Bringing The Noise Down

The increase in industrial production and machine operation speed has intensified noise generation in workshops. There is a need to ensure proper practices to protect workers from diseases associated with noise. By Vasiliki Dimou, Demokrition University of Thrace

Noise pollution can be the cause of a multitude of problems that that modern man is affected by, the most significant being: damage to hearing resulting in hearing loss, cardiac disorders, various health problems like high blood pressure, migraines, ulcer, asthma, pregnancy disorders, learning disabilities in children, loss of efficiency and concentration at work, and sleep disturbance.

At the workplace, exposure to high-level noise can seriously impair communication between employees and, depending on the level, frequency and duration of exposure, it can adversely affect workers’ physical and psychological health. 

One of the most serious consequences of high-level noise is the irreparable damage to human hearing. Exposure to high noise levels at work has been associated with a significant increase in work-related accidents. In addition, occupational noise-induced hearing loss is considered the most frequent work-related disease.

According to the 2nd European Survey on Working Conditions (ESWC), the workplaces that are most exposed to noise are (HSE, 1998):

- Metal Industries

- Timber Industries

- Base metal industries

- Paper industries

- Construction

- Fibre Industries.

Out of the above listed workplaces, the metal and timber Industries are the most hazardous noise-generating environments, on the grounds that they use a series of processes and a great number of machines for the shaping and handling of materials.

These processes produce extremely high and protracted volumes of noise at the workplace. For this reason, the European law sets certain limits to the exposure of workers to noise, according to which noise should, under no circumstances, exceed an average of 87 dB(A) on one hand and on the other for levels exceeding 80 dB(A), proper hearing protection (earplugs or earmuffs) is compulsory (MSFC-STD-267).

 

Adverse Health Implications

Hearing loss is listed among the occupational diseases included in Article 40 of Disease Regulations issued by the Greek Social Security Organization. The same document specifies that a minimum of five years of employment is required to officially recognise a hearing loss and establish it as an occupational disease.

Under the Control of Noise at Work Presidential Decree 85/91, the health of the workers receiving high noise doses should be protected. More specifically, the decree makes it imperative that employers take certain technical and organisational precautions, should levels reach 85 dB(A); in addition, maximum exposure limit for an eight-hour day is set at 90 dB(A).

Physicists use a logarithmic scale for measuring sound pressure level (SPL), namely the decibel dB scale. The decibel is a number that represents the logarithm of a ratio between a given sound pressure and a reference value. The decibel as a logarithmic unit has a very significant role in determining sound levels at workplaces: every increase of sound intensity equal to three dB(A) doubles the energy that the human ear receives, meaning that the double of 85 dB(A) is not 170 but 88 dB(A).

Most sound measuring instruments take into account the variations in the sensitivity of the human ear as far as the frequency of the sounds is concerned. For this reason, various frequency weighting methods have been developed to approximate the way the human ear responds to noise levels. The most widely used method of measurement is called ‘A-weighting’ and the equivalent unit of pressure is dB(Α).

Sustained exposure to 80 dB(Α) throughout the working day is considered to be the safety limit under which a worker does not run the risk of developing occupational noise-induced hearing loss. Noises equal to or exceeding 85 dB(Α) with continuous distribution in the range of acoustic frequencies (from 15 to 20.000Hz) are considered dangerous, regardless of exposure duration, necessitating the use of hearing protectors. 

Maximum permissible noise exposure is set at 115 dB(Α) for a period that does not exceed two minutes per 24 hours. Presidential Decree 85/1991, in accordance with the European Union Directive, requires the reduction of noise at its source so that a worker’s daily exposure does not exceed 90 dB(A). For this reason, when exposures exceed 85 dB(A), employers are obliged to supply workers with personal protective equipment (PPE). 

In the US, under the Occupational Safety & Health Administration, workers with daily exposures to an average noise level of 85 dB(A) or higher must be protected with the implementation of proper preventive measures (reduction of noise emissions, removal of noise sources) or with proper PPE. 

Workers who live in environments with high level noise have reduced opportunities for communication, the consequences of which are far-reaching since it is difficult for signals or warnings of danger to be heard.

 

Noise Level Of Woodworking Machinery 

A research was conducted in timber industries. Three typical sawmills, located in Drama, Northern Greece, were chosen, in which numerous measurements were carried out. The aim of the study was to assess noise generated by various timber processing machines, both at individual workstations and in its totality, as well as the extent of its impact on the staff, consisting of machine operators and the rest of the employees.

At the beginning, the machines were classified into groups depending on the kind of processing they performed. As a result, the following groups were formed:

- Cutting machinery (multi-rip saw, band saw, log cutter, edger, circular saw, planer—moulder, wood profile cutter);

- Planing machinery;

- Other machines (absorption machines, boilers).

Measurements were carried out while machines processed timber coming from spruce, beech, black pine and poplar sp. Subsequently, it was deemed equally necessary to conduct measurements in areas located outside the productive process, such as warehouses and offices, so as to acquire a complete picture of the problem and its effects.

All noise monitoring was conducted with a digital, portable sound level meter designed in compliance with DIN 45633, JIS 1502, IEC 651 specifications. During the sampling process, two kinds of measurements were performed: a) measurement of the overall noise pollution generated in the place, and b) measurement of the noise pollution recorded in each operator workstation. 

In total, seven locations were chosen in the general area and their selection was made on the basis of the layout of the place. Finally, it was decided that the individual workstations of the operators should be of the same number as the machines.

In each assessment site in the general area a total of 40 measurements were carried out (one every 15 seconds), whereas in each machine area 80 measurements were performed (40 with the machine in operation and another 40 with the machine in idling mode.) The processed timber was classified into two groups: the first contained logs of small dimensions, whose diameter in the middle was below 30 cm, whereas the second contained thick logs, with a diameter in the middle of over 30 cm.

 

Location & Length

From the data, it can be observed that noise levels are on average high (in excess of 90 dB(A)) in all sawmills and on certain occasions, they reached almost 99 dB(A). Cutting machinery produces the highest level of noise reaching approximately 97.46 dB(A), whereas planning machinery generates the lowest noise levels (an average of 88.76 dB(A)). 

The rest of the machines produce levels falling between these two extremes. It is noteworthy that all groups of machinery cause noise that is higher than the 85 dB(A) permissible level. The noisiest machines (producing almost 100 dB(A)) were found to be the wood profile cutter, log cutter and absorption machine, followed by multi-rip saw, planer and edger (around 95dB(A)).

Less annoyance is produced by the boiler, whose noise level is at an average of 85.32 dB(A). In other words, it can be seen that only the boiler is within the 85 dB(A) permissible noise limit. The results also reveal that the noise produced is higher in large width logs (with a mean diameter of over 30 cm). This is true for most cutting machines (such as the band saw).

It is noteworthy that in the general area, and not only in the proximity of a machine operator, noise levels are clearly in excess of 85 dB(A), reaching an average of approximately 90 dB(A). At an operator’s workstation, the difference between levels produced by a machine in operation and in idling mode is on average 1.5 dB(A). This difference is considered significant bearing in mind that a three dB difference in actuality means that the ear receives double energy.

The majority of the employees participating in the present study were between 35 and 45 years of age. When asked if noise was a nuisance during work, most of them answered that it was quite annoying but they have become used to it and, generally speaking, they had no hearing complaints. They also said that they made no use of earmuffs or plugs. Their tolerance toward an everyday problem such as noise pollution can be accounted for only by their short period of employment since most of them said that they had been working in sawmills for less than five years.

In the rest of the work areas noise levels are tolerable since they often drop below 55 dB(A) (such as in offices). As far as offices are concerned, as well as places where employee concentration is essential, international standards require that maximum noise exposure be set at 55 dB(A). Under Norwegian law, in jobs where critical communication is involved, noise levels must not exceed 55 dB(A).

According to the findings of the present study, noise levels generated in sawmills are generally above the rationally accepted exposure standards in all parts of the sawmill with the exception of the offices.

The highest volume of noise is emitted from the cutting machinery, especially the multi-rip saw, log cutter and wood profile cutter. The boiler is the only machine that does not exceed the 85 dB(A) permissible level.

The extent of annoyance is also in close relation with the dimensions of the material that is cut and the type of timber. The production area generally gives rise to high level noise, above the acceptable threshold, whereas in the offices and warehouses noise levels are comparatively low.

 

Necessary Measures

Workers and especially operators of most machines are exposed to such noise levels that it is quite possible that their health will be adversely affected on a temporary or permanent basis. The precautions that are necessary to be taken so as to reduce the amount and impact of noise are, first of all, the proper marking by the organisation of noise generating zones with suitable notices. 

In addition, it is imperative that a special program of hearing protection be implemented. In the attempt to improve the noise environment at the workplace, crucial preventive actions to be taken include control of noise at its source; this can be done with measures such as the design of the whole productive process in a specific area aimed at minimising the amount of noise-pollution.

Other measures that organisations can take include:

- Improve the design of machines (such as by supplying them with shock absorbers and anti-vibration mounting, installing protective Plexiglas enclosures). Where possible, use special covers, silencers and generally materials with strong anti-vibration capacity.

When technically feasible, reduce emission of noise by placing a barrier between the noise source and the employee (such as a sound-proof cabin).

- Increase the distance between the noise source and the worker.

- Use special sound absorbing materials on the walls, ceilings and floor of noisy areas. Provide workers with personal protective devices such as suitable earmuffs and plugs.

- Use tools and equipment with anti-noise design. Choose electrical tools instead of compressed air tools. Fit rubber pads that are specially designed to absorb vibration. Maintain equipment properly since poorly maintained machinery can increase sound emissions. Reduce the speed of cutting, sawing and spinning.

- Limit the amount of time an employee spends at a noise source. This can be implemented when workers take it in turns to spend time at very noisy areas.

- Provide quiet areas where workers can spend time in order to gain relief from hazardous noisy environments.

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