Salerno, June 7th and 8th, 2017
1st International Comfort Congress
Ranking of human senses that contribute to passengers’ aircraft interior comfort experience Bouwens Joyce M. A. 1,2, Hiemstra-van Mastrigt S. 2*, Vink P. 2 1
Zodiac Seats US, Department of Human Factors and Ergonomics, 2000 Weber Dr, Gainesville, TX 76240, USA
2
Delft University of Technology, Faculty of Industrial Design Engineering, Landbergstraat 15, 2628 CE Delft, The Netherlands * Corresponding Author: Suzanne Hiemstra-van Mastrigt, e-mail:
[email protected], Phone: +31 15 27 81225, Mobile: +31 628 245 190
Abstract: There are many factors influencing passengers’ comfort, such as expectations and environment. When experiencing comfort, the different human senses all play a role. According to Bubb (2008) [1], six factors determine discomfort: Smell, Light, Vibrations, Sound, Climate and Anthropometry. Bubb [1] presented these factors in a discomfort pyramid, with Smell as most important factor and Anthropometry as least important. The goal of this study is to investigate whether the expectations of aircraft passengers are comparable to the hierarchy of the human senses as proposed by Bubb’s discomfort pyramid [1]. A survey has been conducted among aircraft passengers (respondents with flight experience in the last year). In total 183 respondents between 19 and 64 years old (mean: 30.5, SD: 12.8) were asked to rank six different factors: Smell, Light, Vibrations, Sound, Climate and Anthropometry. These factors were presented to the respondents as 15 different pairs (e.g. Smell-Sound), and respondents were asked to indicate for each pair, which is most important according to them in order to experience comfort. The results of this study suggest that the expectations of aircraft passengers differ from the hierarchy of senses suggested by Bubb [1]. In this study, respondents indicated ‘anthropometry’ as most important, whereas this was the least important factor according to Bubb [1]. The other factors, in reducing order of importance according to the respondents of this study, were ‘noise, smell and climate’, ‘vibration’ and, lastly, ‘light’. However, according to the remarks made by the participants, some factors could be interpreted in different ways. For example, climate does not only refer to temperature, but also to humidity and atmospheric pressure. Therefore, these factors and their influence on comfort and discomfort experience should be studied in more detail.
Keywords: comfort, expectations, human senses
1 Introduction When booking a flight, passengers are looking for comfort and are willing to pay more to get better seat comfort [2]. Since a good and comfortable experience is an indication to return to an airline, most airlines invest in the design of a comfortable airplane interior. There are many factors that influence passengers’ perception of comfort and discomfort, such as expectations and environment [3,4]. Linked to the human senses, according to Krist [5] and Bubb [1], discomfort is influenced by six factors: anthropometry, climate, noise, vibrations, light and smell.
Anthropometry Anthropometry is the scientific study of measurements of the human body. When designing products such as aircraft seats, anthropometric data can be a valuable source of information. A study by Hiemstra-van Mastrigt [6], comparing the dimensions of economy class aircraft seats to anthropometric measurements from a database, showed that current economy class aircraft seats exclude up to 21% of passengers due to the distance between armrests, which is too narrow for the hip width of passengers. If the dimensions of the aircraft seat, such as width of the seat or the seat pitch (distance between two seats) are not well fitted to the passenger, this will have an effect on the perceived discomfort. Climate With a range from 20°C to 27°C on intercontinental flights and 21°C to 31.7°C on continental flights, it can be concluded that the temperature in an airplane cabin varies strongly [7]. Therefore, Kuijer & De Jong [8] suggest that indoor climate conditions can only work when occupants are offered sufficient means for creating their own comfort. Personal thermal systems are integrated in car seats for many years now. Oi et al. [9] found that heated seats effectively improve the occupants’ initial comfort when the air temperature is lower than 15°C, and that heated seats can prevent decreases in toe skin temperature. Pasut et al. [10] found that self-controlled heated and cooled seats enables participants to remain a neutral thermal sensation (neither too hot nor too cold), with an environmental temperature between 16°C and 29°C. However, when the temperature is 25°C, the use of the cooling or heating system will not result in improved comfort. Next to improved thermal experience, air quality is perceived better by participants using the heating and cooling system [10]. Noise and vibrations Aircraft interior sound levels depend on different factors, such as flying speed and altitude, and seat position [11]. The average noise level in an aircraft on cruise flight altitude is 75 dB [12], mainly originating from the aircraft engines. These current sound levels in airplane cabins do not reach the discomfort threshold [13] and highly unlikely cause permanent hearing loss [15], but may result in annoyance among airplane passengers [16], although Quehl states that annoyance caused by sound is based on individual preferences [11]. Mellert et al. [16] found that lower noise levels result in less symptoms of tiredness, difficulty in concentration, swollen feet and headache for flight crew and passengers. Current sound design in an airplane cabin is mainly focused on reducing this noise; however, the use of sound also offers opportunities in terms of positively influencing passenger behaviour. Tasks that require creativity prosper with moderate ambient noise of 50 – 70 dB [17], so the sound of a coffee bar for example can stimulate creativity. Music can also affect comfort and emotion [18]. Classical music is a sound that could calm the passenger. Harmat et al. [19] indicate that this intervention can even help to reduce sleeping problems. As long as there is no heavy turbulence, the experienced accelerations of an aircraft in cruise are not notably heavier than, for example, when travelling by car. This is different than for example trains, where passengers experience a lot of lateral movement which affects their activities such as writing, eating and drinking [20-25]. Light The effects of light (colour) on people’s mood and comfort has also been studied extensively. For example, Schauss [26] suggests that pink should be used in any situation where sudden or uncontrollable aggression is likely, since this colour has a sedative effect on people. According to Sokolova & Fernández-Caballero [27] the colour green, followed by yellow and blue attain the most positive emotions, although this is strongly dependent on the mood and personality (introvert or extrovert), the demographics and age of the person. Also, the use of coloured light could be applied to treat jetlegs [28]. Smell The factor scent is rather complex. People do react on scents; odours can affect mood, physiology and behaviour [29], but they are unable to communicate about smell experiences through words [30], which makes it difficult to research. Nevertheless, it is suggested that scent can support cooperation and interaction [31], peppermint scented questionnaires resulted in more compliance and increased willingness to volunteer [32], whereas citrus scented all-purpose cleaner smell made people clean their spilled breadcrumbs from eating more often [33]. 2
Although a lot of studies have been conducted on the individual factors, the relationship and hierarchy between the different human senses remains underexposed in scientific literature. Research by Quehl [11] on effects of aircraft interior sound and vibration on passenger comfort, shows that the sound pressure level contributed approximately 70 % and the vibration magnitude about 30 % to the comfort evaluation, in accordance with the commonly reported dominance of noise regarding subjective annoyance responses [11]. Krist [5] and Bubb [1] propose a hierarchical model of six discomfort sensations based on Maslow’s hierarchy of human needs, to indicate their relative significance (Fig. 1); anthropometry, climate, sound, vibrations, light and smell. The base layer smell (‘geruch’) is most important, followed by other factors such as vibrations and climate. Improvements on a better fit of the seat by involving anthropometric data seems to be the final concern in the development process of a comfortable seat, according to Bubb’s pyramid.
Fig. 1. Discomfort pyramid (Bubb, 2008) [1]
Assuming that the factors mentioned in the discomfort pyramid give a representative and more or less complete overview of factors to take into account while designing an airplane seat, influences such as expectations are not taken into account in this discomfort pyramid. Therefore, the research question of this study is: What is the order of importance of the factors as contributors to aircraft interior comfort experience based on passenger expectations?
2 Method In a questionnaire, respondents were asked to rank six different human senses: climate, vibrations, light, noise, anthropometry and smell. These senses are presented to respondents as 15 different ‘word pairs’, and respondents were asked which element, according to their expectations, is the most important in experiencing a comfortable aircraft interior. They had to indicate for each of the element pairs (Table 1), which one is more valuable to them by drawing a circle around the most important one. In total 183 respondents between 19 and 64 years old (mean: 30.5, SD: 12.8) with flight experience completed the questionnaire. The number of times each element is indicated as most important is counted (with a maximum of 5 times per element). The scores per human sense are analysed with a Wilcoxon signed rank test, and significance was accepted at p
