ICRP 66 Lung Deposition Model
ICRP (International Commission on Radiological Protection) Publication 66 provides a human respiratory tract aerosol deposition model for evaluating health effects of inhaled particles.
Respiratory Tract Regions
Head Airways (HA)
- Nasal cavity, pharynx, larynx
- Primary mechanisms: Inertial impaction, gravitational settling
- Main deposition region for large particles (>10 um)
Tracheobronchial (TB)
- Trachea to terminal bronchioles
- Mucociliary clearance mechanism
- Deposition region for medium-sized particles
Alveolar (AL)
- Respiratory bronchioles, alveolar ducts, alveoli
- Gas exchange region
- Main deposition region for fine particles (<1 um)
Deposition Mechanisms
Impaction
Large particles cannot follow airflow turns due to inertia and impact airway walls.
\[Stk = \frac{\rho_p D_p^2 U C_c}{18 \mu d}\]
Sedimentation
Particles settle on airway walls due to gravity, primarily in small airways and alveoli.
\[v_s = \frac{\rho_p D_p^2 g C_c}{18 \mu}\]
Diffusion
Ultrafine particles reach airway walls through Brownian motion.
\[D = \frac{k_B T C_c}{3 \pi \mu D_p}\]
Activity Level Parameters
| Activity | Breathing Rate (min-1) | Tidal Volume (L) | Ventilation (L/min) | Breathing Mode |
|---|---|---|---|---|
| Sleep | 12 | 0.625 | 7.5 | Nasal |
| Sitting | 12 | 0.75 | 9 | Nasal |
| Light Activity | 20 | 1.25 | 25 | Mixed |
| Heavy Activity | 26 | 1.92 | 50 | Oral |
Deposition Fraction Curve
The relationship between particle size and total deposition efficiency shows a U-shape:
- Ultrafine particles (<0.1 um): Diffusion dominated, high deposition efficiency
- Accumulation mode (0.1-1 um): Lowest deposition efficiency ("penetration window")
- Coarse particles (>1 um): Impaction and sedimentation dominated, high deposition efficiency
In AeroViz
Usage lives in the guide: Lung Deposition Calculation shows SizeDist.lung_deposition(), its return keys and a per-diameter example.
Health Significance
- HA deposition: Primarily cleared by mucociliary system
- TB deposition: May cause bronchitis, asthma
- AL deposition: Particles may enter bloodstream, affecting cardiovascular system
References
- ICRP (1994). Human Respiratory Tract Model for Radiological Protection. ICRP Publication 66, Ann. ICRP 24(1-3).
- Hinds, W. C. (1999). Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. Wiley.