Limitations of using dosimeters in impulse noise environments

The National Institute for Occupational Safety and Health (NIOSH) investigated the capabilities of noise dosimeters to measure personal exposure to impulse noise. The two leading types of commercially available dosimeters were evaluated in terms of their ability to measure and integrate impulses generated from gunfire during live-fire exercises at a law enforcement indoor firing range. Sound measurements were conducted throughout the firing range using dosimeters, sound level meters, and a measurement configuration that consisted of a quarter-inch microphone and a digital audiotape recorder to capture the impulse waveforms. Personal dosimetry was conducted on eight shooters, an observer, and the range master. Peak levels from gunfire reached 163 decibels (dB), exceeding the nominal input limit of the dosimeters. The dosimeters "clipped" the impulses by acting as if the gunfire had a maximum level of 146 dB. In other cases, however, peak levels (e.g., 108 dB) were below the dosimeter input limits, but the dosimeters still showed a peak level of 146 dB. Although NIOSH recommends that sound levels from 80 to 140 dB (A-weighted) be integrated in the calculation of dose and the time-weighted average, our present data suggest this criterion may be inadequate. These results showed that some instruments are incapable of providing accurate measures of impulse sounds because of their electroacoustic limitations.     

Impulse noise in industrial plants: statistical distribution of levels

Impulse noise generated by industrial machines and occurring at a workplace is a cause of substantial hearing loss in workers. The paper presents data on workplace impulse noise, recorded in three plants of the machine industry. The data were collected in drop-forge, punch-press and machinery shops. The results of the measurements are shown as cumulative relative frequency distributions of the C-weighted peak sound pressure level, L(Cpeak), the A-weighted maximum RMS sound pressure level (SPL), L(Amax), and the A-weighted sound exposure level, L(EA) of isolated acoustic impulse noises. The survey shows that in the drop-forge shop over 90% of acoustic impulses generated by hammer strikes exceed permissible levels of L(Cpeak) = 135 dB and L(Amax) = 115 dB. In the stamp-press shop, only 10-20% of impulses generated during the technological process exceed maximum permissible levels.     

Investigation of sound level conversion as a means of rating ear protector performance.

Sound level conversion, a single-number measure describing the noise reduction afforded by ear protectors, was calculated for 30 ear protectors in 615 industrial noise spectra. The results vindicate the utility of this measure for situations in which the noise hazard is characterised only by C- and A-weighted sound levels. A simple procedure for calculating SLC, accurate within +/- 1dB, is proposed. Minor adjustments of the calculation procedure enable wearer protection rates in the range 50% to 97% to be achieved.     

两种噪声强度测定法用于噪声作业岗位卫生学评价的比较

目的　探讨两种不同方法对工作场所的噪声强度进行测定的效果 ,为噪声作业岗位的卫生学评价提供科学依据。方法　选择有噪声作业的 3个场所 ,且噪声是不连续、非稳态噪声 ,分别用瞬时测定方法和等效连续A声级测定方法对噪声强度进行测定。结果　用瞬时测定方法测得 3个工作场所A、B、C的噪声强度分别是 89 6dB(A)、95 3dB(A)和 92 7dB(A) ,3个工作场所的噪声强度都超过国家职业卫生标准。用等效连续A声级方法测得 3个工作场所的噪声强度分别是 83 8dB(A)、92 5dB(A)和 88 7dB(A) ,根据国家职业卫生标准 ,工作场所A噪声强度未超标 ,工作场所B、C噪声强度超标。结论　对于不连续、非稳态噪声 ,用等效连续A声级方法测定噪声强度比瞬时测定方法更科学合理 ,更客观反映劳动者接触噪声的实际情况     

Low frequency noise and annoyance

Low frequency noise, the frequency range from about 10 Hz to 200 Hz, has been recognised as a special environmental noise problem, particularly to sensitive people in their homes. Conventional methods of assessing annoyance, typically based on A-weighted equivalent level, are inadequate for low frequency noise and lead to incorrect decisions by regulatory authorities. There have been a large number of laboratory measurements of annoyance by low frequency noise, each with different spectra and levels, making comparisons difficult, but the main conclusions are that annoyance of low frequencies increases rapidly with level. Additionally the A-weighted level underestimates the effects of low frequency noises. There is a possibility of learned aversion to low frequency noise, leading to annoyance and stress which may receive unsympathetic treatment from regulatory authorities. In particular, problems of the Hum often remain unresolved. An approximate estimate is that about 2.5% of the population may have a low frequency threshold which is at least 12 dB more sensitive than the average threshold, corresponding to nearly 1,000,000 persons in the 50-59 year old age group in the EU-15 countries. This is the group which generates many complaints. Low frequency noise specific criteria have been introduced in some countries, but do not deal adequately with fluctuations. Validation of the criteria has been for a limited range of noises and subjects.     

A comprehensive investigation of noise exposure in and around an integrated iron and steel works

A comprehensive environmental noise exposure study was carried out in and around a major iron and steel works. The works was located in the central part of the city and was surrounded by residential, commercial, and sensitive receptors. Traffic activity near the plant was significant and added to the background noise level. Considering the variety of noise sources in the plant area and in the neighborhood, a practical approach to measure noise equivalent level in the plant and in the residential, commercial, industrial, and silence zone was adopted. A modular precision integrating sound level meter with statistical analyzer module, octave filter set, and calibrator were used during the measurements. The day and night level, Ldn, was determined. Worker exposure was assessed by determining the speech interference level (SIL), loudness level, and noise rating level at one of the major sources located in the power plant of the steel works. The results indicate that SIL was 94 dBA, loudness level was 112 phons, and the noise rating was in the range of 85-95. A traffic noise index also was determined near the works gates and was in the range of 68-96. The impact on the community is significant as observed from Ldn levels. Some mitigation measures for noise control are also discussed.     

Estimating occupant satisfaction of HVAC system noise using quality assessment index

Noise may be defined as any unwanted sound. Sound becomes noise when it is too loud, unexpected, uncontrolled, happens at the wrong time, contains unwanted pure tones or unpleasant. In addition to being annoying, loud noise can cause hearing loss, and, depending on other factors, can affect stress level, sleep patterns and heart rate. The primary object for determining subjective estimations of loudness is to present sounds to a sample of listeners under controlled conditions. In heating, ventilation and air conditioning (HVAC) systems only the ventilation fan industry (e.g., bathroom exhaust and sidewall propeller fans) uses loudness ratings. In order to find satisfaction, percent of exposure to noise is the valuable issue for the personnel who are working in these areas. The room criterion (RC) method has been defined by ANSI standard S12.2, which is based on measured levels of in HVAC systems noise in spaces and is used primarily as a diagnostic tool. The RC method consists of a family of criteria curves and a rating procedure. RC measures background noise in the building over the frequency range of 16-4000 Hz. This rating system requires determination of the mid-frequency average level and determining the perceived balance between high-frequency (HF) sound and low-frequency (LF) sound. The arithmetic average of the sound levels in the 500, 1000 and 2000 Hz octave bands is 44.6 dB; therefore, the RC 45 curve is selected as the reference for spectrum quality evaluation. The spectral deviation factors in the LF, medium-frequency sound and HF regions are 2.9, 7.5 and -2.3, respectively, giving a Quality Assessment Index (QAI) of 9.8. This concludes the QAI is useful in estimating an occupant's probable reaction when the system design does not produce optimum sound quality. Thus, a QAI between 5 and 10 dB represents a marginal situation in which acceptance by an occupant is questionable. However, when sound pressure levels in the 16 or 31.5 Hz octave bands exceed 65 dB, vibration in lightweight office construction is possible.     

Rock drills used in South African mines: a comparative study of noise and vibration levels

OBJECTIVES: To compare the noise and vibration levels associated with three hand-held rock drills (pneumatic, hydraulic and electric) currently used in South African mines, and a prototype acoustically shielded self-propelled rock drill. METHODS: Equivalent A-weighted sound pressure levels were recorded on a geometrical grid, using Rion NL-11 and NL-14 sound level meters. Vibration measurements were conducted on the pneumatic, hydraulic and electric drills in accordance with the ISO5349-1 (2001) international standard on human exposure to hand-transmitted vibration, using a Brupsilonel and Kjaer UA0894 hand adaptor. PCB Piezo accelerometers were used to measure vibration in three orthogonal directions. No vibration measurements were conducted on the self-propelled drill. RESULTS: All four drills emitted noise exceeding 85 dB(A). The pneumatic drill reached levels of up to 114 dB(A), while the shielded self-propelled drill almost complied with the 85 dB(A) 8 h exposure limit. Vibration levels of up to 31 m s(-2) were recorded. These levels greatly exceed recommended and legislated levels. CONCLUSIONS: Significant engineering advances will need to be made in the manufacture of rock drills to impact on noise induced hearing loss and hand arm vibration syndrome. Isolating the operator from the drill, as for the self-propelled drill, addresses the problems of both vibration and noise exposure, and is a possible direction for future development.     

Compressed air noise reductions from using advanced air gun nozzles in research and development environments

The aims of this study were to evaluate sound levels produced by compressed air guns in research and development (R&D) environments, replace conventional air gun models with advanced noise-reducing air nozzles, and measure changes in sound levels to assess the effectiveness of the advanced nozzles as engineering controls for noise. Ten different R&D manufacturing areas that used compressed air guns were identified and included in the study. A-weighted sound level and Z-weighted octave band measurements were taken simultaneously using a single instrument. In each area, three sets of measurements, each lasting for 20 sec, were taken 1 m away and perpendicular to the air stream of the conventional air gun while a worker simulated typical air gun work use. Two different advanced noise-reducing air nozzles were then installed. Sound level and octave band data were collected for each of these nozzles using the same methods as for the original air guns. Both of the advanced nozzles provided sound level reductions of about 7 dBA, on average. The highest noise reductions measured were 17.2 dBA for one model and 17.7 dBA for the other. In two areas, the advanced nozzles yielded no sound level reduction, or they produced small increases in sound level. The octave band data showed strong similarities in sound level among all air gun nozzles within the 10–1,000 Hz frequency range. However, the advanced air nozzles generally had lower noise contributions in the 1,000–20,000 Hz range. The observed decreases at these higher frequencies caused the overall sound level reductions that were measured. Installing new advanced noise-reducing air nozzles can provide large sound level reductions in comparison to existing conventional nozzles, which has direct benefit for hearing conservation efforts.     

非稳态噪声工作场所噪声暴露测量与评价

[目的]测量和评价非稳态噪声工作场所的8h等效连续A声级（LAeq.8h）、1min等效连续A声级（LAeq.8h）和全天等效声级估算值（LAeq.8h）。[方法]采用个人声暴露计测量LAeq.8h,用声级计测量LAeq.8h。和每个时间段的噪声值,计算出全天的等效声级（LAeq.8h）。应用LAeq.8h和LAeq.8h、LAeq.8T分别测量某输油管道加工厂和某家用电器制造厂239名工人的个体噪声（接触）和相应作业场所噪声（暴露）水平。[结果]两家工厂LAeq.8h均值分别为（89．7±3.8）dB（A）和（90．5±5．7）dB（A）,分别高于LAeqT的（88．0±2．4）dB（A）和（89．2±3．6）dB（A）（P〈O．05或P〈0．01）。与LAeq.8h相比,LAeq.1min采样时间点存在抽样误差。绝大多数工作岗位的LAeq.1min与LAeq.8h均值差大于3dB（A）,所有工作岗位的LAeq.8T均值与LAeq.8h均值差均小于3．0dB（A）。[结论]LAeq.8h能反映在非稳态噪声工作场所工人实际接触噪声暴露水平,LAeq.T比较符合作业工人实际噪声接触水平LAeq.1min。会低估或高估工人噪声暴露水平。     

An inexpensive sensor for noise

Noise is a pervasive workplace hazard that varies spatially and temporally. The cost of direct-reading instruments for noise hampers their use in a network. The objectives for this work were to: (1) develop an inexpensive noise sensor (<$100) that measures A-weighted sound pressure levels within ±2 dBA of a Type 2 sound level meter (SLM; ～$1,800); and (2) evaluate 50 noise sensors for use in an inexpensive sensor network. The inexpensive noise sensor consists of an electret condenser microphone, an amplifier circuit, and a microcontroller with a small form factor (28 mm by 47 mm by 9 mm) than can be operated as a stand-alone unit. Laboratory tests were conducted to evaluate 50 of the new sensors at 5 sound levels: (1) ambient sound in a quiet office; (2) 3 pink noise test signals from 65–85 dBA in 10 dBA increments; and (3) 94 dBA using a SLM calibrator. Ninety-four percent of the noise sensors (n = 46) were within ±2 dBA of the SLM for sound levels from 65–94 dBA. As sound level increased, bias decreased, ranging from 18.3% in the quiet office to 0.48% at 94 dBA. Overall bias of the sensors was 0.83% across the 75 dBA to 94 dBA range. These sensors are available for a variety of uses and can be customized for many applications, including incorporation into a stationary sensor network for continuous monitoring of noise in manufacturing environments.     

High-frequency noise in dentistry

Earlier studies have revealed that dentists have higher hearing thresholds than expected. The aim of this study was to evaluate the noise levels of current dentistry equipment under very controlled conditions. This noise study was carried out in the Acoustics Laboratory of Kuopio Regional Institute of Occupational Health, the background noise of which is about 0 dB(A). Working noise was simulated by drilling a polyacetal plate. During drilling and idling, the noise of the hand pieces was measured over a reflecting plane on the hemisphere surface, the radius of which was 0.3 m, and 10 noise samples were picked for each hand piece. The average sound pressure level and the sound power level of the devices were calculated applying the standard ISO 3744. The measurement and analysis were done in the one-third octave bands of 25-80,000 Hz. The measuring instruments used were the B&K 4135 microphones, the B&K 2633 preamplifiers, the B&K 2811 multiplexer, and the B&K 2133 real-time analyzer with the ZT 0318 high-frequency expansion unit. During the simulated work, the average A-weighted sound pressure level of the new and old hand pieces was 76-82 dB(A), that of the power suction tube 77 dB(A), the saliva suction tube 75 dB(A), and the ultrasonic scaler 83 dB(A). The average ultrasound level of the ultrasonic scaler was 107 dB at the one-third octave band of 25,000 Hz.     

Industrial noise control

Only option E reduced the overall A-weighted level to less than 90 dBA, and in fact, it reduced it to less than 85 dBA, the level at which OSHA requires a hearing conservation program. Thus, a worker could be exposed to the resulting sound level using option E for up to eight hours. The results of all of the other measures required limited exposure, according to Table 1. Untreated (and without hearing protection), the worker could be exposed to the 112-dBA sound level for only about 15 minutes during the day. Option B would allow the employee to be exposed to the 105-dBA sound level for one hour; Option C of 98 dBA for about 2 hours; and Option D of 91 dBA for about 7 hours. These times assume the worker is not exposed to other high noise levels; otherwise, these have to be accounted for, as well. The best solution depends on how long the parts tumbler is in operation and whether barriers or enclosures are practical. Other solutions may exist, as well. It's always best to have a qualified acoustician evaluate the problem and make recommendations.     

广州市部分企业噪声作业工人听力损失现况分析

目的对广州市部分企业噪声作业工人听力损失现况进行分析,以达到保护工人听力的目的。方法以部分企业长期接触噪声的440名工人为研究对象,测量等效A声级(LAeq)。按等能量原则将LAeq和噪声作业工龄合并计算累积噪声暴露量(CNE);用logistic回归模型分析听力损失的相关因素。结果作业环境噪声强度超标率为41.20%,噪声强度均值为(89.30±4.57)dB(A)。440例噪声作业工人听力损失检出率为23.86%,听力损失与耳塞防护、工龄、年龄和CNE存在正相关关系(P0.05)。非条件logistic回归分析结果显示,年龄、工龄可能是听力损失的危险因素(偏回归系数为正值,OR值1)。结论在有佩戴耳塞防护的情况下,CNE作为听力损失的评价指标不敏感,佩戴耳塞仍是目前最好的防护措施。     

Impulse noise and risk criteria

Impulse noise causes evidently more severe hearing loss than steady state noise. The additional effect of occupational impulse noise on hearing has been shown to be from 5 to 12 dB at 4 kHz audiometric frequency. Reported cases for compensated for hearing loss are prevalent in occupations where noise is impulsive. For impulse noise two measurement methods have been proposed: the peak level method and energy evaluation method. The applicability of the peak level method is difficult as even the recurrent impulses have different time and frequency characteristics. Various national risk criteria differ from international risk criteria. In France the maximum A-weighted peak level is 135 dB, and in the United Kingdom the C-weighted peak sound pressure is limited to 200 Pa (140 dB). This criterion of unweighted 200 Pa (140 dB) is used in European Union (EU) directive 86/188 and ISO 1999-1990 regardless of the number of impulses. The American Conference of Governmental Industrial Hygienists (ACGIH) has recommended that no exposure in excess of a C-weighted peak sound pressure level of 140 dB should be permitted. At work places these norms do not cause any practical consequences since the impulses seldom exceed 140 dB peak level. In several occupations the impulses are so rapid that they contribute only a minimal amount to the energy content of noise. These impulses can damage the inner ear even though they cause reduced awareness of the hazard of noise. Based to the present knowledge it is evident that there is the inadequacy of the equal energy principle in modelling the risk for hearing loss. The hearing protectors attenuate industrial impulse noise effectively due to the high frequency contents of impulses. Directive regarding the exposure of workers to the risks arising from noise requires that in risk assessment attention should be paid also to impulsive noise. So far there is no valid method to combine steady state and impulse noise. A statistical method for the measurements of industrial impulse noise is needed to get a preferably single number for risk assessment. There is an urgent task to develop risk assessment method and risk criteria for impulsive noise to meet the requirements of the upcoming European Union noise directive.     

Community noise criteria.

In the fields of community noise abatement and municipal planning, there are new requirements to define an environment of varying noise level by a single number rating method that correlates well with the subjective response of human beings. Typical criteria, either in use of proposed, are LN numbers (noise levels exceeded N% of the time), Leq (the equivalent sound level in dB(A) ), LNP (the Noise Pollution Level), and Ldn (the day-night average sound level in dB(A) ). Instruments available include an environmental noise classifier, a statistical distribution analyzer/recorder combination, and a digital sampling system for field measurements for subsequent interrogation by a programmable calculator.     

Observations of noise exposure through the use of headphones by radio announcers

This study examined the potential risk of hearing loss by commercial radio announcers. This risk is developed through the regular use of headphones. These headphones are used to monitor broadcast transmission and communication information from program producers. To our knowledge there are no published studies of the noise exposure of radio announcers. The experimental method utilised a headphone parallel to the one in use mounted on a wideband, artificial ear. A Sound Level Meter was then used to measure the sound level and then calculate the exposure level. Depending on the feedback level applied to their headphones radio announcers are exposed to potentially damaging levels of noise. Levels measured correlate with results from other studies of long-term average speech spectrum and voice level measurements.     

Effects of the body in personal sampling of noise

In acoustic free fields the human body changes the energy distribution surrounding it, mainly under narrow band or pure tone noise conditions. Hence, sound levels measured close to the body should be intrinsically incorrect if performed via personal sampling. An experiment was carried out to verify whether this statement is still valid in a diffuse field, such as occurs in industrial workplaces. Noise measurements were made in diffuse field laboratory conditions without the presence of a person (steady state) and were repeated close to the ear of a person (perturbed state). The measurements were carried out with integrating precision sound level meters and also with personal noise dose meters. The trials were repeated in an industrial environment. The states 1/3 octave band levels were matched, as also were the equivalent continuous levels. These findings show that in diffuse fields the human body does not significantly affect equivalent continuous level measurements performed near the body. The mean differences between equivalent continuous levels measured by sound level meter were less than 0.3 dBA, and ranged from -0.6 to 0 dBA between levels measured by sound level meter and by personal noise dose meter. The results of the trial performed in the plant showed closer differences between steady and perturbed states and between sound level meter and personal noise dose meter measurements.