Development of a model to predict air contaminant concentrations following indoor spills of volatile liquids

A personal computer spreadsheet model which predicts air contaminant concentrations following indoor spills of volatile liquids has been developed. Three mass transfer models are compared for predicting evaporative flux in the model, the flat plate mass transfer theory, Penetration Theory, and Mackay and Matsugu models. Two methods of predicting spill temperature during evaporation are presented, the isothermal method, which assumes spill temperature remains at ambient throughout evaporation, and the spill temperature method, which predicts spill temperature using equations developed from a heat balance over the spill pool. Dispersion is approximated in the model as a well-mixed room with short-circuiting. Model equations are programmed into a Lotus 1,2,3 spreadsheet. Calculations of room concentration, spill pool surface temperature, and spill area are made at consecutive 20-s intervals following the spill. Model predictions are compared with concentration measurements made after two test spills in a laboratory. The model gives a good first estimate of room concentration, performing best when the spill is assumed to be isothermal and the Penetration Theory or Mackay and Matsugu methods are used to predict evaporation rate. (C) 1997 British Occupational Hygiene Society. Published by Elsevier Science Ltd.