Models for nearly every occasion: Part III – One box decreasing emission models

ABSTRACT

New one box “well-mixed room” decreasing emission (DE) models are introduced that allow for local exhaust or local exhaust with filtered return, as well the recirculation of a filtered (or cleaned) portion of the general room ventilation. For each control device scenario, a steady state and transient model is presented.

The transient equations predict the concentration at any time t after the application of a known mass of a volatile substance to a surface, and can be used to predict the task exposure profile, the average task exposure, as well as peak and short-term exposures. The steady state equations can be used to predict the “average concentration per application” that is reached whenever the substance is repeatedly applied. Whenever the beginning and end concentrations are expected to be zero (or near zero) the steady state equations can also be used to predict the average concentration for a single task with multiple applications during the task, or even a series of such tasks. The transient equations should be used whenever these criteria cannot be met.

A structured calibration procedure is proposed that utilizes a mass balance approach. Depending upon the DE model selected, one or more calibration measurements are collected. Using rearranged versions of the steady state equations, estimates of the model variables—e.g., the mass of the substance applied during each application, local exhaust capture efficiency, and the various cleaning or filtration efficiencies—can be calculated. A new procedure is proposed for estimating the emission rate constant.

KEYWORDS:

• Exposure assessment
• modeling
• one box model
• well-mixed room model

Notes

a The time between applications (t_a) can vary, but will be considered to be a constant in this article.

b This assumes that losses due to adsorption to surfaces or chemical reactions are minimal.