Decibels and Damage: How Loud Is Too Loud?

Sound starts to put your hearing at risk at about 85 decibels. The US National Institute on Deafness and Other Communication Disorders says that sounds at or below 70 dBA are unlikely to cause hearing loss, but long or repeated exposure at or above 85 dBA can. Time matters as much as level: NIOSH recommends limiting exposure to 85 dBA averaged over an eight hour day, and every 3 dB above that halves the recommended time, so at 100 dBA, about the level of a loud concert, the safe limit is less than 15 minutes a day. Damage comes from the death of sensory hair cells in the inner ear, and those cells do not grow back.

Key facts

• 85 dBA for 8 hours is the workplace limit used by NIOSH in the US and by the Australian WHS Regulations, which also set a peak limit of 140 dB(C).
• Every 3 dB doubles the sound energy, so the safe time halves, as Safe Work Australia's code of practice on managing noise explains.
• A sound 10 dB louder is ten times more intense, according to NIOSH.
• Headphones at maximum volume, concerts and sporting events run at 94 to 110 dBA.
• The WHO weekly allowance is 40 hours at 80 dB, or four hours at 90 dB.
• Temporary hearing loss after loud noise usually disappears 16 to 48 hours later, but research suggests it can leave lasting damage.

What is a decibel?

A decibel (dB) is the unit used to express how intense a sound is. WHO describes the decibel as the unit of measurement for sound intensity, and the decibel was named after Alexander Graham Bell.

The scale is logarithmic, not linear. That means the numbers climb slowly while the energy climbs fast. OSHA notes that a small change in decibels means a huge change in the amount of noise and in the potential damage to hearing. Two rules of thumb follow from the physics:

• Plus 3 dB means double the energy. Safe Work Australia's code says an increase of 3 dB represents a doubling, or twice as much sound energy.
• Plus 10 dB means ten times the intensity. NIOSH gives this example to show why decibels are not added like ordinary numbers.

So 100 dB is not "a bit more" than 85 dB. It carries roughly 30 times the sound energy, because 15 dB is five steps of 3 dB, and each step doubles.

What does dBA mean, and why do safety limits use it?

Most hearing limits are written in dBA, or dB(A). The "A" refers to A-weighting, a filter that counts sound the way human ears hear it, giving less weight to very low pitches. ASHA explains that dBA describes the way human hearing perceives sound, and that the higher the dBA, the shorter the time you can safely listen. OSHA likewise measures workplace noise using A-weighted sound levels.

For sudden impact sounds such as gunshots or hammer blows, limits use a peak measure instead. Australia's peak limit is 140 dB(C) at any one time during the day, and ASHA lists impulse noise in dBP, putting firearms at 140 dBP and fireworks at 3 feet at 150 dBP.

How loud are everyday sounds and music?

Published sound levels are averages. Real levels depend on the source, the room and how close you stand. The figures below come from NIDCD, ASHA and WHO.

Sound	Typical level	Source
Whisper	30 dBA	ASHA
Quiet room	40 dBA	ASHA
Normal conversation	60 to 70 dBA	NIDCD
Vacuum cleaner, group conversation	70 dBA	ASHA
Heavy traffic, heard inside a car	85 dB	WHO
Subway, motorcycle, gas mower	91 dBA	ASHA
Hair dryer, kitchen blender	94 dBA	ASHA
Movie theater	74 to 104 dBA	NIDCD
Headphones at maximum volume, concerts, sporting events	94 to 110 dBA	NIDCD
Maximum output of some phones with earbuds, music concert, chainsaw	112 dBA	ASHA
Sirens	110 to 129 dBA	NIDCD
Jackhammer	130 dBA	ASHA
Fireworks show	140 to 160 dBA	NIDCD

Music sits at the top of the everyday range. A personal music player turned all the way up, a gig or a club can match the noise of power tools. That is why WHO's Global standard for safe listening at venues and events recommends a maximum average sound level of 100 decibels, live monitoring of sound levels, and access to quiet zones and hearing protection for audiences.

A quick check needs no equipment: OSHA says that if you need to raise your voice to speak to someone 3 feet away, the noise may be over 85 dBA.

How long can you safely listen at each level?

Safe exposure is a dose: level multiplied by time. The 3 dB rule means each 3 dB step up halves the allowed time. NIOSH sets the starting point at 85 dBA for eight hours and recommends a 3 dBA exchange rate. Australia uses the same energy rule: Safe Work Australia's code says the time a worker can be exposed is reduced by half for every 3 dB increase.

The US legal limit is looser. OSHA's permissible exposure limit is 90 dBA for an 8 hour day with a 5 dBA exchange rate, set out in Table G-16 of 29 CFR 1910.95.

Level (dBA)	Daily time, 85 dBA and 3 dB rule (NIOSH, Australia)	Daily time, OSHA legal limit (90 dBA and 5 dB rule)
85	8 hours	No limit (hearing program required from 85)
88	4 hours	No limit
90	About 2.5 hours	8 hours
91	2 hours	About 7 hours
94	1 hour	About 4.5 hours
95	48 minutes	4 hours
97	30 minutes	3 hours
100	15 minutes	2 hours
105	Under 5 minutes	1 hour
110	About 1.5 minutes	30 minutes

The 85, 100 and OSHA figures are stated by NIOSH, OSHA and 1910.95; the other NIOSH column times follow from halving the time for each 3 dB. The OSHA requirement for a hearing conservation program from 85 dBA as an 8 hour time weighted average explains the first row.

For leisure listening, WHO uses a weekly budget instead of a daily one. Its safe listening guidance gives these times per week:

Level	Safe listening time per week (WHO)
80 dB	40 hours
85 dB	12 hours 30 minutes
90 dB	4 hours
95 dB	1 hour 15 minutes
100 dB	20 minutes
105 dB	8 minutes
110 dB	2.5 minutes
120 dB	12 seconds

Source: WHO, Deafness and hearing loss: Safe listening. WHO also advises that if you use an app to monitor your sound level, it is best to stay below 80 dB on average.

How do the limits differ in Australia, the US and the UK?

The science is shared, but the legal lines differ.

• Australia: the WHS Regulations set 85 dB(A) over 8 hours and 140 dB(C) peak. SafeWork SA adds that the recommended target in ear exposure level for workers is 80 dB(A). The national code also adds 1 to 3 dB to measured levels for shifts of 10 hours or more.
• United States: OSHA's legal limit is 90 dBA with a 5 dB exchange rate, while NIOSH's advisory limit is 85 dBA with a 3 dB rate. At 100 dBA, OSHA allows 2 hours and NIOSH recommends less than 15 minutes.
• United Kingdom: under the Control of Noise at Work Regulations 2005, employers must assess risk and provide training from 80 dB(A), must provide hearing protection from 85 dB(A), and workers must not be exposed above 87 dB(A) after taking hearing protection into account.

None of these limits mean that levels just below them are risk free. They are set to protect most people, and individual sensitivity varies, as the Safe Work Australia code notes when it lists individual susceptibility among the factors behind hearing loss.

How does loud noise damage your ears?

Sound travels down the ear canal, vibrates the eardrum and three small middle ear bones, and sets the fluid in the cochlea moving. NIDCD describes how sensory hair cells ride this wave. Tiny projections on top of them, called stereocilia, bend, opening channels that create an electrical signal for the auditory nerve to carry to the brain.

Loud sound overworks these structures. According to NIDCD, most noise-induced hearing loss is caused by the damage and eventual death of hair cells, and unlike bird and amphibian hair cells, human hair cells do not grow back. Safe Work Australia's code adds that destroyed hair cells cannot be replaced or repaired by any presently known medical treatments, and that noise usually affects high pitched sounds first, so speech starts to sound muffled, especially with background noise.

Very loud single blasts cause a different kind of injury. Gunshots or explosions can rupture the eardrum or damage the middle ear bones, and this loss can be immediate and permanent. Noise can also cause tinnitus, a ringing, buzzing or roaring in the ears or head, which may fade or may continue for life.

What is the difference between a temporary and a permanent threshold shift?

Your "threshold" is the quietest sound you can hear at a given pitch. After a loud night, that threshold can rise, so quiet sounds disappear for a while. This is a temporary threshold shift. NIDCD says such temporary hearing loss disappears 16 to 48 hours later. If the threshold stays raised, it is a permanent threshold shift. A 2009 study in the Journal of Neuroscience defines the pair simply: thresholds may fully recover ("temporary" threshold shift) or stabilize at an elevated value ("permanent" threshold shift).

Safe Work Australia describes how one turns into the other: hazardous noise may cause temporary hearing loss, and with further exposure the ear will gradually lose its ability to recover and the hearing loss will become permanent.

"Temporary" may also be misleading. In that 2009 mouse study, Kujawa and Liberman found that exposures causing moderate, but completely reversible, threshold elevation left hair cells intact but caused acute loss of nerve terminals and delayed degeneration of the cochlear nerve. The authors suggest this could add to difficulty hearing in noisy places and contribute to tinnitus. NIDCD reflects the same concern: although the loss seems to disappear, there may be residual long-term damage. Ringing ears or muffled hearing after a gig are a sign the dose was too high, not a harmless side effect.

How can you keep sound below the damage line?

NIDCD calls noise-induced hearing loss the only type of hearing loss that is completely preventable. The practical steps follow the dose rule:

• Turn it down. Dropping 3 dB doubles your safe time. Keeping personal audio below 80 dB on average fits the WHO guidance.
• Step back. In open space, every doubling of distance from a noise source cuts the level by about 6 dBA.
• Wear earplugs at loud venues. WHO lists wearing earplugs at noisy venues and using well fitted, noise cancelling headphones among the main ways young people can protect their hearing.
• Take quiet breaks. Time away from noise reduces the total dose, which is why the WHO venue standard calls for quiet zones where people can rest their ears.
• Get a hearing check if speech sounds muffled or your ears ring after noise.

The stakes are large. WHO estimates that over 1 billion young adults are at risk of permanent, avoidable hearing loss due to unsafe listening practices, and NIOSH says about 27 million US workers are exposed to hazardous noise at work each year.

Frequently asked questions

Is 85 decibels loud?

Yes, for long periods. It is about the level of heavy traffic heard from inside a car. NIDCD says long or repeated exposure at or above 85 dBA can cause hearing loss, and NIOSH caps a working day at 85 dBA over eight hours.

How long can I listen to music at 100 dB?

Not long. NIOSH recommends less than 15 minutes a day at 100 dBA, and WHO gives 20 minutes per week at 100 dB. Earplugs at a 100 dB concert lower the level reaching your ears and extend that time.

Why does 3 dB make such a difference?

Because the decibel scale is logarithmic, a 3 dB rise means twice as much sound energy. Twice the energy in the same time is twice the dose, so the safe time halves.

Can hearing come back after a loud concert?

Short term dulling often lifts within 16 to 48 hours. Dead hair cells do not regrow, and research in animals shows that even fully recovered thresholds can hide lasting nerve damage.

What sound level is completely safe?

NIDCD says sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure, and WHO lists levels up to 60 dB, normal conversation, as unlimited.

Why do US limits differ from Australian ones?

OSHA's enforceable limit is 90 dBA with a 5 dB exchange rate. NIOSH, the US research agency, recommends a stricter 85 dBA with a 3 dB rate, which is the same approach as the Australian standard.