Keywords: indoor air quality, indoor sources, indoor materials, indoor products, small chamber testing, environmental test chambers, organic emissions, emission factor, emission rate, mass transfer,, ICS Number Code 13.040.01 (Air quality in general)
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Significance and Use
4.1Objectives—The use of small chambers to
evaluate VOC emissions from indoor materials has several
objectives:
4.1.1 Develop techniques for screening of
products for VOC emissions;
4.1.2 Determine the effect of
environmental variables (that is, temperature, humidity, air speed,
and air change rate) on emission rates;
4.1.3 Rank various products and product
types with respect to their emissions profiles (for example,
emission factors, specific organic compounds emitted);
4.1.4 Provide compound-specific data on
various organic sources to guide field studies and assist in
evaluating indoor air quality in buildings;
4.1.5 Provide emissions data for the
development and verification of models used to predict indoor
concentrations of organic compounds; and
4.1.6 Develop data useful to stakeholders
and other interested parties for assessing product emissions and
developing control options or improved products.
4.2Mass
Transfer Considerations—Small chamber evaluation of
emissions from indoor materials requires consideration of the
relevant mass transfer processes. Three fundamental processes
control the rate of emissions of organic vapors from indoor
materials; evaporative mass transfer from the surface of the
material to the overlying air, desorption of adsorbed compounds,
and diffusion within the material.
4.2.1 The evaporative mass transfer of a
given VOC from the surface of the material to the overlying air can
be expressed as:
Thus, the emission rate is proportional
to the difference in vapor pressure between the surface and the
overlying air. Since the vapor pressure is directly related to the
concentration, the emission rate is proportional to the difference
in concentration between the surface and the overlying air. The
mass transfer coefficient is a function of the diffusion
coefficient (in air) for the specific compound of interest and the
level of turbulence in the bulk flow.
4.2.2 The desorption rate of compounds
adsorbed on materials can be determined by the retention time (or
average residence time) of an adsorbed molecule:
The larger the retention time, the slower
the rate of desorption.
4.2.3 The diffusion mass transfer within
the material is a function of the diffusion coefficient (or
diffusivity) of the specific compound. The diffusion coefficient of
a given compound within a given material is a function of the
compound's physical and chemical properties (for example, molecular
weight, size, and polarity), temperature, and the structure of the
material within which the diffusion is occurring. The diffusivity
of an individual compound in a mixture is also affected by the
composition of the mixture.
4.2.4Variables Affecting Mass Transfer—While a
detailed discussion of mass transfer theory is beyond the scope of
this guide, it is necessary to examine the critical variables
affecting mass transfer within the context of small chamber
testing:
4.2.4.1 Temperature affects the vapor
pressure, desorption rate, and the diffusion coefficients of the
organic compounds. Thus, temperature impacts both the mass transfer
from the surface (whether by evaporation or desorption) and the
diffusion mass transfer within the material. Increases in
temperature cause increases in the emissions due to all three mass
transfer processes.
4.2.4.2 The air change rate indicates the
amount of dilution and flushing that occurs in indoor environments.
The higher the air change rate the greater the dilution, and
assuming the outdoor air is cleaner, the lower the indoor
concentration. If the concentration at the surface is unchanged, a
lower concentration in the air increases the evaporative mass
transfer by increasing the difference in concentration between the
surface and the overlying air.
4.2.4.3Air Speed—Surface air speed is a critical
parameter for evaporative-controlled sources as the mass transfer
coefficient (4.3Other
Factors Affecting Emissions—Most organic compounds emitted
from indoor materials and products are non-reactive, and chambers
are designed to reduce or eliminate reactions and adsorption on the
chamber surfaces (see 5.3.1).
In some cases, however, surface adsorption can occur. Some
relatively high molecular weight, high boiling compounds can react
(that is, with ozone) after being deposited on the surface. In such
cases, the simultaneous degradation and buildup on and the ultimate
re-emission from the chamber walls can affect the final chamber
concentration and the time history of the emission profile. Unless
such factors are properly accounted for, incorrect values for the
emission rates will be calculated (see 9.4). The magnitude of chamber adsorption
and reaction effects can be evaluated by way of mass balance
calculations (see 9.5).
4.4Use of
the Results—It is emphasized that small chamber evaluations
are used to determine source emission rates. These rates are then
used in IAQ models to predict indoor concentration of the compounds
emitted from the tested material. Consultation with IAQ modelers
may be required to ensure that the small chamber test regime is
consistent with the IAQ model assumptions. The concentrations
observed in the chambers themselves should not be used as a
substitute for concentrations expected in full-scale indoor
environments.
1. Scope
1.1 This guide provides direction on the
measurement of the emissions of volatile organic compounds (VOCs)
from indoor materials and products using small-scale environmental
test chambers.
1.2 This guide pertains to chambers that
fully enclose a material specimen to be tested and does not address
other emission chamber designs such as emission cells (see instead
Practice D7143).
1.3 As an ASTM standard, this guide
describes options, but does not recommend specific courses of
action. This guide is not a standard test method and must not be
construed as such.
1.4 The use of small environmental test
chambers to characterize the emissions of VOCs from indoor
materials and products is still evolving. Modifications and
variations in equipment, testing procedures, and data analysis are
made as the work in the area progresses. For several indoor
materials, more detailed ASTM standards for emissions testing have
now been developed. Where more detailed ASTM standard practices or
methods exist, they supersede this guide and should be used in its
place. Until the interested parties agree upon standard testing
protocols, differences in approach will occur. This guide will
continue to provide assistance by describing equipment and
techniques suitable for determining organic emissions from indoor
materials. Specific examples are provided to illustrate existing
approaches; these examples are not intended to inhibit alternative
approaches or techniques that will produce equivalent or superior
results.
1.5 Small chambers have obvious
limitations. Normally, only samples of larger materials (for
example, carpet) are tested. Small chambers are not applicable for
testing complete assemblages (for example, furniture). Small
chambers are also inappropriate for testing combustion devices (for
example, kerosene heaters) or activities (for example, use of
aerosol spray products). For some products, small chamber testing
may provide only a portion of the emission profile of interest. For
example, the rate of emissions from the application of high solvent
materials (for example, paints and waxes) by means of brushing,
spraying, rolling, etc. are generally higher than the rate during
the drying process. Small chamber testing cannot be used to
evaluate the application phase of the coating process. Large (or
full-scale) chambers may be more appropriate for many of these
applications. For guidance on full-scale chamber testing of
emissions from indoor materials refer to Practice D6670.
1.6 This guide does not provide specific
directions for the selection of sampling media or for the analysis
of VOCs. This information is provided in Practice D6196.
1.7 This guide does not provide specific
directions for determining emissions of formaldehyde from composite
wood products, since chamber testing methods for such emissions are
well developed and widely used. For more information refer to Test
Methods E1333 and
D6007. It is possible,
however, that the guide can be used to support alternative testing
methods.
1.8 This guide is not applicable to the
determination of emissions of semi-volatile organic compounds
(SVOCs) from materials/products largely due to adsorption of these
compounds on materials commonly used for construction of chambers
suitable for VOC emissions testing. Alternate procedures are
required for SVOCs. For example, it may be possible to screen
materials for emissions of SVOCs using micro-scale chambers
operated at temperatures above normal indoor conditions (see
Practice D7706).
1.9 This guide is applicable to the
determination of emissions from products and materials that may be
used indoors. The effects of the emissions (for example, toxicity)
are not addressed and are beyond the scope of the guide. Guide
D6485 provides an example of
the assessment of acute and irritant effects of VOC emissions for a
given material. Specification of “target” organic species of
concern is similarly beyond the scope of this guide. As guideline
levels for specific indoor contaminants develop, so too will
emission test protocols to provide relevant information. Emissions
databases and material labeling schemes will also be expected to
adjust to reflect the current state of knowledge.
1.10 Specifics related to the
acquisition, handling, conditioning, preparation, and testing of
individual test specimens may vary depending on particular study
objectives. Guidelines for these aspects of emissions testing are
provided here, specific direction is not mandated. The purpose of
this guide is to increase the awareness of the user to available
techniques for evaluating organic emissions from indoor
materials/products by means of small chamber testing, to identify
the essential aspects of emissions testing that must be controlled
and documented, and therefore to provide information, which may
lead to further evaluation and standardization.
1.11 Within the context of the
limitations discussed in this section, the purpose of this guide is
to describe the methods and procedures for determining organic
emission rates from indoor materials/products using small
environmental test chambers. The techniques described are useful
for both routine product testing by manufacturers and testing
laboratories and for more rigorous evaluation by indoor air quality
(IAQ) researchers. Appendix
X1 provides references to standards that are widely employed
to measure emissions of VOCs from materials and products used in
the interiors of buildings. Some of these standards directly
reference this guide.
1.12 The values stated in SI units are to
be regarded as standard. No other units of measurement are included
in this standard.
1.13This 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, health, and environmental practices
and determine the applicability of regulatory limitations prior to
use.
1.14This international standard was
developed in accordance with internationally recognized principles
on standardization established in the Decision on Principles for
the Development of International Standards, Guides and
Recommendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
Standard Practice for Testing and
Sampling of Volatile Organic Compounds (Including Carbonyl
Compounds) Emitted from Architectural Coatings Using Small-Scale
Environmental Chambers
Standard Practice for Determination of
Volatile Organic Compounds (Excluding Formaldehyde) Emissions from
Wood-Based Panels Using Small Environmental Chambers Under Defined
Test Conditions
Standard Practice for Choosing Sorbents,
Sampling Parameters and Thermal Desorption Analytical Conditions
for Monitoring Volatile Organic Chemicals in Air
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