Mapping Workplace Noise: Choose the Right Monitoring Tools

Before you put a hearing conservation program in place, and while it is active, you’ll need to do some occupational noise monitoring. Your noise monitoring will determine whether your workers could be exposed at or above the action level; enable you to identify workers who need to be enrolled in a hearing conservation program; and guide your selection of hearing protection devices.

According to OSHA’s occupational noise standard (1910.95), you can use either area monitoring or personal noise dosimetry for this purpose. Here’s a look at factors affecting your choice and a detailed description of how to use a sound level meter to evaluate noise levels.

Monitoring Rules

Whichever method of noise monitoring you choose, you’ll need to ensure that:

• The monitoring results are representative of workers’ exposures. Because of this, if your workers are highly mobile or sound levels in your facility are highly variable, the standard does require personal dosimetry.
• Employees or their representatives are offered the opportunity to observe any measurements that are taken to characterize their noise exposure.
• Any employees who are exposed at or above the OSHA action level are notified of the results of the monitoring.

Sound Level Meters

A noise survey conducted with a sound level meter can help you develop a “map” of noise levels in the workplace and at employee workstations.

Sound level meters (SLMs) come in different classes or types: research, engineering, and law enforcement applications that require more accurate readings may necessitate a Class 1 or Type 1 SLMs, which are generally accurate to within ±1dB. Class 2 or Type 2 models, which are less expensive, are generally accurate to within ±2 dB—good enough for most workplaces.

Sound level meters take a “snapshot” measurement of sound pressure levels, and they should integrate all continuous, intermittent, and impulsive sound levels from 80 dB to 130 dB into their measurements. To conduct an area survey with an SLM:

• Calibrate the SLM, following the procedure given in the user’s manual.
• Set SLM’s response rate—this is the time period over which it averages its reading before displaying a result—for “Slow.”
• Ensure that the A-weighting filter, which will set the machine to measure in units of dBA, is “on.” Some SLMs have an A-weighting filter that is always on; others have adjustable filters for different applications.
• Hold SLM’s microphone at ear-height and take a reading.

When you record the reading, make sure to note the specific location where the reading was taken. Noise diminishes over distance, or it can vary due to structural factors (the presence of baffles; reverberation noise), so the noise levels right next to a piece of machinery may be significantly different than levels just 3 feet away.

Recalibrate the SLM after you are finished.

If noise levels are fairly constant throughout each shift, this survey will give you a good idea whether employee exposures are likely to exceed OSHA’s exposure limits. If, however, noise levels are variable, intermittent, or punctuated by impact noise, an instantaneous reading from a SLM may not give you sufficient information. To determine noise levels under those conditions, you may want to use an integrating sound level meter (ISLM). This type of meter can give you a reading of average sound levels at a given location over a period of time.

It should also be able to give you a “true peak” reading, letting you know what the loudest sound level was if you are trying to measure impulse or impact noise.