This is a guest blog based on the theme, that some is good, but too much is not good. I have invited Pieter van ‘t Hof ([email protected]) who is the Manager of Research and Development of Dynamic Ear Company to contribute this week.
Suppose you are on a cocktail party which has just started. Only a couple of people around, sound levels are low. Someone comes up to you and says. “What do you have on your ears? why would you be wearing hearing protection? It is so quiet here.” And after a closer look: “By the way, they look awesome, like earrings!” You say: “Well, thank you! The thing is: I really like to wear my hearing protectors. They fit very comfortably in my ear. Because they are able to transfer humidity, my ears feel fresh and the sound is just as normal, only on a lower level. As a matter of fact, I’d rather be here with hearing protection than without, because I understand you better now…. Occlusion? No, I don’t feel occluded at all.”
And then you could argue that you feel less fatigue when you go back home after wearing them. Furthermore, you hear conversation better at a cocktail party, because your brain can’t filter out the background noise that is omnipresent, but your hearing protection can. It reduces the noise to a lower level. The ratio between the speech signal and the noise is still the same, but at the lower level your brain is better able to discriminate. But this is far too technical … after all, its only a party!
The point is that this is how hearing protection should be known. It should be a luxury, like jewelry on your ear. You shouldn’t need to remove your hearing protectors at work,because they are uncomfortable to wear or you can’t understand your co-worker. You should expect more from them.
The problem with the NRR:
However, there is one big issue: it is called overprotection. Hearing protection products (HPD) are derated. You could design the best HPD that scores on all aspects, but if it doesn’t get a Noise Reduction Rating (NRR) of about 21 dB or more you are nowhere. The effective protection according to OSHA is the (NRR-7)/2. Extensive studies have been done on several classes of hearing protectors. And, yes, in some cases it is so hard to fit the products in the ear correctly that some derating might be needed. But this is not because that is just needed for all HPD, but this is because it was designed so poorly that most people aren’t able to place it in the ear. And now we have to wear much more protection than needed.
If you work in an environment with a time weighted average noise level of 99 dB(A), you would need 14 dB effective protection to bring the level back to the safe level of 85 dB(A). This means that you would need a product having an NRR of 35 dB. Only a couple of those products exist. In order to come to a product having this NRR, you would need to subtract 2 times the standard deviation from the average attenuation values (on each octave band value). If you would get to a standard deviation of 3 dB, which is low for such a product, you would need a HPD having an average attenuation of 43 dB. So you need 14 dB and what you get is 43 dB. If no earplugs are available of 35 dB, you would need to wear an earplug and on top of that, a set of earmuffs.
No wonder, people don’t like to wear HPD at work. No wonder they take them off as soon as they can. They are very much over protected.
But it could be different. It could feel like the cocktail party for the worker in the machine shop. It all starts with good design of HPD. The HPD should be so easy use that you will obtain a good acoustical seal, especially after training. Then derating is no longer needed. People could use a product with a 15 dB NRR in the example above and will be safe. They could communicate with their colleagues and their ears will feel great.