Dennis
J. Murphy and William C. Arble
Pennsylvania State University Cooperative Extension
Both
rigid board foam and sprayed-on cellular plastic foam insulations
present serious fire problems when installed as an exposed
finish in farm buildings. Insulation foams are most often
developed from plastic polystyrenes, polyurethanes, and polyisocyanurates.
Table
1. Flame Spread Ratings for Various Materials |
Interior
Finish Material |
Flame
Spread Rating |
Asbestos-cement
board
1/2 in. or 5/8 in. gypsum wall |
0 |
board
(dry wall)
1/2 in. treated (fire retardant) |
15 |
exterior
plywood |
20-25 |
Red
oak lumber |
100 |
Untreated
exterior plywood
(various thicknesses) |
75-200 |
The manufacturers
of these insulations imply that the materials themselves aren't
hazardous, but that improper use or application can create hazards.
But many fire experts say that the materials are hazardous because
of the typical way that they are applied. The reason for the
difference in opinions is the way the insulations have been
tested. The manufacturers tested the flammability of the product
in the horizontal mode. The flame spread in this position is
minimal. However, others have tested the foam insulations in
the vertical position. When tested this way, the results are
far different.
Just
who is technically correct is of little consequence. The fact
that foam insulation has been involved in millions of dollars
of losses to potato and apple storages, swine houses, poultry
plants and other livestock housing is undebated. A common
fact is that fires in buildings with foam insulation have
spread with alarming speed, resulting in clouds of black dense
smoke and devastating loss. It is also a fact that there are
many different foam materials with widely different flammability
but under certain conditions all of these materials will burn.
Even self-extinguishing foams burn (or else they could not
self extinguish under certain situations).
Flame
spread tests of rigid plastic insulation boards show flame
spread ratings ranging from 25-2500, depending on the position
of the board (horizontal or vertical, surface or corner) and
the ignition source. However, in most cases the insulation
flashed over (became fully involved by fire) in slightly over
one minute. This indicates two things; one, that the insulation
does allow rapid flame spread (see Figure 1) and secondly,
that exposed foamed insulation can burn at such a rapid rate
that evacuation of a building lined with this type of insulation
is nearly impossible.
Building
codes typically require that foam insulation be protected
with fire resistant barriers because of the foam's relatively
low decomposition temperature, questionable flame spread,
potential toxic gas generation and high smoke emission. But
exposed cellular plastic insulation has been allowed in farm
buildings because building codes often are not enforced or
are not applicable in rural areas. You should act now to minimize
the fire risks to buildings that contain exposed cellular
plastic insulation. Many insurance companies that sell farm
policies are requiring policy holders to upgrade buildings
with exposed foam insulation by either covering the foam insulation
or removing it completely.
Upgrading
the fire resistance of foam insulation is expensive after
the building has been in use several years. In these buildings
it's too late to consider using alternative insulation systems.
Typical 1982 estimates for adding fire barriers to existing
buildings range between $.75 to $1.50 per square foot.
- The
barrier must stay in place during heat buildup. A gypsum
board (dry wall, "sheet rock," or equivalent) nailed through
foam board into wood framing is probably better than a barrier
board fastened by glue.that could crack.
- The
barrier should prevent the insulation from heating to more
than 250 degrees F above ambient temperature for 15 minutes
after the fire ignites. Gypsum board is more effective than
corrugated metal or metal facing, since metal conducts heat
of the fire directly to the foam, resulting in melt down.
Following
are possible methods of covering exposed insulation in your
buildings:
- 1/2
in. gypsum board nailed in place over the insulation.
- 1/2
in. fire retardant plywood. Fire retardant plywood is not
usually in stock, but can be ordered from most lumber yards.
Make sure the pieces fit tightly and all gaps are sealed.
Ordinary exterior plywood will provide some flame spread
protection for the foam, however, the plywood itself may
burn, thus exposing the insulation.
- 1/2
in. asbestos cement board nailed in place over the insulation.
- 1/2
in. cement based mixture (gypsum-sand or gypsum-vermiculite)
applied on the plastic foam insulation. Durability of this
treatment depends on the competency of the applicator, so
always check on jobs already completed by the applicator.
A few
additional points about cellular plastic insulation and fire
barriers that all farmers should understand:
- Some
cellular plastic foams melt at temperatures as low as 270
degrees. This may be as little as 180-200 degrees over room
temperature.
- Adding
insulation to a building results in holding more heat in
the structure during a fire, permitting greater heat buildup
on wood or other flammable materials.
- Most
cellular plastic foam insulation boards burn quickly at
low temperatures with the same heat release and flame spread
as at high temperatures. This is different from most materials
that start burning slowly and increase their burning rate
as time and temperature increases.
- Flame
retardant additives decrease the possibility of foams catching
fire from contact with a small fire source, such as a torch
or overheated electrical wire. But a larger source of fire
will ignite exposed "flame retardant" foams.
- A
fire test on cellular plastic foams under controlled conditions
and blueprint specifications is quite what may occur with
foam in place for years, subject to aging, mechanical damage,
building modifications, moderate maintenance, and other
changes that normally occur during product lifetime.
- If
you are adding a fire barrier to exposed foam insulation,
be sure the fire barrier is conducive to the environment
it will be exposed to. For example, plywood barriers would
be used in swine confinements rather than gypsum board due
to moisture problems and possible physical damage.
- Asbestos
is a known carcinogen. If asbestos-cement board is used
as a fire barrier and boards must be cut for fitting, wear
a respirator approved for asbestos dust. During sawing,
fibers are likely to be jarred loose from the bonding substance
and become airborne. Currently, there is no known safe level
of asbestos dust, so respiratory protection is crucial.
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
This document
was published in 1988 as Pennsylvania State University Fact
Sheet Safety
20
,
Pennsylvania Cooperative Extension Service. For more information,
contact Pennsylvania State University College of Agricultural
Sciences, Agricultural Engineering Department, 246 Agricultural
Engineering Building, University Park, PA 16802.
Dennis
J. Murphy, professor; William C. Arble, PENNTAP Fire Technologist;
Agricultural Engineering Department, Cooperative Extension
Service, Pennsylvania State University, University Park, PA
16802.
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