A. Behar

Noise exposure--sampling strategy and risk assessment.

Noise exposure surveys are performed to assess risk of hearing loss. Because of the large populations that are usually involved, there is a need for a sampling procedure that will ensure statistically significant results. After the survey has been performed, the risk has to be assessed in a meaningful manner so that management can easily evaluate the situation. In this study noise exposure levels were found to be normally distributed. As a result, the NIOSH sampling method could be applied for noise exposure surveys. Furthermore, it is shown how different degrees of risk can be assessed as the percentage of workers with exposure lower than 85 dBA, higher than 90 dBA or between 85 and 90 dBA. A numerical example in the Appendix shows how the procedure is applied in a practical situation.

Sound attenuation from combinations of earplugs and earmuffs

Abstract It is generally accepted that the total attenuation, when wearing a muff on top of a plug, is 5 dB higher than the highest of the individual attenuations of each of the protectors. A recent paper by A. Damongeoet et al., Appl. Acoust. , 28 (1989) 169-75, lists results from 32 laboratory measurements of attenuations resulting from wearing simultaneously a muff and a plug, performed at five different laboratories. The resulting mean attenuation of the database was 7 dB. However, individual attenuation values ranged from 0·6 to 12 dB, defying the validity of the 5 dB rule. In this paper several attempts for a general rule for predicting the combined attenuation have been postulated, none with success. The conclusion is that a combination of protectors should not be worn unless the resulting attenuation is known.

Measurement of noise inside truck cabins

The measurement of noise inside truck cabins presents a series of problems due to several factors such as changes in the vehicles speed, changes in the external environment, variation in the noise level with the microphone location inside the cabin, the window condition (open or closed), etc. This paper discusses the only existing American standard on the subject and presents guidelines for another, more comprehensive standard, which takes into account several of the variables mentioned above. A real-life situation where those guidelines were applied is described and the results discussed. The measurement technique applied was found to be relatively simple to carry out and the results correspond to users everyday experience, thus validating the proposed method.

A sampling strategy for office noise measurements

Abstract A study was performed to derive a strategy for the measurement of representative office noise indices, such as L eq , L n , etc., by comparing short-duration samples with whole-day measures. The study was performed using dosimeters in 12 office locations with different activities. For the locations measured, it was found that short-duration measurements can provide reliable estimates of whole-day noise levels. Five- or 15-minute samples collected shortly before or after noon break would best represent whole-day L eq and some L n levels.

The high, medium, and low method : a better noise reduction rating ?

This paper compares hearing protector attenuations calculated using National Institute for Occupational Safety and Health (NIOSH) method No. 1 (long method) and the HML method. The study was done on 144 combinations of 12 noises and 12 protectors. In each case, the attenuation was calculated using each of the above methods. The difference between attenuations was used to define the accuracy of the high, medium, and low (HML) method. It was found that the attenuations calculated using the HML method are almost always lower than those calculated using the NIOSH method. However, the differences between both attenuations are well within the field noise level measurement errors. Consequently, the HML method appears to be an acceptable approximation of the NIOSH method, offering the additional advantage of being easier to apply. The higher accuracy of the HML method, when compared to the Noise Reduction Rating (NRR), makes is preferable for applications in industrial hearing conservation programs.

Selection of hearing protectors

Abstract A method for selection of hearing protectors based on attenuation and comfort is presented. For the attenuation, the data provided by the manufacturer are used after being derated. A protector is selected when its attenuation is higher than the measured (or calculated) noise exposure minus the criterion level set by regulations or legislation. When large numbers of workers are involved, group noise exposure and associated standard deviation are to be used. Comfort is assessed by using a specially developed questionnaire. Protectors are distributed to ten workers who have to wear them during an entire shift. The questionnaire is completed prior to and after wearing the protectors.

Noise Exposure — Sample Size and Confidence Limit Calculation

In a previous paper a method for assessing noise exposure levels of workers from the same trade was presented. There was also discussed how to apply the NIOSH sample size method to noise exposed populations. In this paper both subjects are further discussed by including the calculation of confidence limits for the mean noise exposure as well as for the percentage of workers with noise exposure levels beyond a certain level. The calculation of the sample size of a population where standard deviation is known is also discussed.

Attenuation of hearing protectors and the NRR factor

This paper compares dBA levels at the protected ear obtained using the ISO-NIOSH method with the NRR factor recently adopted by the Environmental Protection Agency. The study was done on 144 combinations of 12 noises and 12 protectors. In each case the sound level was predicted using each of the methods. The differences between the levels, E, was used to define the accuracy of the NRR. It was found that the level predicted using the NRR was always higher than measured, the difference ranging between 0 and 11.3 dBA. Because of this rather conservative estimation of the hearing protectors attenuation and the simplicity of its use, the application of the NRR factor in industrial hearing conservation programs is recommended strongly.

Comparison of noise exposure levels between workplaces

As an essential part of any hearing conservation program, noise exposure levels of workers are measured to assess their risk of hearing loss. Whenever the legal limit is exceeded (e.g., 85 dBA, 90 dBA, etc.), measures have to be done to eliminate or reduce the risk. To do so, work practices are re-examined, hearing protection is introduced and/or engineering controls are put in place to reduce noise levels, and consequently, noise exposure levels. This paper presents a process by which several indices are calculated using the average noise exposures of the different work groups (L Trade ) (e.g., 85-90 dBA, 90-95 dBA, etc.). The indices calculated using this method can be used in isolation or combined, so that a more complete picture (more representative rating) be obtained

A signal generator for testing of hearing protectors

Abstract The measurement of the acoustical attenuation of hearing protectors requires a signal generator whose characteristics are specified in the ANSI S3.19-1974 Standard. This paper describes such a generator which was constructed by modifying a regular screening audiometer, including a pink noise generator followed by nine one-third octave band filters and an additional 2·5 dB attenuator. Detailed information on the construction and performance of the generator is provided in the paper. The generator, which is relatively easy to build, has proved to be reliable for uses in the laboratory, as well as in the field.