Effects of impulse noise and continuous steady state noise on hearing.

In this study the effects on hearing induced by occupational exposure to impulse noise were compared with those induced by exposure to continuous steady state noise. Three groups exposed to impulse noise, one group exposed to continuous steady state noise, and an unexposed control group were studied. The hearing thresholds of the groups were measured by a puretone audiometer three times in two workdays. None of the groups showed significant differences between the hearing thresholds measured in the morning, at midday, and in the afternoon. Group 1 with the shortest duration of exposure and group 2 with the intermediate duration of exposure to impulse noise had the highest thresholds at 6000 Hz in both ears. Group 3 with the longest duration of exposure to impulse noise had the highest thresholds asymmetrically, at 4000 Hz in the left ear and at 6000 Hz in the right ear. The group exposed to continuous steady state noise also had the highest thresholds asymmetrically, in the left ear at 6000 Hz. It was concluded that the longer the duration of exposure to impulse noise the wider the region of the frequencies that showed raised threshold shifts in both ears. Impulse noise seemed to produce permanent threshold shifts at 4000 and 6000 Hz after a shorter duration of exposure than continuous steady state noise.     

高强度脉冲噪声发生器及其应用

目的为了研究脉冲噪声对机体的生物效应，我们研制了高强度可调脉冲噪声发生器，它由脉冲控制器、固态继电器、电磁阀和气流扬声器等几部分组成。方法利用该装置进行了脉冲噪声不同宽度对豚鼠听觉系统损伤程度影响的研究。结果高强度可调脉冲噪声发生器具有体积小、使用方便、几个参数可调等优点。结论试验显示，动物的听力损失随着脉冲宽度的增加而加重，组间差异显著。耳蜗毛细胞的缺失范围和缺失率也随脉冲宽度的增加而增大。建议在制订脉冲噪声卫生标准时应考虑长脉宽（如１００ｍｓ以上）的不同宽度的作用。     

Limitations of ambient air quality standards in evaluating indoor environments.

Analysis of the kinds of data used for the derivation of ambient air quality standards (AAQSs) for carbon monoxide and ozone shows that these values are based on the toxicology of the materials and thus are suitable for evaluating potential health effects of indoor environments, especially on the very young, the aged, and the infirm. A similar analysis shows that the AAQSs for suspended particulate matter, nitrogen dioxide, and sulfur dioxide are strictly empirical and that they should not be used for any but their first, intended purpose. The AAQSs for non-methane hydrocarbons are based on photochemical smog production, not injury of any kind, and have no utility for indoor environment evaluation.     

The establishment of the MPEL for impulse noise]

A total of 328 blacksmiths was examined so as to obtain and analyse the physical parameters of noise exposure for its hygienic evaluation and norm setting. The noise parameters were found to vary according to different criteria if underassessed by means of existing standard 3223-85. Comparative study of hearing loss in the blacksmiths according to a standard 1999 revealed a hyperaggressiveness of impulsive noise in close connection with both noise level and length of service. Impulsive noise was recommended to be evaluated according to the peak level and quantity of impulses, but the basement of MAL is possible with the help of standard pattern while the criteria as length of service, quantile of population and the grade of hearing loss are chosen.     

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.