# Noise exposure

Noise adds up on energy, not on decibels. Two hours at 91 dB(A), four at 85 and two at 78 is 86.9 dB(A) for the day — above the 85 dB(A) upper action value, where a plain average of the levels would read 'under it'.

- Its page on this site: [Noise exposure](https://kasq.uk/tools/noise-exposure)
- In the app: [open Noise exposure](https://app.kasq.uk/v3/#tool=noise)

## In the office

Enter each task, its level and its time. Every entry carries its source — measured on site, or declared by the manufacturer under the Supply of Machinery (Safety) Regulations 2008 — and that source prints on the record. The picker in each row offers HSE's own published ranges for common site work as starting points; the record marks them estimated until the level is checked on this site.

## On site

The record tells you how many decibels the hearing protection has to remove. Where exposure is near the values, HSE expects measurement — this tool tells you when you are there.

## What it never does

It does not know what the breaker three metres away adds, or what a shaft does to the sound. A declared figure is measured at the operator in test conditions.

It gives unprotected exposure; whether a particular protector brings the ear under the 87 dB(A) limit value is your calculation, with the protector's data.

## What it counts

What one run counts against a plan's monthly questions is on [the tool's page](https://kasq.uk/tools/noise-exposure) and in the [tools overview](https://kasq.uk/docs/product/tools.md), both written from the same table as the [plans page](https://kasq.uk/plans).

## Questions

### How is daily noise exposure calculated?

Each task's contribution is 10·log10(10^(L/10) × T/8h), where L is the level at the ear in dB(A) and T the time exposed. The day is 10·log10 of the sum of 10^(contribution/10) — energy added, then turned back into decibels. This is the arithmetic in HSE's own noise exposure calculator.

### What are the action values under the Control of Noise at Work Regulations 2005?

The lower exposure action value is 80 dB(A): hearing protection must be made available on request and workers given information and training. The upper exposure action value is 85 dB(A): noise must be reduced so far as is reasonably practicable, hearing protection must be worn and the area marked as a hearing protection zone. The exposure limit value is 87 dB(A), measured at the ear with hearing protection taken into account.

### What are HSE's points?

HSE's points system makes the energy sum easy to do by hand: 100 points is a full shift at 85 dB(A), the scale doubles every 3 dB, and points from different tasks simply add up.

### Which hearing protection should be chosen?

HSE's guide matches the noise level of the task to the protector's Single Number Rating (SNR): roughly 20 or less for 85–90 dB(A), 20 to 30 for 90–95, 25 to 35 for 95–100, 30 or more for 100–105. The protector is chosen for the noisiest task, not for the day's average, and one that puts the ear below 70 dB over-protects.

### Does this replace a noise assessment?

No. It works from the levels you enter — measured, declared by the manufacturer or estimated from HSE's typical ranges — and says which. Where exposure is near the action values, HSE expects measurement on the site itself.