Diffusional Interception
Viruses typically range from about 0.02 to 0.2 micron in size.
For very small particles (less than about 0.1 micron in size), Brownian motion causes particles to be collected on the individual cabin air fibers and pore walls. The smaller the particles, the greater are their random Brownian movements, and the higher the capture efficiency.
Inertial Impaction
Bacteria typically range from about 0.5 to 5 micron in size.
Particles of higher density than air deviate from the air stream path by virtue of their inertia and impact on the solid surfaces or walls of the pores, where they adhere.
Health Effects Associated With Microbial Aerosols
Pathogenic bacteria, viruses and fungal spores may cause infection in humans. Normal activities like breathing, coughing, sneezing and talking disperse millions of these micro-organisms as a fine aerosol. Recirculated air may distribute these microbial aerosols throughout the cabin unless HEPA filtration is employed.
Some of the health effects linked to microbial aerosols are listed below
- Respiratory Impairment
- Pulmonary Diseases
- Nasal Infections
- Asthma
- Ear Infections
- Sinus Diseases
- Irritations and Inflammations
- Skin
- Nose
- Eyes
- Respiratory Tract
- Allergies
- Headaches
- Fatigue
- Nausea, Dizziness
Passenger Susceptibility to Infection
In the complex cabin air environment, passengers and crew may be more susceptible to infection than under normal circumstances. Many factors contribute to this, such as low humidity (typically less than 15% RH), reduced oxygen (because of reduced overall pressure in the cabin during flight), the artificial cabin environment, stress, mechanical vibration, fatigue, jet lag, and contact with people from a wide variety of areas who may carry types of infections not normally encountered.
Pall true HEPA filters reduce the risk of disease transmission from recirculated cabin air.