Safety Tidbit #24 - Average Noise Levels

Americans lead a noisy lifestyle.  Sources of noise vary greatly, lawnmowers, cars, airplanes, trains, PA systems, etc.  We are bombarded by noise wherever we go.  But how much is too much.  OSHA requires a hearing conservation program whenever workers are exposed to noise more than 85 decibels continuously for 8 hours [1910.95(c)].

So what does an average noise exposure look like?  Here is an analogy I used recently with a client.  Say you drive 480 miles (i.e. from Harrisburg, PA to Charleston, NC) and it took you 8 hours to complete.  Your average speed for the trip would be 60 miles per hour.  Now you know you didn’t drive 60 MPH the entire time.  You needed to stop to get gas or a drink, traffic lights, etc.  So there was some amount of time during the trip where your speed was less than 60 MPH (sometimes even stopped).  Therefore, you must have traveled above 60 MPH at some point to get to your destination in 8 hours.  Now, I’m not saying you were speeding, but the point is that if our noise level is 85 decibels for the average and some of the workday we are away from the noise, breaks, repairs, setup, etc. then other times the noise levels are well above 85 decibels.

So, with so many point-sources of noise how do we know when we exceed 85 decibels as an average for the entire day?  Well, you can evaluate the noise from every source and determine how much time is spent using each source and the mathematically add them together.  Or you can use a noise dosimeter that takes readings every minute and catalogs the readings and does the math for you.  Dosimeters are nice because they are very portable, but they also allow you to capture all noise sources (even noise from nearby workers or operations) that also contribute to the worker’s exposure.  But also, you can profile a given period of the workday.  For instance, you can catalog noise exposures for two or three hours.  Employers divide the typical workday into four parts by the AM break, lunch, and the PM break.  Cataloging one of these segments with all of the noise sources during the time can give you a snapshot of the whole day.  Or similarly, an entire operation can be evaluated. This sort of monitoring gives you exposures during a specific task that again gives all of the noise exposure during the task given the specific environmental conditions.

Furthermore, we know workplace conditions change day to day (and even hour to hour) so taking one noise reading one time represents noise exposure for that set of circumstances only.  Ultimately, the industrial hygienist wants to evaluate the exposure of every worker, during every day during every shift.  Unfortunately, we will never be able to gather that much data so we must be as efficient and effective as we can and using dosimeters to gather discreet times of the workday is a good way to gather all of the noise exposure in a given environment and evaluate a given task or workday.

Ultimately, a hearing conservation medical surveillance program must be provided when the average noise exposure exceeds 85 decibels for 8-hours.  That is exposure from all noise sources not just the noise from the individual pieces of equipment.  Furthermore, even if your average noise exposure is below 85 decibels, any time the noise exceeds 85 decibels, I recommend using hearing protection.  You only get one set of ears to hear with so let’s keep them healthy!