Predicted combustion product deposition in the human airway

Fires involving modern polymeric materials produce toxic vapours and particles of widely varying composition and size depending on available oxygen and localized temperatures. Adverse health effects of inhaled combustion-generated particles depend on physiological interactions at the airway deposition site. The present work is a theoretical investigation into the importance of airway humidity and temperature profiles, initial particle size, particle size distribution and ionic concentration on airway particle deposition. A modified numerical model accounting for hygroscopic particle growth was used to predict airway deposition of 0.1-10.0 microm mass median aerodynamic diameter (MMAD) particles. Dynamic humidity profiles were generated with an unsteady state model of heat and water vapour transport. Results suggest that for hygroscopic particles < 2.0 microm, MMAD dynamic end-inspiratory humidity profiles produce up to 250% greater predicted nasopharyngeal deposition than steady state humidity profiles. Assuming combustion products are hygroscopic, these results also suggest that less pulmonary deposition will occur than previously predicted. In addition, higher upper airway concentrations of combustion products may have significant health consequences independent of pulmonary deposition patterns.