Significance and Use
4.1 Emissions of VOCs are typically controlled by internal mass-transfer limitations (for example, diffusion through the material), while emissions of SVOCs are typically controlled by external mass-transfer limitations (migration through the air immediately above the material). The emission of some chemicals may be controlled by both internal and external mass-transfer limitations. In addition, due to their lower vapor pressure, SVOCs generally adsorb to different media (chamber walls, building materials, particles, and other surfaces) at greater rates than VOCs. This sorption can increase the amount of time required to reach steady-state SVOC concentrations using conventional VOC emission test methods to months for a single test (2).
4.2 Thus, existing methods for characterizing emissions of VOCs may not be appropriate or practical to properly characterize emission rates of SVOCs for use in modeling SVOC concentrations in indoor environments. A mass-transfer framework is needed to accurately assess emission rates of SVOCs when predicting the SVOC indoor air concentrations in indoor environments. The SVOC mass-transfer framework includes SVOC emission characteristics and its partition to multimedia including sorption to indoor surfaces, airborne particles, and settled dust. Once the SVOC emission parameters and partitioning coefficients have been determined, these values can be used to modeling SVOC indoor concentrations.
Scope
1.1 This guide is intended to serve as a foundation for understanding when to use emission testing methods designed for volatile organic compounds (VOCs) to determine area-specific emission rates that are typically used in modeling indoor air VOC concentrations and when to use emission testing methods designed for semi-volatile organic compounds (SVOCs) to determine mass transfer emission parameters that are typically used to model indoor air, dust, and surface SVOC concentrations.
1.2 This guide discusses how organic chemicals are conventionally categorized with respect to volatility.
1.3 This guide presents a simplified mass-transfer model describing organic chemical emissions from a material to bulk air. The values of the model parameters are shown to be specific to material/chemical/chamber combinations.
1.4 This guide shows how to use a mass-transfer model to estimate whether diffusion of the chemical within the material or convective mass transfer of the chemical from the surface of the material to the overlying air limits chemical emissions from the material surface.
1.5 This guide describes the range of different chambers that are available for emission testing. The chambers are classified as either dynamic or static and either conventional or sandwich. The chambers are categorized as being optimal to determine either the area-specific emission rate or mass-transfer emission parameters.
1.6 This guide discusses the roles sorption and convective mass-transfer coefficients play in selecting the appropriate emission chamber and analysis method to accurately and efficiently characterize emissions from indoor materials for use in modeling indoor chemical concentrations.
1.7 This guide recommends when to choose an emission test method that is optimized to determine either the area-specific emission rate or mass-transfer emission parameters. For chemicals where the controlling mass-transfer process is unknown, the guide outlines a procedure to determine if the chemical emission is controlled by convective mass transfer of the chemical from the material.
1.8 This guide does not provide specific guidance for measuring emission parameters or conducting indoor exposure modeling.
1.9 Mechanisms controlling emissions from wet and dry materials and products are different. This guide considers the emission of chemicals from dry materials and products. Examples of functional uses of VOCs and SVOCs that this guide applies to include blowing agents, flame retardants, adhesives, plasticizers, solvents, antioxidants, preservatives, and coalescing agents (1).2 Emission estimations for other VOC and SVOC classes including those generated by incomplete combustion, spray application, or application as a powder (pesticides, termiticides, herbicides, stain repellents, sealants, water repellants) (1) may require different approaches than outlined in this guide because these processes can increase short-term concentrations of chemicals in the air independent of the volatility of the chemical and its categorization as a VVOC (very volatile organic compounds), VOC, SVOC, or NVOC (non-volatile organic compounds).
1.10 The effects of the emissions (for example, exposure, and health effects on occupants) are not addressed and are beyond the scope of this guide.
1.11 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.12 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.13 This 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.
