Joseph M. Zulovich
University of Missouri Extension
Fires
in farm buildings cost Missouri agriculture nearly $1 million
per year. This loss could be reduced substantially through
better site selection use of less flammable materials and
some simple fire stopping techniques. This publication describes
some of the construction features that you can use to reduce
the risk of fire loss on your farm.
Fire
normally starts within a single area or room. It spreads over
surfaces and penetrates combustible coverings, moving to adjacent
areas either directly or through natural openings in the building
construction.
Buildings
collapse when the fire has progressed to the point where structural
members are weakened by either burning or excessive heat.
Risk
of loss is reduced whenever we use construction practices
that slow or prevent the normal progression of fire.
Building
location may help prevent fire spread to or from adjacent buildings.
A recommended minimum separation between farm buildings is 50
feet. Farm shops or fuel storage structures should be situated
at least 100 feet from any other buildings. Consider using greater
separation whenever buildings are in alignment with prevailing
winds.
Fire
stops are obstructions placed in concealed passages within buildings
which slow or halt the movement of flame heat and hot gases
from one area to another. They are used most often to block
wall stud spaces or areas between floor joists on multistory
buildings. Solid wood blocks 2 inches thick make effective fire
stops. Wall cavities that are completely filled with non-combustible
insulation do not need fire stopping.
Most
modern agricultural buildings can benefit from fire stopping
in the area above the ceiling and under the roof. This relatively
open space provides a natural tunnel for fire to move throughout
the building once it has burned through the ceiling.
An easy
way to provide fire stops for this area is to cover both sides
of a truss with 1/2-inch gypsum board. The board should cover
the area between the ceiling and the underside of the roof
completely. One of these fire stops should be over each cross-partition
in the building or approximately every 50 feet for buildings
with large rooms.
Properly
constructed walls can be used as fire stops in buildings where
it is desirable to provide more control over fire spread between
adjacent areas. These stops (commonly called fire walls) can
provide time to remove animals or equipment from a portion
of a building.
Consider
using a fire wall whenever two areas with different risk levels
are contained in the same building. For example, a shop constructed
in one end of a machinery storage building should be separated
from the machinery storage area by a fire wall. Other examples
include separation of utility rooms or heating plants from
other areas of the building.
Fire
walls need not be elaborate. In many cases, more careful selection
of materials combined with conventional construction can provide
valuable protection. A standard 2 x 4 stud wall covered with
1/2-inch gypsum board provides a 40-minute fire rating. Ratings
for other types of wall construction can be found in Table
1.
Table
1. Fire resistance ratings for various types of partition
wall construction.
Construction |
Fire
resistance rating (minutes) |
Wood
frame covered (both sides) with: |
1/2-inch
fiberboard |
10 |
1/2-inch
fiberboard, flame proofed |
10 |
1/4-inch
plywood |
10 |
3/4-inch
T&G boards |
20 |
3/8-inch
gypsum wallboard |
25 |
1/2-inch
gypsum wallboard |
40 |
5/8-inch
gypsum wallboard (type X) |
60 |
Cement
asbestos board 3/16-inch thick |
10 |
3/16-inch
cement asbestos board over 3/8-inch gypsum board |
60 |
Masonry
construction |
4-inch
blocks plastered both sides |
60 |
6-inch
blocks |
60 |
6-inch
concrete |
240 |
Fire
moves through a room at a rate that depends on the material
used to cover interior surfaces. Many building materials carry
a flame spread or fire rating, which is an indication of their
ability to resist burning.
Flame
spread or fire ratings are obtained by comparing the burn
rate for a material with the burn rates obtained from the
standardized materials, red oak lumber and asbestos cement
board. Flammable rates for these materials are assigned values
of 100 and 0, respectively, and other materials are given
values that represent a comparison with these numbers. For
example, a material that burns twice as fast as red oak would
receive a flame spread rating of 200.
Flame
spread ratings are sometimes grouped into classes, providing
a general indication of flammability. Class ratings and their
associated flame spread ratings are shown in Table 2.
Table
2. Class, flame spread and suggested use for interior building
materials.
Class |
Flame
spread |
Use |
A |
0-25
| Farm
shops, heating plant rooms, fuel storage, high-risk areas |
B |
26-75
| Confinement
buildings without heating system |
C |
76-200
| Low-risk
buildings, such as hay storage |
D
| 201-500
| Do
not use without protective covering |
|
500+
| Do
not use without protective covering |
Urethane
and styrene foam plastic insulations commonly used in farm buildings
have extremely high flame spread rates. To minimize risk when
using these materials, it is suggested that they be protected
from fire with fire-resistant coatings. Materials that provide
satisfactory protection include the following:
- 1/2-inch
thickness of cement plaster.
- Fire-rated
gypsum board.
- 1/4
- 1/2-inch thickness of sprayed-on magnesium oxychloride.
- Asbestos-cement
board 1/4-inch thick.
Note:
If foam plastic insulations are not protected suitably from
potential fire, your insurance company may refuse to provide
coverage on the structure.
There
are two methods of treating wood to improve its resistance to
fire pressure treatment with special chemicals and painting
with fire-resistant paints.
The
pressure treatment process is similar to that used with the
more familiar wood preserving chemicals. Special waterborne
salts are used that limit the amount of combustible products
released when wood is exposed to flame. Some of the more commonly
used chemicals include monammonium and diammonium phosphate,
ammonium sulfate, zinc chloride, sodium tetraborate and boric
acid.
Fire-retardant
treatment does not prevent wood from burning, nor does it
slow up penetration of fire in structural members. Its main
benefit is to slow the rate of surface spread. It is very
questionable whether the cost of pressure-treated, fire-retardant
wood can be justified for agricultural buildings.
Fire-retardant
paints have low surface flammability and tend to expand or
"foam" when exposed to fire. This expanded layer acts as an
insulation to help keep heat away from the flammable surface
under the paint. Properly applied coatings can reduce the
flame spread for wood products to 25 or less and they are
being applied routinely to some factory finished building
products.
Many
farmers have purchased metal buildings because they believed
them to be "fireproof." The flame spread rating for metal is
0; however, when a fire occurs the unprotected metal frame building
will fail much more rapidly than a wooden structure. This is
particularly true in the case of machinery and other storage
buildings where fire is more likely in the stored product than
in the building itself.
Temperatures
build up very quickly during early stages of a fire and often
spread through a building even more rapidly than the fire
itself. As soon as metal structural members get hot, their
strength decreases rapidly. The result can be complete structural
collapse long before actual flames spread through the building.
Metal
frames can be protected from heat by encasing them in concrete,
by constructing an insulated firewall around them, or by spray-on
insulating coatings. A 1-inch thickness of sprayed-on asbestos
fiber yields a two-hour fire rating for an 8-inch steel I
beam. An unprotected beam has a 10 minute fire rating. In
most cases, protective cost probably is not warranted for
farm buildings. An exception might be the farm shop, which
is a relatively high-risk area usually containing high-value
equipment.
Nearly
all fires start small and grow big. A good fire extinguisher
in the hands of a person who knows how to use it can often prevent
a small fire from becoming a major loss.
To order,
request
G1910
,
Improving Fire Resistance of Farm Buildings (25 cents).
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
Copyright
1998 University of Missouri. Published by University Extension,
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Department
of Agricultural Engineering, University of Missouri-Columbia
Agricultural publication G01910 Reviewed October 1,
1993
Issued in furtherance of Cooperative Extension Work Acts of
May 8 and June 30, 1914, in cooperation with the United States
Department of Agriculture. Ronald J. Turner, Director, Cooperative
Extension Service, University of Missouri and Lincoln University,
Columbia, Missouri 65211. University Extension does
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