ISO/PRF 16976-7

Respiratory protective devices — Human factors — Part 7: Hearing and speech

This document contains information related to the interaction between respiratory protective devices and the human body functions of hearing and speech.

Appareils de protection respiratoire — Facteurs humains — Partie 7: Discours et audition

Le présent document contient des informations relatives aux interactions entre le port d'un appareil de protection respiratoire et les fonctions physiologiques de l'ouïe et de la parole.

General Information

• Status: Not Published
• ICS: 13.340.30 - Respiratory protective devices
• Technical Committee: ISO/TC 94/SC 15 - Respiratory protective devices
• Drafting Committee: ISO/TC 94/SC 15 - Respiratory protective devices
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Completion Date: 24-Jan-2023

Relations

• Revises: ISO/TS 16976-7:2020 - Respiratory protective devices — Human factors — Part 7: Hearing and speech
• Effective Date: 06-Jun-2022

Standards Content (Sample)

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ISO 16976-7:2023(E)
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Date: 2023-01-12xx
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ISO/TC 94/SC 15/WG 5
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Secretariat: SA
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Respiratory protective devices — Human factors — Part 7: Hearing and speech
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Appareils de protection respiratoire — Facteurs humains — Partie 7: Discours et audition Style Definition: AMEND Terms Heading: Font: Bold

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ISO 16976-7:2023(E)
© ISO 2023 Formatted: Pattern: Clear
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All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or

utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,

or posting on the internet or an intranet, without prior written permission. Permission can be

requested from either ISO at the address below or ISO’s member body in the country of the

requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
[e-mail]
www.iso.org
www.iso.org
ii © ISO 2023 – All rights reserved
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ISO 16976-7:2023(E)
Contents Page

Foreword ................................................................................................................................................................... 4iv

Introduction .............................................................................................................................................................. 5v

1 Scope ................................................................................................................................................................ 1

2 Normative references ................................................................................................................................ 1

3 Terms and definitions, and abbreviated terms ................................................................................. 1

3.1 Terms and definitions ................................................................................................................................ 1

3.2 Abbreviated terms ...................................................................................................................................... 2

4 Range of hearing and speech ................................................................................................................... 2

5 Measurement of sound pressure ............................................................................................................ 3

6 Physiology of the ear .................................................................................................................................. 4

6.1 General ............................................................................................................................................................ 4

6.2 Outer ear ........................................................................................................................................................ 5

6.3 Middle ear ...................................................................................................................................................... 5

6.4 Inner ear ......................................................................................................................................................... 5

7 Hearing loss ................................................................................................................................................... 6

7.1 Conductive hearing loss ............................................................................................................................ 6

7.2 Ototoxicity ..................................................................................................................................................... 6

7.3 Presbycusis .................................................................................................................................................... 6

7.4 Noise induced hearing loss (NIHL) ........................................................................................................ 6

7.5 Other types of hearing loss ....................................................................................................................... 6

7.6 Other effects of noise .................................................................................................................................. 6

7.6.1 General ............................................................................................................................................................ 6

7.6.2 Effects on the wearer .................................................................................................................................. 7

8 Noise exposure limits ................................................................................................................................. 9

8.1 Workplace exposure levels and durations .......................................................................................... 9

8.2 Peak limit value .......................................................................................................................................... 12

9 Speech and hearing difficulties ............................................................................................................. 12

Bibliography.............................................................................................................................................................. 14

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ISO 16976-7:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO

collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patents).www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html.www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 94, Personal safety — Personal protective

equipment, Subcommittee SC 15, Respiratory protective devices.

This first edition of ISO 16976-7 cancels and replaces the second edition (ISO/TS 16976-

7:2019), which has been technically revised. Commented [eXtyles2]: Not found, but similar references

exist
The main changes as follows:
ISO/TS 16976-7:2020, Respiratory protective devices —
Human factors — Part 7: Hearing and speech
— requirements more specified.
Formatted: Pattern: Clear
Formatted: Pattern: Clear
A list of all parts in the ISO/TS 16976 series can be found on the ISO website.
Commented [eXtyles4]: Invalid reference: "ISO/TS 16976

Any feedback or questions on this document should be directed to the user’s national standards body. A series"

complete listing of these bodies can be found at
Formatted: Pattern: Clear
www.iso.org/members.html.www.iso.org/members.html.
Formatted: Pattern: Clear
Formatted: Pattern: Clear
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ISO 16976-7:2023(E)
Introduction

For an appropriate design, selection and use of respiratory protective devices, basic physiological

demands of the user should be considered. The function of a respiratory protective device, the way it is

designed and used, and the properties of its material can affect communications: either speech or hearing

or both.

This document belongs to a series of documents providing basic physiological and anthropometric data

on humans. It contains information about hearing and speech associated with wearing respiratory

protective devices.
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INTERNATIONAL STANDARD ISO 16976-7:2023(E)
Respiratory protective devices — Human factors —
Part 7:
Hearing and speech
1 Scope

This document contains information related to the interaction between respiratory protective devices

and the human body functions of hearing and speech.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 1999, Acoustics — Estimation of noise-induced hearing loss

ISO 16972, Respiratory protective devices — Vocabulary and graphical symbols

IEC 61672, Electroacoustics — Sound Level Meters Commented [eXtyles6]: Not found: "IEC 61672"

ISO 1999, Acoustics — Estimation of noise-induced hearing loss
ISO 16972, Respiratory protective devices — Vocabulary and graphical symbols
IEC 61672, Electroacoustics — Sound Level Meters
3 Terms and definitions, and abbreviated terms

For the purposes of this document, the terms and definitions given in ISO 1999, ISO 16972 and the Formatted: Pattern: Clear

following apply.
Formatted: Pattern: Clear

ISO and IEC maintain terminological databases for use in standardization at the following addresses: Formatted: Pattern: Clear

Formatted: Pattern: Clear

— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp

Formatted: English (United States)

— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/

Formatted: English (United States)
Formatted: Adjust space between Latin and Asian text,
3.1 Terms and definitions
Adjust space between Asian text and numbers, Tab stops:
Not at 19.85 pt + 39.7 pt + 59.55 pt + 79.4 pt + 99.25
3.1.1
pt + 119.05 pt + 138.9 pt + 158.75 pt + 178.6 pt +
hearing 198.45 pt

manner in which the brain and central nervous system recognizes and interprets sounds (3.1.5)

Formatted: English (United States)
Formatted: Font: Times New Roman, English (United
3.1.2
States)
ototoxicity
Formatted: Pattern: Clear
damage to hearing (3.1.1) from overexposure to drugs or toxic substances
Formatted: Pattern: Clear
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ISO 16976-7:2023(E)
3.1.3
noise
unwanted sound (3.1.5)
3.1.4
presbycusis
gradual sensorineural hearing (3.1.1) loss due to natural ageing
3.1.5
sound
form of energy that moves through media in waves of pressure
3.1.6
sound pressure

local pressure deviation from the ambient atmospheric pressure caused by a sound (3.1.5) wave

Note 1 to entry: The sound pressure is measured in pascals (Pa).
3.1.7
RMS sound pressure

deviation from the ambient atmospheric pressure caused by a sound wave at an instant in time over a

given period of time
3.2 Abbreviated terms
SPL sound pressure level
NIHL noise induced hearing loss
TWA time-weighted average
STI speech transmission index
SII speech intelligibility index
RMS root mean square
4 Range of hearing and speech

Humans with normal hearing can usually hear sound pressure waves in a frequency range of about 20 Hz

to 20 000 Hz, but the ear is most sensitive to frequencies from 500 Hz to around 4 000 Hz and declines

dramatically in sensitivity as frequencies drop below 500 Hz. Figure 1 depicts the frequency response

Formatted: Pattern: Clear

and sound pressure level response of human hearing and speech. The frequency range is affected by

ageing as explained further in 7.3. Formatted: Pattern: Clear
16976-7_ed1fig1.EPS
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ISO 16976-7:2023(E)
Key
X logarithmic sale of frequency in Hz
Y sound pressure level, in dB
1 pain threshold
2 range of speech
3 hearing threshold
Figure 1 — Range of human hearing and speech
5 Measurement of sound pressure

The measurement of sound pressure is carried out using a sound level meter which shall meet the

requirements of IEC 61672.
Commented [eXtyles8]: Not found: "IEC 61672"
Formatted: Pattern: Clear

The sound pressure level (SPL) is the logarithmic ratio of the sound pressure to a reference sound

pressure and is expressed in decibels (dB) by Formula (1)):
Formatted: Pattern: Clear
Formatted: Pattern: Clear
RMS
L = 20log (1)
p 10
0
where

L is the sound pressure level, in dB, Formatted: Subscript, Not Raised by / Lowered by

p is the root mean square (RMS) sound pressure, in Pa,
RMS
p is the sound reference pressure, in Pa.
0 Formatted: Not Raised by / Lowered by

In air, the reference sound pressure is 20 μPa. That reference is based on the average human threshold

of hearing at a frequency of 1 000 Hz.

When measuring sound pressure level as it relates to human perception, weighting factors, as given in

IEC 61672, are used to represent human loudness perception at different frequencies. The most common

Commented [eXtyles10]: Not found: "IEC 61672"

is the A weighted sound measurement which approximates the human loudness perception at 40 phon

Formatted: Pattern: Clear

(40 dB at 1 000 Hz) and is expressed as dBA. Examples of some typical sound levels are:

Formatted: Pattern: Clear
Librarylibrary: 40 dBA;
Normalnormal 60 dBA;
conversation:
Traffictraffic noise: 80 dBA;
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ISO 16976-7:2023(E)
Metalmetal shop: 100 dBA;
Sirensiren: 120 dBA;
Jetjet engine: 140 dBA.

A perceived difference in sound level occurs at approximately 3 dB, and a perceived doubling of sound

volume occurs with a 10 dB increase in sound pressure level.

Another sound weighting is the C-weighting, which approximates the human loudness perception at

100 phon.
6 Physiology of the ear
6.1 General

The human ear is the sense organ that detects sounds and changes the pressure waves into a signal of

nerve impulses that is sent to the brain. The ear not only receives and converts sound but also plays a

major role in the sense of balance and body position.

As shown in Figure 2, the ear is usually described in three sections: the outer ear (key 1), middle ear Formatted: Pattern: Clear

(key 2) and inner ear (key 3).
16976-7_ed1fig2.EPS
Key
1 outer ear 10 oval window
2 middle ear 11 semi-circular canals
3 inner ear 12 vestibular nerve
4 pinna 13 cochlear nerve
5 external auditory channel 14 cochlea
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ISO 16976-7:2023(E)
6 tympanic membrane 15 Eustachian tube
7 malleus 16 round window
8 incus 17 tympanic cavity
9 stapes
Figure 2 — Physiological ear terms
6.2 Outer ear

The outer ear is the most external portion of the ear. The outer ear includes the pinna (also called auricle),

the ear canal, and the very most superficial layer of the ear drum (also called the tympanic membrane).

In humans, the only visible portion of the ear is the outer ear. The outer ear does help get sound (and

imposes filtering), but the ear canal is very important. Unless the canal is open, hearing will be damped.

Ear wax (cerumen) is produced by glands in the skin of the outer portion of the ear canal. The outer ear

ends at the most superficial layer of the tympanic membrane.

The pinna helps direct sound through the ear canal to the tympanic membrane (eardrum).

6.3 Middle ear

The middle ear, an air-filled cavity behind the ear drum (tympanic membrane), includes the three ear

bones or ossicles: the malleus (or hammer), incus (or anvil), and stapes (or stirrup). The opening of the

Eustachian tube is also within the middle ear. The three bones are arranged so that movement of the

tympanic membrane causes movement of the malleus, which causes movement of the incus, which causes

movement of the stapes. When the stapes footplate pushes on the oval window, it causes movement of

fluid within the cochlea (a portion of the inner ear).

In humans the middle ear (like the ear canal) is normally filled with air. Unlike the open ear canal,

however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The

Eustachian tube connects from the chamber of the middle ear to the back of the pharynx.

The arrangement of the tympanic membrane and ossicles works to efficiently couple the sound from the

opening of the ear canal to the cochlea. There are several simple mechanisms that combine to increase

the sound pressure.

— The first is the “hydraulic principle”. The surface area of the tympanic membrane is many times that

of the stapes footplate. Sound energy strikes the tympanic membrane and is concentrated to the

smaller footplate.

— A second mechanism is the “lever principle”. The dimensions of the articulating ear ossicles lead to

an increase in the force applied to the stapes footplate compared with that applied to the malleus.

— A third mechanism channels the sound pressure to one end of the cochlea and protects the other end

from being struck by sound waves. In humans, this is called “round window protection”.

6.4 Inner ear

The inner ear includes both the organ of hearing (the cochlea) and a sense organ that is attuned to the

effects of both gravity and motion (labyrinth or vestibular apparatus). The balance portion of the inner

ear consists of three semi-circular canals and the vestibule. When sound strikes the ear drum, the

movement is transferred to the footplate of the stapes, which presses into one of the fluid-filled ducts of

the cochlea. The fluid inside this duct is moved, flowing against the receptor cells of the cochlear nerve,

which fire. These stimulate the spiral ganglion, which sends information through the auditory portion of

the eighth cranial nerve to the brain.
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ISO 16976-7:2023(E)
7 Hearing loss
7.1 Conductive hearing loss

Abnormalities such as impacted ear wax (occlusion of the external ear canal), fixed or missing ossicles,

or holes in the tympanic membrane generally produce conductive hearing loss. Conductive hearing loss

may also result from middle ear inflammation causing fluid build-up in the normally air-filled space. In

some cases, conductive hearing loss is reversible.
7.2 Ototoxicity

A number of drugs in clinical use and some substances at the workplace (e.g. styrol) are considered

“ototoxic” and have the potential to cause damage to hearing as a side effect, especially in combination

with noise exposure. Hearing loss caused by ototoxic drugs can be reversible or permanent.

7.3 Presbycusis

Hearing loss caused by natural aging affects the higher frequencies making word recognition difficult, see

Clause 8. It is permanent.
7.4 Noise induced hearing loss (NIHL)

NIHL is caused by exposure to sound levels or durations that damage the hair cells of the cochlea. Initially,

the noise exposure may cause a temporary threshold shift, that is, a decrease in hearing sensitivity that

typically returns to its former level within a few minutes to a few hours. Repeated exposures lead to a

permanent threshold shift, which is an irreversible sensorineural hearing loss. Hearing loss has causes

other than occupational noise exposure. Hearing loss caused by exposure to nonoccupational noise is

collectively called sociocusis. It includes recreational and environmental noises (e.g. loud music, guns,

power tools, and household appliances) that affect the ear the same as occupational noise. Combined

exposures to noise and certain physical or chemical agents (e.g. vibration, organic solvents, carbon

monoxide, ototoxic drugs, and certain metals) appear to have synergistic effects on hearing

[34][35][36][37][39][40][42][43] 3][4][5][6][8][9][11][12]
loss . . Conductive hearing losses, as opposed to sensorineural
hearing losses, are usually traceable to diseases of the outer and middle ear.
7.5 Other types of hearing loss
For more information on other types of hearing loss, see ISO 1999.
7.6 Other effects of noise

Noise exposure is also associated with nonauditory effects such as psychological stress and disruption of

[42][43][4411][12][13]

job performance and possibly hypertension. See References [4514] to [5726]. Noise may

[58][59][60][6127][28][29][30]
also be a contributing factor in industrial accidents .
7.6.1 General

Hearing loss from long term exposure to noise has been recognized as a hazard. The effects of noise can

include increased stress, cardiovascular function (hypertension, changes to blood pressure and/or heart

rate), annoyance, sleeping problems, and mental health. In the workplace, non-auditory effects of noise

also include problems with oral communications.
7.6.2 Effects on the wearer
7.6.2.1 Physiological
The physiological effects can be temporary or permanent.
Examples of temporary physiological effects are
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ISO 16976-7:2023(E)

— the spontaneous response to loud noise, where muscles are required to protect the auditory senses,

— the muscle tension response, where muscles tend to contract in the presence of continuous loud

noise,

— the respiratory reflexes, where the respiratory rhythm tends to change when noise is present,

— changes in the heart beat pattern, and
— changes in the diameter of the blood vessels, particularly in the skin.
7.6.2.2 Performance
Examples of the performance effects would be the
a) Speechspeech intelligibility.

The presence of noise interferes with the understanding of what other people say, including hearing safe

work instructions. This exchange includes for example face-to-face talks, telephone conversations,

audible danger/warning signals, and speech over a public address system.

In order to be intelligible the sound level of speech shall be greater than the background noise at the ear

of the listener. People with otherwise unnoticeable hearing loss find it difficult to understand spoken

words in noisy surroundings.

In a noisy work environment, people are able to converse with difficulty at a distance of one meter for a

short time in the presence of noise as high as 78 dB(A). For prolonged conversations, the background

noise level shall be lower than 78 dB(A).

In a work environment with a low background noise level not exceeding 55 to 60 dB(A) people often can

talk at distances of 2 m to 4 m comfortably, see Table 1.
Table 1 — Speech communication versus level of background noise

Communication (50 to 70) dB(A) (70 to 90) dB(A) (90 to 100) dB(A) (100 to 130) dB(A)

Face-to-face Raised voice level at Very loud or Maximum voice Very difficult to

(unamplified distances up to 2 m shouted voice level at distances impossible, even at a

speech) level at distances up to 25 cm distance of 1 cm
up to 50 cm
Telephone Satisfactory to Difficult to Use press-to-talk Use special equipment
slightly difficult unsatisfactory switch and an
acoustically
treated booth
Intercom system Satisfactory Unsatisfactory Impossible using Impossible using
using loudspeaker loudspeaker loudspeaker

Type of earphone Any Use any earphone Use any in muff or Use insert type or over-

to supplement helmet except ear earphones in
loudspeaker bone conduction helmet or in muffs;
type good to 120 dB(A) on
short-term basis
Public Address Satisfactory Satisfactory to Difficult Very difficult
System difficult
Type of Any Any Any noise- Good noise-cancelling
microphone cancelling microphone
required microphone
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ISO 16976-7:2023(E)

NOTE The information given in this table has been compiled from the data in Reference [323]. Although this is an old

reference, no recent information was found that would change these examples.
b) Annoyanceannoyance.

In noisy environments, people generally prefer to reduce the noise loudness, avoid it, or leave the noisy

area if possible. The same noise could be annoying to some people but acceptable to others. There is no

definite relationship between the degree of annoyance or unpleasantness of noise and the risk of adverse

health effects. For example, very loud music may be pleasant to one group of people and annoying to

another group. Both groups will be equally at risk of hearing loss.

Besides loudness of sound, several other factors contribute to annoyance. Table 2 lists examples of such Formatted: Pattern: Clear

factors.
Table 2 — Factors that affect individual annoyance to noise
Areas of concern Factors
Primary acoustic factors Sound level
Frequency
Duration
Secondary acoustic factors Spectral complexity
Fluctuations in sound level
Fluctuations in frequency
Rise-time of the noise
Localization of noise source physiology
Non-acoustic factors Adaptation and past experience
How the listener's activity affects annoyance
Predictability of when a noise will occur
Is the noise necessary?
Individual differences and personality

NOTE The information given in this table has been compiled from the data in Reference [323].

Although this is an old reference, no recent information was found that would change these examples.

c) Jobjob interference.

Depending of the type of activity, noise can severely affect efficiency of a task performance. The following

examples will illustrate this point.

— A noisy environment could create a hazard, since audible alarms might not be heard.

— A noisy environment interferes with oral communication and thus, interferes with the activity.

Further information can be found in References [10] to [25]. Noise can also be a contributing factor in

Formatted: Pattern: Clear
[26][27][28][29]
industrial accidents .
Formatted: Pattern: Clear
Formatted: Pattern: Clear
8 Noise exposure limits
Formatted: Pattern: Clear
8.1 Workplace exposure levels and durations Formatted: Pattern: Clear
Formatted: Pattern: Clear

Occupational noise exposure should be controlled so that worker exposures are less than the

combination of sound exposure level (SPL) and duration (T), as calculated by Formula (2) and as shown Formatted: Font: Not Italic

in Table 3.
Formatted: Pattern: Clear
480 480 Formatted: Pattern: Clear
T(min)= T(min)= (2)
(SPL−TWA)/3 (SPL−TWA)/3
Field Code Changed
2 2
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ISO 16976-7:2023(E)

where TWA (Time-Weighted Average) noise exposure limits vary with jurisdiction, but are usually

accepted to be 80 dBA or 85 dBA for an eight hour work shift using a 3 dB exchange rate, i.e. the duration

halves for every 3 dB increase in sound pressure level (SPL).
Table 3 — Maximum exposure duration (T)
SPL Maximum duration for TWA = 85 dBA Maximum duration for TWA = 80 dBA
dB h min s h min s
80 25 24 8 0
81 20 10 6 21
82 16 0 5 2
83 12 42 4 0
84 10 5 3 10
85 8 0 2 31
86 6 21 2 0
87 5 2 1 35
88 4 0 1 16
89 3 10 1 0
90 2 31 47 37
91 2 0 37 48
92 1 35 30 0
93 1 16 23 49
94 1 0 18 54
95 47 37 15 0
96 37 48 11 54
97 30 0 9 27
98 23 49 7 30
99 18 54 5 57
100 15 0 4 43
101 11 54 3 45
102 9 27 2 59
103 7 30 2 22
104 5 57 1 53
105 4 43 1 29
106 3 45 1 11
107 2 59 56
108 2 22 45
109 1 53 35
110 1 29 28
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ISO 16976-7:2023(E)
111 1 11 22
112 56 18
113 45 14
114 35 11
115 28 9
116 22 7
117 18 6
118 14 4
119 11 4
120 9 3
121 7 2
122 6 2
123 4 1
124 4 1
125 3 <1
126 2 <1
127 2 <1
128 1 <1
129 1 <1
...

INTERNATIONAL ISO
STANDARD 16976-7
First edition
Respiratory protective devices —
Human factors —
Part 7:
Hearing and speech
Appareils de protection respiratoire — Facteurs humains —
Partie 7: Discours et audition
PROOF/ÉPREUVE
Reference number
ISO 16976-7:2023(E)
© ISO 2023
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ISO 16976-7:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE © ISO 2023 – All rights reserved
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ISO 16976-7:2023(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions, and abbreviated terms .................................................................................................................. 1

3.1 Terms and definitions ...................................................................................................................................................................... 1

3.2 Abbreviated terms .............................................................................................................................................................................. 2

4 Range of hearing and speech .................................................................................................................................................................. 2

5 Measurement of sound pressure ........................................................................................................................................................3

6 Physiology of the ear ........................................................................................................................................................................................ 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Outer ear ...................................................................................................................................................................................................... 4

6.3 Middle ear ................................................................................................................................................................................................... 4

6.4 Inner ear ....................................................................................................................................................................................................... 5

7 Hearing loss ............................................................................................................................................................................................................... 5

7.1 Conductive hearing loss ................................................................................................................................................................. 5

7.2 Ototoxicity .................................................................................................................................................................................................. 5

7.3 Presbycusis ................................................................................................................................................................................................ 5

7.4 Noise induced hearing loss (NIHL) ....................................................................................................................................... 5

7.5 Other types of hearing loss ........................................................................................................................................... ............... 6

7.6 Other effects of noise ........................................................................................................................................................................ 6

7.6.1 General ........................................................................................................................................................................................ 6

7.6.2 Effects on the wearer ..................................................................................................................................................... 6

8 Noise exposure limits .....................................................................................................................................................................................8

8.1 Workplace exposure levels and durations ..................................................................................................................... 8

8.2 Peak limit value ................................................................................................................................................................................... 11

9 Speech and hearing difficulties ........................................................................................................................................................11

Bibliography .............................................................................................................................................................................................................................13

iii
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ISO 16976-7:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 94, Personal safety — Personal protective

equipment, Subcommittee SC 15, Respiratory protective devices.

This first edition of ISO 16976-7 cancels and replaces the second edition (ISO/TS 16976-7:2019), which

has been technically revised.
The main changes as follows:
— requirements more specified.
A list of all parts in the ISO 16976 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 16976-7:2023(E)
Introduction

For an appropriate design, selection and use of respiratory protective devices, basic physiological

demands of the user should be considered. The function of a respiratory protective device, the way it

is designed and used, and the properties of its material can affect communications: either speech or

hearing or both.

This document belongs to a series of documents providing basic physiological and anthropometric data

on humans. It contains information about hearing and speech associated with wearing respiratory

protective devices.
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INTERNATIONAL STANDARD ISO 16976-7:2023(E)
Respiratory protective devices — Human factors —
Part 7:
Hearing and speech
1 Scope

This document contains information related to the interaction between respiratory protective devices

and the human body functions of hearing and speech.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 1999, Acoustics — Estimation of noise-induced hearing loss
ISO 16972, Respiratory protective devices — Vocabulary and graphical symbols
IEC 61672, Electroacoustics — Sound Level Meters
3 Terms and definitions, and abbreviated terms

For the purposes of this document, the terms and definitions given in ISO 1999, ISO 16972 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
hearing

manner in which the brain and central nervous system recognizes and interprets sounds (3.1.5)

3.1.2
ototoxicity
damage to hearing (3.1.1) from overexposure to drugs or toxic substances
3.1.3
noise
unwanted sound (3.1.5)
3.1.4
presbycusis
gradual sensorineural hearing (3.1.1) loss due to natural ageing
3.1.5
sound
form of energy that moves through media in waves of pressure
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ISO 16976-7:2023(E)
3.1.6
sound pressure

local pressure deviation from the ambient atmospheric pressure caused by a sound (3.1.5) wave

Note 1 to entry: The sound pressure is measured in pascals (Pa).
3.1.7
RMS sound pressure

deviation from the ambient atmospheric pressure caused by a sound wave at an instant in time over a

given period of time
3.2 Abbreviated terms
SPL sound pressure level
NIHL noise induced hearing loss
TWA time-weighted average
STI speech transmission index
SII speech intelligibility index
RMS root mean square
4 Range of hearing and speech

Humans with normal hearing can usually hear sound pressure waves in a frequency range of about

20 Hz to 20 000 Hz, but the ear is most sensitive to frequencies from 500 Hz to around 4 000 Hz and

declines dramatically in sensitivity as frequencies drop below 500 Hz. Figure 1 depicts the frequency

response and sound pressure level response of human hearing and speech. The frequency range is

affected by ageing as explained further in 7.3.
Key
X logarithmic sale of frequency in Hz
Y sound pressure level, in dB
1 pain threshold
2 range of speech
3 hearing threshold
Figure 1 — Range of human hearing and speech
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ISO 16976-7:2023(E)
5 Measurement of sound pressure

The measurement of sound pressure is carried out using a sound level meter which shall meet the

requirements of IEC 61672.

The sound pressure level (SPL) is the logarithmic ratio of the sound pressure to a reference sound

pressure and is expressed in decibels (dB) by Formula (1):
p 
RMS
L =20log (1)
 
p 10
 0 
where
L is the sound pressure level, in dB,
p is the root mean square (RMS) sound pressure, in Pa,
RMS
p is the sound reference pressure, in Pa.

In air, the reference sound pressure is 20 μPa. That reference is based on the average human threshold

of hearing at a frequency of 1 000 Hz.

When measuring sound pressure level as it relates to human perception, weighting factors, as given

in IEC 61672, are used to represent human loudness perception at different frequencies. The most

common is the A weighted sound measurement which approximates the human loudness perception at

40 phon (40 dB at 1 000 Hz) and is expressed as dBA. Examples of some typical sound levels are:

library: 40 dBA;
normal conversation: 60 dBA;
traffic noise: 80 dBA;
metal shop: 100 dBA;
siren: 120 dBA;
jet engine: 140 dBA.

A perceived difference in sound level occurs at approximately 3 dB, and a perceived doubling of sound

volume occurs with a 10 dB increase in sound pressure level.

Another sound weighting is the C-weighting, which approximates the human loudness perception at

100 phon.
6 Physiology of the ear
6.1 General

The human ear is the sense organ that detects sounds and changes the pressure waves into a signal of

nerve impulses that is sent to the brain. The ear not only receives and converts sound but also plays a

major role in the sense of balance and body position.

As shown in Figure 2, the ear is usually described in three sections: the outer ear (key 1), middle ear

(key 2) and inner ear (key 3).
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ISO 16976-7:2023(E)
Key
1 outer ear 10 oval window
2 middle ear 11 semi-circular canals
3 inner ear 12 vestibular nerve
4 pinna 13 cochlear nerve
5 external auditory channel 14 cochlea
6 tympanic membrane 15 Eustachian tube
7 malleus 16 round window
8 incus 17 tympanic cavity
9 stapes
Figure 2 — Physiological ear terms
6.2 Outer ear

The outer ear is the most external portion of the ear. The outer ear includes the pinna (also called

auricle), the ear canal, and the very most superficial layer of the ear drum (also called the tympanic

membrane). In humans, the only visible portion of the ear is the outer ear. The outer ear does help get

sound (and imposes filtering), but the ear canal is very important. Unless the canal is open, hearing will

be damped. Ear wax (cerumen) is produced by glands in the skin of the outer portion of the ear canal.

The outer ear ends at the most superficial layer of the tympanic membrane.

The pinna helps direct sound through the ear canal to the tympanic membrane (eardrum).

6.3 Middle ear

The middle ear, an air-filled cavity behind the ear drum (tympanic membrane), includes the three ear

bones or ossicles: the malleus (or hammer), incus (or anvil), and stapes (or stirrup). The opening of

the Eustachian tube is also within the middle ear. The three bones are arranged so that movement

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ISO 16976-7:2023(E)

of the tympanic membrane causes movement of the malleus, which causes movement of the incus,

which causes movement of the stapes. When the stapes footplate pushes on the oval window, it causes

movement of fluid within the cochlea (a portion of the inner ear).

In humans the middle ear (like the ear canal) is normally filled with air. Unlike the open ear canal,

however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The

Eustachian tube connects from the chamber of the middle ear to the back of the pharynx.

The arrangement of the tympanic membrane and ossicles works to efficiently couple the sound from the

opening of the ear canal to the cochlea. There are several simple mechanisms that combine to increase

the sound pressure.

— The first is the “hydraulic principle”. The surface area of the tympanic membrane is many times that

of the stapes footplate. Sound energy strikes the tympanic membrane and is concentrated to the

smaller footplate.

— A second mechanism is the “lever principle”. The dimensions of the articulating ear ossicles lead to

an increase in the force applied to the stapes footplate compared with that applied to the malleus.

— A third mechanism channels the sound pressure to one end of the cochlea and protects the other

end from being struck by sound waves. In humans, this is called “round window protection”.

6.4 Inner ear

The inner ear includes both the organ of hearing (the cochlea) and a sense organ that is attuned to the

effects of both gravity and motion (labyrinth or vestibular apparatus). The balance portion of the inner

ear consists of three semi-circular canals and the vestibule. When sound strikes the ear drum, the

movement is transferred to the footplate of the stapes, which presses into one of the fluid-filled ducts of

the cochlea. The fluid inside this duct is moved, flowing against the receptor cells of the cochlear nerve,

which fire. These stimulate the spiral ganglion, which sends information through the auditory portion

of the eighth cranial nerve to the brain.
7 Hearing loss
7.1 Conductive hearing loss

Abnormalities such as impacted ear wax (occlusion of the external ear canal), fixed or missing ossicles,

or holes in the tympanic membrane generally produce conductive hearing loss. Conductive hearing loss

may also result from middle ear inflammation causing fluid build-up in the normally air-filled space. In

some cases, conductive hearing loss is reversible.
7.2 Ototoxicity

A number of drugs in clinical use and some substances at the workplace (e.g. styrol) are

...

NORME ISO
INTERNATIONALE 16976-7
Première édition
2023-03
Appareils de protection
respiratoire — Facteurs humains —
Partie 7:
Discours et audition
Respiratory protective devices — Human factors —
Part 7: Hearing and speech
PROOF/ÉPREUVE
Numéro de référence
ISO 16976-7:2023(F)
© ISO 2023
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ISO 16976-7:2023(F)
NORME ISO
INTERNATIONALE 16976-7
Première édition
2023-03
Appareils de protection
respiratoire — Facteurs humains —
Partie 7:
Discours et audition
Respiratory protective devices — Human factors —
Part 7: Hearing and speech
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2023

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publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,

y compris la photocopie, ou la diffusion sur l’internet ou sur un intranet, sans autorisation écrite préalable. Une autorisation peut

être demandée à l’ISO à l’adresse ci-après ou au comité membre de l’ISO dans le pays du demandeur.

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Publié en Suisse
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ISO 16976-7:2023(F)
Sommaire Page

Avant-propos .............................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Domaine d'application ...................................................................................................................................................................................1

2 Références normatives ..................................................................................................................................................................................1

3 Termes, définitions et abréviations ................................................................................................................................................ 1

3.1 Termes et définitions ........................................................................................................................................................................ 1

3.2 Abréviations.............................................................................................................................................................................................. 2

4 Gamme de fréquences pour l'ouïe et la parole ..................................................................................................................... 2

5 Mesurage de la pression acoustique ...............................................................................................................................................3

6 Physiologie de l'oreille ...................................................................................................................................................................................4

6.1 Généralités ................................................................................................................................................................................................. 4

6.2 Oreille externe ........................................................................................................................................................................................ 5

6.3 Oreille moyenne ........................................................................................................................................... .......................................... 5

6.4 Oreille interne ......................................................................................................................................................................................... 6

7 Perte d'audition ...................................................................... ............................................................................................................................... 6

7.1 Perte auditive conductive ............................................................................................................................................................. 6

7.2 Ototoxicité .................................................................................................................................................................................................. 6

7.3 Presbyacousie .......................................................................................................................................................................................... 7

7.4 Perte d'audition due au bruit (NIHL) .................................................................................................................................. 7

7.5 Autres types de perte auditive ................................................................................................................................................. 7

7.6 Autres effets du bruit ........................................................................................................................................................................ 7

7.6.1 Généralités ............................................................................................................................................................................... 7

7.6.2 Conséquences sur les personnes concernées............................................................................................ 7

8 Limites d'exposition au bruit ..................................................................................................................................................................9

8.1 Niveaux et durées d'exposition sur le lieu de travail ............................................................................................ 9

8.2 Valeur limite maximale ................................................................................................................................................................ 12

9 Difficultés d'audition concernant la parole et l'audition .......................................................................................12

Bibliographie ...........................................................................................................................................................................................................................14

iii
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ISO 16976-7:2023(F)
Avant-propos

L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes

nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est

en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.

L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents

critères d'approbation requis pour les différents types de documents ISO. Le présent document

a été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2

(voir www.iso.org/directives).

L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de

droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l'élaboration du document sont indiqués dans l'Introduction et/ou dans la liste des déclarations de

brevets reçues par l'ISO (voir www.iso.org/brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l'intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion

de l'ISO aux principes de l'Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir le lien suivant: www.iso.org/iso/fr/avant-propos.

Le présent document a été élaboré par le comité technique ISO/TC 94, Sécurité individuelle — Équipement

de protection individuelle, sous-comité SC 15, Appareils de protection respiratoire.

Cette première édition de l'ISO 16976-7 annule et remplace la deuxième édition (ISO/TS 16976-7:2019),

qui a fait l'objet d'une révision technique.
Les principales modifications sont les suivantes:
— les exigences sont mieux définies.

Une liste de toutes les parties de la série ISO 16976 se trouve sur le site web de l'ISO.

Il convient que l'utilisateur adresse tout retour d'information ou toute question concernant le présent

document à l'organisme national de normalisation de son pays. Une liste exhaustive desdits organismes

se trouve à l'adresse www.iso.org/fr/members.html.
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ISO 16976-7:2023(F)
Introduction

Il convient que la conception, le choix et l'utilisation des appareils de protection respiratoire tiennent

compte des exigences physiologiques fondamentales de l'utilisateur. Le fonctionnement d'un appareil

de protection respiratoire, la manière dont il est conçu et utilisé et les propriétés du matériau qui le

constitue peuvent gêner la communication en affectant l'ouïe, la parole ou les deux.

Le présent document fait partie d'une série de documents fournissant des données physiologiques et

anthropométriques élémentaires concernant l'être humain. Il contient des informations concernant

l'incidence du port d'appareils de protection respiratoire sur l'ouïe et la parole.

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NORME INTERNATIONALE ISO 16976-7:2023(F)
Appareils de protection respiratoire — Facteurs
humains —
Partie 7:
Discours et audition
1 Domaine d'application

Le présent document contient des informations relatives aux interactions entre le port d'un appareil de

protection respiratoire et les fonctions physiologiques de l'ouïe et de la parole.

2 Références normatives

Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie de leur

contenu, des exigences du présent document. Pour les références datées, seule l'édition citée s'applique.

Pour les références non datées, la dernière édition du document de référence s'applique (y compris les

éventuels amendements).
ISO 1999, Acoustique — Estimation de la perte auditive induite par le bruit

ISO 16972, Appareils de protection respiratoire — Vocabulaire et symboles graphiques

IEC 61672, Électroacoustique — Sonomètres
3 Termes, définitions et abréviations

Pour les besoins du présent document, les termes et définitions de l'ISO 1999 et l'ISO 16972 ainsi que les

suivants, s'appliquent.

L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:

— ISO Online browsing platform: disponible à l'adresse https:// www .iso .org/ obp

— IEC Electropedia: disponible à l'adresse https:// www .electropedia .org/
3.1 Termes et définitions
3.1.1
ouïe

fonction/capacité permettant au cerveau et au système nerveux central de reconnaître et d'interpréter

les sons (3.1.5)
3.1.2
ototoxicité

détérioration de l'ouïe (3.1.1) due à une surexposition à des substances médicamenteuses ou toxiques

3.1.3
bruit
son (3.1.5) indésirable
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ISO 16976-7:2023(F)
3.1.4
presbyacousie
perte neuro-sensorielle progressive d'audition ou d'ouïe (3.1.1) liée à l'âge
3.1.5
son
forme d'énergie qui se déplace par ondes de pression
3.1.6
pression acoustique

variation locale de pression par rapport à la pression atmosphérique ambiante causée par une onde

sonore (3.1.5)
Note 1 à l'article: La pression acoustique est mesurée en pascals (Pa).
3.1.7
valeur efficace de pression acoustique

variation de la pression atmosphérique ambiante causée par une onde sonore à un moment donné sur

une période donnée
3.2 Abréviations
NIHL perte d'audition due au bruit (noise induced hearing loss)
RMS valeur efficace (root mean square)
SII indice d'intelligibilité de la parole (speech intelligibility index)
SPL niveau de pression acoustique (sound pressure level)
STI indice de transmission de la parole (speech transmission index)
TWA moyenne pondérée dans le temps (time-weighted average)
4 Gamme de fréquences pour l'ouïe et la parole

Un être humain doté d'une ouïe normale peut généralement percevoir des ondes de pression acoustique

dans une gamme de fréquences approximativement comprise entre 20 Hz et 20 000 Hz, mais l'oreille

est plus sensible à une fréquence comprise entre 500 Hz et 4 000 Hz environ, et sa sensibilité décroît

considérablement lorsqu'il s'agit de fréquences inférieures à 500 Hz. La Figure 1 illustre la réponse

en fréquence et la réponse du niveau de pression acoustique de l'ouïe et de la parole. La gamme de

fréquences est affectée par le vieillissement, comme expliqué en 7.3.
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ISO 16976-7:2023(F)
Légende
X échelle logarithmique de la fréquence en Hz
Y niveau de pression acoustique, en dB
1 seuil de douleur
2 gamme de fréquences de la parole
3 seuil d'audition
Figure 1 — Gamme de fréquences de l'ouïe et de la parole chez l'être humain
5 Mesurage de la pression acoustique

Le mesurage de la pression acoustique s'effectue à l'aide d'un sonomètre qui doit satisfaire aux exigences

de l'IEC 61672.

Le niveau de pression acoustique (SPL) est le rapport logarithmique de la pression acoustique à une

pression acoustique de référence; il s'exprime en décibels (dB) selon la Formule (1):

p 
RMS
L =20log (1)
p 10 
 
L est le niveau de pression acoustique, en dB;
p est la pression acoustique efficace (RMS), en Pa;
RMS
p est la pression acoustique de référence, en Pa.

Dans l'air, la pression acoustique de référence est de 20 μPa. Cette référence est fondée sur le seuil

moyen d'audition à une fréquence de 1 000 Hz chez l'être humain.

Pour le mesurage du niveau de pression acoustique lié à la perception humaine, des facteurs de

pondération, tels que décrits dans l'IEC 61672, sont utilisés pour représenter la perception sonore

humaine à différentes fréquences. Le plus courant est la mesure du son pondéré A qui se rapproche de

la perception sonore humaine en 40 phones (40 dB à 1 000 Hz) et qui s'exprime en dBA. Exemples de

niveaux sonores types:
bibliothèque: 40 dBA;
conversation normale: 60 dBA;
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ISO 16976-7:2023(F)
bruits de circulation: 80 dBA;
atelier de travail des métaux: 100 dBA;
sirène: 120 dBA;
moteur à réaction: 140 dBA.

Une différence de niveau sonore est perçue à environ 3 dB, et un doublement du volume sonore est

perçu lorsque le niveau de pression acoustique augmente de 10 dB.

Un autre type de pondération du son est la pondération C, qui se rapproche de la perception sonore

humaine à 100 phones.
6 Physiologie de l'oreille
6.1 Généralités

L'oreille humaine est l'organe sensoriel qui détecte les sons et transforme les ondes de pression en un

signal d'impulsions nerveuses qui est envoyé au cerveau. Non seulement l'oreille reçoit et convertit les

sons, mais elle joue également un rôle essentiel pour le sens de l'équilibre et la posture.

Comme le montre la Figure 2, l'oreille est généralement représentée en trois sections: oreille externe (1),

oreille moyenne (2) et oreille interne (3).
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ISO 16976-7:2023(F)
Légende
1 oreille externe 10 fenêtre ovale
2 oreille moyenne 11 canaux semi-circulaires
3 oreille interne 12 nerf vestibulaire
4 pavillon 13 nerf cochléaire
5 canal auditif externe 14 cochlée
6 membrane tympanique 15 trompe d'Eustache
7 malléus 16 fenêtre ronde
8 incus 17 caisse du tympan
9 stapès
Figure 2 — Termes relatifs à la physiologie de l'oreille
6.2 Oreille externe

L'oreille externe est la partie la plus extérieure de l'oreille. Elle inclut le pavillon (également appelé

auricule), le conduit auditif et la couche la plus superficielle du tympan (également appelé membrane

tympanique). Chez l'être humain, la seule partie visible de l'oreille est l'oreille externe. L'oreille externe

aide effectivement à percevoir les sons (et exerce un filtrage), mais le conduit auditif joue un rôle très

important. Si le conduit n'est pas ouvert, les sons perçus seront assourdis. Le cérumen est produit par

des glandes situées dans la peau de la partie extérieure du conduit auditif. L'oreille externe se termine

au niveau de la couche la plus superficielle de la membrane tympanique.

Le pavillon aide à diriger le son dans le conduit auditif jusqu'à la membrane tympanique (tympan).

6.3 Oreille moyenne

L'oreille moyenne, qui est une cavité remplie d'air située derrière le tympan (membrane tympanique),

inclut les trois osselets de l'ouïe: le malléus (ou marteau), l'incus (ou enclume) et le stapès (ou étrier).

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ISO 16976-7:2023(F)

L'ouverture de la trompe d'Eustache se trouve également dans l'oreille moyenne. Les trois osselets sont

disposés de sorte qu'un mouvement de la membrane tympanique entraîne un mouvement du malléus,

qui entraîne un mouvement de l'incus, qui entraîne un mouvement du stapès. Lorsque la base de l'étrier

exerce une poussée sur la fenêtre ovale, elle entraîne un mouvement de fluide à l'intérieur de la cochlée

(qui fait partie de l'oreille interne).

Chez l'être humain, l'oreille moyenne (tout comme le conduit auditif) est normalement remplie d'air.

Cependant, contrairement au conduit auditif ouvert, l'air de l'oreille moyenne n'est pas en contact

direct avec l'atmosphère, à l'extérieur du corps. La trompe d'Eustache s'étend de la chambre de l'oreille

moyenne à l'arrière du pharynx.

La disposition de la membrane tympanique et des osselets permet de transmettre efficacement le son

entre l'ouverture du conduit auditif et la cochlée. Plusieurs mécanismes simples se combinent pour

augmenter la pression acoustique.

— Le premier est le «principe hydraulique». La surface de la membrane tympanique est égale à

plusieurs fois celle de la base de l'étrier. L'énergie acoustique heurte la membrane tympanique et se

concentre sur le petit étrier.

— Un deuxième mécanisme est le «principe du levier». Les dimensions des osselets articulés de l'oreille

induisent une augmentation de la force appliquée à la base de l'étrier par comparaison avec celle

appliquée au malléus.

— Un troisième mécanisme canalise la pression acoustique vers une extrémité de la cochlée et protège

l'autre extrémité des ondes acoustiques. Chez l'être humain, ce mécanisme est appelé «protection

de la fenêtre ronde».
6.4 Oreille interne

L'oreille interne comprend à la fois l'organe de l'ouïe (cochlée) et un organe sensoriel qui s'adapte aux

effets de la gravité et du mouvement (labyrinthe ou appareil vestibulaire). La partie de l'oreille interne

associée à l'équilibre est constituée de trois canaux semi-circulaires et du vestibule. Lorsque le son

atteint le tympan, le mouvement est transféré à la base de l'étrier, qui exerce une pression dans un des

conduits de la cochlée remplis de fluide. Le fluide qui se trouve dans le conduit est mis en mouvement et

s'écoule contre les cellules réceptrices du nerf cochléaire, ce qui provoque leur étirement. Ces cellules

stimulent le ganglion spiral, qui envoie l'information au cerveau par la partie auditive du huitième nerf

crânien.
7 Perte d'audition
7.1 Perte auditive conductive

Des anomalies telles que l'accumulation de cérumen (occlusion du conduit auditif externe), des osselets

calcifiés ou manquants, ou une perforation de la membrane tympanique, provoquent généralement une

perte auditive conductive. Celle-ci peut également résulter d'une inflammation de l'oreille moyenne

ayant entraîné une formation de fluide dans la cavité normalement remplie d'air. Dans certains cas, la

perte auditive conductive est réversible.
7.2 Ototoxicité
Un certain nombre de médicaments d'u
...