Noise

Noise is unwanted sound that can cause impairments or damage to health. This article describes the problem of noise exposure at workplaces and the risk to health and safety of the workers. Different noise effects as hearing loss, physiological effects, work-related stress and increased risk of accidents are explained. The main sectors having noise problems are identified, including the music and entertainment sector. The noise assessment in accordance with the European Directive 2003/10/EC and the relevant measurement standards are explained. Different strategies of noise control are presented: noise control by design, choosing quiet machines, measures on the transmission path and organisational measures. 

Outline

Millions of employees in Europe are exposed to noise at work and all the risks this can entail. According to the European Working Conditions Telephone Survey 2021 (EWCTS 2021) 17% of the workers in the EU report that are often or always exposed to loud noise at work^[1]. Noise-induced hearing loss is one of the most prevalent recognised occupational diseases in the EU^[2] . While hearing loss is most obviously a problem in industries such as manufacturing, construction and agriculture, it can also be an issue in the entertainment sector, such as orchestras and discotheques. Exposure to noise also impacts communication and audibility, increasing the risk of accidents. Even relatively low noise levels can cause problems in the workplace because the noise is annoying and disturbing. Noise can give rise to stress reactions that have a detrimental effect on the ability to concentrate and on productive efficiency ^[3][4]. These problems are recognised for instance in call centres and sectors such as education and healthcare.

Hearing loss

Chronic hearing loss

Noise exposure at the workplace over many years may lead to irreversible hearing loss. A zero level of risk is difficult to determine but researchers agree that daily sound exposure levels of 75 dB(A) and lower pose little or no risk for noise-induced hearing loss. From 80 dB(A) and especially if levels reach or exceed 85 dB(A), people are at greater risk of permanent hearing loss^[5].

The incidence of noise-induced hearing loss can be described as follows: Following exposure to noise, for example during the working shift, the sensitivity of the ear is temporarily reduced. This can be demonstrated audiometrically as a temporary shift in the hearing threshold (temporary threshold shift). The affected individual has the sensation of his or her ears being blocked. The hearing may gradually recover if it is given a sufficiently long break. This may take hours or even days. If however the recuperation period is not sufficient for the sense of hearing to recover completely and partial deafness from the previous day is still present at the beginning of the next shift, a metabolic deficit (metabolic fatigue) remains which over a longer period causes the hair cells of the inner ear to die ^[6][7][8]. The consequence of this is a permanent hearing loss. Subsequent exposure to noise causes the symptoms to be worse over time.

Experience shows that the sense of hearing degrades with age, even in the absence of any particular adverse exposure to noise (age-related hearing loss – presbycusis) ^[9] . There is no cast-iron physiological rule that ageing must be accompanied by hearing loss. On average however, older people can generally be expected to have lower hearing sensitivity, particularly at higher frequencies. In this case, the damage can primarily be found in the inner ear. In addition, ageing may be accompanied by stiffening of the mechanism of the middle ear. This in turn also has an influence at low frequencies.

Noise-induced hearing loss is a particularly insidious condition, since it occurs virtually unnoticed by the affected individuals. They feel no pain and initially can communicate easily because hearing loss begins at higher frequencies around 4,000 Hz. Under continued exposure to noise, the hearing loss gradually spreads into lower frequency ranges including those of speech. As a result, the affected individuals have difficulty following a conversation, particularly in acoustically unfavourable environments and with strong background noise. The drop in hearing sensitivity with increasing age intensifies this problem. Ultimately, those who have suffered hearing loss are barely able to converse even in quiet environments, and easily become increasingly isolated. Hearing aids can compensate only partially for the hearing loss.

Acute hearing loss (acoustic trauma)

In addition to the hearing loss from long-term noise exposure (metabolic fatigue), direct structural damage to the hair cells may occur if a certain exposure threshold is exceeded^{[6] [10][11]}. In this case the hair cells break off as a result of excessive mechanical strain. This is described as traumatic or acute hearing loss.

A risk of acoustic trauma exists under exposure to extremely high noise pulses with peak sound-pressure levels L_Cpeak of 140 dB and higher, e.g. gunshots, explosions or the burst of a truck tyre can cause such high noise impulses. A single noise event of this kind may be sufficient to create permanent damage to an unprotected ear (i.e. in the absence of hearing protection). Acute acoustic trauma is often accompanied by perforation of the eardrum and ear bleeding after noise damage ^[12][13] .

Other causes of hearing loss

Noise is however not the only possible cause of hearing loss. Illnesses such as COVID-19 have been associated with a risk of developing sudden sensorineural hearing loss^[14]. Other reasons may be stiffening of the mechanism of the middle ear (otosclerosis), degenerative processes in the inner ear, exacerbated or premature ageing, infections, head injuries, certain forms of medication, and ototoxic substances (e.g. exposure to ototoxic chemicals at work)^[15]. 

Tinnitus

Noise-induced hearing loss may be accompanied by tinnitus. Tinnitus is usually described as the perception of phantom sound in the ears or head that are either temporary or permanent, following excessive sound exposure^[5]. For example, people with tinnitus may perceive a ringing or whistling sound that may be continuous or intermittent. One type of tinnitus arises from muscle spasms that cause clicks or crackling around the middle ear. Tinnitus can result from other causes than noise, e.g. neurological damage, ear infections, nasal allergies. Tinnitus may cause irritability, fatigue and sometimes even clinical depression^[16] .

Physiological effects, work-related stress

Employees may be distracted and irritated at work even by relatively low sound-pressure levels, upwards of approximately 30 dB(A). The causes include air-conditioning systems, PC cooling fans, and often conversations at adjacent workplaces. In the first instance, mental responses such as annoyance, tension and nervousness are observed^[3][4][17] . The reactions vary widely from person to person and are linked not only to the level of the noise exposure, but also to the complexity of the task performed, the individual's attitude to the noise, and their instantaneous physical and mental constitution. Exposure to noise above approximately 60 dB(A) is shown to lead to vegetative responses, for example increased respiratory and cardiac frequency, increased blood pressure and higher stress hormone values. These are clearly stress responses which, in conjunction with exposure over many years to other occupational stresses, may harm the cardiovascular or gastrointestinal systems^[18][19]. Multiple reviews indicate harmful effects of occupational noise on the cardiovascular system (i.e., hypertension)^[20]. The physiological and psychological effects of exposure to occupational noise can also negatively impact sleep among workers^[21]. Disruptive noise exposure and the associated stress responses have an impact upon the mental workload^[22][23] and work performance. This impact increases as a function of the complexity of the work to be performed ^[24]. The impact of noise can be offset in the short term by increased concentration and effort. Work procedures are checked more frequently or simple solutions sought. However, due to the associated effort and fatigue, lower productivity and a higher error rate must be taken into account. Therefore, investments in noise reduction measures can be profitable even at relatively low sound pressure levels, since they lead to higher productivity and quality.

Increased risk of accidents

Occupational noise exposure increases the risk of workplace accidents^[25]. Stress and a higher mental workload can bring about unsafe behaviour and startle reactions. In addition, higher noise levels obstruct the ability to hear warning signals, monitor equipment, react to environmental sounds (e.g. approaching forklift), and coordinate with other workers^{[24] [26]}.

Exposure to noise is a problem in every industry sector, even in office environments. The problem of noise induced hearing loss is most likely to be found in industries such as manufacturing, construction and agriculture . Data from the EWCTS 2021 show that the workers from the Construction and Transport sector indicate more often that they are exposed to loud noise in comparison with other sectors (figure 1)^[1].

Figure 1: Are you exposed to loud noise? By sector (%) – EWCTS 2021

Source: ^[1]

Data from the third European Survey of Enterprises on New and Emerging (ESENER-2019)^[27] show that around 30% of the establishments report the presence of loud noise as a risk factor. This percentage remained more or less the same between 2014 and 2019. The sector of the Construction, waste management, water and electricity supply has the highest percentage of establishments reporting noise as a risk factor (almost 60% in 2019) followed by Manufacturing (almost 50% in 2019) (figure 2)^[27].

Figure 2: Risk factor present in your establishment – loud noise (%) – ESENER 2019

Source:^[27] 

Within the framework of the 2007, 2013 and 2020 ad hoc modules of the EU labour force survey (EU-LFS) data are collected on work-related health problems. The survey brings together data on health problems and their causality as perceived by the respondents themselves and refers to all work-related health problems (physical or mental health problems) which the respondent had suffered during the year before the end of the reference week of the survey and which the respondent considered as being caused or made worse by his/her current or past job. 0,1% of the respondents in 2020 reported they suffered from a work-related hearing disorder in the previous year (figure 3)^[28]. 

Figure 3: Work-related health problems – LFS 2007, 2013, 2020

Source: ^[28]

EU-Directives with relevance to noise at work

The Noise Directive 2003/10/EC^[29] is an individual directive within the meaning of Article 16 of Framework Directive 89/391/EEC^[30]. It defines the minimum health and safety requirements regarding the exposure of workers to the risks arising from noise. This Directive replaced the previous Directive 86/188/EEC on the protection of workers from the risks related to noise exposure at work and it introduced lower exposure action levels and limit values in order to avoid hearing loss of the workers. Under the 2003 noise directive the employer is obliged to assess and, if necessary, measure the noise exposure of the workers. The defined exposure action values require different preventive measures when these values are exceeded (see section "Prevention measures based on the EU-Directive 2003/10/EC"). The exposure limit values, after taking account of the attenuation of hearing protection, must not be exceeded. The noise directive 2003/10/EC should be seen in the context of other directives:

• The Framework Directive 89/391/EEC of 12 June 1989^[30] states general principles of prevention and places obligations on employers to guarantee a safe working environment. The employer has to take measures necessary to avoid risks and to evaluate the risks which cannot be avoided. Workers must be provided information and training and are subjected to adequate health surveillance.
• The Machine Directive 2006/42/EC of 17 May 2006^[31] lays down essential safety and health requirements of machinery. It requires technical noise reduction at the source and a declaration of noise emission, which has to be part of the instruction manual and of the technical brochures used to sell the machine. In 2023, Directive 2006/42/EC has been repealed by Regulation (EU) 2023/1230 on machinery^[32]. This Regulation applies from 20 January 2027.
• The Council Directive 89/656/EEC of 30 November 1989 on the minimum health and safety requirements for the use by workers of personal protective equipmen^t[33]  (PPE directive) provides minimum requirements for the assessment, selection and correct use of hearing protectors (personal protective equipment).

Prevention measures based on the EU-Directive 2003/10/EC

The 2003 noise directive requires an up-to-date assessment of the risks from noise exposure at the workplace^[34]. The assessment and, if necessary, measurement of noise exposure shall be planned and carried out by competent services at suitable intervals applying objective measuring methods. Considering the actual state of standardisation this means, that the measurements should be performed according to the generally recognised standard ISO 9612^[35]. For the risk assessments according the directive the following noise parameters are used:

• noise exposure level L_EX,8h: A-weighted equivalent sound pressure level for a representative working day related to eight hours,
• peak sound pressure level L_C,peak: highest C-weighted peak level during a representative working day.

As a basis for the prediction of the risk and the decision on appropriate prevention measures the noise directive introduces exposure action values. Additional exposure limit values are defined in order to avoid irreversible damage to workers hearing. The limit values take account of the attenuation provided by individual hearing protectors worn by the workers, that is to say, the limit values correspond to the individual noise exposure of the ear. The defined action values and limit values are listed in table 1. 

Source: ^[36]

When these exposure values are exceeded, different prevention measures are required: 

If one of the lower exposure action values is exceeded (L_EX,8h ≥ 80 dB(A) or L_C,peak ≥ 135 dB(C))

• the employer shall ensure that the involved workers receive information and training on the risks resulting from noise exposure (Article 8),
• preventive audiometric testing shall be available for the workers, where the assessment indicate a risk to health (Article 10, §2),
• appropriate, properly fitting hearing protectors shall be made available to workers (Article 6, §1a).

If one of the upper exposure action values is exceeded (L_EX,8h ≥ 85 dB(A) or L_C,peak ≥ 137 dB(C))

• the employer is required to establish and implement a programme of technical and/or organisational measures intended to reduce the noise exposure (Article 5, §2),
• workplaces shall be marked with appropriate signs (Article 5, §3),
• workers shall have the right to have his/her hearing checked by a doctor or by another suitably qualified person under the responsibility of a doctor (Article 10, §2).

Exposure limit values (Exposure with respect to the attenuation of a hearing protector) (L_EX,8h = 87 dB(A) or L_C,peak = 140 dB(C))

• these limit values may in no circumstances be exceeded! (Article 3),
• if, despite of taken measures, exposures above the exposure limit values are detected, the employer shall take immediate action to reduce the exposure to below the limit values.

The particular characteristics of the music and entertainment sectors require practical guidance to allow for an effective application of the provisions laid down in the noise directive 2003/10/EC^[29]. Therefore, Member States are invited to develop practical guidelines which would help workers and employers in those sectors to attain the above-named levels.

Noise measurement strategies

ISO 961235  specifies the measurement and assessment of occupational noise and provides a stepwise approach to determine the noise exposure level L_EX,8h as an indicator for the risks from noise exposure at the workplace. Optionally the determination of the highest C-weighted peak sound pressure level L_C,peak is required. The procedure according to ISO 9612 contains the following steps: work analysis - selection of measurement strategy – measurements - uncertainty calculation. Three measurement strategies are offered:

• task-based measurement: the working shift of a nominal day is analysed and split up into a number of representative tasks, and for each task separate measurements are taken,
• job-based measurement: a number of random samples of sound pressure levels are taken during the performance of particular jobs,
• full-day measurement: sound pressure level is measured continuously over complete working-days.

The selection of the appropriate measurement strategy is influenced by several factors such as the complexity of the work situation, number of workers involved, effective duration of the working day, and amount of detailed information required. 

The Directive 2003/10/EC (Article 5) requires the risks arising from exposure to noise to be eliminated or reduced to a minimum taking account of technical progress and of the availability of measures to control the risk at the source^[34]. Different noise reduction measures are listed in the directive, such as 

• noise reduction by technical means,
• choose of other working methods,
• appropriate maintenance programmes for work equipment,
• organisational measures of noise control.

Noise control by design

Since machines can normally be considered the major source of noise in the workplace, the design of low-noise machines as required by the machinery Directive 2006/42/EC - as well as by Regulation 2023/1230/EU that will replace the machinery Directive in 2027 - is an essential measure to reduce noise at the workplace. The two parts of the standard EN ISO 11688^[37]  may assist the machine manufacturers in designing quieter machines: Part 1 explains the basic model of noise generation in machines distinguishing between airborne, liquid-borne and structure-borne sources. Additionally, a comprehensive guidance on how to influence the different sources, transmission paths and radiating surfaces is given. Part 2 provides an introduction into the physics of low-noise design. In order to quantify the effect of specific noise reduction measures some simple formulas for the physics of noise generation, transmission and radiation are presented.

Noise control by choosing quiet machines

The employer or operator of a machine is usually not in the position to change the fundamental design of the machine and to realise a low-noise machine by himself. But when buying new machinery they can use the noise emission declaration made by the manufacturer under the machinery directive (2006/42/EC). This declaration on noise emission should help the buyers of machinery identify low noise models and should give the producers of quiet machines an advantage on the market. Consequently, a low noise emission should become a quality parameter for machines. A machine with a high sound quality would emit less noise and should result in a reduced noise exposure at the workplace. On the basis of the declared noise emissions the potential customer can choose the machine with the lowest noise emission as intended by the 2003 noise directive. 

Noise reduction on the transmission path

Noise exposure in workspaces is composed of the sound directly emitted by machines and equipment and of the sound reflected by walls and ceiling. By giving ceiling and/or walls a sound-absorbing surface, it is possible to reduce the reflected sound and thus reduce the noise exposure at the workplaces concerned. It is important to consider room acoustics when planning new work areas, as a retrofit is usually much more elaborate and expensive. According to the 2003 noise directive, workrooms are to be designed so that the sound propagation conditions conform to the state of technology. Room acoustic parameters are not governed by European Directives, but some national regulations define values which are in accordance with the state of technology. Recommended values are also to be found in EN ISO 11690-1^[38] .

As the fitting of absorbing materials can be extremely costly it is useful to calculate the effect of different room configurations before installation. Depending on the initial situation, noise reductions of roughly 1 to 6 dB(A) can be achieved in the proximity of machines, and even 10 dB(A) and more at greater distance from the noise sources.

Organisational measures of noise control

The organisation of work can limit the intensity and the duration of noise exposure, for instance by:

• keeping the number of workers in noisy areas to a minimum,
• task rotation,
• scheduling noisy activities for when fewer workers are exposed,
• having appropriate work schedules with adequate rest periods,
• transfer noisy machines or activities in a separate room.

Noise reduction by personal protective means

There are many cases where a risk remains after all feasible noise controls are in place. If the remaining risks cannot be prevented by other means, workers should use individual hearing protectors:

• the employer must make individual hearing protectors available to workers, if the noise exposure exceeds the lower action values,
• the workers must use the hearing protector, if noise exposure matches or exceeds the upper action values,
• the individual hearing protectors should be selected to eliminate the risk to hearing and at least to reduce the exposure below the exposure limit values^[39].