Daily Noise Exposure: How the Published Limits Are Built

Quoting a level alone is meaningless. Noise exposure accumulates, so a limit has to say over how long, and it has to say how much extra level cancels out how much less time. That trade-off is the exchange rate.

A 3 dB exchange rate follows the equal-energy principle from physics: 3 dB is roughly a doubling of sound energy, so the permitted time halves. A 5 dB rate is more permissive and reflects a historical policy compromise rather than an acoustic relationship.

This is Table G-16 from the US occupational noise standard, reproduced without alteration. It is an enforceable limit on assessed worker exposure.

NIOSH's recommended exposure limit is 85 dBA as an eight-hour time-weighted average with a 3 dB exchange rate. Because the exchange rate is stricter, the recommendation diverges further from the OSHA table as levels rise.

NIOSH is explicit that this is a recommendation for occupational settings. It has no legal force of its own, and it is not framed as a safe allowance for leisure noise.

Directive 2003/10/EC uses a daily exposure value, LEX,8h, with three thresholds: a lower action value of 80 dB(A), an upper action value of 85 dB(A) and an exposure limit value of 87 dB(A), each paired with a peak pressure value.

The distinction that matters is procedural. Action values trigger employer duties — information, protection availability, health surveillance — and are assessed without hearing-protector attenuation. The limit value must not be exceeded at the ear, and it does take protector attenuation into account.

It is tempting to take a spot reading, look it up in a table and read off a permitted time. That is not what the tables are for. They apply to an assessed exposure over a defined period, measured with calibrated instrumentation, usually with dosimetry.

A single reading from any meter, including ours, describes one moment at one position. Combining it with a table would produce a number with no evidential basis, so this site does not do it.

There is a further reason to be cautious. The occupational frameworks assume a structured working week with quiet recovery between shifts, and they were derived from workplace exposure data. Leisure exposure often has a different shape entirely, so borrowing the table for a festival day or a long flight stretches it beyond what its own authors claim for it.

A compliance assessment does not consist of walking around with a meter. A worker wears a dosimeter for a representative shift, the instrument integrates the exposure continuously, and the result is reported as a time-weighted average, often alongside the peak levels encountered.

Where exposure varies through the day, the standards combine the fraction of each level's permitted duration that was used, so a loud half-hour and a moderate afternoon are added as a dose rather than compared as readings. That is why two workplaces with identical maximum readings can have very different compliance positions.

The practical consequence for anyone assessing their own environment is that duration is the variable worth attention. Reducing the time spent in the loudest part of a job usually changes the dose more than shaving a few decibels off the source.