Physical Hazards of Noise and Protection Measures Report (Assessment)

Summary

This paper discusses some of the important aspects of noise as a physical hazard. Firstly, the physical characteristics of noise are discussed. Secondly, the main effects are examined with particular attention to noise–induced hearing impairment. In this section human perception of sound and the mechanism that result in hearing impairment are elaborated. Next the measurement of noise is discussed in much greater details. Finally, the mitigation measures for noise at workplace are looked at. It should be emphasized that due to the broad nature of the topic, the content presented here is by no means exhaustive. Further literature research on the subject may be necessary for some cases.

Introduction

According to the 2010 national hazard exposure worker surveillance report by Safe Work Australia, between 28 % and 32 % of the workers in Australia are exposed to non-trivial [≥ 85bB(A)] loud noise generated during their work(Safe Work Australia 2010). The report also states that workers generally have inadequate training on how to prevent hearing damage with only 41% percent of workers have received such training (executive summary). This report is in agreement with that of BHP Billiton conducted in 2003 whose findings indicated 51% of employees in Australia who do not use hearing protectors are exposed to noise levels above exposure limits (Australian Safety and Compensation Council (ASCC)2006). Kumis and Apps (2007) have also found out that a majority of Australian workers are affected by preventable occupational noise-induced hearing loss(NIHL) (127). Data from the Noise exposure and the provision of noise control measures in Australian workplaces 2010 report from National Hazard Exposure Worker Surveillance (NHEWS) survey show that a high percentage of workers (>40 %) exposed to loud noise(above 84bBA) are found in manufacturing, construction, transport, storage, agriculture, forestry and fishing sectors (ASCC 2006). NIHL also continue to exert considerable economic burden on the national government for example in the period 1998/99 to 2001/02 NIHL it represented 19 % of all disease related-claims (ASCC 2006).

Effects of noise

Sound can be defined as dynamic changes in pressure above and below the ambient pressure of a medium that has elasticity and viscosity (Ostergaard 2003, p. 20). The fluctuations areas due to the oscillatory motion of the particles of the medium. Liquids gases and solid produce different sounds due to different molecular arrangements. Noise has been defined as unwanted sound that may impair hearing and cause other health effects (SafeWork SA 2008, p.4). Broadly, sources of noise can be categorized into two: community noise and Industrial noise. Some of the community noise sources include: transportation, hobbies (e.g. amplified music), recreation (radios, TV, motor races etc) and air conditioners. Industrial sources include factories, textile industries, airplane industries etc. Noise in industries is generated by processes such as drilling, blasting, cutting, material handling, ventilation, crushing, conveying and raw material processing (Donoghue 2004, p.283). Passchier-Vermeer and Passchier (2000) analyzed the evidences for several health effects that have been associated with occupational noise exposure. They found sufficient evidence of noise on hearing impairment, elevated blood pressure, Ischemic heart disease, sleep and awakening pattern, elevated heart rate and moodiness (Passchier-Vermeer & Passchier 2000, p.125). However they cited evidences for other putative noise effects as “limited” in regard to Immune based effects, birth weight, psychiatric disorders, jobs absenteeism, psychosocial well being, hormone levels and performance next-day (125). Hearing impairment is the most researched effect of occupational noise exposure(Conche-Barrient, Campbell-Lendum & Steenland 2004, p.4).Permanent Noise-Induced Hearing Loss(NIHL) results from irreversible damage to the inner ear (Spellman & Bieber 2011,p.11). Studies have shown that there is increased risk of hearing impairment at sound levels of 90 dB(A) while a lifetime noise exposure at 85 dB(A) presented a “marginal risk” for the same (Lutinan 2000, p.274). The damage can be due to exposure to sudden or prolonged excessive sound level. Very loud noise may cause temporary threshold shift lasting for hours that may be accompanied by a ringing sensation called tinnitus. Repeated and prolonged exposure to excessive noise may result in permanent threshold shift characterized by a much serious hearing impairment. Consequences of NIHL include social isolation, impaired communication, decreased work performance, susceptibility to injuries, treatment/management expenses among others (Conche-Barrient, Campbell-Lendum & Steenland 2004, p.4).

Noise measurements and quality assurance

Noise measurement is an important step in developing noise control strategies. Noise is measured to assess compliance with legal exposure levels, license requirement, or to investigate a noise complaint (Noise Measurement Manual 2000, p.3). Most countries require noise assessment be carried out by a certified industrial hygienist. Audiologist or a technician with sufficient training can also be allowed. The method of measuring noise depends on policy of the zone of assessment and the type of working premise being investigated. Measurement may be conducted outdoor, indoor or at remote locations. Noise or sound is as a result of small changes in atmospheric pressure brought about by alternating compression and expansion of air that propagate in all directions from a source (Passchier-Vermeer and Passchier 2000, p. 123).Sound can be characterized by the magnitude of pressure variation and its frequency (Cherrie, Howie & Semple 2010, p.147).The sound pressure range from <20 micropascal to > 200 Pascal. However measuring sound in pressure units (Pascal) would give very large values. To correct this, a logarithms scale of sound pressure is therefore used to obtain shorter figures for sound and noise exposure measures (Passchier-Vermeer and Passchier 2000,p. 123).The unit of measurement of sound pressure level is decibel(dB).In the decibel scale,0dB, reference level is equivalent to 20 µPa.The human ear is not equally sensitive to sound of different frequencies (Passchier-Vermeer and Passchier 2000,p. 123). It responds best in the middle (e.g. 500 Hz to 4000 Hz) and high frequencies and worst in low frequencies (SafeWork, Southern Australia (SA) 2008, p.2).Thus “a spectral sensitivity factor is used that rates sound pressure levels at different frequencies in a way comparable to the human ear” (Passchier-Vermeer and Passchier 2000,p. 123). One of these sensitivity factor is the A-weighted sound pressure level (L) expressed as dB (A) and referred to as sound level (Passchier-Vermeer and Passchier 2000, p. 123).Sound level is the basic metric from which other measurements for long term exposure to noise are derived (Passchier-Vermeer and Passchier 2000, p. 123).To measure variations in sound levels at different workplaces a number of indices have been developed. A common one is the equivalent continuous sound level over a period of time, T (L_Aeq, T). L_Aeq is defined as “a steady level that would have emitted the same “A” weighting sound energy over the same time as the actual fluctuating noise” (Gardiner & Harrington 2005, p.232) Common occupational exposure period, T is 24hours and 8 hours. Another parameter, Single event noise exposure level (L_AX ), is used for short duration exposure and it represents the level “which if lasted for 1 second would emit the same energy as the actual event”( Gardiner & Harrington 2005, p.232).Additionally, Statistical levels (L_n) used include L₁₀ for measuring the peak of unsteady noise and L₉₀ for assessing “background” noise. Occupational measurement of noise would involve the use of Sound Level Meter (SLM) to determine noise above permissible limits. To determine individual noise dose of workers, a dosimeter is used. The basic components of a typical dosimeter or SLM is a microphone that converts sound waves to electrical impulse and an electronic circuitry that modifies and amplifies the signal according to the demands of the user (Cherrie, Howie & Semple 2010, p.148).The three main types of noise measuring equipment are Sound Level Meter (SLM), Integrated Sound Level Meter(ISLM) and Personal Noise Dosimeter (PND)( Cherrie, Howie & Semple 2010, p.148).SLM and ISLM are held by the person measuring while the PND is worn by the worker being assessed. The dosimeter is usually positioned near the hearing zone of the worker say shirt collar in the course of normal work shift. Dosimeter can provide real time measurements sound level and duration in terms of dose, time-weighted average and parameters such as peak level, equivalent sound level and sound exposure level (Franks, Stephenson & Merry 1996, p.88). The choice of the SLM will depend on the area of usage.Type-0 are commonly used as standard laboratory reference, Type-1 for lab and field use in specified controlled environment and Type-3 for noise surveys(“Noise pollution and its control”). Type-2 is for general use. The SLM used must comply with relevant precision standards defined by the Australian Standard. The time constants used for the SLM standards are slow (S) of 1 second and Fast (Fast) of say 125 milli seconds. Relatively standard sounds are measured using the “fast” response while unsteady sound use “slow” response (“Noise pollution and its control”).Graphic recorders may also be attached to SLM. To measure impulse noise levels such as hummer blows, impulse meters are used. Calibrators are required for checking the accuracy of the SLM. To ensure accuracy and stability of a sound level meter and to reduce to the minimum any differences in equivalent measurements taken with instruments of various makes and models, quality control and checking procedures must be included as part of normal operations (Noise Measurement procedures manual 2004, p. 14).In Australia, like in many other developed nations, the acceptable occupational noise limit is 85 dB (A) for an 8-hour work shift. A-weighted sound pressure above 85dB (A) and a C-weighted peak sound pressure level of 140 dB(C) all referenced to 20µPa are considered “excessive noise” (Workplace Health and Safety Regulation 2008, sect. 138 p.116).

Sampling methodology

A general order of measuring noise using a Sound Level Meter may involve first checking the battery to ensure it has enough power to last throughout the measurement period. Next the instrument and its calibrator should be left to attain temperatures equivalent to that of the assessment area. Afterward the Instrument can be switched on to “warm up”. The Instruments can then be calibrated with their calibrators and set to “slow response” based on the usage manuals. Before actual measurement, the memory must be reset to clear all previous measurement. To commence actual measurement, the microphone is turned on. The recording session is started and start time is noted. At the end of the sampling period, the measuring instrument is stopped, removed from the worker’s body and final reading recorded. The measuring instrument should be recalibrated at the end of the sampling. The validity of the result will be determined by the degree of discrepancy between the two calibrations with respect to the applicable Australian standard (Safe Work Australia (Western Australia) 2005). For static measurement, the SLM is set to dB (A) or dB(C) for daily and peak exposure assessment respectively. In this type of measurement, the instrument should be held at arm’s length from the body and at the required distance from the ground (Cherrie, Howie & Semple 2010, p.154). where noise measurement targets a worker, the microphone is held closer to the ears of the worker one at a time and readings are recorded. For personal noise dosimeters (PND) it is required that the microphone be directed towards the major source of noise in case of multiple sound sources. Also, workers with the PND should be briefed about handling of the devices as any slight impact on it will result in incorrect measurement. The final measurements should be explained to the management and employees and copies be sent to the necessary authorities if required. To minimize blocking effect of the measurer’s body the instruments may be placed on a tripod or held at a specific distanced(based on manufacturers manual) by a cable or flexible boom (Cherrie, Howie & Semple 2010, p.154). During measurement background noise and presence of reflective noise from say worker’s hand held tools should not be ignored. These factors may significantly raise the final reading and hence affect the validity of the measurement results. Most standards require a separate measurement for background noise. When the type of measurement is meant to be the basis for selecting hearing protectors, it may be necessary to measure intensity of noise at each octave to obtain protectors that match the frequency of the noise. In this case, class 1 SLM with octave band facility and suitable calibrators for the SLM’s microphone are used (Cherrie, Howie & Semple 2010, p.157). Errors in noise dosimetry can be caused by windy weather especially for outdoor measurement. This can be minimized by using porous foam shield over the microphone (Cherrie, Howie & Semple 2010, p.155).Reflection from the worker’s body or hand-held tools may also increase readings.

Potential errors and minimization

Noise measurement results are affected by a number of factors which should be taken into account. SLM or a dosimeter microphone can record higher reading in windy weather. To minimize this error, a microphone windshield can be used. Also, the state temperature, wind speed, wind direction, cloud cover, relative humidity and rain condition during the measurement should be recorded alongside the results (Noise measurement procedures manual 2004, p.16). Physical obstruction such as nearby workers near a measuring microphone may also influence final results. In such cases extension cable or remote control should be used as directed by the devices manufacturer. To avoid errors, all the measuring devices must be ensured to be in good order before the start of measurement. Reflecting surfaces such as buildings, topographical features (fence or dense hedge) should also be completely avoided (Noise measurement procedures manual 2004). However, most noise manual will provide ways to conduct measurement in such areas. Other features likely to influence results include tonality (e.g. whining, droning), modulation (e.g. siren) and impulsiveness (e.g. banging or thumping) (Environment Protection (Noise) Regulation 1997, summary of regulation). In case where these characteristics cannot be eliminated during noise measurement they should be factored in the measured levels.

Operator safety

Although noise measurement does not pose an injury risk, precaution should be taken personnel undertaking the measurement against drowning, injury, contracting water-borne diseases and loss of equipment (Noise measuring manual for use in testing compliance 2000, p.4). For protection against solar UV radiation and exposure to aerosol mists, the measurer should protect skin by applying sunscreen to vulnerable areas such as back of neck, hands and knees. A safety helmet should also be worn to protect against falling objects especially in the designated areas. Wide brimmed hats can also be worn to protect the head, tips of ears and neck from UV radiation. If the measurement is to be conducted in industrial premises with heavy equipment, safety boots with steel toe caps and instep protection should be worn. To lessen the discomfort from noise in the zone of measurement, ear muffs and plugs can be worn.

Frequency analysis

To make it easy to investigate noise by measuring sound pressure at varying frequencies, the range at which the ear perceives low and very high frequency is divided into bands (Gardiner and Harrington 2005, p.227). Each band is one octave wide. The bands are labeled based on the geometric mean of the upper and lower frequencies of the constituent bands. Standards bands have mean frequencies of 63, 125, 250, 500, K,2K, 4K and 8K Hz. Band analysis is useful in investigating frequency distribution of noise (Gardiner and Harrington 2005, p.227). ¹/₃ octave bands are preferred as they give “less loss of detail” during evaluation (Gardiner and Harrington 2005, p.227).

Applicable Legislation and Standards in Australia

Noise regulation laws in Australia although based on same standards defined by Australian Standards are not consistent nation-wide. All states and territories have their local regulations. For example, workplace noise exposure is regulated by the Occupational Health, Safety and Welfare Regulation 1995, in Southern Australia, Workplace Health and Safety Regulation 1997 in Queensland, Environmental Management and Pollution Control (Miscellaneous Noise) Regulations 2004 in Tasmania and Environment Protection (noise) regulation 1997(Revised 2008) in North Western Australia to mention just but a few.

Some of the applicable standard related to noise pollution are: standard AS/NZS 1270 for Acoustic hearing protectors, AS/NZS 1269 for occupational noise management, standard AS 1259 for sound level meters, AS/NZS 4476 for acoustic octave-band and fractional octave band filters, AS1055 for Description and measurement of environmental noise and standard AS2659 guide to the use of sound measuring equipment (portable sound level meter)

Noise control and Hearing protectors

Noise control is aimed at reducing hazardous exposure to the point where the risk to hearing impairment is reduced to the minimum possible level. Noise management may involve a systematic implementation of engineering and administrative controls in addition to augmentation by hearing protectors but only as final abatement measure. Engineering controls can be employed and resolve noise problems for most noise sources (Frank, Stephenson & Merry 1996, p.19). Engineering control in noise management can be defined as “any modification or replacement of equipment, or related physical change at the noise source or along the transmission path (with the exception of hearing protectors) that reduces the noise level at the employees ear”(Frank, Stephenson & Merry 1996, p.19). Strategies for engineering control involve reducing noise at the source, interrupting the noise path, reducing reverberation, and reducing structure-borne vibration. The implementation of such controls may constitute installing a muffler, erecting acoustical enclosures and barriers, installing sound absorbing material, installing vibration mounts and providing proper lubrication (Frank, Stephenson & Merry 1996, p.19). Businesses and factories are also encouraged to “buy quiet” by purchasing machinery with low noise output. Administrative measure to limit employees exposure to excessive noise may include workers rotation, labeling of noise-hazardous areas and equipment, training employees on noise effect, sources and use of hearing protectors, implementation of hearing conservation program, formulating operation standards for excessively noisy tasks among others(Spellman & Bieber 2011,p.41). When engineering and administrative controls fail to yield appreciable results, employers must implement and monitor various approved hearing protectors. These include expandable form plugs, moulded plug, reusable plugs, canal caps and ear muffs.

Conclusion

Noise at work place and also in the general public is a serious concern going by the volume of literature pertaining to its study and impact on the health of the general population. This is because prolonged excessive noise has been shown to cause adverse effects such as permanent noise-induced hearing loss.

Statistics show a significant number of Australian workers are affected by noise at workplace. The national government is also affected as individuals with permanent loss of hearing continue to draw support claims. Scientific evidence of effects of noise has forced to take measure to ensure that workers and the general public are not exposed to dangerous levels of noise. Occupation hygienist are charged with the task of conducting noise assessment at workplace. Noise measurement is conducted using a set of tools, namely: the Sound Level meter and dosimeters. The Australian standard develops standards with direct the usage of these instruments and the analysis of their findings. These standards have been incorporated into noise regulations of many states and territories of Australia.

Premises that by nature of their operations produce loud noise are supposed to undertake control measure if their noise levels exceed permitted limits. Engineering and administrative control strategies form the first step in reducing excessive noise level. When these two controls fail to yield significant reduction in sound levels, hearing protectors such as ear muffs and earplugs must be used.

Reference List

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