A BRIEF INTRODUCTION TO PASSENGER AIRCRAFT CABIN AIR QUALITY
Article published in ASHRAE Journal -October 2020
Summarized by
Reinhard Schuetz, P. Eng.
Calgary, Alberta, Canada
The Airline Industry, virtually in complete ‘contradiction’ to the report by ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers), keeps claiming that passenger air quality is ‘cleaner’, ‘healthier’ and ‘safer’ than the air in offices and hospitals. The following is a digest of ASHRAE’s “Technical Feature” report (available on ASHRAE website) related to those claims:
Report Conclusion: “Aircraft travel currently poses a relatively high risk of a person acquiring a virus infection, compared with many other public spaces. High air rate changes and HEPA filters may sound good, but the parameters that are important are occupancy density, the rate of supply of virus-free outdoor and filtered air to occupants, the duration of any virus exposure and relative humidity.”
Article published in ASHRAE Journal -October 2020
Summarized by
Reinhard Schuetz, P. Eng.
Calgary, Alberta, Canada
The Airline Industry, virtually in complete ‘contradiction’ to the report by ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers), keeps claiming that passenger air quality is ‘cleaner’, ‘healthier’ and ‘safer’ than the air in offices and hospitals. The following is a digest of ASHRAE’s “Technical Feature” report (available on ASHRAE website) related to those claims:
- Relative Humidity (RH) on an aircraft is ‘dry’ (about 10%) compared to an average of about 45%RH in other human occupied spaces.
- Low RH has been associated with increased infection risk (eg: higher influenza in winter than summer).
- In ‘dry’ air, transmission distance of droplets/aerosols containing micro-organisms can be up to 4.5m, or about 5-rows either way.
- RH components can pass behind the cabin insulation and condense on the cold fuselage, allowing for potential microbial growth.
- HEPA filters are designed to capture 0.3µm (micron) size or larger particles. (However, viruses and chemicals can be as small as 0.01µm and 0.0001µm, respectively).
- Due to confined cabin space, viral ‘concentrations’ on airplanes can be about 2x greater than in schools and 3x greater than in offices.
- Higher occupant density potentially creates both a social distancing issue and higher viral exposure.
- High ‘air changes per hour’ (ach) is not an indicator of virus-free air supply on commercial passenger aircrafts.
- Ventilation standards need to specify more than HEPA filters alone.
- Masks are not a viable long-term solution, nor 100% effective.
- Aerosols escaping via peripheral mask leakage can still move around the cabin perhaps up to 5-rows way.
- Trapping a wearer’s exhaled humid breath could create microbial growth if mask is not regularly and properly disinfected.
Report Conclusion: “Aircraft travel currently poses a relatively high risk of a person acquiring a virus infection, compared with many other public spaces. High air rate changes and HEPA filters may sound good, but the parameters that are important are occupancy density, the rate of supply of virus-free outdoor and filtered air to occupants, the duration of any virus exposure and relative humidity.”
