ASTM D6305-08(2015)e1

Standard Practice for Calculating Bending Strength Design Adjustment Factors for Fire-Retardant-Treated Plywood Roof Sheathing

SIGNIFICANCE AND USE
5.1 This practice develops treatment factors that shall be used by fire retardant chemical manufacturers to adjust bending strength design values for untreated plywood to account for the fire-retardant treatment effects. This practice uses data from reference thermal-load cycles designed to simulate temperatures in sloped roofs of common design to evaluate products for 50 iterations.  
5.2 This practice applies to material installed using construction practices recommended by the fire retardant chemical manufacturers that include avoiding exposure to precipitation, direct wetting, or regular condensation. This practice is not meant to apply to buildings with significantly different designs than those described in 1.3.  
5.3 Test Method D5516 caused thermally induced strength losses in laboratory simulations within a reasonably short period. The environmental conditions used in the laboratory-activated chemical reactions that are considered to be similar to those occurring in the field. This assumption is the fundamental basis of this practice.
SCOPE
1.1 This practice covers procedures for calculating bending strength design adjustment factors for fire-retardant-treated plywood roof sheathing. The methods utilize the results of strength testing after exposure at elevated temperatures and computer-generated thermal load profiles reflective of exposures encountered in normal service conditions in a wide variety of continental United States climates.  
1.2 Necessarily, common laboratory practices were used to develop the methods herein. It is assumed that the procedures will be used for fire-retardant-treated plywood installed using appropriate construction practices recommended by the fire retardant chemical manufacturers, which include avoiding exposure to precipitation, direct wetting, or regular condensation.  
1.3 The heat gains, solar loads, roof slopes, ventilation rates, and other parameters used in this practice were chosen to reflect common sloped roof designs. This practice is applicable to roofs of 3 in 12 or steeper slopes, to roofs designed with vent areas and vent locations conforming to national standards of practice, and to designs in which the bottom side of the sheathing is exposed to ventilation air. These conditions may not apply to significantly different designs and therefore this practice may not apply to such designs.  
1.4 Information and a brief discussion supporting the provisions of this practice are in the Commentary in the appendix. A large, more detailed, separate Commentary is also available from ASTM.2  
1.5 The methodology in this practice is not meant to account for all reported instances of fire-retardant plywood undergoing premature heat degradation.  
1.6 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Aug-2015
• ICS: 91.060.20 - Roofs
• Technical Committee: D07 - Wood
• Drafting Committee: D07.07 - Fire Performance of Wood

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D6305 − 08 (Reapproved 2015)
Standard Practice for
Calculating Bending Strength Design Adjustment Factors
for Fire-Retardant-Treated Plywood Roof Sheathing
This standard is issued under the fixed designation D6305; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made to Appendix X1 in October 2015.
1. Scope 1.6 Thevaluesstatedininch-poundunitsaretoberegarded
as standard. The values given in parentheses are mathematical
1.1 This practice covers procedures for calculating bending
conversions to SI units that are provided for information only
strength design adjustment factors for fire-retardant-treated
and are not considered standard.
plywood roof sheathing. The methods utilize the results of
1.7 This standard does not purport to address all of the
strength testing after exposure at elevated temperatures and
safety concerns, if any, associated with its use. It is the
computer-generated thermal load profiles reflective of expo-
responsibility of the user of this standard to establish appro-
sures encountered in normal service conditions in a wide
priate safety and health practices and determine the applica-
variety of continental United States climates.
bility of regulatory limitations prior to use.
1.2 Necessarily, common laboratory practices were used to
develop the methods herein. It is assumed that the procedures
2. Referenced Documents
will be used for fire-retardant-treated plywood installed using
2.1 ASTM Standards:
appropriate construction practices recommended by the fire
D9Terminology Relating to Wood and Wood-Based Prod-
retardant chemical manufacturers, which include avoiding
ucts
exposure to precipitation, direct wetting, or regular condensa-
D5516TestMethodforEvaluatingtheFlexuralPropertiesof
tion.
Fire-Retardant Treated Softwood Plywood Exposed to
1.3 Theheatgains,solarloads,roofslopes,ventilationrates,
Elevated Temperatures
and other parameters used in this practice were chosen to
reflectcommonslopedroofdesigns.Thispracticeisapplicable 3. Terminology
toroofsof3in12orsteeperslopes,toroofsdesignedwithvent
3.1 Definitions:
areas and vent locations conforming to national standards of
3.1.1 Definitionsusedinthispracticeareinaccordancewith
practice, and to designs in which the bottom side of the
Terminology D9.
sheathing is exposed to ventilation air. These conditions may
3.2 Definitions of Terms Specific to This Standard:
not apply to significantly different designs and therefore this
3.2.1 bin mean temperature—10°F (5.5°C) temperature
practice may not apply to such designs.
ranges having mean temperatures of 105 (41), 115 (46), 125
1.4 Information and a brief discussion supporting the pro-
(52),135(57),145(63),155(68),165(74),175(79),185(85),
visionsofthispracticeareintheCommentaryintheappendix.
195 (91), and >200°F (93°C).
Alarge, more detailed, separate Commentary is also available
from ASTM.
4. Summary of Practice
1.5 Themethodologyinthispracticeisnotmeanttoaccount 4.1 The test data determined by Test Method D5516 are
for all reported instances of fire-retardant plywood undergoing usedtodevelopadjustmentfactorsforfire-retardanttreatments
premature heat degradation. to apply to untreated-plywood design values. The test data are
used in conjunction with climate models and other factors and
the practice thus extends laboratory strength data measured
after accelerated aging to design value recommendations.
This practice is under the jurisdiction ofASTM Committee D07 on Wood and
is the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.
Current edition approved Sept. 1, 2015. Published October 2015. Originally
approved in 1998. Last previous edition approved in 2008 as D6305–08. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D6305-08R15E01. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Commentary on this practice is available from ASTM Headquarters. Request Standards volume information, refer to the standard’s Document Summary page on
File No. D07–1004. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6305 − 08 (2015)
5. Significance and Use 6.3.1 For untreated specimens, linear regressions of the
form:
5.1 This practice develops treatment factors that shall be
M 5 a D 1b (3)
usedbyfireretardantchemicalmanufacturerstoadjustbending ~ !
strengthdesignvaluesforuntreatedplywoodtoaccountforthe
where:
fire-retardant treatment effects. This practice uses data from
M = average maximum moment,
reference thermal-load cycles designed to simulate tempera-
D = number of days of elevated temperature exposure,
tures in sloped roofs of common design to evaluate products
a = constant, and
for 50 iterations.
b = intercept.
5.2 This practice applies to material installed using con-
shall be fitted to the maximum moment and exposure time
structionpracticesrecommendedbythefireretardantchemical
dataforeachelevatedtemperatureexposure.Averagemoments
manufacturers that include avoiding exposure to precipitation,
for untreated specimens conditioned at room temperature but
direct wetting, or regular condensation. This practice is not
not exposed to elevated temperature prior to testing shall be
meant to apply to buildings with significantly different designs
included as zero day data in the regression analysis.
than those described in 1.3.
6.3.2 The intercept of the regression obtained in 6.3.1 for
5.3 Test Method D5516 caused thermally induced strength the untreated specimens shall be designated the unexposed
losses in laboratory simulations within a reasonably short average. If a negative slope of the untreated specimen regres-
period. The environmental conditions used in the laboratory- sion is not obtained, the average of the mean maximum
activatedchemicalreactionsthatareconsideredtobesimilarto
moments at each exposure period, including zero, shall be
thoseoccurringinthefield.Thisassumptionisthefundamental consideredtheunexposedaveragemomentforuntreatedspeci-
basis of this practice.
mens.
NOTE 2—The intercept value obtained in 6.3.2 may be different from
6. Procedure to Calculate Strength Loss Rate
the unexposed, untreated value used in 6.2.1 for determining R .
o
6.1 The procedure is a multistep calculation where first an
6.4 The slope and intercept of the linear relationship be-
initialstrengthlossisdetermined,thentheratesofstrengthloss
tweentheratiosanddaysofexposureforallelevatedtempera-
at various temperatures are calculated, and finally the initial
tures shall be determined by linear regressions of the form:
loss and rates are combined into the overall treatment adjust-
R 5 k ~D!1c (4)
t,i t
ment factor.
where:
6.2 Usetheload-carryingcapacityinbending,referredtoas
R = test ratios of average maximum moments,
maximum moment (M), as the controlling property for pur- t,i
D = number of days of elevated temperature exposure,
poses of determining allowable spans.
k = slope, and
t
6.2.1 The ratio of the average maximum moment (M) for
c = intercept.
unexposed treated specimens to the average moment for
unexposed untreated specimens shall be designated the Initial Include the ratio for treated specimens conditioned at room
treatment effect, R , associated with the room temperature temperature but not exposed to elevated temperature prior to
o
conditioning exposure of T . testing as zero day data in the regression analysis.
o
6.4.1 If a negative slope is not obtained in 6.4, there was no
R 5 M /M (1)
o TRT, UNEX UNTRT,UNEX
apparentstrengthlossattheexposuretemperatureandalternate
6.2.2 If testing is done at more than one temperature, R
procedures described in 7.2 are required.
oi
shallbedeterminedateachtemperatureandusedinsubsequent
6.4.2 The slope k from 6.4 shall be adjusted to a 50%
t
rate calculations for that specific temperature. The average of
relative humidity (RH) basis by the following equation:
these values, R shall be used in initial treatment effect
o,avg
k 5 k 50/RH (5)
~ !
50,i t i
calculations (see 7.1).
where:
6.3 The average maximum moment ( M) of the treated
k = slope at 50% RH at temperature i, and
specimens conditioned at the same temperature for the same 50,i
RH = elevated temperature test RH.
i
period of time shall be computed. The ratio of these moments
to the moment of the untreated, unexposed specimens as
6.5 IfTest Method D5516 protocol testing was only done at
obtained in 6.3.1 and 6.3.2 shall be designated the test
one elevated temperature, rates at other temperatures shall be
treatment ratio, R. Include the ratio for specimens conditioned
t estimated by the use of Arrhenius equation, which states that
at room temperature but not exposed to elevated temperature
therateofachemicalreactionisapproximatelyhalvedforeach
prior to testing.
10°Cthetemperatureisreduced.(Conversely,therateapproxi-
mately doubles for each 10°C that the temperature is in-
R 5 R 5 M /M (2)
t test TRT, UNEX, EX UNTRT,UNEX
~ !
creased.)
(per 6.3.2)
6.5.1 If testing was done at only one temperature, then to
NOTE 1—When end matching of treated and untreated specimens is
allowfortheuncertaintyinonlyonemeasurementoftheratio,
employed to reduce variability in accordance with Test Method D5516,
the rate k shall be increased by 10% prior to theArrhenius
use the ratio of the matched pairs from each panel to calculate the panel 50,i
mean. The average of the panel means shall be used to calculate R. calculations. If testing was done at two temperatures, then the
t
´1
D6305 − 08 (2015)
TABLE 1 Reference Thermal Load Profiles
rate at each temperature shall be increased by 5% prior to the
Arrhenius calculations. Sheathing Mean Cumulative Average Days/Year
A A A
Bin Temperature, °F(°C) Zone 1A Zone 1B Zone 2
NOTE 3—Increasing the rate of k has the effect of increasing the
105(41) 10.960 34.281 10.970
50,i
115(46) 8.053 24.911 8.308
apparent strength loss.
125(52) 8.597 13.529 5.041
6.5.2 The Arrhenius equation is used to estimate rates at
135(57) 7.865 6.856 1.532
145(63) 6.798 0.960 0.283
other temperatures.The rate constant, k at temperature, T,is
2, 2
155(68) 5.083 . .
related by
165(74) 0.586 . .
175(79) . . .
k Ea T 2 T
~ !
50,i 1 2
In 5 (6) 185(85) 0.021 . .
k RT T
2 1 2
195(91) 0.021 . .
$200(93) 0.021 . .
where:
A
Zone Definition:
4,5
Ea = 21 810 cal/mol (91 253 J/mol) (1),
R = 1.987 cal/mol-°K = (8.314 J/mol-°K) = gas constant,
(1) Minimum roof live load or maximum ground snow load#20
and
psf (#958 Pa)
T and T are in °K. A. Southwest Arizona and Southeast Nevada
1 2
(Area bound by Las Vegas, Yuma, Phoenix,
6.6 Compute capacity loss as the negative value of the rates Tucson)
B. All other qualifying areas
(k ) for bin mean temperatures of 105 (41), 115 (46), 125 (52),
(2) Maximum ground snow load >20 psf (>958 Pa)
135 (57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85), 195
(91), and >200°F (93°C).
NOTE 4—Use the negative values of the rates (k ) for CLT since CLT is
expressed as a loss.
6.9 Annual Capacity Loss—Total annual capacity loss
6.7 IfTestMethodD5516testingwasdoneatthreeormore (CLT) due to elevated temperature exposure shall be deter-
elevated temperature exposures, capacity losses shall be estab-
mined for locations within each zone as the summation of the
lished by fitting a linear regression to the natural logarithm of product of the capacity loss per day (CL) rate from 6.6 and the
the negative of the slopes of the regressions obtained in 6.4 at
cumulative average days per year from 6.9 for each mean bin
each exposure temperature and 1/T where T is in °K. temperature.
i i
NOTE 5—This constructs an Arrhenius plot using classical chemical
7. Treatment Factor
kineticstechniques,whichisthesimplestmodelingapproach.Othermore
sophisticated modeling techniques are available but require a different
7.1 For each zone, a treatment adjustment factor (TF) shall
procedure for calculating strength loss rates.
be calculated as:
6.7.1 If Test Method D5516 testing was done at two
TF 5 1 2 IT 2 n CF CLT (7)
@ ~ !~ !#
temperatures, the two rate constants (k ) calculated from Eq 6
where:
shall be averaged for each bin mean temperature.
TF = treatment adjustment factor ≤1.00 - IT,
6.8 Reference Thermal Load Profiles:
IT = initial treatment effect = 1-R ,
6.8.1 The cumulative days per year the average sheathing
n = number of iterations = 50,
temperature falls within 10°F (5.6°C) bins having mean
CF = Cyclic factor = 0.6, and
temperatures of 105 (41), 115 (46), 125 (52), 135 (57), 145
CLT = total annual capacity loss.
(63), 155 (68), 165 (74), 175 (79), 185 (85), 195 (91), and
7.2 If testing was only done at one exposure temperature
>200°F (93°C) represent a thermal load profile. The profiles
that was 168°F (76°C) or greater and a negative slope was not
tabulated below, based on reference year weather tape infor-
obtained in 6.4, there was no apparent strength loss and hence
mation for various locations, an indexed attic temperature and
no annual capacity loss can be calculated. In this case, the
moisture model developed by the Forest Products Laboratory,
treatment adjustment factor will be the lesser of the initial
and a south-facing roof system ventilated as required by the
treatment effect (1-R ) or 0.90, which reflects the 10%
applicable code having dark-colored shingle roofing, shall be
o
allowance for uncertainty in only measuring at one tempera-
considered the standard thermal environments fire-retardant-
ture.
treated plywood roof sheathing is exposed to in different snow
load zones (4). The specific model inputs used were 0.65
TF 5lesserof ~1 2 R ! or0.90 (8)
o
shingle absorptivity and a ventilation rate of 8 air changes per
7.2.1 If the exposure temperature was less than 168°F
hour (ach). See Table 1.
(76°C) and a negative slope was not obtained in 6.4, then the
exposure testing must be repeated at a higher temperature that
either exceeds 168°F (76°C) or causes a negative slope in 6.4.
The boldface numbers in parentheses refer to a list of references at the end of
the text.
Pasek and McIntyre (1) have shown that the Arrhenius parameter, E , for
a
phosphate-based fire retardants for wood averages 21 810 cal/mol (91 253 J/mol). This factor was derived by comparing the mechanical property data obtained
Other values are appropriate for fire retardants that are not phosphate based. from plywood exposed to continuous elevated temperatures to data obtained from
A descriptio
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D6305 − 08 D6305 − 08 (Reapproved 2015)
Standard Practice for
Calculating Bending Strength Design Adjustment Factors
for Fire-Retardant-Treated Plywood Roof Sheathing
This standard is issued under the fixed designation D6305; 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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorial corrections were made to Appendix X1 in October 2015.
1. Scope
1.1 This practice covers procedures for calculating bending strength design adjustment factors for fire-retardant-treated plywood
roof sheathing. The methods utilize the results of strength testing after exposure at elevated temperatures and computer-generated
thermal load profiles reflective of exposures encountered in normal service conditions in a wide variety of continental United States
climates.
1.2 Necessarily, common laboratory practices were used to develop the methods herein. It is assumed that the procedures will
be used for fire-retardant-treated plywood installed using appropriate construction practices recommended by the fire retardant
chemical manufacturers, which include avoiding exposure to precipitation, direct wetting, or regular condensation.
1.3 The heat gains, solar loads, roof slopes, ventilation rates, and other parameters used in this practice were chosen to reflect
common sloped roof designs. This practice is applicable to roofs of 3 in 12 or steeper slopes, to roofs designed with vent areas
and vent locations conforming to national standards of practice, and to designs in which the bottom side of the sheathing is exposed
to ventilation air. These conditions may not apply to significantly different designs and therefore this practice may not apply to such
designs.
1.4 Information and a brief discussion supporting the provisions of this practice are in the Commentary in the appendix. A large,
more detailed, separate Commentary is also available from ASTM.
1.5 The methodology in this practice is not meant to account for all reported instances of fire-retardant plywood undergoing
premature heat degradation.
1.6 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D9 Terminology Relating to Wood and Wood-Based Products
D5516 Test Method for Evaluating the Flexural Properties of Fire-Retardant Treated Softwood Plywood Exposed to Elevated
Temperatures
3. Terminology
3.1 Definitions:
3.1.1 Definitions used in this practice are in accordance with Terminology D9.
3.2 Definitions of Terms Specific to This Standard:
This practice is under the jurisdiction of ASTM Committee D07 on Wood and is the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.
Current edition approved Aug. 1, 2008Sept. 1, 2015. Published September 2008October 2015. Originally approved in 1998. Last previous edition approved in 20022008
ε1
as D6305 – 02D6305 – 08. . DOI: 10.1520/D6305-08.10.1520/D6305-08R15E01.
Commentary on this practice is available from ASTM Headquarters. Request File No. D07–1004.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6305 − 08 (2015)
3.2.1 bin mean temperature—10°F (5.5°C) temperature ranges having mean temperatures of 105 (41), 115 (46), 125 (52), 135
(57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85), 195 (91), and >200°F (93°C).
4. Summary of Practice
4.1 The test data determined by Test Method D5516 are used to develop adjustment factors for fire-retardant treatments to apply
to untreated-plywood design values. The test data are used in conjunction with climate models and other factors and the practice
thus extends laboratory strength data measured after accelerated aging to design value recommendations.
5. Significance and Use
5.1 This practice develops treatment factors that shall be used by fire retardant chemical manufacturers to adjust bending
strength design values for untreated plywood to account for the fire-retardant treatment effects. This practice uses data from
reference thermal-load cycles designed to simulate temperatures in sloped roofs of common design to evaluate products for 50
iterations.
5.2 This practice applies to material installed using construction practices recommended by the fire retardant chemical
manufacturers that include avoiding exposure to precipitation, direct wetting, or regular condensation. This practice is not meant
to apply to buildings with significantly different designs than those described in 1.3.
5.3 Test Method D5516 caused thermally induced strength losses in laboratory simulations within a reasonably short period. The
environmental conditions used in the laboratory-activated chemical reactions that are considered to be similar to those occurring
in the field. This assumption is the fundamental basis of this practice.
6. Procedure to Calculate Strength Loss Rate
6.1 The procedure is a multistep calculation where first an initial strength loss is determined, then the rates of strength loss at
various temperatures are calculated, and finally the initial loss and rates are combined into the overall treatment adjustment factor.
6.2 Use the load-carrying capacity in bending, referred to as maximum moment (M), as the controlling property for purposes
of determining allowable spans.
6.2.1 The ratio of the average maximum moment (M) for unexposed treated specimens to the average moment for unexposed
untreated specimens shall be designated the Initial treatment effect, R , associated with the room temperature conditioning
o
exposure of T .
o
R 5 M /M (1)
o TRT, UNEX UNTRT,UNEX
6.2.2 If testing is done at more than one temperature, R shall be determined at each temperature and used in subsequent rate
oi
calculations for that specific temperature. The average of these values, R shall be used in initial treatment effect calculations
o,avg
(see 7.1).
6.3 The average maximum moment ( M) of the treated specimens conditioned at the same temperature for the same period of
time shall be computed. The ratio of these moments to the moment of the untreated, unexposed specimens as obtained in 6.3.1 and
6.3.2 shall be designated the test treatment ratio, R . Include the ratio for specimens conditioned at room temperature but not
t
exposed to elevated temperature prior to testing.
R 5 R 5 M /M (2)
t test TRT, UNEX, EX UNTRT,UNEX
~ !
(per 6.3.2)
NOTE 1—When end matching of treated and untreated specimens is employed to reduce variability in accordance with Test Method D5516, use the
ratio of the matched pairs from each panel to calculate the panel mean. The average of the panel means shall be used to calculate R .
t
6.3.1 For untreated specimens, linear regressions of the form:
M 5 a~D!1b (3)
where:
M = average maximum moment,
D = number of days of elevated temperature exposure,
a = constant, and
b = intercept.
shall be fitted to the maximum moment and exposure time data for each elevated temperature exposure. Average moments for
untreated specimens conditioned at room temperature but not exposed to elevated temperature prior to testing shall be included
as zero day data in the regression analysis.
6.3.2 The intercept of the regression obtained in 6.3.1 for the untreated specimens shall be designated the unexposed average.
If a negative slope of the untreated specimen regression is not obtained, the average of the mean maximum moments at each
exposure period, including zero, shall be considered the unexposed average moment for untreated specimens.
NOTE 2—The intercept value obtained in 6.3.2 may be different from the unexposed, untreated value used in 6.2.1 for determining R .
o
´1
D6305 − 08 (2015)
6.4 The slope and intercept of the linear relationship between the ratios and days of exposure for all elevated temperatures shall
be determined by linear regressions of the form:
R 5 k D 1c (4)
~ !
t,i t
where:
R = test ratios of average maximum moments,
t,i
D = number of days of elevated temperature exposure,
k = slope, and
t
c = intercept.
Include the ratio for treated specimens conditioned at room temperature but not exposed to elevated temperature prior to testing
as zero day data in the regression analysis.
6.4.1 If a negative slope is not obtained in 6.4, there was no apparent strength loss at the exposure temperature and alternate
procedures described in 7.2 are required.
6.4.2 The slope k from 6.4 shall be adjusted to a 50 % relative humidity (RH) basis by the following equation:
t
k 5 k ~50/RH ! (5)
50,i t i
where:
k = slope at 50 % RH at temperature i, and
50,i
RH = elevated temperature test RH.
i
6.5 If Test Method D5516 protocol testing was only done at one elevated temperature, rates at other temperatures shall be
estimated by the use of Arrhenius equation, which states that the rate of a chemical reaction is approximately halved for each 10°C
the temperature is reduced. (Conversely, the rate approximately doubles for each 10°C that the temperature is increased.)
6.5.1 If testing was done at only one temperature, then to allow for the uncertainty in only one measurement of the ratio, the
rate k shall be increased by 10 % prior to the Arrhenius calculations. If testing was done at two temperatures, then the rate at
50,i
each temperature shall be increased by 5 % prior to the Arrhenius calculations.
NOTE 3—Increasing the rate of k has the effect of increasing the apparent strength loss.
50,i
6.5.2 The Arrhenius equation is used to estimate rates at other temperatures. The rate constant, k at temperature, T , is related
2, 2
by
k Ea ~T 2 T !
50,i 1 2
In 5 (6)
k R T T
2 1 2
where:
4,5
Ea = 21 810 cal/mol (91 253 J/mol) (1),
R = 1.987 cal/mol-°K = (8.314 J/mol-°K) = gas constant, and
T and T are in °K.
1 2
6.6 Compute capacity loss as the negative value of the rates (k ) for bin mean temperatures of 105 (41), 115 (46), 125 (52), 135
(57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85), 195 (91), and >200°F (93°C).
NOTE 4—Use the negative values of the rates (k ) for CLT since CLT is expressed as a loss.
6.7 If Test Method D5516 testing was done at three or more elevated temperature exposures, capacity losses shall be established
by fitting a linear regression to the natural logarithm of the negative of the slopes of the regressions obtained in 6.4 at each exposure
temperature and 1/T where T is in °K.
i i
NOTE 5—This constructs an Arrhenius plot using classical chemical kinetics techniques, which is the simplest modeling approach. Other more
sophisticated modeling techniques are available but require a different procedure for calculating strength loss rates.
6.7.1 If Test Method D5516 testing was done at two temperatures, the two rate constants (k ) calculated from Eq 6 shall be
averaged for each bin mean temperature.
6.8 Reference Thermal Load Profiles:
6.8.1 The cumulative days per year the average sheathing temperature falls within 10°F (5.6°C) bins having mean temperatures
of 105 (41), 115 (46), 125 (52), 135 (57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85), 195 (91), and >200°F (93°C) represent
a thermal load profile. The profiles tabulated below, based on reference year weather tape information for various locations, an
indexed attic temperature and moisture model developed by the Forest Products Laboratory, and a south-facing roof system
ventilated as required by the applicable code having dark-colored shingle roofing, shall be considered the standard thermal
The boldface numbers in parentheses refer to a list of references at the end of the text.
Pasek and McIntyre (1) have shown that the Arrhenius parameter, E , for phosphate-based fire retardants for wood averages 21 810 cal/mol (91 253 J/mol). Other values
a
are appropriate for fire retardants that are not phosphate based.
A description of other models is available in Refs (2) and (3).
´1
D6305 − 08 (2015)
TABLE 1 Reference Thermal Load Profiles
Sheathing Mean Cumulative Average Days/Year
A A A
Bin Temperature, °F(°C) Zone 1A Zone 1B Zone 2
105(41) 10.960 34.281 10.970
115(46) 8.053 24.911 8.308
125(52) 8.597 13.529 5.041
135(57) 7.865 6.856 1.532
145(63) 6.798 0.960 0.283
155(68) 5.083 . .
165(74) 0.586 . .
175(79) . . .
185(85) 0.021 . .
195(91) 0.021 . .
$200(93) 0.021 . .
A
Zone Definition:
(1) Minimum roof live load or maximum ground snow load #20
psf (#958 Pa)
A. Southwest Arizona and Southeast Nevada
(Area bound by Las Vegas, Yuma, Phoenix,
Tucson)
B. All other qualifying areas
(2) Maximum ground snow load >20 psf (>958 Pa)
environments fire-retardant-treated plywood roof sheathing is exposed to in different snow load zones (4). The specific model
inputs used were 0.65 shingle absorptivity and a ventilation rate of 8 air changes per hour (ach). See Table 1.
6.9 Annual Capacity Loss—Total annual capacity loss (CLT) due to elevated temperature exposure shall be determined for
locations within each zone as the summation of the product of the capacity loss per day (CL) rate from 6.6 and the cumulative
average days per year from 6.9 for each mean bin temperature.
7. Treatment Factor
7.1 For each zone, a treatment adjustment factor (TF) shall be calculated as:
TF 5 12 IT 2 n CF CLT (7)
@ ~ !~ !#
where:
TF = treatment adjustment factor ≤1.00 - IT,
IT = initial treatment effect = 1-R ,
n = number of iterations = 50,
CF = Cyclic factor = 0.6, and
CLT = total annual capacity loss.
7.2 If testing was only done at one exposure temperature that was 168°F (76°C) or greater and a negative slope was not obtained
in 6.4, there was no apparent s
...