Spatial and temporal visualization of gases and vapours in air using computed tomography. Numerical studies

Numerical studies were performed to evaluate a new method for human exposure assessment and source monitoring, based upon optical remote sensing (ORS) and computed tomography (CT). With an ORS-CT system, two-dimensional maps of chemical concentrations in air, with good spatial and temporal resolution, can be created over a confined space such as a workplace room. The ORS-CT system was evaluated using 15 simulated test maps that model the generation and dispersion of contaminant plumes over time. A program simulated field measurements from these maps assuming different remote sensing scan times. Using these measurements, reconstructed maps were generated and compared with original maps. Qualitative and quantitative methods were used to evaluate the effect on reconstruction quality of sample time, number of iterations used by the maximum likelihood expectation maximization reconstruction algorithm and sample density. For this study, scanning an entire room in 10 min was adequate for exposure evaluation, source monitoring and leak detection. (C) 1997 British Occupational Hygiene Society.