6.3 Measurement and assessment of noise exposure

Question 1

Test

Probable noise level

A risk assessment will be
needed if the noise is like this
for more than:

Answer 1

The noise is intrusive but normal conversation is possible
80dB 6 hours

You have to shout to talk to someone 2 m away
85dB 2 hours

You have to shout to talk to someone 1 m away
90dB 45 minutes

Question 2

Workplace noise survey – methodology

Factors to consider

Answer 2

Location of measurement

Duration of measurement

Sample measurements for a group

Mobile workers and highly variable daily exposures

Measurements close to the ear

Sources of error and other factors influencing the
measurement result

Question 3

Location of measurement

Answer 3

When measuring to estimate a person’s noise exposure, measurements should be
taken at every location the person works in or passes through during the working
day, and the time spent at each location should be noted.

Exposures to sound pressure levels (SPL) below 75 dB are not typically recorded as
they are insignificant in relation to the daily noise exposure action levels.

Measurements should be made at the position occupied by the person’s head,
preferably with the person not present. If the operator needs to be present while the
measurements are made (to control a machine or process, for example) the
measurements should be made with the microphone positioned approximately 15cm
away from the operator’s head on the side where noise levels are higher. This is
close enough to obtain a reliable measure of the noise exposure, but not so close
that reflections cause errors.

To avoid making large numbers of measurements where, for example, the SPL is
changing or if the person is moving within a noisy area, the worst case should be
taken and measurements made at the noisiest location, or during the loudest
periods.

Alternatively, carrying out a spatial-average measurement by following the
movement of the worker may provide a representative measure of the noise
exposure.

When using a dosemeter the microphone should be positioned on the shoulder
(ideally on the shoulder joint) and measures taken to prevent it touching the neck,
rubbing on or being covered by clothing or protective equipment. The dosemeter
body should be placed securely in a pocket or on a belt where it can be safe from
damage during the measurement.

Question 4

Duration of measurement

Answer 4

The noise level to which an individual employee is exposed will normally change
throughout the day as different jobs are done and different machines or materials are
used at different times.

Enough noise measurements should be taken to account for all these changes, and
the sound level and the person’s exposure duration at each noise level should be
recorded.

With a sound level meter measurements should be:
 made at each position or during each job or task
 made over a long enough period to obtain a representative measurement of the
level the person is exposed to.

The LAeq for the entire period may need to be measured but often a shorter
measurement can be sufficient.

In general:
 If the noise is steady, a short sample LAeq measurement may be enough.
 If the noise is changing, wait for the LAeq reading to settle to within 1 dB.
 If the noise is from a cyclic operation measure the LAeq over a whole number of
cycles.

The measurement should cover all significant noise during the job or task, especially
any short-duration, high-level noise exposures which may have a significant impact
on the true LAeq.

Noise dosemeters are designed to operate for long periods. They are ideal for
measurements over an entire shift, or for a period of several hours during a shift.

If measurements are made over part of a shift the period of your measurement
should cover all significant noise exposure, so as to be typical of the working day
and to enable a reliable prediction of the full daily exposure.

Very short measurements should be avoided as they can be inaccurate due to the
limited resolution of the dosemeter’s display.

Steps should be taken to try and ensure that the dose reading relates to actual true
noise exposure, not false input from unrepresentative noise sources when the meter
is not supervised, for example: artificial bangs to get a ‘better score’, or tampering
with the microphone.

Question 5

Sample measurements for a group

Answer 5

If several workers work in the same area, the exposure for them all may be
estimated from measurements in selected locations and for appropriate durations to
determine the highest exposure that someone is likely to receive.

Question 6

Mobile workers and highly variable daily exposures

Answer 6

For some jobs (such as maintenance) the work and the noise exposure will vary from
day to day so there is no typical daily exposure. For people in these jobs,
measurements need to be made of the range of activities undertaken, possibly over
several days. From these measurements the likely daily exposure for a nominal day
or days should be estimated.

Question 7

Measurements close to the ear

Answer 7

Measurements close to the ear, such as sound from a communication headset, or
under a motorcycle helmet, require specialist equipment and procedures.

Question 8

Sources of error and other factors influencing the

measurement result

Answer 8

The relevant variables should be revealed during an analysis of the work under
consideration and during measurements. If significant contribution from sources of
error is detected, the measurements should be rejected or corrected.

The measured noise exposure and the uncertainty in the result depend on the
measurement method used. A dosemeter tends to increase the potential false
contributions to measurements and thereby the measured sound pressure level.

However, using a hand-held sound-level meter may lead to an underestimation of
the worker’s noise exposure. This is particularly connected to the difficulty in
assessing the contribution from close-to-ear sound levels and noise from hand-held
tools.