In animal studies in several different species, we have produced irreversible nerve damage in the ear with two hours of continuous exposure to noise at 100 to 104 decibels (dB). There is every reason to believe that human ears are just as sensitive. Most daily exposures in our lives do not continue for that long. Nevertheless, it is prudent to avoid unprotected exposure to any sounds in excess of 100 dB.
Many sounds in daily life take us into a danger zone. Concert venues and clubs routinely produce peak levels of 115 dB and average levels in excess of 105 dB. Gas-powered leaf blowers and lawn mowers reach levels at the users' ears between 95 and 105 dB, as do power tools such as circular saws. Frequency of the sounds matters. The more high-pitched whine of a belt sander is more dangerous at the same decibel level than the lower-pitched roar of an undermuffled motorcycle. Jackhammers produce levels of 120 dB even for passersby, and the rapid-fire impulses of the metal rod on concrete produce lots of the dangerous high-pitched sounds.
What can we do? These days almost all of us have access to surprisingly accurate sound-level meters in our pockets or purses. There are numerous free or inexpensive apps for iOS and Android phones that provide reliable readings of sound pressure produced by a musical instrument or a car backfiring to within 1 to 2 dB of the most expensive professional sound-monitoring equipment. The app for iOS that worked best for me, Sound Level Meter Pro, is still under $20 and gave me readings in my laboratory that were accurate to less than 0.1 dB.
Once you are aware of which sounds in your environment are potentially dangerous, the good news is that effective ear protection is cheap, easy to use and extremely portable. If properly inserted, the foam-type insert plugs can attenuate the sound level by 30 dB in the most dangerous frequency regions. Roll one between your fingers to squeeze it into the thinnest cylinder you can and then quickly insert it as deeply in your ear canal as you can. It is no more difficult or dangerous to do so than putting in earbud headphones. Let them slowly expand, and within a minute you are ready to rock and roll.
If you are attending a concert, these foam earplugs provide too much sound muffling. When you want to hear the sound but just at a lower (safe) level, use “musicians' ear plugs.” Several brands are available online for $10 to $15 a pair. They are designed to provide 10 to 20 dB of sound attenuation, with equal muffling of low- and high-pitched sounds, so that the timbre of music is unaffected.
Most important, pay attention to what your ears are telling you. If you have left an event or an activity sensing that sounds seem muffled, like you have cotton in your ears, or if you have ringing in your ears, odds are that you have destroyed some auditory nerve synapses. Don't despair but try not to let it happen again.