October 15, 2020, ©. Leeham News: Yesterday the USTRANSCOM and its US Air Force Air Mobility Command (AMC) published the results of extensive airliner COVID infection risk tests. The tests, which were made to check the risks for DOD personnel using commercial flights, were made on United 777-200 and 767-300 aircraft in cooperation with United.
The tests checked aerosol dispersion of the virus in the cabins for both simulated flights and real flights. The result was you need to sit next to an infectious person for 54 hours to inhale a viral load that could make you sick (worst case).
Last week we could report about simulation results from Airbus, Boeing, and Embraer. We also presented the latest statistics from IATA about actual flight infections. In Boeing’s case, we could say they had verified their CFD cabin simulations with actual tests.
Boeing supported the DOD tests with United. The results of the test are in the DOD report you find here. The US Transport Command did the test to understand the risks for their personnel when flying on commercial flights.
The report describes an elaborate test setup with a mannequin head as an index person and 40 IBAC (Instantaneous Biological Analyzer and Collector) samplers spread over the cabin (Figure 1).
The tests checked aerosol dispersion from 300 simulated breathing and cough events, using aerosolized viruses represented by microspheres of 1um and 3um diameter. A total of 11,500 breathing zone samples were collected during simulated flights (aircraft on the ground with air-conditioning on) and real flights at 35,000ft.
Tests were made with and without masks and with the mannequin breathing and coughing. The results support the OEMs’ results from last week. In many ways, it goes further than these as the DOD report includes a discussion and assumption of required viral load to get COVID from an inhaled aerosol.
There is a lot to get from this report as it’s concrete in its tests, its results, and the conclusions from the tests. Here the main conclusion in the Recommendations section:
For the 777 and 767, at 100% seating capacity transmission model calculations with a 4,000 viruses/hour shedding rate and 1,000 virus infectious dose show a minimum 54 flight hours required to produce inflight infection from aerosol transmission.
The report also states why it reaches this result:
The dispersion data (Figures 14-17) demonstrates the dominant protective factors, as tested, are the airframe’s high air exchange rates, downward ventilation design and HEPA-filtered recirculation and that other test conditions have measurable but minimal effects for aerosol risk. The dispersion data also shows that inflight, ground, and boarding conditions provide similar protection provided the air exchange rates are similar and maintained.
The extract mentions other test conditions, meaning gaspers are on or off and risks during ground and boarding conditions. The effects of gasper use are measurable but inconsequential. Hence gaspers can be used for personal comfort as required. The on-ground and boarding remarks are only for when you are in the cabin and its air stream. No tests or discussions are made for Jetbridge or Gate conditions.
These results are the same as from the OEMs. The cabin flow, including its turbulent parts, is very effective in dispersing and moving viral particles away from the passenger’s inhalation zone.
The OEMs have analyzed whether shields between seats, as proposed by cabin seat manufacturers, shall be introduced. All three OEMs conclude their positive effect is minimal and they have major other drawbacks for safety evacuations and in case of fire. The OEMs will not support the introduction of such devices.
The DOD tests should conclude the discussion about being infected while in flight. It’s time to turn the attention to where there are remaining risks, the phases before entering the aircraft, and when stepping out.
There are obvious risks in these parts that can be mitigated with disciplined behavior. Right now passengers are left without concrete recommendations for these phases of flights. Such are badly needed.