Reduced time exposure noise

This involves reducing the time during the working day that the employee is exposed to the hazard, either by giving the employee other work or rest periods. It is only suitable for the control of health hazards associated with, for example, noise, display screens and hazardous substances. However, it is important to note that for many hazards there are short-term exposure limits as well as normal working occupational exposure limits over an 8-hour period (see Chapter 16). Short-term limits must not be exceeded during the reduced time exposure intervals. 

In addition to reduced time exposure of employees to the noise source, there is a simple hierarchy of control techniques ... 

A limitation of the magnetic prism-based EELS detection system is the spectrum drift in the energy dispersion direction. Various sources of instability in the microscope contribute to this effect High voltage fluctuation, magnetic field creep etc. This places a fundamental limit on the useful exposure time. Experimental efforts in electron spectroscopy consist largely in reducing unwanted electrical noise and specimen drift. 

Use administrative controls such as scheduling to limit woiker exposure to many workplace hazards such as working in hot areas. However, OSHA prohibits employee scheduling to meet the requirement of air contaminant exposure limits. The scheduling of maintenance and other high exposure operations during evenings or weekends can reduce exposures. Use job rotation to limit repetitive motion tasks or reduce the exposure time to occupational noise hazards. Use a work-rest schedule for very hazardous or strenuous tasks. 

OSHAhas estimated a safe maximum noise level of 85 dB. The time-weighted average (TWA) is an exposure for an 8-h to a noise level not exceeding 90 dB. If this level exceeds 85 dB, OSHA requires the employer to institute a hearing conservation program (HCP). Therefore, if a company wants to avoid loss claims under worker compensation laws, it must not only meet the prescribed legal standards, but also attempt to reduce noise to the lowest possible level (< 80 dB). 

In summary, it is clear that the o-Ps lifetime determined via the PALS technique provides accurate information on the apparent mean size of the nanoholes, which comprise the free volume in amorphous polymers. It also seems well established (see Chapter 11) that provided that the noise level in the PALS spectrum is sufficiently reduced, the distribution of o-Ps lifetimes can be obtained, which generates information regarding nanohole-size distribution. Concerns have been raised about the utility of the o-Ps intensity, I3, to characterize the number density of nanoholes and hence the fractional free volume via Eq. (12.2), because the value of I3 can be influenced significantly by the presence of species that inhibit or enhance positronium formation. We feel that we can utilize I3 values to evaluate fl actional free volumes via Eq. (12.2), provided either that the sample is rejuvenated by heating above Tg prior to measurement, and/or experiment indicates that the value of I3 remains constant within experimental error, during the time of exposure to the positron source. 

Employers and employees should not rely too heavily on ear protectors. In practice, they reduce noise exposure far less than is often claimed, because they may be uncomfortable or inconvenient to wear. To be effective, ear protectors need to be worn all the time when in noisy places. If left off for even a short time, the best protectors cannot reduce noise exposure effectively. 

You then need to use the nomogram below in Fig. 10.2 to work out the total noise dose, by adding up the fractions of dose each of the exposures above represent US readers should note that the action level set by law in the USA is 90 dBA, aird that U S law specifies that the permissible exposure time is reduced by half for each 5 dBA increase in sound pressure level (29 CFR 1926.52). 

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