The measurements of human inhalability of ultralarge aerosols in calm air using mannikins

An idea was first introduced during the 1970s that particles cannot produce adverse health effect unless they are inhaled into the human respiratory t ract. Since then several studies have been carried out to investigate the i nhalable fraction of ambient aerosols. However, the previous studies were c onfined to the conditions of external convective flow and particle aerodyna mic diameter smaller than 100 mu m. This paper reports the results from an inhalability study for particle aerodynamic diameter for a range of diamete rs which include diameters greater than 100 mu m under a condition of no ex ternal convective flow. The concept of mass balance was used in this study to derive an equation for determining the ambient particle concentration fr om which inhalability was calculated. The results suggested that difference in ventilation demands between adults and children does not affect inhalab ility, however, the inhaled dose was significantly higher in adults than ch ildren because of higher ventilation demand of adults. In terms of the brea thing mode, the inhalabilities of oronasal breathing for people at heavy ex ercise are much higher than those of nasal breathing which simulates breath at rest and moderate exercise. The inhalability curve derived from this st udy indicated that a cutoff diameter for zero inhalability exists, which sh ould be considered in the future revision of ACGIH inhalable aerosols crite ria. (C) 1999 Elsevier Science Ltd. All rights reserved.