Experimental Study about Effect of Cabin Air Pressure on Human Auditory Sensation

Transcription

1 Topic C5. Thermal comfort and built environments Experimental Study about Effect of Cabin Air Pressure on Human Auditory Sensation Haiying Wang 1, Liang Li 1, Songtao Hu 1, and Guodan Liu 1 1 Department of Environment and Municipal Engineering, Qingdao Technological University, Qingdao,China * Corresponding why3305@126.com Keywords: Experiments, Cabin, Air pressure, Auditory evaluation SUMMARY During cruising, the cabin pressure is typically maintained at 0.8kpa (about 0.8atm). Such cabin pressure could cause changes in human perception systems, especially for auditory sensation. Experiments were performed in a decompression chamber to check on this effect. During the experiments, the air pressure was set at 1atm, 0.9atm and 0.8atm. 24 subjects participated in the experiments. The questionnaire included subjective sensation about the noise, comfort and fidget, etc. Heart rate and blood pressure were also tested. The results showed that people became more sensitive to noise as air pressure decreased and people felt the noises were more annoying and uncomfortable. The heart rate tested showed that the subjects heart rate increased as pressure decreased and the change was related to objective vote, e.g., the unpleasantness caused by noise could cause the increase of heart rate. The change of blood pressure was not obvious in all conditions. INTRODUCTION Cabin environment, which is more complex and special than buildings, is getting more and more attention. In order to improve the comfortableness and satisfy the needs of passengers, many research works had been carried out (Lindgren, et al., 2002). During cruising, the cabin pressure is typically maintained at 0.8atm, which is equivalent to altitude about 1800m. Compared to normal pressure environment that most people live in, the decrease of air pressure in cabin could cause changes in human perception about the external environment. Some studies had shown that when stayed in cabin pressure people s thermal sensation, skin temperature and heart rate were a little different from that in normal pressure (Wang et al. 2010, Cui et al., 2014). The auditory sensation might also be influenced as the hearing organs of auditory meatus and eardrum are exposed to such environment directly. Most of the studies about noise are focus on its negative effect on emotion, work efficiency and health. In early 1970s, researcher had begun their studies on the effect of noise on task efficiency and psychological performance (Smith, 1989, Umemura et al., 1998). Lots of laboratory studies had been carried out. The reaction of people to different kinds of noise like music, language, traffic noise, et al. played in different levels had been explored widely (Hongisto, 2005, Dalton et al., 2007). There were health consequences of elevated sound levels. Elevated workplace or other noise could cause hearing impairment, hypertension, ischemic heart disease, annoyance, sleep disturbance, and decreased performance. Elevated noise levels could create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors (Kryter, 1994).

2 Noise inside the air cabin could be more annoying, because it lasted for the whole traveling time and was accompanied with other unpleasant factors, like vibration and low humidity, et al.. Passengers on board have always felt a bit unwell about their ears during the process of climbing and landing, because the pressure change in the cabin will lead to the pressure imbalance between middle ear cavity and the environment and might cause hearing impairment. As the plane flies placidly, the inside pressure tends to be stable. Yet, the lower pressure is possibly having negative impact on auditory sensation. In this study, experiments had been performed to investigate the effect of cabin air pressure on auditory sensations. METHODS: The experiments were performed in a decompression chamber which could simulate different levels of air pressure. The details about the chamber could be found in reference (Wang et al., 2010). During experiments the temperature was kept at 24 with accuracy of ±0.5 and the relative humidity was ranged from 60% to 70%. In the experiments, the air pressure was set at 1atm, 0.9atm and 0.8atm. Three kinds of noise: white noise, language and music were tested. The noise were marked as noise 1 (85dB white noise), noise 2 (65dB), noise 3 (70dB language) and noise 4 (70dB music). 24 subjects (14 males and 10 females, college students) participated in the experiments. The participants were divided into 6 groups. Each group participated in the experiments randomly. The schedule of experiments was shown in Figure 1. 30min 15min 15min 10min 15min 15min 10min 15min 15min 20min P A T D A T D A T E 1atm 0.9atm 0.8atm P: Preparation A: Adaption T: Test E: End of the experiment Figure 1. The schedule of experiments As the available equipments testing auditory sensation was quite limited, the experiment was mainly based on questionnaire. The questionnaire was used to evaluate subjective sensation about the noise, comfort and fidget, etc., which was listed in Table 1. The heart rate and blood pressure were also tested to judge the physiological effect of noise and air pressure on human. The heart rate and blood pressure were tested by hemodynamometer (OMRON) and the measured values were recorded manually. Content of questionnaire Auditory sensation Table 1. The content and scale of questionnaire Scale Representative Content of Scale Representative meanings questionnaire meanings -3 Silent Fidget 0 Fretless -2 very quiet 1 A little fidget -1 Quiet with a little 2 Fidget noise can be heard 0 Feeling well, not 3 Very fidget noisy 1 A little noisy 4 Unbearable fidget

3 2 noisy, yet acceptable 3 Very noisy, Unacceptable Comfort 0 Comfortable Fatigue 0 Feel fine 1 A little 1 A little tired uncomfortable 2 Uncomfortable 2 tired 3 Very uncomfortable 3 Very tired 4 Unbearable 4 Exhausted RESULTS Figure 2 showed the results of auditory sensation for the four kinds of noise in different air pressure. It could be seen that subjects evaluation was not only related to category of noise and noise level, but also pressure. Noise 1 and 2 were white noise of different levels. Compared to noise 3 (language), white noise felt much more lousy. Noise 4 (a classical music played at 70dB) was just well. Yet, the mean value of votes was increasing as the pressure became lower for all noises. In another word, subjects felt them noisier as pressure decreased. The increment of mean auditory sensation vote between 1atm and 0.8atm was 0.35 for noise 1, 0.58 for noise 2, 0.35 for noise 3 and 0.28 for noise 4. Figure 2. Auditory sensation Figure 3 showed the subjects mean vote on comfortableness. When the pressure was 1atm, noise 1 was uncomfortable, noise 2 and noise 3 felt the same, and noise 4 was nearly comfortable. When it came to 0.8atm, the votes were a little higher than that at 1atm, which showed that the same noise would feel less comfortable as pressure decreased.

4 Figure 3. Mean votes on comfort Figure 4 showed the fidget sensation caused by the four noises. The change of mean vote was similar to that of comfort. Despite of the category of noise, under lower pressure the mean vote increased and people tended to be a little more bothered. Figure 4. Mean votes on fidget Figure 5 was the fatigue sensation vote. As pressure decreased, the variation of fatigue vote was larger than the other votes. The change of noise1 from 1atm to 0.8atm was 0.9, for noise 2 was 0.6, for noise 3 was 0.7, and for noise 4 was 0.2. It seemed that in lower environment the increment of fatigue vote was related to category of noise. The most unpleasant noise would make people more easily get tired. And it would be worsened in cabin pressure.

5 Figure 5. Vote of fatigue The above analysis showed that the most intolerable noise was noise 1, the white noise at higher levels. The cabin noise was mostly caused by engine and the noise spectrum was similar to white noise, which made the control of cabin noise more important. And the questionnaire also showed that despite the noise category and levels, short-time low pressure environment exposure had negative influence on people s subjective sensations. This suggested that in the control of cabin noise this side-effect should also be considered. Figure 6 expressed the effect of noise and air pressure on subjects heart rate. The heart rates under noise 3 and 4 were almost the same, while the heart rate under noise 1 was the largest in all conditions. The subjects heart rates were increased as pressure was lowered for the four kinds of noise. This might explain the negative effect on subjects auditory sensation of lower pressure. When people were exposed to uncomfortable noise that led to negative sensations, their heart rate could be affected. Figure 6. Heart rate In Figure 7, both the diastolic and systolic pressure was compared. The change of blood pressure was not quite obvious. It seemed that systolic pressure didn t change much as

6 pressure decreased. For the four kinds of noise, the diastolic pressure increased at 0.8atm compared to 1atm. Among that, the diastolic pressure for noise 2 showed a little fluctuation, which increased at 0.9atm. This might be caused by misoperation. Though the change of diastolic pressure was not significant, the increment was somehow related to the negative effect of lowered pressure. Figure 7. Blood pressure CONCLUSIONS The results of experiments showed that people became more sensitive to noise as air pressure decreased. Their evaluation to noise increased in cabin pressure, which meant that people felt the noises were more annoying, uncomfortable and they were getting more tired. For the three kinds of noise tested in the experiments, music felt better than languages and white noise was the worst. The heart rate tested showed that the subjects heart rate increased as pressure decreased and the change was related to objective vote, e.g., the unpleasantness caused by noise could cause the increase of heart rate. The change of systolic pressure was not obvious and the diastolic pressure increased a little as air pressure was decreased to 0.8atm in most conditions. Experiments in this study found that decreased air pressure had negative effect on people s auditory sensation. In order to achieve comfortable cabin environment, the noise level should be controlled more stringently or measures should be taken to protect people form such effects. Because the testing methods of subjects objective reaction were quite limited, the study was mainly based on subjective questionnaires. Further studies on objective auditory parameters are needed. ACKNOWLEDGEMENT The authors would like to thank the college students who participated in the experiments. The research is financially supported by the National Key Basic Research and Development Program of China (the 973 program) through grant number 2012CB It is also

7 financially supported by the National Science Foundation of China, under the contract of No REFERENCES Cui W., Ouyang Q., and Zhu Y Effect of air pressure on human thermal sensation and physiological parameters. Proceedings of the 6th International Conference on Indoor Air Quality and Climate Indoor Air, Hongkong, China, Topic A7. Dalton B.H. and Behm D.G Effects of noise and music on human and task performance: A systematic review. Occupational Ergonomics, 7, Hongisto V A model predicting the effect of speech of varying intelligibility on work performance. Indoor Air, 15(6), Kryter K.D The Handbook of Hearing and the Effects of Noise: Physiology, Psychology, and Public Health. Boston: Academic Press, ISBN Lindgren T. and Norbäck D Cabin air quality: indoor pollutants and climate during intercontinental flights with and without tobacco smoking. Indoor Air, 12(4), Smith A A review of the effects of noise on human performance. Scandinavian Journal of Psychology, 30(3), Umemura M. and Honda K Influence of music on heart rate variability and comfort--a consideration through comparison of music and noise. J Hum Ergol (Tokyo), 27(1-2), Wang H., Hu S., Liu G., and Li A Experimental study of human thermal sensation under hypobaric conditions in winter clothes. Energy and Buildings, 42(10),