Noise exposure levels

Some permissible noise exposure levels for single sources are provided in Table 3-8. 

Title 29 CFR, Section 1910.95 of the Occupational Safety and Health Act (OSHA) pertains to the protection of workers from potentially hazardous noise. Table 8.7 shows OSHA permissible noise exposure levels. 

Use of hearing protection in both occupational and non-occupational environments is intended to help reduce noise exposure levels and noise-induced hearing loss (NIHL). In the absence of feasible engineering and administrative noise reduction control methods, use of earplugs or earmuffs is common practice. Unfortunately there are still many myths surrounding the use and effectiveness of hearing protection devices (HPDs). In this article, some of the more common myths and the realities are addressed. 

Research demonstrates that construction workers are regularly overexposed to noise. The extent of daily exposure to noise in the construction industry depends on the nature and duration of the work. For example, rock drilling—up to 115 dBA, chain saw—up to 125 dBA, abrasive blasting—105 to 112 dBA, heavy equipment operation— 95 to 110 dBA, demolition—up to 117 dBA, and needle guns—up to 112 dBA. Exposure to 115 dBA is permitted for a maximum of 15 minutes for an 8-hour workday. No exposure above 115 dBA is permitted. Traditional dosimetric measurements may substantially underestimate noise exposure levels for construction... 

The hearing conservation program requires anployers to monitor noise exposure levels in a manner that will accurately identify employees who are exposed to noise at or above 85 decibels (dBA) averaged over eight working hours, or an 8-hour TWA. That is, employers must monitor all employees whose noise exposure is equivalent to or greater than a noise... 

If it is not reasonably practicable to reduce noise exposure levels to below 90dB(A) LEP,d then the employer is required to provide personal hearing protection (Reg. 8). An alternative to personal protection is the provision of hearing havens from which the worker can carry out his duties. Areas where there remains a hearing risk shall be designated ear protection zones and be identified as such (Reg. 9). 

If it is not reasonably practicable to reduce noise exposure levels to below the lower exposure action value of 80dBALEPd then the employer is... 

Figure 2. Percentage of workers with noise exposure levels lower or upper than 85 dB(A).

When analysing these studies it could be find some shortcomings like variable use of hearing protection by study subjects, fairly crude assessment of ambient noise exposure levels, and limitations of hearing assessed at only one point in time. They had limited or even no data to address the effects of noise exposures below 85 dB (A) (Rabinowitz et al., 2013). 

Rabinowitz, P.M., Galusha, D., Dixon-Emst, C., Slade, M.D. Cullen, M.R. 2007. Do ambient noise exposure levels predict hearing loss in a modem industrial cohort Occup Environ Med, 64, 53-9. 

Table 10.3 OSHA Permissible Noise Exposure Levels...

Noise. Technical differences exist between personal noise dosimeters and high accuracy sound level meters and these may alter the usual preference for personal monitors. But it is exposure to noise rather than general room noise that must be estimated for comparison with noise exposure criteria, the logarithmic expression and alternative means of summation (3 vs 5 db doubling) compHcate statistics. Exposure criteria for both dose and peak exposure must be evaluated, and space and time variabiUty of noise intensity can be immense. 

The description of the physical characteristics of ventilation noise is based on more reliable knowledge than the description of the human effect. Misconceptions about the levels and frequency characteristics of ventilation noise are still common. This in turn has sometimes led to wrong suggestions about the measures that should be taken in order to eliminate the effects of a ventilation noise exposure. 

The results clearly indicated that the ventilation noise was perceived as most acceptable when the tone was situated in the low er part of the frequency range. The experience of disturbance and the associated effects occur at exposure levels above the auditory perception threshold. Above this level, the risk of these effects increases as the perceived loudness increases, provided that the other conditions remain constant. Since the loudness can be predicted relatively accurately by means of technical measurements, any differences in the degree of disturbance can also be predicted by reference to these measurements, provided that they are dependent on differences in the loudness. 

Both OSHA and the EPA have provided information on permissible noise exposures. Protection from noise is required when sound levels exceed those provided below. These are measured on the A scale at a slow response on a standard sound-level meter (except for certain alarms, etc.) as provided by OSHA. 

If the variations in noise level involve maxima at intervals of 1 s or less, it is to be considered continuous. When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. Exposure to different levels for various periods of time are to be computed according to the following formula ... 

Swenberg et al. (2008) came to different conclusions in a review of the dose-response literature for mutations and DNA adducts, which are biomarkers of exposure. They concluded that biomarkers of exposure (DNA adducts) are usually linear at low doses down to zero (except when the chemical-induced adduct is also formed endogenously, in which case there is a plateau at the endogenous exposure level, and the adduct level of de minimus exposures below endogenous amounts will be lost in the noise of the background). In contrast, they found that biomarkers of effect... 

Figure 5.29 The IP. (a) The absorption efficiency as a function of wavelength and phosphor thickness, t. From Amemiya et al (1988a) with permission, (b) (Noise/signal)out versus exposure level for film and IP. The dashed line is for a hypothetical photon counter of 10% efficiency. The solid line is for an ideal detector, (c) Measured line spread functions along (i) the laser scanning direction, and (ii) the IP scan-...

An AEG is important in determining the exposure level to the detector and to the hreast, hut its key roles are to assist in achieving a predetermined signal-to-noise ratio (see next section) and a reasonable radiation dose to the breast rather than determining the image brightness or contrast. 

The set-up of the measurement is identical to that of the NPS measurement in the lEC 62220-1-2 standard (lEC 2007). A 2-mm thick aluminium attenuator is positioned as closely to the X-ray tube as possible to minimise the influence of scatter and all removable parts are taken out of tbe X-ray beam, including tbe anti-scatter grid and compression paddle. By making images at different detector exposure levels, and fitting (3.3), the presence of additional noise sources can be evaluated as shown in Fig. 3.4. 

There are also levels of noise exposure which must not be exceeded ... 

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