Weighting, decibels

The term noise refers to any unwanted sound, either a pure tone or a mixture of frequencies. Since the sensitivity of the ear is frequency dependent, as illustrated by the above table, noise level is expressed in a frequency-weighted scale, known as A-weighting. Decibel readings on this scale are designated as dBa. Typical noise levels from various sources are illustrated in this table ... 

A fire or gas alarm will be communicated through audible alarms, usually supplemented by a public address system. In high-noise areas (80 A-weighted decibels (dBA) and greater) visible strobes can also be provided. 

For the characterization of noise the A-weighted sound level (U) is now almost exclusively employed (values in A-weighted decibels dBA), i.e., the A-weighting is now specified for the rating of sounds irrespective of loudness level and is no longer restricted to low-level sounds. 

T is the reference duration in hours for a measured A-weighted sound level L in decibels dBA... 

Sound level As defined by OSHA, ten times the common logarithm of the ratio of the square of the measured A-weighted sound pressure to the square of the standard reference pressure of 20 micropascals measured in decibels (dB). 

Noise is generally measured in decibels weighted to the A scale which approximates the ear s response to noise. Therefore, most readings are given as dB(A) or dBA. This single number covers a wide range of frequencies. A decibel is a logarithmic value to the base 10. Therefore, if the decibel value is increased by 10 the noise exposure has doubled. More sophisticated noise analyses will consider the actual pressure on a person s eardrum and will consider the frequency of the noise waves. 

Who Train employees who are exposed to noise at or aboye an 8-hour time-weighted ayerage of 85 decibels... 

FIGURE 13.10 A and C weighting curves for taking measures of overall decibel levels. 

T or F—OSHA s hearing conservation program does not include all employees exposed to an eight-hour time weighted average sound level of 85 decibels. 

OSHA requires that organizations with workers exposed to decibel levels exceeding 85 decibels (dBA) implement a Hearing Conservation Program. OSHA identifies 90 dBA, based on the results of an 8-hour time-weighted average (TWA), as the safe level of noise exposure. The 90 dBA... 

A-weighted noise level in decibels, a scale weighted to the approximate frequency response of the human ear. 

Generally, noise levels above the 85-decibel level (dBA), expressed as an 8-hour time-weighted average, trigger the requirement for a hearing conservation program. Certain impact or impulse noise levels may also be present and mandate the use of hearing protection. 

Administer a continuing, effective hearing conservation program IF employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) OR equivalently, a dose of fifty percent. 

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