trated on exposure levels for the attending public, rather than employees who may be at ... total personal noise exposure, especially amongst young employees.
Ann. occup. Hyg., Vol. 46, No. 5, pp. 455–463, 2002 © 2002 British Occupational Hygiene Society Published by Oxford University Press DOI: 10.1093/annhyg/mef051
Noise Exposure and Hearing Loss among Student Employees Working in University Entertainment Venues S. SADHRA1*, C. A. JACKSON1, T. RYDER1 and M. J. BROWN2 1Institute
of Occupational Health, University of Birmingham, University Road West, Edgbaston, Birmingham B15 2TT; 2Victoria Hospital, Morecambe, UK
Received 7 September 2001; in final form 31 January 2002 Objectives: Most studies to date on sound levels in entertainment establishments have concentrated on exposure levels for the attending public, rather than employees who may be at greater risk of hearing loss. Of particular concern are young employees. The aim of this pilot study was to (i) estimate typical sound levels in different areas where amplified music was played, (ii) measure temporary threshold shift (TTS) and (iii) estimate the dependence of hearing threshold shifts on measured noise levels. Methods: This study focused on students working part-time (up to 16 h/week) in music bars and discotheques in a university entertainment venue. All 28 staff were invited to participate in the study. Pre- and post-exposure audiometry was used to determine hearing threshold at both high and low frequencies. Personal dosemeters and static measurements were made to assess noise levels and frequency characteristics. A questionnaire was used to determine patterns of noise exposure and attitudes to noise levels and hearing loss. Results: Of the 28 student employees working in the three areas, 14 (50%) agreed to take part in the study, giving 21 pre- and post-shift audiograms. The mean personal exposure levels for security staff were higher than those of bar staff, with both groups exceeding 90 dB(A). The maximum peak pressure reading for security staff was 124 dB. Although TTS values were moderate, they were found to be highly significant at both low and high frequencies and for both ears. Twenty-nine per cent of subjects showed permanent hearing loss of more than 30 dB at either low or high frequencies. The correlation between TTS and personal exposure was higher at 4 kHz than the low and high frequencies. Conclusions: Contemporary music may be an important yet little considered contributor to total personal noise exposure, especially amongst young employees. Employees need to be better informed of risks of hearing loss and the need to report changes in hearing acuity. Suggestions are made on strategies for improving the assessment of noise exposure in entertainment venues. Keywords: hearing loss; temporary threshold shift; entertainment venues
sound intensity and the genetic vulnerability of individuals. Over the past 20 yr the power of amplification that is affordable has increased steadily, hence the increase in the potential for hearing damage. Most studies to date on sound levels in entertainment establishments have concentrated on the public attending various music functions or the musicians (Axelsson and Lindgren, 1978; McBride et al., 1992). A few studies have also investigated hearing loss from the use of personal cassette players, or PCPs (Rice et al., 1987). Two excellent reviews have been published on noise exposure from leisure activities (Clark, 1991) and the hearing of classical musicians
INTRODUCTION
Exposure to loud music, especially among young people, is an important source of concern. It has been estimated that some young music lovers will have sustained significant permanent hearing loss by their mid-twenties (Carter et al., 1982). Discotheques and modern day ‘Fun Pubs’ have had a long-standing association with playing pre-recorded and amplified music for entertainment. The risk of hearing loss from amplified music is dependent on exposure duration, *Author to whom correspondence should be addressed. Tel: +44-121-414-6008 455
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(Palin, 1994). More recently, an epidemiological study on the evaluation of hearing damage from amplified music showed a gradation of audiometric damage from discotheques to PCP to rock concerts (Bisch, 1996). This study also reported a significant difference between the hearing thresholds of people who listen to PCPs for >7 h/week and those who frequently attended concerts when matched with control groups. Noise levels in nightclubs have been reported to frequently exceed 90 dB(A), with peaks as high as 109 dB(A) (Bickerdike and Gregory, 1980). In previous unpublished studies peak values from music in excess of 140 dB(A) have been recorded. The Institute of Hearing Research, in their review of hearing damage from leisure activities (Institute of Hearing Research, 1986), gave a mean 8 h Leq level of 95–98 dB(A) for discotheques. Whilst some data is available for discotheque attendees, very little attention has been given to noise exposure and the risk of hearing loss of employees in discotheques and other leisure or entertainment functions. Clearly the employees in such establishments are exposed more routinely and thus are at a greater risk of hearing damage. A detailed study of discotheques in Hong Kong showed that employees can be exposed to loud noises for up to 8.6 h/day, 6 days/week. In contrast, members of the public (18–30 age group) who attend discotheques are exposed, on average, to high noise levels for only 3.1 h on 1.5 occasions/week (Tan et al., 1990). Within entertainment venues there is a common core of employee types, namely management, bar staff, security and disc jockeys (DJs), who may be routinely exposed to high noise levels. The majority of these employees tend to be young adults working on a part-time basis and may show signs of subjective hearing loss, which may not be identified in its early stages. Furthermore, hearing loss patterns may change in young adults during the initial years of noise exposure. Studies on young adults exposed to music have reported shifts in maximum hearing loss with duration of exposure. Korpert and Winker (1994) measured hearing thresholds of 38508 people aged 14–18 yr from 1971 to 1991 and reported maximum hearing loss at 4 kHz at the start of the observation period, while at the end it had shifted to 6 kHz. Listening to music via stereo headphones was stated to be the major cause for the threshold shift. Modern nightclubs and discotheques provide a variety of styles of music, therefore it is possible that substantially different noise levels can be encountered on each occasion. These components have made it difficult for many researchers to calculate meaningful and accurate noise exposure levels, resulting in inconsistent study designs (Institute of Hearing Research, 1986). Furthermore, a number of studies have been limited by using audiometric data
alone, without noise exposure data or noise exposure data without audiometric data. The infrequent high sound exposure to music may produce temporary threshold shifts (TTS), transient hearing impairment in which there is an increase in the hearing threshold. The rate of TTS recovery varies in individuals from several minutes to several days (Clark, 1991). Repeated TTS over the course of a few weeks to a few years may lead to accumulated cellular damage, causing a permanent threshold shift (PTS). Although TTS cannot predict the extent of PTS, it is a good early indicator of permanent damage (Luz et al., 1973). A few studies have investigated TTS in pop musicians (Axelsson and Lindgren, 1978) and those attending rock concerts (Ulrich and Pinheiro, 1974). These studies showed moderate TTS (up to 30 dB at 4 KHz) with recovery within a few days of exposure. The extent of hearing loss amongst adults, especially younger adults, is becoming of increasing concern to both the government and prospective employers. Early signs of PTS may go unrecognized until individuals start their employment with companies who may routinely conduct pre-employment audiometry. However, pre-employment audiometry is not considered important or relevant in a number of work environments where individuals with hearing loss may not be identified nor made aware of risks factors. This pilot study focused on students who worked part-time (up to 16 h) in music bars and discotheques in a university entertainment venue. The aim of this study was to estimate typical sound levels and frequency characteristics of music played in clubs and to assess whether the student staff experienced TTS after noise exposure. The dependence of TTS on measured noise levels was also investigated, as well as knowledge and attitudes of noise levels and hearing loss amongst bar and security staff. METHODOLOGY
Music premises This study was conducted in a university Students’ Guild, which comprised three areas used for musical entertainment, i.e. bars and discotheques. All three areas had hard wooden floors and no soft furnishings. Area 1: bar. A bar room (10 × 30 m) open 7 nights/week. For 3 nights a coin-operated juke box provides music; on the other 4 nights music is provided by a mobile disco situated in the bar area. The number of customers determines the time the bar remains open, the earliest closing time being 23:30 and the latest 02:00. The music is furnished via a system of 10 speakers suspended from the ceiling, located in corners of the room.
Noise exposure and hearing damage at university entertainment venues
Area 2: discotheque and bar. A disco (13 × 20 m) with a bar open 3 nights/week from 21:00 until 02:00. Music is provided via a fixed system with two main speakers, both 2 m in height on a stage 6 m high, located ∼15 m from the bar. Area 3: discotheque. A disco (13 × 30 m) without a bar, which is used only when the number of attendees is expected to be particularly high. It is also used for occasional live music performances. The hall has a high ceiling (∼14 m), with a 2 m high speaker stack system in each of the four corners of the room. Selection of subjects for personal dosimetery and audiometry The Students’ Guild employed a total of 124 staff comprising 112 part-time and 12 full-time staff. The majority of the part-time staff were students who worked as either security or bar staff. All 124 staff were invited to complete a general noise survey questionnaire (see below). All 28 staff working in the three music areas over three sampling days were invited to participate in the study. This involved pre- and post-shift audiometry and wearing of a personal dosemeter for the duration of the workshift. All staff volunteers were given written information explaining the purpose of the study. Those who agreed and completed the consent form were then asked to complete a questionnaire to obtain information on exclusion conditions applied to the study group. The exclusion factors included one or more of the following: history of chronic ear disease, head injury or concussion, significant exposure to noise other than loud music (blasts or explosions at a close distance, shooting, motor sports, etc.), significant exposure to loud music within the past 24 h (which precluded participants from taking part on two successive days/shifts), prolonged or regular use of ototoxic drugs (antibiotics and anti-rheumatics) and perforated or damaged tympanic membranes. The staff who met the selection criteria underwent a visual examination of the external auditory meatus by the occupational health nurse. Examination of the aural canals was undertaken using a Keeler ophthalmoscope fitted with an auroscope attachment. If one or both outer ears were found to have an obstruction, subjects were excluded from the study. Audiometry Guild staff who met the basic criteria for selection underwent audiometry testing to establish TTS for each workshift. Pure tone audiometric testing was carried out before exposure at the beginning of each shift. Audiometry was conducted following the HSE guidelines (Health & Safety Executive, 1995) as closely as possible. Otoscopic examinations were undertaken immediately before testing. All equipment was maintained and calibrated according to the
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manufacturers’ instructions. Background noise levels in the audiometry test room were measured during the course of each pre- and post-test session using a hand-held grade 1 Rion SLM. The audiometry was conducted using a Kamplex Computer Audiometer model BA 20, fitted with a noise excluding headset. The pre- and post-shift audiograms enabled a comparison of hearing thresholds across the frequency range 0.5–8 kHz for both the right and left ears. Postexposure audiometry was conducted 10 min after finishing a shift and leaving the music areas. Noise exposure monitoring: personal and static The noise levels were measured in all three bars and discotheques (areas 1–3) over three consecutive days in a week in June 2000. Noise monitoring was conducted from 18:00 to 00:45 in area 1 and 21:00 to 02:15 in areas 2 and 3. The music functions planned for the week of the study were deemed to be typical of a mid-term week. A static monitoring point was established within each of the three music areas where employees (bar and security staff) of the Guild spent the majority of their time. A sound level meter (SLM) was placed behind the bars in areas 1 and 2 and close to where security staff spent most of their time in area 3. In each case the SLM microphone (fitted with a windshield) was attached to an extension cable and suspended from the ceiling ∼2 m above the floor and 0.5 m from any obstruction such as posts and light fittings. The static SLMs were set to record the ‘A’ weighted sound pressure levels and octave band analysis (OBA) data for the duration of the music being played. The OBA data was measured over the frequency range 63–8000 Hz. Following the pre-shift audiogram, bar employees were fitted with a personal noise dosemeter. Dosemeter microphones were attached to the shirt collar of the subjects. Due to the requirement for some of the staff to use radio communications with an earpiece, the dosemeter microphone was fitted to the collar on the opposite side to where the subject normally wore their earpiece. The battery powered dosemeter was clipped to the subjects’ waist belt opposite to the radio, to avoid the possibility of radio interference. The dosemeters were worn throughout the subjects’ shifts and removed prior to the postshift audiogram for that evening. SLM types and data handling Static noise levels and OBA data were collected using two portable grade 1 SLMs, a Rion NA29E and a Svan 912A. Both instruments were calibrated at 94 dB(A) before use and the calibration re-checked at the end of each sampling period. Personal monitoring was conducted with Brüel & Kjær 4428 and CEL 460 personal noise dosemeters. All dosemeters were class 2 with an accuracy of ±1.5 dB and all were cali-
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Table 1. Static noise measurements and calculated LEP,d Sampling duration (min)
Area 1 (juke box)
Area 1 (mobile disco)
Area 2
Area 3
315
375
315
320
Mean Leq [dB(A)]
88.7
98.3
97.8
93.1
Leq range [dB(A)]
82.6–95.2
87.5–101.9
92.9–103.7
86.6–101.7
Estimated LEP,d [dB(A)]
86.9
97.2
95.9
91.3
brated pre- and post-survey using calibrators specified by the dosemeter manufacturers. The stored data from the CEL 460 dosemeters were downloaded using CEL Sound Track v.1.2 and were transferred directly to a Microsoft Excel file for cleaning. The data recorded with Brüel & Kjær 4428 dosemeters were transferred manually. The following information was recorded from the dosemeters; sampling duration, noise dose (LAeq) and peak exposure level expressed in dB(A). The LEP,d values were calculated using LAeq values obtained from both the dosemeters and the static SLMs. General questionnaire A questionnaire was despatched using e-mail to all 124 Guild staff. The questionnaire was simple to complete and could be returned at no expense via e-mail. The questionnaire was divided into four sections detailing: • •
• •
length of employment, work shift patterns and exposure to amplified music at work; non-occupational exposure to music including PCPs, playing an instrument, attending live concerts, shooting, motor sports, etc.; use of hearing protection; knowledge and attitudes to noise levels and hearing loss.
Data analysis Once cleaned, the translated files from the sound monitoring equipment were imported into SPSS for analysis. One-way analysis of variance (ANOVA) and within subject t-tests were carried out to make univariate comparisons of the monitored staff and between the pre- and post-shift audiograms at the recorded frequencies. Using SPSS, the hearing thresholds for both ears were assessed and the results from the pre- and postexposure audiograms were correlated in order to establish whether there were any differences in hearing threshold post-exposure at different frequencies. Similarly, analysis was made to examine differences in TTS for both ears at different noise exposure levels and different audiometric frequencies.
RESULTS
Questionnaire respondents and survey subjects The university Students’ Guild employed 112 parttime and 12 full-time staff, which included 60 security staff (48%), 46 bar staff (37%), seven bar managers (6%), five security managers (4%) and six technicians/DJs (5%). Part-time staff (students) were permitted to work 16 h/week and, depending on job type, may work 2, 3 or 4 nights/week. Full-time staff worked a maximum of 45 h/week over 4 nights with occasional overtime. Over the duration of the study both the security and bar staff worked 4 nights of ∼10 h/shift. Of the 28 staff working in the three areas, 14 (50%) agreed to take part in the study, with some of the employees participating on more than one occasion. In total 21 pre- and post-shift audiograms were obtained. Four of the 14 subjects worked fulltime and four were females. The mean age of the student employees was 22 yr (range 20–25) and for full-time staff 33 yr (range 22–40). Noise measurements Table 1 shows the noise level ranges measured at the static monitoring points where most employees spent the majority of their time over the shift. The mean static Leq noise levels for the three entertainment areas ranged from 89 to 98 dB(A). The bars were in operation all the time whilst the music was being played, therefore the employees were exposed throughout the sampling periods shown in Table 1. Figure 1 shows the variation in the Leq values recorded at the static sampling points from 20:00 to 02:00. The LEP,d values for employees (bar staff) were calculated using the Leq static measurements and found to be in the range 87–97 dB(A) (Table 1). Although these values do not take account of short breaks that staff take during the evening they do provide an estimate of an 8 h equivalent noise dose for comparison with noise action levels as defined in the British Noise at Work Regulations 1989 (NAWR) (Health & Safety Executive, 1989). Octave band analysis was performed to determine the frequency spectrums for the music type played in the three areas. Figure 2 shows the OBA data for
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Fig. 1. 15 min Leq for the three music areas over 6 h.
Fig. 2. Octave analysis for two music areas, over 4 h band.
areas 1 and 2 over the duration of the sampling period. Figures 1 and 2 show that the noise intensity increased gradually from 21:30 to 00:30. The highest 15 min static Leq were recorded at 23:15 for areas 1 and 2 and 00:30 for area 3. The most prominent frequencies for area 1 were 500 and 1000 Hz and for
area 2 were 1000 and 2000 Hz. OBA data also showed that over the duration of the function the lower frequencies (250 and 500 Hz) became more prominent. Table 2 shows the results of the personal dosemetry for the bar and security staff. The mean
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Table 2. Staff personal exposure levels n Bar staff Security staff
Mean sampling time (min)
Mean Leq [dB(A)]
SPL (max) [dB(A)] Mean LEP,d [dB(A)]
8
310
89.8
112.9
87.7
13
345
94.2
123.6
93.7
Table 3. Mean threshold shifts on post-exposure audiograms for 13 of the 14 subjects (21 audiograms) Frequency (kHz)
P
Left
4.0
Right 8.2
