Personal exposure in a ventilated room with concentration gradients.

The fact that many people spent more than 90% of their time in a more or less artificial indoor environment (i.e. office, factory, home, transport vehicles etc.) stresses the importance of a proper indoor exposure assessment. When the personal exposure in a ventilated room is to be determined one may choose to perform a series of measurements or to use a model for calculation. Both approaches may lead to erroneous results if they are not treated properly. For instance C.E. Rodes et al. (1991) summarize various measurements from the literature and state that there may be considerable deviations between measurements using personal exposure monitors (PEM) and micro environmental monitors (MEM), typical PEt-l/MEM ratios were found in the interval from 1.58 to 13.40. Exposure models usually treat the indoor micro environments as well mixed compartments where the concentration of a certain component is found by a simple mass balance. When the ventilated room is addressed the air is thus regarded as being fully mixed which implies that no concentration gradients exist. In a ventilated room concentration gradients will occur if a contaminant source is present. The order of magnitude of the gradients is determined by the effectiveness of the air distribution system and large differences are found between the different types of ventilation systems as well as between different designs of the same type (P.V. Nielsen, 1992). This paper deals with personal exposure in rooms with concentration gradients and persons present. Results from case studies including a breathing thermal manikin in a displacement ventilated room and in a wind channel are presented.