DEVELOPMENT OF UNSTEADY INDOOR CONTAMINANT CONCENTRATION DISTRIBUTIONS FOR RISK ASSESSMENT OF HIGH CONCENTRATION AND SHORT-TERM EXPOSURE (PART 1): FUNDAMENTAL EXPERIMENTS USING SMALL GLASS CHAMBER AND VALIDATION OF PREDICTION ACCURACY

Risk assessments of chemical substances are essential and, in particular, risk estimation is of paramount importance to ensure the health of workers. However, measurement of the concentrations of chemical substances in the working environment, which are generally based on field/personal exposure measurements, are not always feasible. To precisely predict the transient concentration distribution of chemical substances, we developed a numerical model for the emission of gas-phase chemical pollutants from mixed solutions in case of a liquid chemical leakage accident. In this study, we conducted computer fluid dynamics (CFD) analysis incorporating the proposed model and using experimental results for the time-dependent concentration of the emissions at various ambient temperatures. As first step of numerical modeling development, we focused on ammonia as chemical substances and conducted fundamental experiments in a small chamber to identify the transient gas-phase emission characteristics from binary mixture solution. The experimental value showed that higher ambient temperatures led to higher initial ammonia concentration. However, after 40 minutes, the temperature dependence was minimal, and at higher temperatures, the exhaust concentration approached zero sooner. In this study, the saturated gas-phase concentration of ammonia estimated from the Henry model was incorporated into the CFD as the wall surface boundary condition. The experimental test chamber geometry was precisely reproduced for the numerical analysis. Here, the flow field in the test chamber was assumed to be in the steady state. Based on the steady air flow profile, non-steady state analyses of the emission and diffusion of ammonia in the chamber were analyzed. The numerical analysis results showed the same tendency, and nearly reproduced the experimental values. This study proposed an unsteady non-uniform concentration distribution analysis method based on CFD to predict the amount of a toxic gas-phase chemical compound generated from a liquid solution in consideration of temperature effect.