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Investigation of cabin ventilation strategies impact on aircraft cabin air quality and passengers’ comfort and wellbeing through subject study in realistic aircraft environment

Periodic Reporting for period 1 - ComAir (Investigation of cabin ventilation strategies impact on aircraft cabin air quality and passengers’ comfort and wellbeing through subject study in realistic aircraft environment)

Reporting period: 2018-11-01 to 2020-04-30

The quality of the air we breathe is crucial for our health, well-being and comfort, and cognitive performance. Many contaminants can contribute to the degradation of the quality of air, among others, including volatile organic compounds (VOC) emitted from different sources, including humans. Humans also exhale carbon dioxide used as a marker of air quality but recently supposed to modify the quality of air as well. The exposure to air is occurring in different environments, which are characterized by specific pollutants. One of them is aircraft cabins, where relatively brief but substantial exposure is taking place during travel. Aircraft cabins present indoor environments with distinctive features, where passengers are exposed to a mixture of outside and recirculated air. They include conditions such as high occupant density, inability to leave the environment, low relative humidity, and need for pressurization.
The ComAir study, funded by the Clean Sky 2 Initiative of the European Union, aims to investigate the impact of cabin air quality on passengers’ comfort and well-being with a particular focus on the effects of reducing outdoor air intake and passenger density. The primary reason for this work is to provide an optimal cabin environment for passengers with as low as possible environmental impact of cabin systems in terms of fuel burn and pollutant emissions. Besides, the results of the ComAir study serve as a basis for the development of a so-called adaptive environmental control system (A-ECS), which is intended to improve air distribution in the cabin while reducing the fuel consumption of a commercial aircraft. To meet the project objectives, the effects on aircraft cabin air quality were tested of various proportions of bleed air in the total air supplied to the cabin in the fully and half occupied cabin. Also, the impact of an elevated level of carbon dioxide (CO2) was examined, as well. All tests were performed during simulated flights carried out in the Flight Test Facility low-pressure vessel, which contains a mock-up of an actual airplane cabin. Realistic profiles of cabin pressure, noise and vibrations, temperature, and relative humidity were applied. Two different experimental designs were used. In the first one, a 2 (‘occupancy’) X 4 (‘air ventilation regime’) factorial design was used. Occupancy (factor) denotes the number of people in the aircraft (half vs. fully occupied cabin) and examines the psychological important well-being factor of proxemics. The four air ventilation regime levels were: baseline with typical aircraft airflow regimes per person, ASHRAE 161 requirement (standard recommendation), ASHRAE 161 half (half of the recommended flow), and a recirculation regime with a target CO2 concentration close to regulatory limit of 5,000 ppm.
In the second design that used the results of the first design, a 2 (VOC) X 2 (CO2) test matrix was examined to investigate the disentangled effects of two major drivers of air quality levels affecting well-being; at the moment CO2 is mostly used in regulations as a proxy for air quality without knowing the separate impact of VOCs and CO2. Results of these study designs will help to advance knowledge on the following overall objectives: Determination of key contaminants / chemical compounds and particles impacting cabin air quality; assessment of the impact of different air quality / various recirculation regimes and cabin environment parameters on passenger comfort; development of an air quality metric and validation with subject ratings and test results; and synthesis of results into recommendations for future cabin air quality standards to ensure passengers well-being and comfort while at the same time flying as ecologically sound as possible.
To reach the study objectives, the project used two main approaches: an extensive literature review and human subject experiments in the cabin mock-up. Extensive literature reviews on typical flight environments and parameters, as well as indoor / cabin air quality and pollutants, served as input for the experimental designs and, in turn, will be extended to form an air quality metric substantiated by the subjects’ reaction to different air regimes. A test battery consisting of reliable and valid instruments to measure passengers’ comfort and well-being on the one hand and environmental parameters on the other were developed and aligned with a typical sequence of a 4.5 hour-long flight. Screening and check-in procedures approved by an ethics committee were set into place to ensure that all subjects recruited and participating in the exposure experiments in the cabin mock-up were informed about the study, had given their consent, and could participate without harm.
Overall, 686 people representative of flight passengers in age and sex participated in the randomized controlled studies containing sixteen simulated flights, about 80 (4 flight), or 40 (12 flights) persons per flight. During each flight, concentrations of air pollutants were monitored, and passenger data on comfort, health, and well-being, as well as on cognitive performance and physiological arousal, were regularly measured. First analyses have been conducted for baseline flights with a traditional ventilation regime. They show that environmental exposures in the cabin mock-up were comparable with real aircraft cabin measurements, as found in the literature review. Overall, people felt rather comfortable during baseline flights. The occupancy (factor) had a strong impact on the well-being and comfort of participants, but only a few and small effects on the comfort and well-being of the traditional air regime could be detected; however, it is plausible that these effects were related to environmental conditions. Although passengers did not rate odor negatively, a blind panel of subjects trained to assess air quality rated odor as perceptible and slightly unpleasant. Main odorants detected during simulated flights were attributable to human emissions.
In the next steps, the effects of increased recirculation air regimes on passengers’ comfort and well-being will be further analyzed. The results will be integrated with environmental data and synthesized into air quality metrics that can be used to help develop the AECS system and give recommendations for future cabin air quality standards.
ComAir is one of the few studies that investigates aircraft cabin air quality effects on passengers under real-world conditions with large-scale experimental studies and probably the only one that used the Gold standard of medical and psychological study design by randomly assigning a large number of people to the different conditions instead of using cross-over designs, repeatedly exposing the same, smaller number of people to different environments. This design allows statements on causation, extrapolation and generalization of study findings as well as application in practice.
View into the empty cabin of the Flight Test Facility
Participant filling in questionnaire (reenacted scene)