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|Year : 2005 | Volume
| Issue : 26 | Page : 3--9
The use of hearing protectors among forest, shipyard and paper mill workers in Finland--a longitudinal study
E Toppila1, I Pyykko2, J Starck1,
1 Finnish Institute of Occupational Health, Finland
2 Tampere University Hospital, Tampere, Finland
Finnish Institute of Occupational Health, Topeliuksenkatu 41 Helsinki
From 1953 to 1995 the usage rate of hearing protective devices (HPD) was tracked at a paper mill, a shipyard, and in selected areas of forestry work. For each work period, observations were made of HPD use among workers. In the paper mill, the usage rate increased steadily from 1965. In 1990, 39% of workers used HPDs full-time. At the shipyard, the usage rate remained low up to the mid-1980s, but thereafter the proportion of full-time users rose to 70%. A similar trend was noted in forest workers, with the full-time use at 97% by the 1990s. Due to the increased usage rate in all measured industries, the mean effective noise level at the ear has decreased to below 85 dB.
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Toppila E, Pyykko I, Starck J. The use of hearing protectors among forest, shipyard and paper mill workers in Finland--a longitudinal study.Noise Health 2005;7:3-9
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Toppila E, Pyykko I, Starck J. The use of hearing protectors among forest, shipyard and paper mill workers in Finland--a longitudinal study. Noise Health [serial online] 2005 [cited 2022 Aug 19 ];7:3-9
Available from: https://www.noiseandhealth.org/text.asp?2005/7/26/3/31645
In Europe, around 50 million people are exposed to potentially hazardous levels of environmental noise, facing a risk of noise-induced hearing loss (NIHL). The loss in economic terms is substantial, at a minimum 0.2 % of national net income. This equals about 400 billion Euros annually at European Community level (Rantanen et al, 2001). This includes direct and indirect costs related to production. The indirect costs do not include factors related to reduced quality of life. The quality of life includes: social isolation, increased unemployment and difficulties in family life due to communication difficulties related to hearing handicap.
Noise-induced hearing loss (NIHL) is considered to be one of the most common occupational health hazards of any country. When NIHL is moderate to severe, it leads to speech distortion, reduced word discrimination, noise intolerance and tinnitus. Reduced oral communication is a social handicap. NIHL also reduces the perception of warning signals, environmental sounds and music. Consequently, NIHL may lead to social isolation, decreased worker productivity and morale, and an increase of job-related accidents. There are no global or European Community figures available for the prevalence of NIHL. Such figures, if they did exist, would provide a database that would allow focused control methods to reduce the risk at national level and work place level; and even at an individual level.
During the early eighties in Finland, about 300 000 workers (Ministry of Labour, 1980) were daily exposed to noise levels exceeding the a weighted equivalent level of 85 dB, which is the action limit in Finland. This number decreased to about 200 000 workers by the mid-nineties (Tyo ja terveys Suomessa, 2000). The number of reported cases of noise-induced hearing loss was around 2000 in the beginning of the '80s and has decreased to between 1000 - 1300 cases (Riihimaki et al., 2004; Karjalainen et al., 2001) in the 1990s, tending to level at about 900 cases at 2000 [Figure 1]. This decrease is partially due to the diminishing number of people exposed to noise in their work environment. The efficiency of counter measures to noise is more difficult to demonstrate.
The most common counter measure is the use of Hearing Protective Devices (HPDs). In most cases, this should be sufficient, since the noise levels are generally below 95 dB in 90 % of the enterprises (Register on occupational exposures for physical and chemical agents, 1999). According to laboratory measurements (Comite Europeen de Normalisation (CEN), parts 1 and 2, 1993), most earmuffs on the market can provide more than 20dB attenuation against typical industrial noise.
In field conditions, the situation is more complicated as people lack motivation to use HPDs (Berger et al., 1983; Foreshaw and Cruschley, 1981). Several researchers have shown that laboratory tests overestimate the attenuation of the protectors under investigation (Foreshaw and Cruzhley, 1981; Casali and Park, 1991; Merry et al., 1992). Furthermore, if the protectors are in poor condition, the attenuation tends to further deteriorate.
When evaluating the performance of HPDs, one of the most important parameters is the usage rate (Toppila et al., 1998; Comite Europeen de Normalisation (CEN), 1993), which is the ratio of time the worker uses a hearing protector in relation to the duration of exposure to noise above 85 dB. The effective protection can be calculated using equation 1. When applying this equation it can be seen that the type of protector is insignificant, if the usage rate does not approach 100% [Figure 2].
In studies, the usage rate of hearing protectors has varied a great deal. Between 1953 and 1992 in the paper mill, HPDs were used 55% of all work hours (Nieminen et al., 2000). Recently, higher usage rates have been found at the shipyards at 70% (Pekkarinen, 1987), and in forest work at 90% (Pyykko et al., 1989). These studies were intended to analyse the risk of noise induced hearing loss (NIHL), and they combined all noise exposure together. They provided no information on whether any improvement in usage rates has occurred over time.
A new noise directive (2003/10/EC) shall be brought in to force the laws, regulations and administrative provisions necessary to comply with the directive latest 2006 (European Commission, 2003/10/EC, 2003). The new directive will fix the daily noise exposure levels and peak sound pressure for exposure limit values and exposure action values:
a) Exposure limit values: LEX,8h =87 dB(A) and P peak =200 Pa respectively.
b) Upper exposure action values: LEX,8h =85 dB(A) and P peak = 140 Pa respectively.
c) Lower action values: LEX,8h=80 dB(A) and P peak =112 Pa respectively.
When applying the exposure limit values, the determination of the worker's effective exposure shall take account of the attenuation provided by the individual HPDs worn by the worker. The exposure action values shall not take account of the effect of any such protection. In the risk assessment, the following factors have to be included: a) exposure to impulse noise, b) combined effects from the interactions between noise and ototoxic substances and between noise and vibrations, c) any effects concerning the health and safety of workers belonging to particularly sensitive groups. When the noise exposure level exceeds the lower exposure action values, the employer shall make HPDs available to workers, and HPDs shall be used where noise exposure levels match or exceed the upper action values. HPDs shall be selected to eliminate the risk to hearing or to reduce the risk to a minimum.
The purpose of this study was to determine in what way the use of hearing protectors has changed during the past five decades in large scale industries.
Methods and material
The cross-sectional sample included forest workers (N=100) from Northern Finland, as well as paper mill (N=406) and shipyard (N=176) workers. Data collection occurred in 1995 for the paper mill workers and in 1990 for the shipyard workers. For the forest workers, it was a part of a follow-up study that was conducted between 1972 and 1995 (Koskimies et al., 1992). Their respective occupational health care centres provided the data for the paper mill and shipyard workers. For the present study, information was collected on work exposure to noise and hearing protector use in different occupations. Complete work histories were obtained for 675 workers, and 7 workers were not included due to missing data. For exposure evaluation purposes the work histories were divided into work periods, during which the exposure level was relatively constant and the worker's occupation did not change. The total number of work periods between the years of 1953 and 1995 was 1873. The mean duration of a work period was 5.6 years ± 6.4 years and the duration ranged from 1 month to 35 years [Figure 3]. The work periods were classified based on their end date into categories of 5-year intervals. The first category consisted of work periods ending in 1951-1955 and the last one of periods ending in 1991-1995. The noise exposure was measured as A-weighted equivalence level by qualified industrial hygienists. During a normal working day, simultaneous measurements inside and outside the HPDs were conducted utilising a miniature microphone and a portable 2-channel noise dose meter (Pekkarinen, 1987; Chang-Chun et al., 1989). These measurements were done with 21 paper mill workers in 1985, 28 shipyard workers in 1986, and 20 forest workers in 1989. Each measurement consisted of a 10-minute sampling period. The workers used their own hearing protectors. The type of HDP depended on the workplace and remained relatively stable throughout the study. The real world attenuation of HPD was calculated as the difference between the mean sound pressure levels outside and inside the protector. At the paper mill, the mean noise level was 93 dB, 93-95 dB at the shipyard, and 95-97 dB in forest work. The mean attenuation of the HPDs was 15 dB in forest work, 17 dB at the paper mill, and 20 dB at the shipyard (Nieminen et al., 2000). The usage rate was collected using a written self-report questionnaire. The workers were asked to evaluate whether they use HPDs always, often, half-of the time, sometimes, or never. These usage rates were assumed to correspond to approximately 100%, 75%, 50%, 25% and 0% usage rates respectively. In order to take into account the usage rate and true attenuation the effective noise exposure level at the ear canal was calculated using the following formula (1).
L = noise level outside the HPD (Pekkarinen,1987 (dB(A))
L' =effective noise exposure level (dB(A))
A= measured attenuation of the HPD (dB) c= usage rate/100
The effective protection was obtained simply as the difference L-L'.
The time period between 1965 and 1970 marked the beginning of HPD use at the paper mill. Thereafter the mean effective protection of HPDs has continuously increased. Between 1991 and 1995, the mean effective protection was 12 dB when using formula 1. At the shipyard, the usage was low up to the mid-eighties, after which it increased rapidly. A similar phenomenon occurred in forest work [Figure 4]. The usage of HPDs in forest work started to increase at about the same time as at the shipyard. The difference between the start times of usage may be insignificant since the category of 1981-1985 consisted of only 4 forest workers. The second smallest category consisted of 25 forest workers for the work period ending in 1966-1970. The largest category consisted of 467 paper mill work periods ending in 19861990. Therefore, the category sizes are large enough with the exception of the smallest category.
In the late 1960s, only about 10% of the paper mill and shipyard workers reported that they used HPDs all the time. The forest workers reported no HPD use at all [Figure 5]. Twenty years later, reported full time use was 39% at the paper mill, 70% at the shipyard, and 97% in forest work [Table 1]. Part time usage was common in paper mill industry (22%), and in shipyard (17%), but not in forest work. The percentage of workers using HPDs part of the time was always less than 25%. The highest percentage was in the paper mill industry and lowest in forest work.
According to present Finnish legislation, employers must provide appropriate HPDs for the workers, and use is mandatory. However, when evaluating the worker's right for compensation due to hearing loss, the use of HPDs is not taken into account. Since the workers receive no monetary gain for overestimating their usage rate, the likelihood of overestimation is diminished. Additionally, to decrease bias, the questionnaires are anonymous in nature.
The study reveals two different patterns in the use of HPDs. At the paper mill, the number of users has risen slowly, though there is still far from full-time use, whereas in the forest work and at the shipyard the usage rate increased rapidly in the mid-eighties, and has remained high ever since. The reason for this may be that work clothes were introduced to the shipyards and in the forest industry. Earmuffs and helmets were included as part of the work uniform. At the paper mill, similar clothing was regarded as unnecessary. The new directive (2003/10/EC) assumes that protectors are used always when noise level exceed 85 dB. This study shows that this assumption is not always valid and thus efforts must be made to promote the use of hearing protectors. In risk assessment the protection efficiency of HPDs is taken into account. The protection efficiency is predictable only if the HPDs are properly fitted and users are motivated. There are several other factors such as cold/heat, comfort of HPDs, and variation of noise levels that affect the usage rates. The effect of these factors must be studied case by case.
During the course of the study, the attenuation of HPDs was assumed to have remained unchanged. This assumption is quite reasonable as the basic construction of protectors has been the same. Thus, the change in attenuation due to individual wear and tear of the HPD is larger than the change due to the use of a different model (Pekkarinen, 1987). Errors related to the usage rate evaluation are non-linear. At a high usage rate of close to 100 %, the effective protection is very sensitive to the rate; however, with a rate below 90 % this error becomes insignificant [Figure 2].
Hearing conservation precautions are progressing well in the enterprises included in this study. However, this progress cannot be generalised, since the enterprises under study are large ones, which traditionally take labour protection seriously. This is not necessarily the case with small and medium-size enterprises.
The results show that by the mid-eighties the enterprises concerned achieved a safe noise level. The mean age of a worker to develop compensated NIHL was over 50 years (Riihimaki & al 2004). The workers currently in their fifties were over 40 when they started to use HPDs, and thus have typically been exposed to hazardous noise for over 20 years prior to the use of HPDs. Most of the damage to their ears had already occurred before protectors were taken into regular use. Thus, it is reasonable to believe that in the near future a decrease in the number of compensated NIHL cases should be evident.
The usage of HPDs was at an adequate level in the forest work. In the mid-eighties, at the shipyard and the paper mill, the rates were still quite low, though a growing trend has been evident. There is no available data for the shipyard from between 1991 and 95, which prevents the examination of such trends at the shipyard. It is likely that the usage rate will increase due to growing risk awareness and the fact that young people are used to wearing protectors from the beginning.
The use of HPDs has increased to such a degree that it has had a real impact from the mid-eighties. This positive trend has not yet been reflected in the statistics of the compensated cases of NIHL, due to the fact that this kind of response is always delayed by several years. The usage rate is now at a very high level in forest work, but still has room for improvement at shipyards and paper mills.
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