A kinetic model for human blood concentrations of gaseous halocarbon fire-extinguishing agents.

ABSTRACT

A simple kinetic model for calculating the blood concentration history of humans exposed to time-varying concentrations of gaseous, halocarbon fire-extinguishing agents is described. The kinetic model was developed to extend experimental physiologically based pharmacokinetic (PBPK) models for arterial blood concentration of halocarbons, obtained from constant concentration exposure of dogs to time-varying exposure conditions for humans. In the present work, the simplified kinetic model was calibrated using published PBPK-derived arterial concentration histories for constant concentration exposure to several common fire-extinguishing agents. The calibrated kinetic model was then used to predict the blood concentration histories of humans exposed to time-varying concentrations of these fire-extinguishing agents in ventilated compartments and the results were compared with PBPK-derived data for the agents. It was found that the properly calibrated kinetic model predicts human arterial blood concentration histories for time-varying exposures as well as the PBPK models. Consequently, the kinetic model represents an economical methodology for calculating safe human exposure limits for time-varying concentrations of gaseous halocarbon fire-extinguishing agents when only PBPK-derived human arterial blood concentration histories for constant exposure conditions are available.