ASTM D6841-02

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 6841 – 02
Standard Practice for
Calculating Design Value Treatment Adjustment Factors for
Fire-Retardant-Treated Lumber
This standard is issued under the fixed designation D 6841; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers procedures for calculating treat-
responsibility of the user of this standard to establish appro-
ment adjustment factors to be applied to design values for
priate safety and health practices and determine the applica-
fire-retardant-treated lumber used at ambient temperatures
bility of regulatory limitations prior to use.
[service temperatures up to 100°F (38°C)] and as framing in
roof systems.
2. Referenced Documents
1.2 These design value treatment adjustment factors for the
2.1 ASTM Standards:
properties of extreme fiber in bending, tension parallel to grain,
D 9 Terminology Relating to Wood
compression parallel to grain, horizontal shear and modulus of
D 5664 Test Method for Evaluating the Effects of Fire-
elasticity are based on the results of strength tests of matched
Retardant Treatments and Elevated Temperatures on
treated and untreated small clear wood specimens after condi-
Strength Properties of Fire-Retardant-Treated Lumber
tioning at nominal room temperatures [72°F (22°C)] and of
D 6305 Practice for Calculating Bending Strength Design
other similar specimens after exposure at 150°F (66°C). The
Adjustment Factors for Fire-Retardant-Treated Plywood
test data are developed in accordance with Test Method
Roof Sheathing
D 5664. Guidelines are provided for establishing adjustment
factors for the property of compression perpendicular to grain
3. Terminology
and for connection design values.
3.1 Definitions:
1.3 Treatment adjustment factors for roof framing applica-
3.1.1 Definitions used in this practice are in accordance with
tions are based on computer generated thermal load profiles for
Terminology D 9.
normal wood roof construction used in a variety of climates as
3.2 Definitions of Terms Specific to This Standard:
defined by weather tapes of the American Society of Heating,
3.2.1 bin mean temperature—10°F (5.5°C) temperature
Refrigerating and Air-Conditioning Engineers, Inc.
2 ranges having mean temperatures of 105 (41), 115 (46), 125
(ASHRAE). The solar loads, moisture conditions, ventilation
(52), 135 (57), 145 (63), 155 (68), 165 (74), 175 (79) and
rates and other parameters used in the computer model were
185°F (85°C).
selected to represent typical sloped roof designs. The thermal
3.2.2 thermal load profile—the cumulative time per year in
loads in this practice are applicable to roof slopes of 3 in 12 or
each 10°F (5.5°C) temperature bin.
steeper, to roofs designed with vent areas and vent locations
conforming to national standards of practice and to designs in
4. Summary of Practice
which the bottom side of the roof sheathing is exposed to
4.1 Test results developed in accordance with Test Method
ventilation air. For designs that do not have one or more of
D 5664 are used in conjunction with computer generated
these base-line features, the applicability of this practice needs
thermal load profiles to calculate treatment factors that are
to be documented by the user.
applied to published design values for untreated lumber. These
1.4 The procedures of this practice parallel those given in
treatment adjustment factors account for the combined effect of
Practice D 6305. General references and commentary in Prac-
fire-retardant-treatment and service temperatures.
tice D 6305 are also applicable to this practice.
1.5 This practice is written in inch-pound units with SI units
5. Significance and Use
provided in parentheses for information only.
5.1 Fire-retardant-treatments are used to reduce the flame-
spread characteristics of wood. Chemicals and redrying condi-
tions employed in treatments are known to modify the strength
This practice is under the jurisdiction of ASTM Committee D07 on Wood and
properties of the wood product being treated. This practice
is the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.
Current edition approved Nov. 10, 2002. Published January 2003.
American Society of Heating, Refrigerating, and Air-Conditioning Engineers,
Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA 30329. Annual Book of ASTM Standards, Vol 04.10.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D6841–02
untreated values is a more conservative measure of treatment effect than
gives procedures for fire-retardant chemical manufacturers to
the median or the average of the individual matched specimen ratios.
use to calculate the effects of their treatment on lumber used in
normal and elevated temperature service conditions.
7.2 The ratio of the average property value for unexposed
5.2 The effect of fire-retardant treatments on the strength of
treated specimens to the average value for unexposed untreated
lumber used in roof framing applications is time related. In this
specimens shall be designated the initial treatment ratio, R .
o
practice, the cumulative effect on strength of annual thermal
7.3 Using the ratios of average treated to untreated speci-
loads from all temperature bins is increased 50 times to
mens exposed to elevated temperature for the same period of
establish treatment adjustment factors for fire-retardant treated
time, R , determine by least squares the linear regression.
ti
lumber roof framing.
R 5 a 1 k ~D! (1)
ti t
5.3 The procedures of Test Method D 5664 employ an
elevated temperature intended to produce strength losses in a where:
short period of time. Although the exposure is much more R = ratio of average treated to untreated values,
ti
D = number of days specimens exposed at elevated tem-
severe than that which occurs in an actual roof system, the
perature,
chemical reactions that occur in the laboratory test are consid-
a = intercept, and
ered to be the same as those occurring over long periods of
k = slope, strength loss rate.
time in the field. t
7.3.1 The ratio, R , for unexposed specimens (conditioned
o
5.4 Treatment adjustment factors developed under this prac-
at room temperature only) shall be included in the regression
tice apply to lumber installed in accordance with construction
analysis.
practices recommended by the fire-retardant chemical manu-
7.3.2 A property for which the strength loss rate, k,isnot
facturer which include avoidance of direct wetting, precipita- t
negative is assumed to be unaffected by the elevated tempera-
tion or frequent condensation. Application of this practice is
ture exposure.
limited to roof applications with design consistent with 1.3.
7.3.3 The strength loss rate, k , shall be adjusted to a 50
t
percent relative humidity (RH) basis by the equation:
6. Test Data
k 5 k ~50/RH ! (2)
6.1 Test Method D 5664 describes the procedures used to 50 t i
obtain the data needed to calculate the ratios of average treated
where:
and average untreated values for the strength properties.
k = strength loss rate at 50 % RH, and
6.1.1 Procedure 1 of Test Method D 5664 provides data for
RH = elevated temperature test RH.
i
comparing the initial effects of fire-retardant treatments to
7.4 Calculate strength loss per day rates for bin mean
untreated controls for bending, tension parallel, compression
temperatures of 105 (41), 115 (46), 125 (52), 135 (57), 145
parallel, and horizontal shear properties. The procedure uses
(63), 155 (68), 165 (74), 175 (79), and 185°F (85°C) using the
small clear specimens.
Arrhenius equation:
6.1.2 Procedure 2 of Test Method D 5664 provides data for
ln ~k /k ! 5 @E ~T 2 T !# / RT T (3)
50 2 a 1 2 1 2
assessing the differential trends between treated and untreated
specimens on bending and tension parallel properties over the
where:
course of a prolonged exposure to elevated temperature. The
k = strength loss rate at bin mean temperature,
4,5
procedure uses small clear specimens.
E = 21 810 cal/mol, (91 253 J/mol),
a
6.1.3 Procedure 3 of Test Method D 5664 is an optional
R = 1.987 cal/mol-K (8.314 J/mol-K), gas constant,
procedure to provide additional information on size effects.
T = test temperature, K, and
The results are used to modify the test results for the small T = bin mean temperature, K.
clear specimens of Procedure 1 and 2.
7.4.1 Where the treatment effect was evaluated at more than
6.2 Specimens subjected to prolonged exposure to elevated
one elevated temperature [for example 130°F (54°C) and
temperature are exposed in a controlled environment of 150 6
150°F (66°C)], the strength loss rates associated with the bin
4°F (66 6 2°C) and $ 50 % relative humidity. Durations of
mean temperatures shall be calculated for each temperature
exposure are 36, 72, and 108 days.
separately and the rates averaged for determination of capacity
loss values associated with thermal load profiles.
7. Calculation of Strength Loss Rates
8. Calculating Capacity Loss for Roof Framing
7.1 For each species and property evaluated, calculate the
Applications
ratio of the average treated value to the average untreated value
8.1 Thermal load profiles applicable to roof framing are
for the specimens conditioned at room temperature only
(unexposed specimens) and for specimens exposed for the given in Table 1. The loads represent the cumulative days per
year framing temperatures fall within 10°F (5.5°C) of the bin
same period of time at elevated temperature.
7.1.1 The treated and untreated specimen averages used to mean temperatures of 105 (41), 115 (46), 125 (52), 135 (57),
calculate each ratio shall include the same number of speci-
mens and each treated specimen value shall be matched to an
untreated specimen value obtained from the same source piece
Pasek, E. A. and McIntyre, C. R., Heat Effects on Fire-Retardant Treated Wood,
J. Fire Sci., 8, Nov.-Dec. 1990, pp. 405-420.
of lumber.
Pasek and McIntyre have shown that the Arrhenius parameter, E , for
a
NOTE 1—Test data show that the ratio of average treated and average phosphate-based retardants for wood averages 21 810 cal/mol (91 380 J/mol.).
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D6841–02
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