When Does Noise Start Damaging Your Hearing? The 85 Decibel Rule

Where the 85 Comes From

In 1998 NIOSH, the U.S. agency for workplace health research, set a recommended exposure limit of 85 A-weighted decibels (dBA) averaged over an eight-hour workday. NIOSH considers exposures at or above that level hazardous. It's the number most hearing-safety advice traces back to.

Two details matter. First, it's an average over time, not a ceiling you can't touch for a second. Second, even NIOSH says it doesn't protect everyone: when it set the limit, it acknowledged that about 8% of workers could still develop hearing loss. So NIOSH recommends wearing hearing protection whenever noise is above 85 dBA, no matter how short the exposure.

How Long Is Safe: The Halving Rule

NIOSH uses a 3 dB exchange rate. Every 3 dB increase cuts the allowed time in half. Here is its table of how long you can stay at each average level before you've used up a full day's dose:

The table assumes you spend the other 16 hours of the day, and the weekend, in quieter surroundings. It also assumes a workplace. NIOSH built the limit for a forty-year working career, so treat it as a yardstick, not a guarantee.

Where Everyday Sounds Land

NIDCD publishes average levels for familiar sounds. These are ranges, so a particular theater, bike or stadium can land anywhere inside them.

Look at the concert row against the NIOSH table. At 100 dBA, a full day's dose is gone in 15 minutes. NIDCD's rule of thumb is simple: avoid sounds that are too loud, too close, or last too long.

You can check a level yourself. NIOSH's bulletin points to sound level meters and smartphone sound measurement apps, and says that if the readout shows 85 dB(A) or higher, you should reduce the noise, limit your time, or use hearing protection. A single reading above 85 isn't automatically harmful, because the limit is an average, but I'd treat it as the signal to act.

What the 85 Does Not Cover

This is where most online summaries go wrong. NIOSH says plainly that its limit is for the workplace, and that it isn't meant to protect against general environmental or recreational noise. It doesn't account for hunting, power tools, earbuds, playing in a band, or concerts and games, which add to your overall risk.

For the general public, NIOSH points to a 1974 EPA report that recommended 70 dB(A) averaged over 24 hours, or 75 dB(A) over eight hours. The EPA said it shouldn't be read as a standard or regulation, and it was set to protect against hearing loss and annoyance. The two numbers differ partly because the NIOSH limit assumes a rest period and the EPA one is averaged over 24 hours with none. So 85 is a reasonable "put the plugs in" line, and it isn't a promise that anything below it is harmless.

Individual risk also varies. NIOSH lists how loud, how long, how much rest your ears get between exposures, and your own susceptibility.

What Noise Does Inside the Ear

NIDCD explains that most noise-induced hearing loss comes from damage and eventual death of the hair cells in the inner ear. Unlike bird and amphibian hair cells, human ones don't grow back.

A few effects show up before the permanent kind:

• Temporary dullness. Muffled hearing after loud noise can fade within 16 to 48 hours. NIDCD says recent research suggests there may be residual long-term damage even though the loss seems to disappear.
• Ringing. Loud noise can cause tinnitus, which may fade or may continue for life.
• One-time blasts. Gunshots or explosions can rupture the eardrum or damage the middle ear bones immediately. NIOSH says most noise loss, though, is accumulated damage from repeated exposure.

NIDCD cites a 2011-2012 CDC study that found at least 10 million U.S. adults under 70 (6%), and perhaps as many as 40 million (24%), have hearing test features suggesting noise damage in one or both ears.

What to Do About It

If You Already Wear Hearing Aids

Noise protection still matters once you have some loss, and NIDCD says noise-induced loss is the one type that is completely preventable. I haven't found a reliable general rule for wearing aids in loud places, so I won't make one up. Two things I can point to: the FDA requires every OTC hearing aid's instruction brochure to include a caution about hearing protection, and a caution about excessive sound output. Read those sections before the concert or the shop work. If you're not sure, ask whoever fit your aids.

Wondering whether the aids themselves can hurt your hearing? That's a separate question, and I covered it here: do hearing aids make your hearing worse.

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