Noise dosimeter basics

Millions of workers each year are exposed to levels of sound and noise in the workplace that can cause hearing loss. Companies are using noise dosimeters and sound level meters to help establish their corporate hearing protection program standards, and determine where within their plants workers need to be wearing hearing protection equipment.

The 3M Quest dosimeters we rent are fairly easy to use. But as our customers are using noise dosimeters more and more, we've noticed them asking some basic questions that aren't covered in the manuals. Here are a few:

On the reports… what's the difference between the TWA and the Projected TWA? Will one of these by the 8-hour TWA as required by OSHA?

The standard TWA (time weighted average) is calculated based on measurements that have already been taken. Projected TWA is an average calculated by using average sound level trends to project an estimated sound level for the duration of the 10 hour study. Example: If you sample for 1 hour and the TWA = 80dB the projected TWA may be 85dB based on projecting the sound level trends over an 8 hour period. TWA and projected TWA readings are often close if they are not the same value. Since the test will be going 10 hours, the TWA will conform to OSHA.

 

Should I just use the default settings for a standard OSHA noise survey? Why is the Upper Limit set at 115…should that be higher in case we see some extremely high DB levels?

The upper limit is a setting used to calculate the total amount of time that measured noise levels exceeded the value of the upper limit. It will record measurements above the 115dB limit and calculate the amount of time levels exceeded 115dB rather than stop measuring when sound levels exceed the limit.

 

Do I need to do the "setup" before we test? Or can I just enter the names etc., into the DMS after the testing?

We recommend that all setup parameters, including the name and internal clock, be configured prior to testing. Before we ship noise dosimeters to our rental customers, Raeco Rents technicians set the devices to the local time. But it's always a good idea to check, so you'll know your test results are accurate.

 

If the dosimeter is set with a “projected time” of 8 hours, is it a problem to run the test for 10 hours?

It's not a problem, but it's best to make project time reflect the actual test time. There are implications for tests run shorter or longer than the standard eight hours.

 

Do I really need to calibrate right before every use? Will the day before suffice?

3M Quest recommends calibrating the dosimeter immediately before starting the test for the most accurate readings. Calibrating the night before will not drastically affect the readings, but they will be more accurate if you calibrate the dosimeters right before using them. A post-test calibration is also suggested to confirm any fluctuations from 114dB from the start of the test to end.

Want to learn more, see all the articles we've posted about sound level and noise measurement.  Confused about the use of sound level meters vs noise dosimeters, or Type 1 vs Type 2 microphones? Check our earlier sound level and noise measurement FAQ.