All of us at some point have been exposed to really loud sounds—be it listening to your iPod at near-full volume most of the day, getting on a plane or train, being stuck in traffic with impatient drivers and their equally unforgiving car horns, or passing by a construction site with jackhammers and chain saws.
Not very comfortable right? All these everyday exposures to loud noises are potentially hazardous if the damage is severe enough, suffered repeatedly over a long term and if you are exposed to it without wearing appropriate hearing protection devices.
Does exposure to a particularly loud sound—a fire alarm—cause enough damage to affect our sense of hearing? There are two aspects to this question: how high is it on the decibel level and for how long were the ears exposed?
The British Standard for fire alarm installation states that the sound pressure level of alarm signals should not be less than 65dB(A) or 5dB(A) above any background noise louder than 60dB(A) and lasting more than 30 seconds, although not exceeding 120dB(A). In areas where there is a sleeping risk, sounder devices should produce a minimum of 75dB(A) at bedhead levels with all doors shut.
These are indeed loud sounds guaranteed to wake you up from even your sweetest dreams but thankfully, many fire alarm systems designs take into consideration that that the sound level emitted should not be so high as to cause permanent hearing damage.
Just how loud is too loud, and how long of an exposure is hazardous? According to the American Academy of Audiology (http://www.audiology.org/practice/resources/PublishingImages/NoiseChart16x20.pdf), exposure to over 85 dB for extended periods can already cause permanent hearing loss. Very loud noises from 90 dB to 119 dB are dangerous when the ears are exposed unprotected for over 30 minutes. At 120 dB, exposure for over 30 seconds is already dangerous. At 130 dB and beyond hearing protection is already required even for slight exposure.
It’s not pleasant to suddenly hear a loud and unpleasant electronic screaming, but we do need to be jolted out of our senses when it becomes a safety issue as when a fire alarm sounds to tell us to get out of a smoking building immediately. After all, what good is having a fire alarm if it’s not loud enough for people to seriously take notice?
It’s also worth noting that fire alarms are designed to be really loud considering the fact that most fires start during the night or early morning hours, a time when most people are asleep and we’re not as fully sensitive to sounds as we are when awake. Another reason for its ear-splitting volume is that it must be loud enough for people with some degree of hearing loss to effectively hear.
Now if you were caught in a fire emergency or missed a fire drill notice, minimise your risk of hearing loss by buying a pair of ear plugs or ear muffs to wear when the alarm goes off. It’s a small price to pay compared to the embarrassment of having to ask people to speak louder during conversations even though others can hear them just fine.