Development of CPSC nano-particle modeling tools

Abstract

Engineered nanoparticles (ENP) are being used in many applications including consumer products. There are many different means by which ENPs may be incorporated into these products (freely-dispersed, embedded, reactive or passive) which can impact the potential for consumer exposure to ENPs. This study was motivated by the desire to better understand inhalation exposure to ENPs, and this report addresses airborne ENPs that could affect indoor air quality (IAQ). Occupant exposure to airborne nanoparticles can be characterized by indoor airflow and contaminant transport analysis models. The U.S. Consumer Product Safety Commission (CPSC) is working with the National Institute of Standards and Technology (NIST) to develop modeling tools to enable evaluation of consumer exposure to airborne ENPs in the built environment.NIST has developed two tools, the first is an online tool that provides estimates of indoor exposure to airborne particles. This first tool, referred to as the single-size particle tool, is based on the NIST multizone modeling software, CONTAM, and demonstrates some of the capabilities that an aerosol exposure assessment tool should entail. The second tool, referred to as the sizeresolved tool, includes additional physical models that account for the properties of nanoparticles that may impact their transport within the built environment including some beyond those that CONTAM is currently capable of modeling, e.g., coagulation. This report describes the development and application of these two analysis tools that could provide the basis of modeling consumer exposure to ENPs for future development.

A tool to model the Fate and Transport of Indoor Microbiological Aerosols (FaTIMA)

“…This web-based tool runs as a client-side application within a web browser. The development process, theory, assumptions, and verification and validation test cases were presented in the documentation of a previously developed web-based tool [9]. The current document serves mainly as a user guide for FaTIMA with a section that provides modeling considerations to help inform the user when working with FaTIMA.…”

“…The CONTAM program consists of a graphical user interface, referred to as ContamW, and a solver, referred to as ContamX, which is written in the C programming language, and converted to JavaScript to run in a web-based environment [4]. The benefit of this approach is that FaTIMA is running the ContamX solver, that has been well validated [5][6][7][8] and is considered by many to be the de facto tool for whole building airflow and indoor air quality analysis.…”

“…The benefit of this approach is that FaTIMA is running the ContamX solver, that has been well validated [5][6][7][8] and is considered by many to be the de facto tool for whole building airflow and indoor air quality analysis. The development process, theory, assumptions, and verification and validation test cases were presented in the documentation of a previously developed web-based tool [9].…”

“…Deposition velocities for upward facing (floors), vertical (walls), and downward facing (ceilings) surfaces are presented based on the Lai and Nazaroff (2000) model in Figure 6 through Figure 8 for a particle density of 1.0 g/cm 3 over a range of friction velocities. Deposition velocities for other particle densities and size ranges can be calculated using the size-resolved modeling tool previously developed by NIST [4]. Figure 6 also provides the particle settling velocity for upward facing surfaces.…”

“…Note: Particle Deposition velocities and rates provided in Figure 6 through Figure 9 are based on a particle density of 1.0 g/cm 3 . Deposition velocities for densities other than 1.0 g/cm 3 can be obtained using a size-resolved particle modeling tool previously developed by NIST [4]. Deposition rates of smaller particles (dominated by diffusion) are not affected by density, but those of larger particles (dominated by gravitational forces) are proportional to density.…”