Appendix A: Noise measurement equipment
In general, the following instruments are appropriate for the measurement of occupational noise exposure (adapted from CSA Standard Z107.56-13, “Measurement of Noise Exposure”):
- Sound Level Meter: A sound level meter that meets at least the Type 2 requirements of American National Standards Institute (ANSI) S1.4 -1983 (R1997), “Specification for Sound Level Meters or International Electrotechnical Commission (IEC)”, IEC 61672-1 “Electroacoustics - Sound level meters”, used on an A-weighting network and on slow response.
- Integrating Sound Level Meter: An integrating sound level meter that meets at least the Type 2 tolerance requirements of ANSI S1.4 – 1983 (R1997), “Specification for Sound Level Meters” or IEC 61672-1,“ Electroacoustics - Sound level meters” , with an A-weighting network , a dynamic range of at least 50 dB, and a crest factor capability of at least 30 dB. “Dynamic range” is the range in dB over which the instrument operates within the tolerances stated by the manufacturer. “Crest factor” is the difference in dB between the peak sound pressure level and the equivalent sound pressure level measured over a specified time interval.
- Noise Dosimeter: A noise dosimeter with Type 2 tolerance according to ANSI S1.25-1991, “Specification for Personal Noise Dosimeters”, ANSI S1.4 – 1983 (R1997), “Specification for Sound Level Meters” or IEC 61672-1, “ Electro-acoustics - Sound level meters” with an A-weighting network, a dynamic range of at least 50 dB, a crest factor capability of at least 30 dB, and a threshold level at least 10 dB below the applicable criterion level (in this case, 75 dBA or less). Dosimeter settings should be: 85 dBA criterion level; 3 dB exchange rate and threshold no higher than 75 dBA (preferably zero).
Impulse/Impact noise: A dosimeter or integrating sound level meter with a higher crest factor capability must be used for impulse or impact noise such as the sounds produced by a drop forge or blasting operations.
The following table is adopted from CSA Standard Z107.56-13, “Measurement of Noise Exposure”, clause 4.3 Instrument Selection. It may be used as a guide in selecting the most appropriate instrument.
|Dosimeter||All occasions, particularly when a worker cannot be accompanied or work has an unpredictable pattern. Most useful when work cannot be easily split into discrete activities.||Maximum sound level may exceed instrument range. Crest factor of sound may exceed instrument capability. Data collection is difficult to witness.|
|Integrating sound level meter||All occasions. Most useful when work can be easily split into discrete activities.||Maximum sound level may exceed instrument range. Crest factor of sound may exceed instrument capability where workers are exposed in an unpredictable fashion to different sound levels. However, in many cases a space average over the working area can provide a good estimate of the noise exposure of such people.|
|Sound level meter||Only useful when work can be easily split into discrete activities during which sound levels are steady.||Cannot adequately measure non-steady (> ±3 dB) or impulse sound.|
- Crest factors exceeding 30 dB are rare but may occur with highly impulsive sounds such as those produced by drop forging and blasting. In these cases, an instrument with a higher crest factor capability should be used.
- A side benefit of the use of an integrating sound level meter is the possibility of identifying the contribution to workers’ noise exposure of different activities and noise sources for later use in a noise-control program. Logging dosimeters may also be useful for generating this information.
- A sound level meter can sometimes be used to define high noise level areas in which hearing protectors should be worn.
- When sound levels vary slowly enough to allow readings to be taken, a sound level meter may be used to obtain Lp,i by taking a series of measurements at regular intervals. The Leq, t can then be calculated from Lp, i using Clause C.3 of the CSA standard.
- Some instruments can be affected by radio interference and strong electromagnetic fields. This situation can be verified by using a dummy microphone or a calibrator fitted but not turned on, to attenuate the noise at the microphone. If the sound level measured does not drop significantly, interference should be suspected.
- In many cases the same instrument can be used either as a dosimeter or as an integrating sound level meter.
- The use of dosimeters and integrating sound level meters can complement each other. It is recommended that both types of measurement be taken as a cross-check of the results. In many cases, the same instrument can be used for both.
- There is evidence of a systematic difference of up to 2 dB between readings obtained using dosimeters and integrating sound level meters. This Standard does not provide a correction for this effect but instead attempts to specify microphone locations (on the outer edge of the shoulder) to minimize it. It is expected that other sources of variation will tend to obscure this effect in most cases.
Note: This material is reproduced from CSA Standard CAN/CSA-Z107.56-13, “Measurement of Noise Exposure. While use of this material has been authorized, CSA shall not be responsible for the manner in which the information is presented, nor for any interpretation thereof.
Impulse or impact noise
As stated in Note (1) below the table, a dosimeter or integrating sound level meter with a higher crest factor capability must be used for highly impulsive noise such as the sounds produced by a drop forge or blasting operations. In the 2015 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices, the ACGIH (American Conference of Governmental Industrial Hygienists) states, “By using the instrumentation specified by ANSI S1.4 – 1983 (R1997), “Specification for Sound Level Meters”, ANSI S1.25 -1991, “Specification for Personal Noise Dosimeters”, or IEC 804, “Integrating-Averaging Sound Level Meters”, impulsive or impact noise is automatically included in the noise measurement. The only requirement is a measurement range between 80 and 140 dB and the pulse range must be at least 63 dB.”
Note: “Pulse range” is the difference in dB between the peak level of an impulse signal and the root mean square or geometric average.