Workplace Noise Measurements

Simple measurements in the workplace The primary requirement for making noise measurements in the workplace is to assess whether workers are being exposed to too much noise where they work. Although this is mainly a problem in manufacturing industries the assessment of personal noise exposure at work must be carried out in all companies to be sure that harmful noise levels are not being exceeded. As a simple rule of thumb if you must raise your voice to hold a conversation with someone at work then it is likely that the noise level is around 85 dB and measurements must be carried out to verify the true levels. Over exposure to high noise levels will lead in time to deterioration in worker's hearing capability and this is a one way reduction. It does not improve if the noise exposure is stopped. A simple instrument to check noise levels is the CEL-254. Other simple sound level meters such as the CEL-320S can also be used and can be converted to a personal noise dosimeter by simply substituting the stalk microphone for a cable microphone assembly that can be clipped to the worker.	typical sound level meter for workplace noise use
National regulations exist in almost all industrialized countries which give actual noise limits on the amount of noise allowed in the workplace. These are usually expressed as an average level as an 'A' weighted noise level over a working day with an overall limit on any single high impulsive noise level. The amount of noise during the normal working day is expressed as having been received for a standard 8 hour period no matter how long the actual worker's day lasts. This is called the time weighted average level or TWA. An overall upper limit on the highest single noise level that can be tolerated is also specified in many regulations. This is usually measured as the peak noise level measured without the effect of the 'A' frequency weighting at the low frequencies as a 'C' or Linear level. The CEL-320S or CEL-360S are suitable integrating sound level meters to use for obtaining Lavg or TWA results. Intrinsically safe CEL noise dosimeters are also available for use in hazardous areas.	worker exposed to noise
Noise dosimetry The TWA is usually given as a decibel value such as 90 dBA for 8 hours but can also be expressed as a noise dose where the 100% allowable noise dose is also equivalent to a continuous noise level of 90 dB for the 8 hours. In European regulations the limit is called the "daily personal exposure level" written as LEP,d. This is similar in concept to the American OSHA noise limit although they are not measured or calculated in exactly the same way. In the USA a threshold noise level is specified that ignores noise levels below the threshold value as not being significant compared with the higher levels of noise experienced in a typical workplace. Certain tasks must be carried out when noise exposure exceeds the stated "action level", usually set at 85 dBA for an 8 hour day period. Intrinsically safe CEL noise dosimeters are also available for use in hazardous areas.	example of an OSHA direct report printout
The TWA or Noise Dose can be found by measurements with a traditional sound level meter or with a personal noise dosimeter. The sound level meter is a hand held instrument used by a qualified safety officer to gather the different noise levels produced by different machines or work processes. The personal noise dosimeter is a small noise meter worn on the worker for as long as the whole day if necessary. It collects all the noise the worker receives by means of a small microphone remotely mounted on the shoulder close to the ear. Multiple measurements in noise dosimeters allow a number of workers to be monitored without having to download the results after each separate measurement. CEL-320 or CEL-360 personal noise dosimeters can be used for this work. Intrinsically safe CEL noise dosimeters are also available for use in hazardous areas. An even smaller instrument called a *Micro* Noise Dosimeter may also be used as a dosimeter. This unit clips on to the shoulder area close to the ear and has an integral microphone, power supply and memory to store the time history data. It is quite small and inconspicuous when in use. The CEL-350 Noise Dose Badge is an example of this type of instrument.	a personal noise dosimeter a micro noise dosimeter without cable microphone
At the end of the measurements using either the sound level meter or the noise dosimeter the safety officer or occupational hygienist can review the noise readings and compare against the limits in force. Instruments that "log" the noise levels during the measurements are very useful to see how the noise exposure changed during the day. In this way any remedial work to reduce the overall noise exposure can be properly directed to those times of the day when the noise levels were highest. Direct printouts from the noise meters can assist the operator to prepare a record for the wearer's personnel file. Storage of noise readings in the instrument's memory allows the noise measurements to be transferred to a personal computer for permanent archiving. The CEL-350 Dose badge or CEL-360 logging noise dosimeter and the CEL-450, CEL-480 and CEL-490 logging sound level meter are suitable for this work.	time history variation of noise at work
Hearing protection When noise measurements show that the levels are too high then steps must be taken to reduce noise exposure for the workforce. Ideally this should be done by engineering means to reduce the noise levels of the machines or manufacturing processes. As an interim solution it may be necessary to provide personal hearing protection to workers. These are in the form of ear muffs that fit over the ears or ear plugs which fit inside the ear canal. More noise measurements are required to be able to choose the correct protectors. These should be either octave band measurements using an octave band analyzer or a simpler method to find the noise reduction rating, NRR. The NRR value is found by using an instrument that can measure the workplace noise using the 'A' and 'C' frequency corrections. The NRR is then found from the difference between the overall 'C' and 'A' weighted noise levels. The CEL-440.B, *CEL-450.B* or CEL-553.C sound level meters are ideal for measuring the frequency content of industrial noises to specify the correct hearing protectors for workers.	hearing protectors for use in high noise levels