A numerical study on firefighter nasal airway dosimetry of smoke particles from a realistic composite deck fire

Inhalation exposure to smoke particles emitted from fire grounds could induce respiratory and cardiovascular diseases to firefighters and emergency responders. Understanding the detailed smoke-particle deposition distribution and dosages in nasal airway is of significant value to inhalation risk assessment. In this study, a realistic firefighter nasal airway model, accounting for facial features and external environment was employed to study the inhalation and deposition of smoke particles emitted from a composite deck fire. Particle size distribution and concentration used in the simulation were from the Underwriters Laboratories' large-scale fire experimental data. Deposition patterns and a method for calculating particles dosimetry (in number, mass and surface area) were analyzed. The dosages in the firefighter nasal cavity, middle turbinate, middle meatus, onto the face and penetrated under various inspiration rates were discussed. The aspiration ratio was also considered in the exposure inhalation risk assessments. Three deposition hot spots were identified in the nasal cavity: nasal vestibule, nasopharynx and middle meatus. The breathing flow rate did not affect the aspiration ratio significantly, while the particle density was an obvious impact factor to aspiration ratio of larger size of micron particles (> 5 µm). Greater than 97% of number dosages were from nanoparticles in all simulated areas, yet the nanoparticle mass dosages and surface dosages only took up around 50%. In addition, majority (about 98%) of particles in composite deck fire scenario penetrated into lower airways or even into the lungs. Meanwhile, the dosages in all metrics onto the face were less than those in nasal cavity, but higher than those in the middle meatus and turbinate. Smaller sized particles (such as nanoparticles) were more likely to deposit onto the face than being inhaled into nasal cavity at high flow rate due to the intensive diffusion. Mass carrier (larger sized) particles tended to run into middle turbinate than to middle meatus.