85 Decibels: Whose Criterion It Is and What It Means

The reason 85 dB feels universal is that three influential frameworks all use it, for different purposes. Understanding which one a page means is the difference between a useful figure and a meaningless one.

An eight-hour time-weighted average is a dose, not a loudness. A shift that spends most of its time quiet and twenty minutes very loud can average to the same figure as a steadily moderate one.

This is also why the exchange rate matters. Under NIOSH's 3 dB rule, based on equal sound energy, each 3 dB increase halves the permitted time. Under OSHA's 5 dB rule it takes 5 dB. The two produce different answers for the same working day, and that difference is a policy choice, not a measurement disagreement.

It is not a point at which hearing damage starts. The research literature does not establish a single human threshold below which exposure is harmless and above which it is not; susceptibility varies between people, and the mechanisms of temporary and permanent change are still an active research area.

It is also not a limit for brief sounds. A door slam or a passing siren may momentarily exceed 85 dB without producing a working day that averages anywhere near it.

And it is not medical advice. If you are concerned about your hearing, an audiologist with an audiogram can tell you something a decibel figure never can.

The honest use of 85 dB outside work is as a prompt rather than a rule: if an environment is loud enough that you must raise your voice to be heard at conversational distance, and you are in it for hours, that is a reasonable cue to reduce exposure or take breaks.

That reasoning does not need a precise number, which is fortunate, because a precise number for your own exposure needs a calibrated instrument and a full measurement period rather than a spot reading.

It also helps to know what the figure does not cover. Occupational criteria assume an eight-hour working day followed by a quiet recovery period, roughly five days a week, over a working life. A festival weekend, a long-haul flight or a daily commute on headphones do not map onto that structure, which is why leisure noise is usually discussed with separate, softer guidance.

Criteria like 85 dBA come out of exposure-response work: large occupational datasets relating measured noise exposure over years to measured hearing threshold shifts, combined with a judgement about how much excess risk across a working lifetime is acceptable.

The judgement part is why the numbers differ between bodies even when the underlying science is shared. A regulator weighing enforceability and cost can land on a different figure from a health institute stating what it would recommend on health grounds alone, and the European legislator, working with a limit value plus action values, structures the problem differently again.

None of that makes any of the figures arbitrary. It does mean the correct question is never whether 85 dB is the real limit, but whose limit it is, over what period, and assessed how.