ASTM F1868-98
(Test Method)Standard Test Method for Thermal and Evaporative Resistance of Clothing Materials Using a Sweating Hot Plate
Standard Test Method for Thermal and Evaporative Resistance of Clothing Materials Using a Sweating Hot Plate
SCOPE
1.1 This test method covers the measurement of the thermal resistance and the evaporative resistance under steady-state conditions, of fabrics, films, coatings, foams, and leathers, including multi-layer assemblies, for use in clothing systems.
1.2 The range of this measurement technique for thermal resistance is from 0.002 to 0.2 K-m2/W and for evaporative resistance is from 0.01 to 1.0 kPa-m2/W.
1.3 The values in SI units shall be regarded as standard.
1.4 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.
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Designation: F 1868 – 98
Standard Test Method for
Thermal and Evaporative Resistance of Clothing Materials
Using a Sweating Hot Plate
This standard is issued under the fixed designation F 1868; 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.
INTRODUCTION
Clothing is often made of materials that impede the flow of heat and moisture from the skin to the
environment. Consequently, people may suffer from heat stress or cold stress when wearing clothing
in different environmental conditions. Therefore, it is important to quantify the thermal resistance and
evaporative resistance of clothing materials and to consider these properties when selecting materials
for different clothing applications.
1. Scope F 1291 Test Method for Measuring the Thermal Insulation
of Clothing Using a Heated Manikin
1.1 This test method covers the measurement of the thermal
F 1494 Terminology Relating to Protective Clothing
resistance and the evaporative resistance, under steady-state
2.2 Other Standards:
conditions, of fabrics, films, coatings, foams, and leathers,
ISO 11092 Textiles–Physiological Effects–Measurement of
including multi-layer assemblies, for use in clothing systems.
Thermal and Water-Vapour Resistance Under Steady-
1.2 The range of this measurement technique for thermal
State Conditions (Sweating Guarded-Hotplate Test)
resistance is from 0.002 to 0.2 K·m /W and for evaporative
NFPA 1971 Protective Clothing for Structural Fire Fight-
resistance is from 0.01 to 1.0 kPa·m /W.
ing
1.3 The values in SI units shall be regarded as standard.
NFPA 1977 Protective Clothing and Equipment for Wild-
1.4 This standard does not purport to address all of the
land Fire Fighting
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to consult and
3. Terminology
establish appropriate safety and health practices and deter-
3.1 Definitions:
mine the applicability of regulatory limitations prior to use.
3.1.1 clo, n-, n—unit of thermal resistance defined as the
2. Referenced Documents insulation required to keep a resting man (producing heat at the
rate of 58 W/m ) comfortable in an environment at 21°C, air
2.1 ASTM Standards:
movement 0.1 m/s, or roughly the insulation value of typical
C 177 Test Method for Steady-State Heat Flux Measure-
indoor clothing.
ments and Thermal Transmission Properties by Means of
3.1.1.1 Discussion—Numerically the clo is equal to 0.155
the Guarded-Hot-Plate Apparatus
K·m /W.
D 1518 Thermal Transmittance of Textile Materials
3.1.2 evaporative heat transmittance, n—time rate of undi-
E 177 Practice for Use of the Terms Precision and Bias in
rectional evaporative heat transfer per unit area, in the steady
ASTM Test Methods
state, between parallel planes, per unit difference of water
E 641 Practice for Conducting an Interlaboratory Study to
vapor pressure of the planes.
Determine the Precision of a Test Method
3.1.2.1 Discussion—Evaporative heat transmittance is ex-
pressed as watts per square metre of test specimen per
This test method is under the jurisdiction of ASTM Committee F-23 on
Protective Clothing and is the direct responsibility of Subcommittee F23.60 on
Human Factors. Annual Book of ASTM Standards, Vol 11.03.
Current edition approved June 10, 1998. Published August 1998. Available from American National Standards Institute, 11 West 42nd St, New
Annual Book of ASTM Standards, Vol 04.06. York, NY 10036.
3 7
Annual Book of ASTM Standards, Vol 07.01. Available from National Fire Protection Assoc., 1 Batterymarch Park, Quincy,
Annual Book of ASTM Standards, Vol 14.02. MA 02269.
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.
F1868–98
kilopascal of vapor pressure difference between the test plate that the boundary layers of the bare plate and the boundary
and the environment (W/m ·kPa). The evaporative heat trans- layers of the fabric test specimen are equal.
mittance may consist of both diffusive and convective compo- R = total thermal resistance of the test specimen and the air
ct
nents. layer.
3.1.7 total clo, n—clo plus the thermal resistance from the
3.1.3 evaporative resistance, n—reciprocal of evaporative
air boundary layer, (clo ).
heat transmittance expressed in kilopascals, square metre of
t
3.1.8 total heat loss, n—the amount of heat transferred
test specimen per watt.
through a material or a composite by the combined dry and
3.1.3.1 Discussion—The evaporative resistance for several
evaporative heat exchanges under specified conditions ex-
different cases is determined in this method:
A
pressed in watts per square meter,
R = apparent total evaporative resistance of the fabric test
ef
3.1.8.1 Discussion—This single criterion for comparing
specimen only, when evaluated non-isothermally. The term
fabric assemblies was developed as a special case by the
apparent is used as a modifier for total evaporative resistance
National Fire Protection Assoc. The specific conditions used by
to reflect the fact that condensation may occur within the
NFPA are a 35°C fully sweating hot plate surface in a 25°C
specimen.
A
65 % RH environment.
R = apparent total evaporative resistance of the fabric test
et
3.2 For definitions of other terms related to protective
specimen, liquid barrier, and surface air layer when evaluated
clothing used in this test method, refer to Terminology F 1494.
non-isothermally. The term apparent is used as a modifier for
total evaporative resistance to reflect the fact that condensation
4. Significance and Use
may occur within the specimen.
4.1 The thermal resistance and evaporative resistance pro-
R = evaporative resistance of the air layer on the surface of
ebp
vided by a fabric, batting, or other type of material is of
the liquid barrier without a fabric test specimen (that is, bare
considerable importance in determining its suitability for use in
plate). This property reflects the instrument constant and the
fabricating protective clothing systems.
resistance of the liquid barrier, and in conjunction with R ,is
et
4.2 The thermal interchange between people and their
used in the calculation of R .
ef
environment is, however, an extremely complicated subject
R = intrinsic evaporative resistance of the fabric test specimen
ef
that involves many factors in addition to the steady-state
only. In the calculation of this value, the assumption is made
resistance values of fabrics and battings. Therefore, thermal
that the boundary layers of the bare plate and the boundary
resistance values and evaporative resistance values measured
layers of the fabric are equal.
on a hot plate may or may not indicate relative merit of a
R = total evaporative resistance of the fabric test specimen,
et
particular material or assembly for a given clothing applica-
the liquid barrier, and the surface air layer.
tion. While a possible indicator of clothing performance,
3.1.4 permeability index (i ),n-, n—the efficiency of evapo-
m
measurements produced by the testing of fabrics has no proven
rative heat transport in a clothing system.
correlation to the performance of clothing systems worn by
3.1.4.1 Discussion—An i of zero indicates that the cloth-
m
people. Clothing weight, drape, tightness of fit, and so forth,
ing system allows no evaporative heat transfer. An i of one
m
can minimize or even neutralize the apparent differences
indicates that the clothing system achieves the theoretical
between fabrics or fabric assemblies measured by this test
maximum evaporative heat transfer allowed by its insulation.
method.
3.1.5 thermal transmittance, n—time rate of unidirectional
4.3 The thermal resistance of clothing systems can be
heat transfer per unit area, in the steady state, between parallel
measured with a heated manikin in an environmental chamber
planes, per unit difference of temperature of the planes.
according to Test Method F 1291.
Thermal transmittance is also known as thermal conductance
4.4 Departures from the instructions of Test Method F 1868
and the heat transfer coefficient.
may lead to significantly different test results. Technical
3.1.5.1 Discussion—Thermal transmittance is expressed as
knowledge concerning the theory of heat flow, temperature
watts per square metre of test specimen per kelvin difference
measurement, and testing practices is needed to evaluate which
between the test plate and the environment (W/m ·K). The dry
departures from the instructions are significant. Standardiza-
heat flux may consist of one or more conductive, convective,
tion of the method reduces, but does not eliminate the need for
and radiant components.
such technical knowledge. Report any departures from the
3.1.6 thermal resistance, n—reciprocal of thermal transmit-
instructions of Test Method F 1868 with the results.
tance, expressed in kelvin, square metre of test specimen per
5. Apparatus
watt.
3.1.6.1 Discussion—Thermal resistance for several different
5.1 Hot Plate—The guarded flat plate shall be composed of
cases is determined in this method: a test plate, guard section, and bottom plate, each electrically
R = thermal resistance of the air layer on the surface of the maintained at a constant temperature in the range of human
cbp
plate without a fabric test specimen (that is, bare plate). This skin temperature (33 to 36°C). The guard section shall be
property reflects the instrument constant and is used to stan- designed to prevent lateral loss of heat from the test plate. The
dardize the plate, and in conjunction with R , is used in the guard section shall be wide enough to minimize heat loss and
ct
calculation of R . moisture transport through the edges of the test specimen under
cf
R = intrinsic thermal resistance of the fabric test specimen the conditions of the test. The bottom plate shall prevent
cf
only. In the calculation of this value, the assumption is made downward loss of heat from the test plate and guard section. A
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.
F1868–98
system for feeding water to the surface of the test plate and at points at the centers of the guard section on both sides of the
guard section is also needed. See Test Methods D 1518, C 177, plate. Spatial variations in air velocity shall not exceed 610 %
of the mean value.
and ISO 11092 for information on hot plates.
5.6.4 Temporal Variations—Temporal variations shall not
5.2 Temperature Control—Separate independent tempera-
exceed the following air temperature 6 0.1°C, relative humid-
ture control is required for the three sections of the hot plate
ity 6 4 %, and air velocity 6 10 % of the mean value for data
(test plate, guard section, and bottom plate). Temperature
averaged over 5 min.
control may be achieved by independent adjustments to the
voltage or current, or both, supplied to the heaters using solid
6. Materials
state power supplies, solid-state relays (proportional time on),
6.1 Water—For the evaporative resistance measurements in
adjustable transformers, variable impedances, or intermittent
Parts B, C, and E, distilled water shall be used to wet the test
heating cycles. The three sections of the plate shall be
plate surface.
controlled to the same temperature to within 6 0.1°C.
6.2 Liquid Barrier—For the evaporative resistance mea-
5.3 Power Measuring Instruments—Power to the hot plate
surements in Parts B, C, and E, a liquid barrier shall be used to
test section shall be measured to provide an accurate average
cover the test plate so that water does not contact the test
over the period of the test. If time proportioning or phase
specimen. The permeability index of the liquid barrier shall be
proportioning is used for the power control, then devices that
greater than 0.7, where i = .061 (R /R ). Examples include
m cbp ebp
are capable of averaging over the control cycle are required.
untreated cellophane film, microporous polytetraflouroethylene
Integrating devices (watt-hour transducers) are preferred over
film, and so forth.
instantaneous devices (watt meters). Overall accuracy of the
6.3 Calibration Fabrics —A calibration fabric is required
power monitoring equipment must be within 6 2 % of the
for the calibration in Part C. Sources for the calibration fabric
reading for the average power for the test period.
are given in Footnote 8.
5.4 Temperature Sensors—Temperature sensors may be
7. Sampling and Preparation of Test Specimens
thermistors, thermocouples, resistance temperature devices
(RTDs), or equivalent sensors. The test plate, guard section, 7.1 Sampling—Test three specimens from each laboratory
and bottom plate shall each contain one or more temperature
sampling unit.
sensors that are mounted flush with the hot plate surface and in 7.2 Specimen Preparation—Use test specimens large
such a manner that they measure the surface temperature enough to cover the surface of the hot plate test section and the
guard section completely. Remove any undesirable wrinkles
within 6 0.1°C.
from the test specimens. Possible techniques for removing
5.5 Controlled Atmosphere Chamber—The hot plate shall
wrinkles include smoothing, free-hanging, pressing, steaming,
be housed in an environmental chamber that can be maintained
ironing, and so forth.
at selected temperatures between 20 and 35°C. The walls of the
7.3 Conditioning—Allow the test specimens to come into
test chamber shall not be highly reflective, and the wall
equilibrium with the atmosphere of the testing chamber by
temperature shall be 6 0.5°C of the air in the chamber. The
conditioning them in the chamber for a least 4 h.
relative humidity shall be maintained at selected levels be-
tween 40 and 65 %.
8. Part A - Thermal Resistance
5.6 Measuring Environmental Parameters—The air tem-
8.1 Test Conditions:
perature, relative humidity, and air velocity shall be measured
8.1.1 Temperature of the Test Plate, Guard Section, and
as follows:
Bottom Plate—Maintain the temperature of these sections at 35
5.6.1 Relative Humidity Measuring Equipment—Either a
6 0.5°C and without fluctuating more than6 0.1°C during a
wet-and-dry bulb psychrometer or a dew point hygrometer
test.
shall be used to measure the relative humidity and calculate the
...
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