Institute and Clinic for Occupational, Social and Environmental Medicine, University Hospital, LMU Munich, Germany.
Fraunhofer Institute for Building Physics IBP, Holzkirchen Branch, Germany.
Environ Res. 2023 Jan 1;216(Pt 4):114770. doi: 10.1016/j.envres.2022.114770. Epub 2022 Nov 9.
Aircraft cabins are special environments. Passengers sit in close proximity in a space with low pressure that they cannot leave. The cabin is ventilated with a mixture of outside and recirculated air. The volume of outside air impacts the carbon footprint of flying. Higher recirculation air rates could be considered to save energy and divert less kerosene from producing thrust.
To investigate whether higher recirculation air rates in aircraft cabins negatively affect passengers' health and well-being and if occupancy plays a role in this.
In a 2 (occupancy: full and half-occupied) X 4 (ventilation regime) factorial design with stratified randomization, participants were exposed in an aircraft segment in a low-pressure tube during a 4-h simulated flight. Ventilation regimes consisted of increasing proportions of recirculated air up to a maximum CO concentration of 4200 ppm. Participants rated comfort, health symptoms, and sleepiness multiple times. Heart rate (variability), as stress marker, was measured continuously.
559 persons representative of flight passengers regarding age (M = 42.7, SD = 15.9) and sex (283 men) participated. ANCOVA results showed hardly any effect of both factors on self-reported health symptoms, strong main effects of occupancy on comfort measures, and interaction effects for sleepiness and physiological stress parameters: Participants in the half-occupied cabin hardly reacted to increased recirculation air rates and show overall more favorable responses. Participants in the fully occupied cabin reported higher sleepiness and had stress reactions when the recirculation air rate was high.
This large-scale RCT shows the importance of occupancy, a previously neglected factor in indoor air research. The proximity of other people seems to increase stress and exacerbate reactions to air quality. Further studies on causal pathways are needed to determine if recirculation air rates can be increased to reduce the carbon footprint of flying without detrimental effects on passengers.
飞机客舱是一种特殊的环境。乘客在一个无法离开的低压环境中近距离就座。客舱的通风采用外部空气和再循环空气的混合方式。外部空气的体积会影响飞行的碳足迹。提高再循环空气的比例可以节省能源，并减少用于产生推力的煤油。
研究飞机客舱中更高的再循环空气率是否会对乘客的健康和福祉产生负面影响，以及乘客的占有率是否会对此产生影响。
采用 2（占有率：满员和半满员）×4（通风模式）析因设计，采用分层随机化，参与者在低压管中的飞机段内进行 4 小时模拟飞行时暴露于其中。通风模式包括增加再循环空气的比例，直到 CO 浓度达到 4200 ppm 的最大值。参与者多次对舒适度、健康症状和困倦程度进行评分。连续测量心率（变异性）作为应激标志物。
559 名代表飞行乘客的人员参与了研究，他们的年龄（M=42.7，SD=15.9）和性别（283 名男性）具有代表性。协方差分析结果表明，这两个因素对自我报告的健康症状几乎没有影响，占有率对舒适度测量有很强的主效应，而对困倦和生理应激参数有交互效应：半满舱的参与者对增加的再循环空气率几乎没有反应，总体反应更为有利。满员舱的参与者报告困倦程度更高，当再循环空气率较高时，会产生应激反应。
这项大规模 RCT 研究表明占有率的重要性，这是室内空气研究中以前被忽视的一个因素。与其他人的接近程度似乎会增加压力，并加剧对空气质量的反应。需要进一步研究因果途径，以确定是否可以增加再循环空气率以减少飞行的碳足迹，而不会对乘客产生不利影响。
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