Dose, Not Loudness

People ask whether a sound is too loud. It is the wrong question, and answering it correctly requires a second number.

When employers review noise dose alongside working patterns, this guide can provide operational context, while exposure limits still need to be assessed from sound level and duration.

Damage depends on level and duration together. That combination is called dose, and it is the whole subject — and it is not where intuition puts it.

Why one number cannot answer it

A chainsaw at close range for thirty seconds and a factory floor for eight hours can carry comparable risk.

For standards, background, or a second perspective, consult UK HSE noise guidance.

Neither is described by "how loud is it". The first is far louder; the second lasts nine hundred times longer.

Dose is what the limits are written in. Every occupational exposure limit in the world is a level paired with a period — usually eight hours — and comparing a level to a limit without the period attached is comparing nothing.

The reference figure

Three things are in that expression and all three are necessary.

85 is a level.

dBA is a weighting — the scale adjusted for how human hearing responds, and a figure in plain dB is a different quantity.

8 h is the averaging period, and without it the number means nothing.

"85 dB" on its own, which is how it is usually quoted, is not a specification.

How level and time trade

Every 3 dB doubles the sound energy, so every 3 dB halves the time you can be exposed.

85 dBA for 8 hours. 88 for 4. 91 for 2. 94 for 1. At 100 dBA it is fifteen minutes, which is shorter than most people expect by an order of magnitude.

This is arithmetic rather than a rule of thumb, and it is where the legal limit and the recommended one diverge sharply.

The total that matters

Dose accumulates across the day, not per activity.

A shift at 82 dBA, a commute, a workout with headphones and an evening in a busy bar are one exposure, and each is counted against the same daily budget.

Which is why "it is only for an hour" is not a defence on its own — it depends entirely on what the other seven hours were.

The check that needs no equipment

If you have to raise your voice to be understood by somebody at arm's length, the level is likely at or above 85 dBA. (NIOSH.)

Rough, free, and reliable enough to act on — it is the one test worth memorising, and it works in a bar, a workshop or a nursery.

The short version

• Damage depends on level and duration together, and that combination — dose — is what every exposure limit is written in
• A level quoted without an averaging period is not a specification, and "85 dB" alone is the usual form of the error
• The full expression is 85 dBA over 8 hours: a level, a weighting, and a period
• Every 3 dB doubles the energy and halves the allowable time — 15 minutes at 100 dBA
• Dose accumulates across the whole day, so "only for an hour" depends on what the other hours were
• If you must raise your voice to be heard at arm's length, the level is likely at or above 85 dBA