale and Fighting a SB fire
- From: David Eisenberg strawnet@...
- Date: Fri, 21 Dec 2007 00:55:44 -0500
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
Joyce had forwarded the info about this fire and the inquiry from Don
Fisher to a few of us before it showed up here on GSBN. I want to share
what I wrote in response and the brief exchange that followed with
Martin Hammer. I also want to share what I wrote in an article for The
Last Straw issue #16 in the Fall of 1996. My article appeared in the
Hard Knocks section of TLS and was entitled "Burned Again." It was
about a fire that happened here in Tucson at a steel framed structure
with almost identical circumstances. I've include the text of that
article below because I think it is still relevant.
First, here's part of what I wrote back to Joyce, Martin Hammer, Bruce
King and Bob Bolles last week and Martin's response and my reply to
...This brings up something that I keep thinking and then forgetting
about in relation to something important that may be missing in sb
codes - addressing exposed straw in assemblies and elsewhere like at
interfaces - top of wall, where other walls or wall systems abut bales,
behind rainscreens, etc. This shouldn't be allowed. No reason to treat
straw differently than other types of flammable construction. Martin, I
can't remember if there was anything new related to this in your new
proposed code for California. And, Joyce, it seems like it might be
worthwhile to devote part of an issue of TLS to fire issues at some
I've always (and I mean for at least 15 years) told people to treat
exposed straw in cavities, spaces, interfaces as flammable and to
either spray it with a recognized and effective fire retardant, or a
heavy clay slip, coat it with earth or other plaster, drywall compound,
anything that will keep the straw from supporting a fire. This should
be covered very clearly in the code.
Regarding not allowing exposed straw surfaces as you describe below, it
is currently not addressed in the proposed California SB Appendix, but
it should be. Certainly at rain screens or other areas where there is a
large air space / straw surface interface (especially a vertical one).
I'm not as convinced for the need where another material/element has
direct and continuous contact with a bale surface (e.g., box beams,
last stud in a stud wall). I also need to think about the right
language for this, in such a
way as to allow reasonably sized truth windows.
I actually didn't really intend for what I wrote to include places with
that kind of continuous contact with other materials. I was thinking
about places where there would likely be gaps or spaces, like a few
times I've seen intersecting walls attached to blocks that are attached
to the surface of the bales, creating a gap behind the last stud,
situations like that are what I had in mind. I'm glad that you agree
that this is something that should be addressed in the code. BTW, I
also think that, especially in cold climates, interior truth windows
should be glazed so you don't just have a big hole into the wall. I had
to laugh once many years ago when I was being shown a nice straw bale
home in Colorado, where they had just explained all the detailing they
had done to deal with air leakage and then showed me a truth window
with over a square foot of totally exposed straw behind a rustic,
non-sealing hinged door. Ahhh, well...
Here is the article from TLS...
The Last Straw #16/Fall 1996
by David Eisenberg
This is not the first time we have had to report a fire in a straw bale
structure under construction . It would be wonderful if we could say
it were the last. Once again we have been fortunate that no one was
injured. There are lessons to be learned from each of these
occurrences and we strive to learn them and share them with everyone.
On October 1st, just west of Tucson, Arizona, a bale-wrapped steel
frame combination studio/garage caught fire while welding was being
done. The building, which had unfinished bales stacked on-edge on the
outside of the steel framing, was destroyed by the ensuing fire.
Contributing factors to the fire and its rapid spread are similar to
those reported previously here. And it is worth noting that the other
flammable materials in the building contributed heavily to the speed
and intensity of the fire. Nonetheless, the straw initially burned
quickly enough to spread the flames beyond the ability of those present
to control them.
A welding contractor was at work when a flash from his welding rod set
the straw on fire. Very quickly after the fire began, a fire
extinguisher was used to apparently douse the flames. However, the
fire extinguisher actually drove the flames through the unfilled spaces
between the bales to the outside. While the smoke and cloud from the
extinguisher was clearing, the flames were spreading along and up the
wall on the outside. Though this was noticed within minutes, the
flames were able to spread and reach the plywood and OSB sheathing in
the eaves, facias and on the roof and spread with great speed and
intensity all around and over the building.
Critical factors appear to have been: welding in close proximity to the
straw without taking adequate precautions to insure the straw was fully
protected; orientation of the bales, which were placed on-edge which
exposed the polypropylene strings to the fire and thus as they burned
through the straw was unbaled and started falling out of the walls;
there were many open spaces between the ends and corners of the bales
which had not been stuffed with straw or straw and mud, leaving many
easy paths through the walls for the flames; there was loose straw on
the floor and around the outside of the building; and of course, there
was not sufficient appreciation for the vulnerability of unfinished
bale walls to fire.
Though unrelated to the cause, the fire in this particular building
raises the issue of the potential of a fire developing in the stud wall
cavity, between the interior wall finish, whatever it may be, and the
exposed straw up against the studs (on the interior side of the bales).
When finished, the exterior of the bale wall would presumably have a
plaster finish on it, protecting it from fire. However, unless some
action is taken to fire treat or cover the inside bale/stud wall
interface, there is the potential for a fire to develop and spread in
this space, fed by the air that is available in this cavity. It would
seem prudent to treat the bales with a flame retardant or coat them
with a thin layer of plaster or some other fire resistant material,
even a clay slurry that could be sprayed on after the bales were
stacked. Another approach, though somewhat costly would be to sheath
the interior of the frame wall with sheetrock before the bales are
stacked, thus isolating them.
In a similar fashion, it has been suggested that a layer of sheetrock
on the underside of the roof bearing assembly would provide close to a
one hour fire barrier to prevent a roof fire from spreading down into
the top of the bale wall. And it has also been suggested that
sheetrock could be laid on top of bales used for attic insulation,
adding a measure of fire protection within the roof.
The bottom line here, is that we must be careful and attentive to the
dangers that exist for buildings while under construction, as well as
for situations we may create through our designs or methods of
construction that make them vulnerable to fire even after they are
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