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|Year : 2014
: 16 | Issue : 70 | Page
|Assessment of the noise annoyance among subway train conductors in Tehran, Iran
Mansoureh Hamidi1, Amir Kavousi1, Somayeh Zaheri1, Abolfazl Hamadani1, Roksana Mirkazemi2
1 Department of Health, Safety and Environment, Shahid Beheshti University of Medical Sciences, Tehran, Iran
2 Hooman Research Collaborators Institute, Tehran, Iran
Click here for correspondence address
|Date of Web Publication||20-Jun-2014|
Subway transportation system is a new phenomenon in Iran. Noise annoyance interferes with the individual's task performance, and the required alertness in the driving of subway trains. This is the first study conducted to measure the level of noise and noise annoyance among conductors of subway organization in Tehran, Iran. This cross sectional study was conducted among 167 randomly selected train conductors. Information related to noise annoyance was collected by using a self-administered questionnaire. The dosimetry and sound metering was done for the conductors and inside the cabins. There were 41 sound metering measuring samples inside the conductors' cabin, and there were 12 samples of conductors' noise exposure. The results of sound level meter showed that the mean Leq was 73.0 dBA ± 8.7 dBA and the dosimetry mean measured Leq was 82.1 dBA ± 6.8 dBA. 80% of conductors were very annoyed/annoyed by noise in their work place. 53.9% of conductors reported that noise affected their work performance and 63.5% reported that noise causes that they lose their concentration. The noise related to movement of train wheels on rail was reported as the worst by 83.2% followed by the noise of brakes (74.3%) and the ventilation noise (71.9%). 56.9% of conductors reported that they are suffering from sleeplessness, 40.1% from tinnitus and 80.2% feeling fatigue and sleepy. The study results showed the high level of noise and noise annoyance among train conductors and the poor health outcome of their exposure to this level of noise.
Keywords: Dosimetry, noise annoyance, sound level meter, subway conductor, work performance
|How to cite this article:|
Hamidi M, Kavousi A, Zaheri S, Hamadani A, Mirkazemi R. Assessment of the noise annoyance among subway train conductors in Tehran, Iran. Noise Health 2014;16:177-82
| Introduction|| |
Subway transportation system is a new phenomenon in Iran with around one decade work history. The subway transportation is extended from east to west and north to south of Tehran in four lines, namely line 1, 2, 4 and 5 and transfers around 2 million passengers, daily. Still there is no research on health hazard of this system to the general population or subway conductors.
Subway conductors have a very sensitive task that any error or failure in their work can endanger lives of thousands individuals. Media has reported many cases of accidents of passengers in the subway of Tehran; however, there is no actual data in this regards. "Speed, Accuracy and Safety" is the motto of subway organization in Iran, which demands maximum alertness and vigilance of its train conductors.
The term noise is attributed to any kind of irritating and obtrusive sound.  Noise pollution is one of the environmental health hazards. Noise induced stress is a result of inability to ignore, block out or otherwise cope with the unwanted sound, or if it is able to do so, only at a cost.  Noise can have negative effects on concentration, productivity, work capacity and increases the risk of accidents  and causes annoyance in many people.  Noise annoyance is a result of emotional processes related to many factors including personality of individuals and the noise level. The level of noise related disturbances and especially annoyance, varies between individuals, because, although noise is always interpreted in the central nervous system, it generates secondary and tertiary reactions that are not controlled by the brain cortex. The stimulation of these reaction pathways lead to involuntary reflexes, which in chronic exposure creates a give-up feeling, develop by reduced corporal and mental functions and usually causes annoyance as it stimulates the reactions of fear and flight. 
A very long-term exposure to noise might lead to a reaction of exhaustion or defeat which leads to disturbance in secretion of some hormones such as growth hormone, catecholamine, , possibly followed by a decrease in function of the immune system and change of mood into apathy and decrease in social contacts.  This might be more severe in case of train conductors who have to work alone and in isolation of others.
Noise has different effects on mental performance, it mostly deteriorates semantic processing of mental task (involve comparing meanings of a stimulus), while it does not affect, or even facilitates physical processing (require comparing physical characteristics of stimulus).  Therefore, noise can have a direct negative effect on performances required in conducting a subway train. Furthermore, it has been shown that intermittent sound is more detrimental to performance, compared with a steady noise of the same level. 
The noise exposure level is associated with the individuals' annoyance level. The respective dose-response relations are characterized by a considerable variation due to individual and situational factors.  The noise index that is used for measuring the noise exposure level is Leq. Due to the relative simplicity of evaluating Leq from the time history of the noise signal and in the absence of any better predictors, researchers in environmental noise believe that there is some convincing reason for continuing reference to the Leq index among many other related noise rating indices that was proposed by different researchers. However, it is more conservative to consider the level of noise annoyance and sensitivity along with the measuring noise exposure level, when assessing the effects of noise pollution is concerned, because according to some authors, factors like noise sensitivity and attitude toward the noisy situation, account for more variation on annoyance level and related effects than do noise exposure parameters. 
The right to health imposes a serious responsibility to the public health system to ensure the safety of public transport in each country. Among the direct and most obvious effects of sound on awake subjects, are the negative interference of sound with the individual's speech communication, concentration ability and consequently the performance of tasks,  which lead to the annoyance of the subject and consequently, may interfere with the required alertness and caution while performing tasks like driving behaviors. Therefore, this study was conducted to measure the level of noise and noise annoyance among conductors of subway organization in Tehran, Iran.
| Methods|| |
This cross-sectional study was conducted to assess the level of noise annoyance among train conductors of Tehran Subway Organization and measure the sound level that they are exposed in their work place and the noise level emitted in their cabin during July 2012.
Participants were 167 of the train conductors of Tehran Subway Organization, which were selected of the total 835 conductors by simple random sampling. All the subway conductors were males, as no female were recruited as train conductors in Iran.
Information was collected by using a self-administered questionnaire which included demographic, job related and annoyance related information. Job related information included the line of train work, work history, number of working hours and number of hours being in the cabin, extra work and shift work. Level of noise annoyance was measured using information on the level of annoyance by two Likert scales: The first scale was a single question "how much your work place noise annoys you when you are at work" which was scored from 0 to 10 developed by Guoqing et al.  and the second question was "In the last 1 year, how much the noise level of your work place annoyed you," which was scored in a 6 points Likert scale range from 0 (no annoyance) to 5 (very high). Noise sensitivity was measured subjectively by a single question "To what extent do you consider yourself sensitive to noise?" on a Likert scale of 11 points (0 to10). The level of disturbance in their normal life and work function and type of noises that cause the maximum disturbance, noise induced health problems and the timing that creates most disturbance data were collected, too.
Most of the questions on the level of noise annoyance, noise sensitivity and health effects of noise was taken exactly from questionnaire developed by "The International Knowledge Center for the Local Environment" in The Netherland (available from: http://rigolett.home.xs4all.nl/ENGELS/quest/questionnaire.htm).
The validity of the questionnaire was tested by using 10 experts' opinion on the content validity and relevancy of each question, which showed a level of agreement more than 70%, and reliability was measured by Cronbach's alpha, which showed a reliability level of 0.512 for annoyance, 0.613 for disturbances, 0.668 health impacts and 0.795 for types of noise questions, which showed an acceptable or desirable level of reliability for each subclass of questions. ,
Three trained interviewers distributed the questionnaires among conductors during their resting time in a 3 days' time period.
The dosimetry was done for the noise that conductors were exposed and the sound level metering was done inside their cabin (in two points of each cabin). The dosimetry device for the noise that conductors were exposed was a dosimeter model CEL-420 made in UK, which was calibrated before installing to the conductors collars by a calibrator model CEL-282. The sound level meter device for the noise inside conductors' cabin was a sound level meter model CEL-62X made in UK, which was calibrated before use by a calibrator model CEL-110/2.
There were 41 noise measuring samples inside conductors' cabin, 21 of them were in line 1, 8 in line 4 and 12 in line 5 in seven different cabins of trains and in totally eight different trips. There were 12 samples that measured conductors' exposure to noise. Thirty two samples (78.0%) were done in motion and 9 (22.0%) in stop status. Twenty three samples (56.1%) were done in head cabins and 18 (43.9%) in rear cabins. Sampling was carried out from 10:30 am to 18:50 pm.
Statistical Package for Social Sciences version 15.0 for windows (IBM Corporation, New York, United States) was used to analyze the data. The data analysis was performed using descriptive statistics and analytical statistics was performed using Chi-square tests, correlation and t tests.
The study procedures and objectives were explained to the participants. Participants were ensured that the data is kept confidential and only investigators would have access to it and that they would face no disciplinary action for their responses, nor would the data be analyzed on an individual basis. The study participants gave verbal consent to participate in the study.
| Results|| |
Part 1: Results of dosimetry and sound level metering
The results of sound level meter inside the cabin showed that the mean maximum sound pressure level (SPL) was 84.0 ± 5.6 dBA (range 72.9-98.3 dBA), the mean minimum SPL was 65.4 ± 3.6 dBA (range 57.6-73.3 dBA) and the mean Leq was 73.0 dBA ± 8.7 dBA (range 63.8-80.7 dBA).
The mean noise dose that conductors were exposed to was 130-150% of the standard allowed noise dose and the mean time weighting average (8 h) exposure was 50.70 ± 17.70 dBA of the standard allowed noise dose. The mean measured Leq was 82.1 dBA ± 6.8 dBA (range 75.2-98.1 dBA), the mean maximum SPL was 101.3 dBA ± 11.4 dBA (range 89.2-128.7 dBA), the mean SPL average was 65.9 dBA ± 32.8 dBA (range 0.0-88.6 dBA) and the mean SPL peak was 126.1 ± 7.3 (range 114.6-142.9 dBA).
Part 2: Noise annoyance assessment results
Demographic and job related information
[Table 1]. shows the demographic characteristics of subway conductors. All the conductors were males in the age group of 22-43 years with a mean age of 29.3 ± 3.2 years. One hundred and thirteen conductors were married (68.1%) and 97.9% of those who married, had one or two children. The educational level of conductors was a bachelor in 33.5% of cases (n = 55) and diploma or college level in 66.5% (n = 109) of the cases. Their mean work history was 5.2 ± 2.8 years. On average they were working 10.3 ± 2.0 h a day and were in conductor cabin 6.02 ± 1.3 h in a day. Maximum conductors were working in line 1 (44.9%, n = 75). 3.0% of them had an additional job and almost all the conductors were shift workers (98.8%). 89.4% (n = 144) of conductors reported that they were doing extra work which was more than 12 h/week in 42.4% of cases.
|Table 1: Demographic and work related characteristics of train conductors (n = 167)|
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Noise annoyance information
[Table 2] shows the level of noise annoyance of the conductors. 48.4% of conductors (n = 78) reported high annoyance and 32.3% (n = 52) reported very high annoyance due to noise in their work place. On a Likert system of 0-10 points, on average the conductor scored their level of noise annoyance as 7.1 ± 3.2 and the level of their sensitivity to noise as 6.2 ± 3.2. 45.5% of conductors (n = 76) reported that noise causes disturbance in their sleep, 53.9% (n = 90) reported that noise disturbance affect their work performance, 51.5% (n = 86) reported that noise causes intolerance in them while interacting with passengers or co-workers, 49.7% (n = 83) reported that noise disturbs their phone conversation and 63.5% (n = 106) reported that noise causes that they lose their concentration. Regarding the type of noise that annoy them more, the noise related to movement of train wheels on the rail was reported as the worst by 83.2% followed by the noise of brakes (74.3%) and the ventilation noise in 71.9% of cases. 35.0% of conductors reported the time that they feel most disturbed by noise is noon time.
Nearly 93.4% of conductors (n = 156) reported that noise should be controlled in their work place. 61.7% (n = 103) reported that they are willing to change their job due to so much noise in their working environment and 98.1% of conductors mentioned that they are not willing to work in a place with a higher salary but more noise [Table 2].
Health related issues
Nearly 56.9% of conductors (n = 91) reported that they are suffering from sleeplessness and 3.7% (n = 6) were using medication to sleep. About 42.0% of conductors (n = 78) reported that they have/had ear problem and half of them still are suffering from it. 42.7% of conductors (n = 67) reported that they are suffering from tinnitus. 83.2% of conductors (n = 134) reported that they are feeling fatigue and sleepy [Table 3].
The association between noise, noise annoyance, noise sensitivity and noise disturbance level.
In the mean SPL of 84.0 ± 5.6 dBA (range 72.9-98.3 dBA) and the mean Leq of 82.1 dBA ± 6.8 dBA (range 75.2-98.1 dBA), 80.7% of conductors were highly annoyed/annoyed of the noise in their work place based on the 6 scores Likert system.
As it was expected, there was a significant correlation between noise annoyance level and noise sensitivity scores (r = 0.645, P = 0.000). [Table 4] shows the association between noise annoyance scores, noise disturbance level and health outcome under the above mentioned noise pollution level. There was a significant association between the level of noise disturbance and noise annoyance. The level of annoyance was more among them who reported that noise disturbs their inside peace (P = 0.037), affect their concentration (P = 0.011), disturb their phone conversation (P = 0.000), disturbance their work performance (P = 0.024) and disturb their sleep (P = 0.000). Furthermore, there was a significant association between some of the health impact of noise and noise annoyance, those who reported sleeplessness and tinnitus had a higher level of noise annoyance (P = 0.035 and P = 0.037, respectively) [Table 4].
|Table 4: The association between noise annoyance level and noise disturbance level|
Click here to view
| Discussion|| |
This study is the first Iranian study that assessed the level of noise and noise annoyance among conductors of Tehran subway. The health and safety of conductors and their optimum work performance is directly related to the health and safety of thousand passengers that travel daily by the subway system, as a cheap and fast way of travel. The study participants were 171 young male conductors with work history on average of 5 year, who spend on average 10 h in the work place and 6 h in the conductor cabin daily.
The study results showed that the conductors' noise exposure level was very high. The average 8-h Leq was 82.1 dB, which is much above the recommendation of the World Health Organization (WHO).  The WHO  recommended a 16-h daytime Leq of 55 dB and approximately, a 45 dB night time LEQ to prevent "serious annoyance." WHO further recommends that, during the night, the maximum level (fast) of any single event should not exceed 60 dB. To prevent annoyance, WHO recommends levels that are 5 dB lower - a daytime Leq of 50 dB and a night-time Leq of 40 dB. European Environment Agency in good practice guide on noise exposure and potential health effects showed that the noise level at the threshold of Leq 50 dB(A) has an adverse effect on performance by affecting learning and memory in chronic and acute exposure. 
This study showed that the level of noise annoyance among the conductors was very high. In a Likert scale of 11 points (0 to10),  the mean score was 7.2 (very close to the score of 8-10 which is defined as highly annoyed by Guoqing et al.). More than 95% of the conductors reported that the noise in their work place is very high/high and more than 80% reported that they are very annoyed/annoyed by the noise in their work place. WHO defines health as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity, therefore, a high level of annoyance caused by environmental noise should be considered as one of the environmental health burdens too. 
Around half of the conductors reported that the noise disturbs their sleep. Frei et al.  study showed that effects of nocturnal traffic noise on objective sleep quality are independent of perceived noise annoyance, whereas the association between self-reported sleep quality and noise is mediated by noise annoyance.
More than half of conductors reported that noise adversely affects their work performance and cause intolerance in them or distraction. Error in conducting a subway train can results in a disaster, endangering life of thousand individuals. Smith and Stansfeld  in their studies on people living in areas with a high level of aircraft-noise showed that their everyday errors (failures of attention, memory and action) appear more frequently, compared to people living in low-noise areas.
The most reported disturbing noises were noise of wheels on the rails, train brakes and ventilation noise. This can be a reflection of low quality infrastructure; the type of rails and wheels and brakes are not standard or from good materials (due to sanctions most of materials are from China and of poor quality), or negative assessment of the noise source due to long term exposure to noise and annoyance as described by Guski.  Furthermore ignoring the health and safety of conductors is reflected in the ventilations, which make high level of noise and need repair or replacement. The conductors cabins is supposed to be sound proof to control the level of noise, but low level of maintenance has resulted in high level of noise pollution inside cabins.
Almost all the conductors suggested that noise should be controlled in their work place and more than half of them mentioned that they are willing to find another job to get rid of this noisy environment, which is a reflection of the level of their frustration. Subway conductors are trained human resources that have passed minimum 2 years of training to be qualified for conducting a subway train, but this frustration can lead to waste of the most precious resources of subway organization, which are the human resources.
Although, the conductors were at the young age group and with short duration work history, but their health was affected by their noisy work environment. Nearly 56% of them reported sleeplessness and more than 40 present reported ear problem or tinnitus. The auditory effects of noise on people have been quite well-known for some decades.  Fioretti et al. in their study showed a significant correlation between sleep disorders and tinnitus annoyance.  Feeling fatigue was reported by more than 80.0% of the conductors. All these information shows severe health deterioration of conductors, which can become more severe by increasing their work history. Poor health outcome due to noise pollution and noise sensitivity has been reported by many studies before. ,, .
Study of burden of disease from environmental noise in Europe showed that estimated DALYs lost from environmental noise are 61,000 years for ischemic heart disease, 45,000 years for cognitive impairment of children, 903,000 years for sleep disturbance, 22,000 years for tinnitus and 654,000 years for annoyance in the European Union Member States and other western European countries. 
This study showed that there was a significant correlation between noise annoyance level score and noise sensitivity score, as it is expected that those who are more sensitive to noise, become more annoyed of a noisy environment. Furthermore, this study showed that those reported a higher level of disturbance in the required work performance skills like concentration, conversation and work performance were more annoyed of noise in their work place. However, it was found a disturbance like feeling intolerance with passengers or colleagues were not related to the level of noise annoyance and may have other causes like mood and personality trait. Also a significant association was found between noise annoyance level and suffering from some health outcome like sleeplessness, tinnitus or annoyance may be a result of this health outcome too.
This study did not investigate many other long term effects of noise pollution like hypertension , and disturbance in hormonal secretion and cardiovascular diseases. Rylander has reported increased blood pressure and disturbances of hormonal secretion due to a reaction from exhaustion of central nervous system in terms of the defeat reaction. 
| Conclusion|| |
This study showed the high level of noise and noise annoyance among train conductors and the poor health outcome of the conductors.
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Department of Health, Safety and Environment (HSE), Shahid Beheshti University of Medical Sciences, Daneshju Blvd, Tehran 1983963113
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4]