Fire Hazard Classification
There are numerous similar
instances over the years in which redwood's fire resistance has
aided in stopping fires or in which redwood has been specified
because of its fire-resistive property. Fire walls of crib construction
have given excellent service in warehouses and commercial buildings.
Curtain walls and fire stops of redwood have stopped fires in
many structures, including warehouses and bridges.
Redwood does not ignite easily
and it burns slowly because it contains little or no volatile
resins or oils to aid in combustion. Once flame has covered the
surface, a layer of char is developed which adheres to the unburned
wood beneath. This retards further combustion, and in many fires,
this layer of charred wood has prevented the fire from doing
more than superficial damage to the structure.
Fire Hazard Classification
Fire hazard classification
rates three buring characteristics of materials--flame spread,
fuel contributed, and smoke development--on an arbitrary scale
in which asbestos cement board is rated 0 and nominal 1-inch
untreated red oak lumber is rated 100. The lower the rating,
the more flame resistant is the material.
Poperty damage and loss of
life by fire are closely related to how fast the flame spreads,
how much fuel is added to the fire by the various materials of
which a building is contructed, and the quantity of smoke and
Flame spread. Of the three
ratings, flame spread is the most important and the most commonly
used. All four model building codes, the Uniform Building Code
(UBC), Basic Building Code (BOCA), National Building Code (NBC)
and Southern Standard Building Code (SSBC) require certain minimum
flame spread ratings for interior finish materials.
The Uniform Building Code lists
three flame-spread classes:
|Flame Spread Classification (UBC Table 42-A)
Flame Spread Classififcation
The BOCA flame-spread Classes
are similar to those of the UBC, while NBC and SSBC have only
two flamespread groups: 0-75 and 76-200.
Ratings of Redwood Lumber
In April 1971, Underwriters'
Laboratories conducted their standard fire hazard classification
tests on nominal 1- by 6-inch and nominal 3/8- by 6-inch untreated
redwood lumber including both heartwood and sapwood.
Fire hazard classification
tests were conducted in accordance with Underwriters' Laboaraties,
Inc., "Standard Test Method for Fire Hazard Classification of
Building Materials" (UL723), and ASTM Standard E82-81A, "Standard
Method of Test for Surface Burning Characteristics of Buidling
The moisture content of the
lumber samples tested ranged from 5.9 to 8.2 percent--well within
the requirements of the standard.
The results of the fire hazard
classification tests are shown in Table II. The flame-spread
rating of 65 for 1-inch redwood lumber qualifies this material
as Class II under the UBC.
In 1981, tests were conducted
at the University of California Fire Test Laboratory in Berkeley
to determine whether redwood is suitable for rooftop decks and
walking surfaces by qualifiying as a Class B system as tested
under U.L. 790. As a result of these tests, the International
Conference of Building Officials and Bureau of Buidling Inspection
of the City and County of San Francisco have determined that
panels made from Certified Kiln Dried redwood heartwood meet
the requirements of the Uniform Building Code for use as walking
surfaces over existing fire retardant roofs. ICBO has issued
Research Report #4101 which provides details for the construction
of rooftop decks in accordance with the study. The San Francisco
BBI has issued General Approval 706 C67 in regard to this matter.
|Redwood Lumber Fire Hazard Classification
1" nominal redwood lumber*
3/8" nominal redwood lumber
* The net surfaced size
tested was 3/4 inch. Lumber surfaced to 11/16 inch will also
qualify for a flame-spread rating of 75 and less (Class II
UBC) by extrapolation between the values obtained from the
nominal 1-ich and nominal 3/8-inch lumber tests.
At present, less importance
is given to ratings of fuel and contributed and smoke development
by the majority of building codes, although some--e.g., the
San Francisco city code--require certain minimums. Redwood's
ratings for these factors are included in the table above.
The results of these tests
permit the use of redwood in a wider range of interior uses than
heretofore. The UBC classification allows the use of redwood
without fire retardant treatment or coating for many interior
applications where code restrictions otherwise rule out untreated
As a Class II material, 1-inch
redwood lumber can be used for interior walls and ceiling finish
any place in all types of buildings under the UBC except for
enclosed vertical exitways and a few other minor-use areas requiring
Class I materials. Under the NBC an SSBC, with very few exceptions,
1-inch redwood lumber can be used for interior walls and ceiling
The flame-spread classification
of 3/8-inch redwood lumber, while not qualifying as Class II,
is comparably low for products of this thickness.
A test of the magnitued necesary
to include all possible patterns is not only impractical, but
unnecessary. Based up on test results, all widths, patterns,
surfaces, and textures in these thickneesses qualify for similar
For comparative purposes, some
flame-spread rates of other material are shown in the table below.
|Flame-Spread Rate of Other
Fire retardant treated lumber
Red oak lumber
Ponderosa pine lumber
Building Code. International
Conference of Building Officials, Whittier, California, 1982.
on Fire Hazard Classification of Redwood Lumber. Underwriters' Laboratories, Inc., Subject
723. Assignment 71SC509. March 16, 1971.
Hazard Classification. Card Data Service. Underwriters' Laboratories, Inc., 1971.