Noise acceptable levels

The extent to which a ventilation noise is perceived as disturbing depends not only on its dB(A) level, but also on the spectral distribution and the presence of tones or intermittent components in the noise. From an experiment carried out on respondents exposed to ventilation noises with different characteristics in a simulated office room, it emerged that the highest acceptable level was about 7 dB higher for ventilation noise with a superimposed tone at 30 Fiz than for other types of noise. In another experiment, it was found that the tolerance level was much higher for a tone than for a noise at 100 Hz, whereas the opposite tendency applied at 1000 Hz. ... 

Noise can constitute a danger to health, and therefore adequate precautions must be taken to protect personnel who are required to be in such an environment. The Health and Safety at Work, etc. Act 1974 has the power to control noise emissions, but the subject is complex. If it is anticipated that noise will exceed acceptable levels then... 

The band gap figures in Table 5.3 signify the temperature sensitivity of the materials and the practical ways in which these materials can be used as detectors. Just as Ge transistors have much lower maximum operating temperatures than Si devices, so do Ge detectors. As a practical matter both Ge and Si photon detectors must be cooled in order to reduce the thermal charge carrier generation (noise) to an acceptable level. This requirement is quite aside from the lithium precipitation problem which made the old Ge(Li), and to some degree Si(Li) detectors, perishable at room temperature. 

In the literature, there is some discussion regarding how detection limits are defined, calculated, and interpreted. It is therefore important to state clearly how the detection and quantitation limits should be calculated in the validation protocol. Both the USP and the ICH guidelines similarly define the LOD and LOQ in ways that are widely accepted in the industry. In the most straightforward case, any compound detected with a response at about 3 times the noise response level is construed to be at its LOD. For the LOQ, the value is... 

Because of high resistivity values, it has not been possible to measure the noise characteristics of pure polymer samples. To reduce the resistivity to an acceptable level, carbon black (4-6.5% ) was added to the polymer under investigation. The resistivity level of the samples was 10 -10 ohm-cm. 

When trying to eliminate or minimize the effect of 60-Hz sources, it is sometimes useful to use a dummy source, such as a fixed 100-kS2 resistor attached to the electrodes. By employing a dummy source as one of the input signals, the output of the differential amplifier represents only contributions from interfering sources. If noise can be reduced to an acceptable level (at least by a factor of 10 less than EEG signals), it is likely that uncontaminated EEG records can be obtained. 

Personal protective equipment (PPE)—specitied as the next level of protection when administrative and engineering controls do not reduce noise hazards to acceptable levels. It is to be used in addition to administrative and engineering controls. 

The effects of dust particulates, noise and vibration from operating machinery, dumping activities and traffic are harmful to the local environment. These can be reduced to an acceptable level with sensitive planning of operations, siting of boundaries, erection of barriers, and use of machinery assisted with silencers. 

Analysis of sound travel will help when planning noise control in a room. Noise travels away from a source. The energy level in a sound field will decay with the square of the distance from a source. However, most rooms have reflective surfaces, such as floors, walls, and ceilings. Placement of noise sources in a layout can help with noise control. For example, placement of noise sources in a comer near highly reflective floor, ceiling and walls will concentrate noise energy in one location and one direction. Conversely, placement of noise sources away from reflective surfaces may give noise a chance to dissipate to an acceptable level. 

As with other types of hazards, the employer must implement feasible engineering controls and work practices before resorting to PPE such as earplugs or earmuffs. If engineering and work practice controls do not lower employee exposure to workplace noise to acceptable levels, then employees must be provided with appropriate PPE. 

Furthermore, because of the different levels of noise sensitivity in humans, it is extraordinarily difficult to define generally acceptable noise limits which will prevent damage to a person s hearing. Under infrasound (frequency < 16 Hz) individual parts of the human body and organs can be stimulated to produce resonance vibrations. Under prolonged exposure to ultrasound (frequency > 20,000 Hz) the human body may respond with leucopenia. Sound or noise intensity levels above 3 W/cm, when applied for more than 10 min may cause the periosteum to become detached from the bone. 

Random electrical noise or pickup at mains frequency is also likely to be a problem because of the need to keep the exciting signal small. Careful shielding of the cell and detection circuits will usually be needed to reduce this kind of interference to an acceptable level. 

Has there been a determination that noise levels in the faciUties are within acceptable levels ... 

Most photoionization experiments require extended data acquisition to increase both the ion count statistics and the signal-to-noise ratio to acceptable levels, particularly in the threshold region where the photoion count rate can be extremely low. It is not unusual for some experiments to last for 24 hours or more. However, as the reduction in random noise only increases as the square root of the accumulated counts, there is a practical limit to the improved quality of data obtained using this technique. 

If engineering controls are not effective in reducing noise to an acceptable level, then hearing protection must be used. There are two basic types of hearing protection ear plugs and ear muffs. Ear plugs are inserted into the ear canal and ear muffs cover the ears. Details to do with each are provided in the NIOSH publication referenced above. 

---