WHY EVEN A SINGLE HANDCLAP COULD SEND YOU DEAF

THE human ear is incredibly sensitive, able to distinguish a wide range of sounds, from the gentle whisper of a breeze in the trees to the roar of a plane taking off. ‘ To put these differences into perspective the sound of jet aircraft is 1,000,000,000,000 (a trillion) times more intense than the quietest audible sound,’ explains Chris Plack, professor of audiology at the University of Manchester.

This is why if you were close up to a jet taking off, it could deafen you. But because sound intensity drops off with distance, if you are further away, the sound would obviously be less damaging.

The maximum safe level for a sound near you is 80 decibels. A decibel is a complicated measure of the intensity of a sound based on its frequency and its effect on our hearing.

A more intense sound, i.e. higher decibels, can start damaging the delicate hair cells and nerves in the inner ear.

‘Damage depends on the length of time you are exposed to the noise and the intensity of that noise [the decibels),’ says Professor Plack. ‘The greater the volume, the shorter the exposure time before damage occurs.’

A single exposure to an ear-splitting sound can cause immediate and permanent hearing loss. However, lower — but still damaging — decibels over 80 dB can cause more gradual loss if you are repeatedly exposed to that level.

This hearing loss can initially be hard to detect. ‘But if your ears are ringing afterwards, it is a sign that the hair cells are traumatised,’ says Professor Plack.

The hair cells can recover after short exposures but repeated daily exposures will result in cell death and permanent damage.

So how dangerous are everyday sounds?

Here we estimate their decibels and suggest how close you would have to be for damage to occur.

The higher the decibels, the more likely it is that even a single episode could cause permanent damage. Avoiding repeated expo- sure to decibels above 80 is important for preventing permanent hearing damage.

160 TOY pistol fired close to the ear. As well as damage to hair cells, the eardrum can burst.

110 POLICE siren at 10m; rock concert (probably anywhere in the venue); or someone shouting at maximum effort around 1m away. All three can damage hearing after 1 ½ minutes’ exposure per day.

100 NIGHTCLUB; diesel truck at 10m; MP3 player or Walkman played at maximum volume. These can damage hearing after 15 minutes’ exposure a day.

90 FIRE ALARM or burglar alarm at 10m. Can damage hearing after 2½ hours a day.

Standing at a busy city intersection, listening to screaming children close by; operating a lawnmower; maximum volume of a TV; typical volume of an MP3 player. Can damage hearing after 2½ hours a day.

85 AVERAGE factory floor; electric shaver. Can damage hearing after eight hours’ solid exposure.

80 Hairdryer; alarm clock. This is the safe maximum decibel level, so anything below this will not damage your hearing, but you may find the noise irritating. 75

DISHWASHER. 70 CITY street; noisy restaurant; vacuum cleaner. 60 CONVERSATION; tumble dryer, normal piano practice; TV sound at home when being watched by people with normal hearing. 45 REFRIGERATOR hum; noise level in public library. 30 WHISPER in ear. 20

LEAVES fluttering. 0 HEARING threshold. Humans can hear sounds between 0 and 140 decibels. 0 doesn’t mean there isn’t any sound, it’s just that we can’t hear it.