by Neil Bauman, Ph.D.
A man wrote:
While doing research I have found that many web sites have different views on safe exposure times to loud sounds. Some web sites will say that you should not be exposed to noises that exceed 80 dB for more than 8 hours, other say 85 dB and some even say 90 dB.
I don’t know which one is right. Do you have, or know where I could get, a reliable ‘safe exposure time’ table?
I can well understand your confusion based on reading the various links you sent.
Part of the confusion is between what researchers currently say is damaging levels of sound, and what the politicians/bean counters actually write into the Occupational Safety and Health Administration (OSHA) regulations, and how often they update these regulations.
In the past, it was considered that 90 dB was the safe limit for an 8-hour day’s exposure to sound. Then they cut the time in half for every 5 dB above that level.
The problem is that sound levels double for each 3 dB increase, so this wasn’t accurate in the first place. It looked good on paper, and was easy to calculate, but it did not reflect reality.
Later, researchers discovered that 90 dB was still causing hearing loss, so OSHA set the regulations lower to 85 dB. But this time they got the incremental business correct. So for every 3 dB increase, the safe exposure time is halved.
Each state (and each province in Canada) sets their own regulations. As a result, some use the older standard, and some the newer one. For example, Ontario in Canada just last month changed their regulations down from 90 dB to 85 dB. It can take years for the government departments to keep up with the findings of the researchers.
The current state of affairs is that “they” consider it safe for your ears to be exposed up to 80 dB of sound 24 hours a day. Next year, “they” may find that this is still too high and drop it some more.
You see, everyone’s ears are different. Some ears are more “robust” than others, and thus can stand higher levels of sound without damage. I think they are trying to set the safe levels for all ears, not just the robust ones.
Therefore, if you keep the sound level down to well below 80 dB (the Environmental Protection Agency [EPA] and the World Health Organization [WHO] recommend a maximum of 70 dB for continuous exposure), the feeling is that you will not damage your hearing at all.
When looking at the 80 dB as a base and 85 dB as a base, you need to realize that these are actually these are one and the same thing since they use different time limits. Those that start at 80 dB use 24 hrs as their time limit. Those that use 85 dB use 8 hours as their time limit—essentially the same thing. Here’s why.
If you take 85 dB for 8 hours, then in would be 82 dB for 16 hours and 79 dB for 32 hours. So interpolating, 80 dB is roughly 24 hours. (If you want to be technical, it is actually 25 hours and 24 minutes.)
Below are the supposedly safe exposure times (if you take the 80 dB level at 24 hours/85 dB at 8 hours as your base). For each 3 dB increase in sound level, you reduce the time by half. So here is how this time/loudness scale looks:
80 dB 24 hrs.
82 dB 16 hrs.
85 dB 8 hrs.
88 dB 4 hrs.
91 dB 2 hrs.
94 dB 1 hr.
97 dB 30 mins.
100 dB 15 mins.
103 dB 8 mins.
106 dB 4 mins.
109 dB 2 mins.
112 dB 1 min.
115 dB 30 secs.
118 dB 15 secs.
121 dB 8 secs.
124 dB 4 secs.
127 dB 2 secs.
130 dB 1 sec.
According to the OSHA, unprotected exposure to continuous noise above 115 dB of any duration is not permitted.
The EPA/WHO scale looks like this—much more conservative.
70 dB 24 hrs.
73 dB 12 hrs.
76 dB 6 hrs.
79 dB 3 hrs.
82 dB 1.5 hrs.
85 dB 45 mins.
88 dB 22 mins.
91 dB 11 mins.
94 dB 6 mins.
97 dB 3 mins.
100 dB 1.5 mins.
103 dB 45 secs.
105 dB 22 secs.
107 dB 11 secs.
110 dB 6 secs.
113 dB 3 secs.
116 dB 1.5 secs.
119 dB <1 sec.
(In all cases, I have rounded the numbers, so the precise figures are a bit different—but this is so much easier to read and understand.)
The thing a person should ask themselves is simply, “Why stay as close to the ear-damaging line as possible, rather than stay as far away from it as possible?” This should be especially significant in light of the fact that these “safe levels” keep dropping as more research is done.
To further complicate matters, safe sound levels are affected by certain pollutants in the air, especially organic solvents (and even tobacco smoke). For example, when the pollutants in factories and mills are kept at the “safe” OSHA level and the noise is kept at the “safe” OSHA level, they found that hearing loss was still occurring. Thus, in the presence of such pollutants, the safe sound levels must be dropped even further.
Another factor to consider is that these are average sound levels. This means that at any given time there may be very loud ear-damaging sounds, and then the rest of the time, lesser sound levels, but the “average” says it is safe.
Much better to wear sound dosimeters that record the actual sound levels as they vary from moment to moment, and use that to calculate the safe exposure time.
I suggest that you use conservative figures in calculating safe sound levels. At the very least, use the one with the base of 80 dB for 24 hours, and go from there. However, recognize that if you have particularly sensitive ears, even this may not be enough, especially if there are certain pollutants in the air. Thus to be really safe, you may want to use the EPA/WHO base of 70 dB for 24 hours and go from there.
As you can see, it is not simple to nail down a safe standard that works for everyone in all situations. So to be safe, protect your ears more, rather than seeing how close to the line you can go.