Sound Level Meters and Workplace Noise Protection
Noise is an extremely common workplace hazard. Some noises are intermittent, like the sound of a brake press; others are continuous, like a rumbling boiler. Exposure to excessive noise over a long period is likely to result in hearing loss. To reduce the risk of hearing loss reaching a point where impacts quality of life—such as when a person has trouble discerning one voice or communicate in a crowd or party—workplace noise levels can be measured with a Sound Level Meter (SLM).
Why not just get opinions on whether a workplace is too loud or not? The fact is that aural perception is very subjective; different people experience the same sound at different levels. SLMs are therefore an inarguable method of measuring noise level. Consistent and periodic measuring of workplace noise levels is important not only to protect workers’ hearing, but also the company against personal health and legal liability.
A Sound Level Meter is a handheld device that measures sound level in decibels. This is accomplished by a microphone measuring small air pressure variations. These variations are transformed into electrical signals, which are converted into the readout.
Calibration of the SLM prior to and after taking measurements is important. The calibration procedure will be described in the equipment manual.
The correct way to use the SLM is to hold it at ear level and arm’s length. How the microphone is pointed in relation to the source of noise is usually unimportant. However, pointing it away from walls will help ensure accurate results. SLMs can be set to FAST or SLOW response levels. Workplace measurements should be made on the SLOW response level: this is the time length the SLM will average its reading over.
SLMs come in different Types. Type 1 are for applications requiring higher levels of precision. Type 2 are almost always suitable for industrial and workplace use.
Wind or air flow caused by fans will affect the reading. To counteract this, a windscreen accessory may be available. The windscreen covers part of the microphone that would be most affected by excessive air flow.
A setting may be available on an SLM showing results in dB(A). Some Sound Level Meters only report readings in this way. dB(A) means lower frequencies have been filtered out of the reading: this is called the A-weighting. Why would this be offered? Human beings hear high frequencies more easily than low frequencies. Thus the instrument adjusts the scale of results to the way the human ear really hears. Also, it provides one numeric measure integrating sound levels at all frequencies.
For a general idea, a quiet room will typically read at 40 dB(A); a hand-held circular saw one metre away, 115 dB(A). The Criterion Level is what is allowable for an 8-hour work shift. For noises that are louder, a factor called the Exchange Rate comes in to play. The exposure above the Criterion Level must be limited to shorter periods as the sound level increases. In Canada, the noise exposure limits are typically 85 dB(A) in the provinces and territories. Quebec has a 90 dB(A) limit, and Federal jurisdictions have an 87 dB(A) limit. You will typically find noise exposure limits in various provincial and territorial Occupational Health and Safety regulations. Federal and other territorial safety and labour acts may also contain information about noise limits.
Once locations and causes of excessive workplace noise have been identified, measures can be taken to eliminate or reduce their effects. Personal protective equipment should be viewed as an intermediate solution while permanent ways of decreasing sound levels are developed.