EN ISO 9241-6:1999

SLOVENSKI STANDARD
01-januar-2002
Ergonomske zahteve za pisarniško delo s slikovno zaslonsko opremo - 6. del:
Navodila za delovno okolje (ISO 9241-6:1999)
Ergonomic requirements for office work with visual display terminals (VDTs) - Part 6:
Guidance on the work environment (ISO 9241-6:1999)
Ergonomische Anforderungen für Bürotätigkeiten mit Bildschirmgeräten - Teil 6:
Leitsätze für die Arbeitsumgebung (ISO 9241-6:1999)
Exigences ergonomiques pour travail de bureau avec terminaux a écrans de
visualisation (TEV) - Partie 6: Guide général relatif a l'environnement de travail (ISO
9241-6:1999)
Ta slovenski standard je istoveten z: EN ISO 9241-6:1999
ICS:
13.180 Ergonomija Ergonomics
35.180 Terminalska in druga IT Terminal and other
periferna oprema IT peripheral equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 9241-6
First edition
1999-12-01
Ergonomic requirements for office work
with visual display terminals (VDTs) —
Part 6:
Guidance on the work environment
Exigences ergonomiques pour travail de bureau avec terminaux à écrans
de visualisation (TEV) —
Partie 6: Guide général relatif à l'environnement de travail
A Reference number
ISO 9241-6:1999(E)
ISO 9241-6:1999(E)
Contents
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 General guiding principles .5
5 Guidance on natural and artificial lighting.5
6 Guidance on sound and noise .8
7 Guidance on mechanical vibrations .9
8 Guidance on electromagnetic fields and static electricity .10
9 Guidance on thermal environment .12
10 Guidance on space organization and workplace layout.13
Annex A (informative) Lighting .15
Annex B (informative) Methods for measuring and evaluating sound .23
Annex C (informative) Measurements, evaluation and assessment of whole-body vibrations .28
Annex D (informative) Thermal environment.29
Bibliography.31
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
ii
© ISO ISO 9241-6:1999(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 9241-6 was prepared by Technical Committee ISO/TC 159, Ergonomics, Sub-
Committee SC 4, Ergonomics of human-system interaction, Working Group WG 3, Control, workplace and
environmental requirements.
ISO 9241 consists of the following parts, under the general title Ergonomic requirements for office work with visual
display terminals (VDTs):
 Part 1: General introduction
 Part 2: Guidance on task requirements
 Part 3: Visual display requirements
 Part 4: Keyboard requirements
 Part 5: Workstation layout and postural requirements
 Part 6: Guidance on the work environment
 Part 7: Requirements for display with reflections
 Part 8: Requirements for displayed colours
 Part 9: Requirements for non-keyboard input devices
 Part 10: Dialogue principles
 Part 11: Guidance on usability
 Part 12: Presentation of information
 Part 13: User guidance
 Part 14: Menu dialogues
 Part 15: Command dialogues
 Part 16: Direct manipulation dialogues
 Part 17: Form filling dialogues
Annexes A to D of this part of ISO 9241 are for information only.
iii
ISO 9241-6:1999(E) © ISO
Introduction
This part of ISO 9241 applies to work systems as defined in ISO 6385 with visual display terminals (VDTs) as
described in ISO 9241-1. Office work with VDTs can be performed in various environments. These environments
can influence both the comfort and performance of the user. In addition, the work environment can be influenced by
specific characteristics of the VDTs and related equipment (for example, printers, computers).
This part of ISO 9241 has been prepared to give guidance on the determination of environmental conditions which
enhance user comfort and performance. Enhancing the interaction between users and environments often requires
a well-balanced trade-off. For this reason, this part of ISO 9241 provides guiding principles as generic goals, basic
aspects for each item (for example, lighting, noise) and gives guidance on developing integrated solutions under
given circumstances (for example, methods of controlling the acoustic environment for a given task and a given
environment).
iv
INTERNATIONAL STANDARD  © ISO ISO 9241-6:1999(E)
Ergonomic requirements for office work with visual display
terminals (VDTs) —
Part 6:
Guidance on the work environment
1 Scope
This part of ISO 9241 provides guidance on basic principles for the ergonomic design of the work environment and
the workstation, taking into account lighting, effects of noise and mechanical vibrations, electrical and magnetic
fields and static electricity, thermal environment, space organization and workplace layout.
This part of ISO 9241 is applicable to the work environment and workstation in those work systems where a visual
display terminal (VDT) is used for office work.
However, this part of ISO 9241 does not specify the technical characteristics of the equipment needed to satisfy
those equipment-related guidelines associated with the work environment.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO 9241. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 9241 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
registers of currently valid International Standards.
ISO 1996-1, Acoustics — Description and measurement of environmental noise — Part 1: Basic quantities and
procedures.
ISO 2631-1, Evaluation of human exposure to whole-body vibration — Part 1: General requirements.
ISO 2631-2, Evaluation of human exposure to whole-body vibration — Part 2: Continuous and shock-induced
vibration in buildings (1 to 80 Hz).
ISO 5349, Mechanical vibration — Guidelines for the measurement and the assessment of human exposures to
hand-transmitted vibration.
ISO 6385, Ergonomic principles in the design of work systems.
ISO 7730:1994,
Moderate thermal environments — Determination of the PMV and PPD indices and specification of
the conditions for thermal comfort.
ISO 8995:1989, Principles of visual ergonomics — The lighting of indoor work systems.
ISO 9241-6:1999(E) © ISO
ISO 9241-3:1992, Ergonomic requirements for office work with visual display terminals (VDTs) — Part 3: Visual
display requirements.
ISO 9241-7, Ergonomic requirements for office work with visual display terminals (VDTs) — Part 7: Requirements
for display with reflections.
ISO 9612, Acoustics — Guidelines for the measurement and assessment of exposure to noise in a working
environment.
ISO 11690-1:1996, Acoustics — Recommended practice for the design of low-noise workplaces containing
machinery — Part 1: Noise control strategies.
IEC 61000-4-2:1995, Electromagnetic compatibility (EMC) — Part 4: Testing and measurement techniques —
Section 2: Electrostatic discharge immunity test.
IEC 61000-4-8:1993, Electromagnetic compatibility (EMC) — Part 4: Testing and measurement techniques —
Section 8, Power frequency magnetic field immunity test.
3 Terms and definitions
For the purposes of this part of ISO 9241, the terms and definitions given in ISO 6385, ISO 1996-1, ISO 11690-1
and the following apply.
3.1
adaptation, visual
process by which the state of the visual system is modified by previous and present exposure to stimuli that may
have various luminances, spectral distributions and angular subtenses
[IEC 60050(845):1987, IEC 845-02-07]
3.2
clothing insulation
resistance of a clothing ensemble to dry heat loss from the body (convection, radiation, conduction)
NOTE Adapted from ISO 9920:1995.
3.3
colour rendering
effect of an illuminant on the colour appearance of objects by conscious or subconscious comparison with the
appearance under a reference illuminant
[IEC 60050(845):1987, IEC 845-02-59]
3.4
colour rendering index R
a
mean of the CIE 1974 special colour rendering indices for a specified set of eight test colour samples
[IEC 60050(845):1987, IEC 845-02-63]
3.5
colour temperature
the temperature of a Planckian radiator whose radiation has the same chromaticity as that of a given stimulus
[IEC 60050(845):1987, IEC 845-03-49]
3.6
draught rating
percentage of people predicted to be bothered with draught
[ISO 7730:1994]
© ISO ISO 9241-6:1999(E)
3.7
flicker
impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution
fluctuates with time
[IEC 60050(845):1987, IEC 845-02-49]
3.8
general lighting
substantially uniform lighting of an area without provision for special local requirements
[IEC 60050(845):1987, IEC 845-09-06]
NOTE General lighting can be thought of as the lighting of a room to achieve approximately the same visual conditions at
all places in the room.
3.9
glare
condition of vision in which there is discomfort or a reduction in the ability to see details or objects, caused by an
unsuitable distribution or range of luminance, or to extreme contrasts
[IEC 60050(845):1987, IEC 845-02-52]
3.10
glare by reflection
glare produced by reflections, particularly when reflected images appear in the same or nearly the same direction
as the object viewed
[IEC 60050(845):1987, IEC 845-02-54]
3.11
illuminance
(at a point of a surface), the quotient of the luminous flux (dF ) incident on an element of the surface containing the
v
point, by the area (dA) of that element
[IEC 60050(845):1987, IEC 845-01-38]
3.12
lighting, localized
lighting designed to illuminate an area with a higher illuminance at certain specified positions, for instance those at
which work is carried out
[IEC 60050(845):1987, IEC 845-09-08]
3.13
luminance balance
ratio between the luminances of the displayed image and its adjacent surround, or sequentially viewed surfaces
NOTE Adapted from the definition of “luminance” given in IEC 60050(845):1987, IEC 845-01-35.
3.14
mean radiant temperature
uniform temperature of an imaginary enclosure in which radiant heat transfer from the human body is equal to the
radiant heat transfer in the actual non-uniform enclosure
[ISO 7726:1998]
3.15
operative temperature
uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat
by radiation plus convection as in the natural non-uniform environment
NOTE Adapted from ISO 7726:1998.
ISO 9241-6:1999(E) © ISO
3.16
predicted mean vote
PMV
index that predicts the mean value of the votes of a large group of persons on a 7-point thermal sensation scale
[ISO 7730:1994]
3.17
predicted percentage of dissatisfied
PPD
index that predicts the mean value of the thermal votes of a large group of people exposed to the same environment
as a quantitative prediction of the number of thermally dissatisfied people
NOTE Adapted from ISO 7730:1994.
3.18
radiant temperature asymmetry
difference between the plane radiant temperature of the two opposite sides of a small plane element
[ISO 7726:1998]
3.19
rating level
LAR
equivalent continuous A-weighted sound pressure level during a specified time interval plus adjustment for tonal
character and impulsiveness
NOTE Adjustment for tonal character DL = 0,5 dB according to subjective assessments. Impulsiveness is specified only if
T
DL = L - L > 2 dB, both according to ISO 11690-1.
I IAeq Aeq
3.20
relative humidity
ratio between the partial pressure of water vapour in humid air and the water vapour saturation pressure at the
same temperature and the same total pressure
[ISO 7726:1998]
3.21
reverberation
continuation of a sound in an enclosed space after the source has stopped; a result of reflections from the boundary
surfaces of the room
3.22
turbulence intensity
ratio of the standard deviation of the local air velocity to the local mean air velocity
[ISO 7730:1994]
3.23
workplace
arrangement of workstations allocated to one person to complete a work task
[ISO 9241-5:1998]
3.24
workstation
assembly comprising display equipment with or without a central processing unit, which may be provided with a
keyboard and/or input device and/or software determining the operator/machine-interface, optional accessories,
peripherals and the immediate work environment
[ISO 9241-5:1998]
© ISO ISO 9241-6:1999(E)
4 General guiding principles
Improving the ergonomic properties of the design of workstation, work equipment and work environment, will help to
improve user performance, reduce errors and discomfort, and will help to improve their overall well-being.
Environmental design should incorporate adequate control by the individuals over their environmental conditions.
The interference of environmental factors with the relevant characteristics of the equipment should be kept as low
as possible. The unwanted influence of the equipment on the work environment should also be minimized.
NOTE “Interference” in this sense means that the function of a given device is impaired by the influence of a specific
environmental factor.
The characteristics of the work equipment and the work environment are considered under the following headings:
 natural and artificial lighting;
 sound and noise;
 mechanical vibrations;
 electromagnetic fields and static electricity;
 thermal environment;
 space organization and workplace layout.
NOTE This part of ISO 9241 does not address any potential health effects associated with electromagnetic radiation
emissions from equipment and environment.
5 Guidance on natural and artificial lighting
5.1 General
Visual tasks associated with work with most visual displays differ primarily in three ways from the visual tasks
related to traditional office work.
 The main visual object, the visual display unit, is in a vertically oriented position.
 The main visual object can be environment dependent (for example, because of reflections, loss of contrast
and colour information caused by ambient light) to a high degree.
 The elevated line-of-sight increases the importance of the consideration of the characteristics of the visual
environment.
5.2 Basic aspects
5.2.1 Visual tasks
In regard to the type of office work performed with a visual display terminal, a basic distinction should be made
between two types of visual tasks:
a) assimilation of data presented on the display screen (for example, reading texts, viewing graphs, observing
processes or perceiving and distinguishing symbols on the VDT screen);
b) assimilation of data presented on passive media (for example, reading texts or viewing graphs on paper or
perceiving and distinguishing symbols on the VDT keyboard).
ISO 9241-6:1999(E) © ISO
These different types of visual tasks, each considered on its own, indicate that the lighting should fulfil various user
requirements. The lighting system should have sufficient flexibility to match the needs of users of display screens
and passive media.
Correct lighting will not compensate for situations where a user's vision is not adequate or has not been adequately
corrected for the task.
5.2.2 Basic design goals
A good lighting installation should be designed to fulfil its intended functions and should be compatible with the work
environment. Relevant factors include the following:
 favourable distribution of the luminance and contrasts in the workroom;
 the illuminance in the horizontal and vertical planes;
 the ratio between the illuminance in the two planes.
In addition, it is important to consider that
 the lighting of many work environments is produced by a combination of natural and artificial light;
 windows perform a dual function that involves
 visual contact with the outside, and
 creating an adequate and acceptable level of luminance(s) on the inside;
 the quality criteria for artificial lighting are specified in the introduction of ISO 8995:1989 and include the
following aims of visual ergonomics:
 “to optimize the perception of visual information used during the course of work;
 to maintain an appropriate level of performance;
 to guarantee maximum safety;
 to provide acceptable visual comfort.”
 the resulting quality can be affected by the presence of uncontrolled daylight.
In many situations, the installation of workstations and work equipment can be varied, based on the needs of work
organization or users. Well designed lighting systems take into account frequent changes in workstation layout,
equipment and work space layout.
5.3 Luminance distribution in the work space
The luminance distribution in the field of vision should be selected so that
 visual conditions are enhanced,
 glare is avoided,
 perception of relevant task objects is ensured,
 modelling of three-dimensional objects, for example faces, is enhanced,
 a well-balanced luminance distribution is achieved,
 visual communication is improved, and
 safety at work is not impaired.
© ISO ISO 9241-6:1999(E)
For acceptable visual conditions, as well as for psycho-physical reasons, a balanced luminance distribution in the
field of vision is beneficial.
Further information on lighting is given in annex A, together with a guide to selecting the type of lighting (see A.8).
5.4 Glare control
Glare should be avoided by suitable design and installation of the work equipment and the work environment.
In this connection, a distinction is made between
 direct glare,
 glare by reflection.
Direct glare refers to glare (see ISO 8995) from luminaires and other light-emitting surfaces (lamps, illuminated
ceilings, sky, obstructions like adjacent buildings with reflecting glass surfaces). Glare can be caused by excessive,
simultaneous local or successive differences in luminance in the field of vision. It relates both to large space-
confining surfaces and to objects in the immediate and wider surroundings. The degree of impairment depends on
the apparent size, luminance and position of the source of interference in the field of vision and on the state of
adaptation of the viewer.
Glare by reflection is glare caused by reflected light (see ISO 8995). It can be caused by specular reflections
resulting in a distinct image of the original object or by diffuse reflections resulting in high luminances. Glare by
reflection can affect both task performance and comfort. Task performance can be affected if the reflected image of
a visual object obscures the task on the display or on other visual objects. In addition, the contrast ratio of images
can be lowered to an extent that readability or visibility is impaired. Comfort can be affected directly by luminance
imbalance caused by the reflected image or indirectly by impairing visual functions.
To avoid glare by reflection, displays with a reflection-control treatment appropriate for the task and environment
intended should be used (see ISO 9241-7). ISO 9241-7 specifies three classes of VDTs. Class I is considered
suitable for general office use whereas Class II is suitable for most, but not all, office environments. Class III
monitors require a specially controlled luminous environment for use. To achieve acceptable visual conditions,
either the visual environment should be controlled according to the category of the display used or the appropriate
category for the display should be selected considering the visual environment.
Methods for the restriction of glare are discussed in A.3. As a result of different characteristics of the work
equipment or work environment, the appropriate method for a particular workstation can be different.
The selected methods for glare control should ensure that a comfortable posture can be maintained. This means
that the glare control method should not impose any postural restrictions on the user. With respect to windows,
adequate measures should be taken to control glare from windows. Such measures should be selected to allow
user control and to maintain visual contact with the outside.
For avoiding or restricting glare by reflection on a VDT, different methods can be applied. The adequate
combination should be selected with respect to the needs of the particular user and circumstances at the particular
workstation (see annex A). These methods can be used in isolation or in combination with each other.
When applying the methods for avoiding glare by reflection, it should be remembered that an appropriate match
between the VDT and the environment is not the product of a single factor, and that the methods given in Figure A.2
represent different approaches. Different types of display (for example, cathode ray tubes (CRTs) with curved
surfaces or flat panel displays) may require different measures to achieve the same level of visual comfort. In
general, positive polarity displays with adequate additional reflection control measures should be used as a
preferred solution.
Glare control by artificial lighting (luminaire design, correct positioning of luminaires) should be taken into account
when planning the work space. Shielding the glare source from the display position by movable partitions or similar
techniques is a measure that should be applied if other lighting-related measures are not applicable in a given
situation.
Glare control by correct location of the display and/or the workstation can be realized by applying one or more of the
possibilities described in A.3.
ISO 9241-6:1999(E) © ISO
Where multiple displays are used, a combination of the measures described in this part of ISO 9241 may be
needed.
6 Guidance on sound and noise
6.1 Basic aspects
The purpose of the details given in this clause is to provide guidance on improving workstations and workrooms
acoustically for activities on visual display terminals.
Unlike those acoustic events which serve the specific purpose of transmitting information (for example, verbal
communication and warning signals), the term noise is used for acoustic events which disturb, are undesired or
have an adverse effect. Undesired effects of noise can be classified as follows:
 impaired hearing;
 undesired reactions of the central and autonomic nervous system;

 hindrance of verbal and other communication;
 reduced performance and cognitive functioning;
 annoyance.
The annoyance and undesired effects of noise at the workplace should be assessed by the rating level (L ) (see
AR
ISO 9612). Furthermore, the information content of the noise and nature of the work should be taken into account
when assessing noise.
Undesirable effects of noise, such as reduced performance, annoyance and reactions of the nervous system, are
more likely the more difficult and complex the task performed. These effects manifest themselves as a drop in
performance in memory processes, i.e. prompt recall, retention and acquisition of information when continuous
attentiveness and concentration are required, and in complex processing techniques. Information-containing sounds
(including speech, machine sounds with a distinctive time sequence) can also impair the performance at low noise
levels. Human speech as an undesired sound can interfere with acoustic communication, as well as the mental
capabilities associated with short-term memory. Noise, in particular information-containing sound, result in
disturbances to the attention and impairment of verbal communication. This is true for both face-to-face and
mediated communication.
NOTE For offices with multiple workplaces, it is not necessary to remove all sound from extraneous sources in a work
environment, because in an environment which is “too quiet” even low-level sound from nearby conversation and equipment
can be distracting.
Building services and office architecture can cause noise by different mechanisms. With regard to the building
services, there is the noise from air supply through grills and dampers, ductwork transmitted fan noise and cross-
talk between areas through ductwork. With regard to the architecture, there is noise break-through between
partitions and cross-talk through ceiling and floor voids between areas.
6.2 Reduction of noise effects
In order to avoid undesirable effects of noise, the rating level L at the workplace should be low enough to perform
AR
the intended tasks. Noise exposure in workplaces [35 dB(A) to 55 dB(A)] which should not be exceeded for specific
tasks is given in ISO 11690-1. In order to achieve this, the noise emission from work equipment should be low
enough not to interfere with the performance of the task. However, these general measures may not be applicable
in certain environments, for example, where a number of people need to use a telephone. Therefore, in such cases
single factors (for example, noise from external sources) should be identified and appropriate noise-control
measures considered with regard for relevant user needs (for example, improving verbal communication, reducing
unwanted communication and annoyance). Basic aspects of noise control are displayed in Figure 1.
The relationship between different control measures and the specific goals for their introduction is shown in
Figure B.1.
© ISO ISO 9241-6:1999(E)
When replacing or purchasing equipment and machinery for workrooms, relevant data given in equipment
specifications for the noise emission from these equipment and machines should be taken into account.
Furthermore, the workrooms should be acoustically designed so that the rating level is acceptable for the intended
task. The selection of the appropriate control measures depends upon the task to be performed and the
characteristics of the noise. Noise control strategies and measures are described in ISO 11690-1 and ISO 11690-2.
Further information, including methods for measuring and evaluating sound and noise are discussed in annex B.

NOTE Derived from Figure 1 of ISO 11690-2:1996.
Figure 1 — Basic aspects of noise control
7 Guidance on mechanical vibrations
7.1 Basic aspects
Mechanical vibrations (defined in ISO 2041) are periodically occurring changes in physical location. They can
influence or impair the user, the function of working devices or parts of them. These effects have generally been
well researched (see annex C).
Examples of vibration in the work environment relating to office work include air-conditioning systems, impact
printers and the proximity of the workstation to industrial activities that are liable to cause vibrations.
7.2 Reduction of effects of mechanical vibrations
7.2.1 General
7.2.1.1 Types of effect
This subclause provides guidance for limiting the presence of vibrations at the workplace and in workrooms.
Mechanical vibrations at certain levels acting on the users or their working devices can adversely influence health
and safety at work. Moreover, they can impair the user well-being and her/his perception of the information
displayed and the use of controls, for example keyboards. This impairment can take the following form:
a) effect on the user;
b) effect on the legibility of optical devices;
c) effect on the use of operating elements.
7.2.1.2 Effects of mechanical vibrations on the user
When mechanical vibrations act on the user’s body (for example, feet, buttocks, hands, head), a nuisance, work
hindrance, drop in performance and damage to health can occur depending on the evaluated vibration intensity (see
ISO 2631-1, ISO 5349). For the perception of optical displays, vibrations in the range 2 Hz and the resonance range
of the eyeball (16 Hz to 32 Hz) are generally of importance. Certain forms of vibration result in a decrease in visual
acuity of up to 20 %. At a vibrational stress in the vertical or lateral axis of the body, considerable increases in the
perception times (up to 50 fold) can be expected.
ISO 9241-6:1999(E) © ISO
7.2.1.3 Effects of mechanical vibrations on the legibility of optical devices
The effect of vibrations on time-constant displays (for example, printed symbols) impairs perception differently from
the perception of time-variable displays (for example CRTs). In general, the legibility or visibility of time-constant
displays suffer from vibration less strongly than time-variable displays do. Line-oriented text is more prone to
[21]
degradation than grey scale images on the same device [see Çakir and Çakir (1988) ]. The impact of vibrations
on the legibility also depends on the VDT display characteristics (for example, the refresh rate of the screen). With
simultaneous vibratory excitation of body and optical displays, the impacts can be amplified.
7.2.1.4 Effects of mechanical vibrations on the use of operating elements
The effect of vibrations on controls and input devices (for example, keyboard, mouse, etc.), can result in loss of
performance (speed and accuracy).
7.2.2 Avoidance of vibration effects
The development and propagation of mechanical vibrations should, where possible, be avoided entirely or be
reduced at the source. The selection of low-vibration equipment and work processes is the best means of achieving
this. There is a large number of measures that can be taken to further reduce vibration at the point of excitation and
the transmission paths. These should be adapted to the individual requirement. If vibration-damping systems are
not properly coordinated, an increase in vibration can result.
NOTE For basic information on vibration reduction, reference should be made to ISO 2017 and ISO 10846 and also
EN 1299 (examples are given in VDI 2062 sheet 2 and VDI 3831)
If the vibration cannot be adequately reduced at the point of excitation, measures to reduce vibration should be
employed on the transmission paths. Where necessary, affected items at the workstation or even entire working
areas should be isolated from the sources of vibration excitation. Attention should be paid to this when planning and
setting up workplaces, since it is then that the necessary measures can be carried out most effectively and
economically.
In the case of work environments in which vibration stress cannot be fully avoided, measures should be taken to
ensure that the legibility of displays and usability of operating elements, for example controls, are not impaired.
8 Guidance on electromagnetic fields and static electricity
8.1 Basic aspects
In this clause, possible influences of static electric and magnetic fields, extra-low-frequency (ELF) magnetic fields
and electromagnetic fields on the image quality of visual displays, especially of CRT displays are discussed, for
example:
 static (terrestrial) magnetic fields influence CRT uniformity;
 static magnetic fields of all origins influence convergence on colour-CRT displays;
 ELF magnetic fields from the electrical power distribution system or from nearby sources including nearby
CRTs can influence CRT jitter (for maximal spatial instability, see 5.24 of ISO 9241-3:1992).
In this part of ISO 9241, only some effects of electric and magnetic fields are described (for example jitter) that can
influence the assimilation of information from visual displays.
Electric and magnetic fields can impair the quality of optical displays and the transmission of signals from parts of
the work equipment.
The influence of electromagnetic fields on the optical displays can show up in the form of distortion (Moiré effect) or
jitter.
Static electricity originating from the screen can reduce the legibility of the display by dust collection. Static
discharges caused by the friction of carpets, clothing or furniture textiles (especially in winter when relative humidity
is low) can cause annoyance and interferences with the equipment.
© ISO ISO 9241-6:1999(E)
While potential sources should be specified for the lowest possible electromagnetic emission considered by
applicable product and environmental safety standards, it is important to also take into consideration the possible
cumulative effects resulting from the interaction of several potential local sources. Such local sources (for example
emissions from power transmission lines, train or tram routes in the vicinity, internal emissions from machinery,
power supply) and their interactions cannot be fully anticipated by the designers of a VDT. Therefore, the effects of
such local sources should be evaluated in the particular environment, if necessary.
8.2 Avoiding adverse influences from the environment
The quality of the optical display should not be unacceptably impaired by the influences of electric and magnetic
fields external to the display. An unacceptable impairment can be regarded as the exceeding of the maximum
values specified in ISO 9241-3 for locus-dependent distortion of the images or character shapes, time-dependent
fluctuation in character location and time- or locus-dependent distortions as well as colour distortions.
Unacceptable impairments can be caused either by other equipment at the workplace or by external fields with
origins outside the workplace. In order to avoid possible impairments of the first kind, the installation guidance of the
manufacturer should be followed. Managing display distortion caused by interfering external fields can be
accomplished in two ways:
 shielding, screening, altering, relocating or removing the source;
 shielding or screening the device.
Because of the variety of combinations of equipment characteristics (screening, other installations in the room) and
the characteristics of the interference fields (field-strength vectors, frequencies, homogeneity of the fields, etc.),
suitable measures cannot be stated directly.
The following measures can prevent or reduce the effects of external static and dynamic fields:
 physical screening of the source
 physical separation, relocation or re-orientation of the source
 screening or adaptation of the affected display.
The immunity of visual display units to external line-frequency magnetic fields is different for different display
technologies. CRT-displays possess different immunity levels depending on their technical design. Most CRT-
displays meet ISO 9241-3 in ambient magnetic fields up to 0,02 A/m. In many office areas, the strength of the
magnetic fields can exceed this value and, thus, can cause jitter problems. Where such problems are detected, a
reorientation of the specific display unit can be sufficient to treat the problem.
In the case of undesirable interactions of a specific display with a given environment, it should be determined
whether the following engineering measures have been introduced in the design of the display under consideration.
a) Dynamic
 Circuit-engineering measures or metallic screening of the housing (for example, vapour deposition on the inner
sides of the housing, coating with conductive lacquer and fault-free contacting).
 Screening of the deflection coils by highly permeable materials.
 Field damping by inverse eddy-current induction.
Standard EMC testing requirements (see IEC 61000-4-8) specify testing and measurement techniques for external
line-frequency magnetic fields.
b) Static
Use of equipment withstanding electrostatic discharges according to IEC 61000-4-2.
NOTE Other EMC requirements may need to be considered.
 Demagnetization of the display.
 Antistatic treatment of the display surface.
ISO 9241-6:1999(E) © ISO
The following environmental measures can be helpful in the case of problems with existing equipment:
 antistatic room furnishings (floor coverings, furniture);
 increasing humidity (see 9.2.5).
9 Guidance on thermal environment
9.1 Basic aspects
The thermal conditions at the workstations directly influence the comfort and performance of the users. The
introduction of VDTs into the workspace leads to additional heat load and changes air movements. The purpose of
9.2 is to describe the relevant thermal parameters and to describe how to adapt these parameters to human needs
in order to provide an acceptable thermal environment which prevents possible adverse effects to comfort and
health. (See annex D.)
The relevant parameters which affect the occupants of work spaces are the following:
 Personal parameters:
 thermal insulation of clothing;
 activity level.
 Environmental parameters:
 air temperature;
 mean radiant temperature;
 air velocity;
 humidity.
Thermal comfort can be reduced by
 unwanted local cooling,
 radiant asymmetry from cold and hot surfaces,
 draught (air velocity),
 a vertical air temperature difference between head and feet that is too high, and
 floor surface temperatures that are too high or too low.
Local heat build-up caused by thermal radiation or warm air, either from sources in the equipment or climatic effects
(for example solar gain) should be avoided by suitable control of thermal conditions combined with careful
disposition of heat load from equipment and other electrical heat sources in the work space.
A model that describes the relation among relevant parameters for thermal comfort and provides a measure of the
combined influence of these parameters on the general thermal sensation (PMV-index, PPD-index) is presented in
ISO 7730. Detailed information on activity levels can be found in ISO 8996. For thermal insulation of clothing,
detailed information is given in ISO 9920.
9.2 Relevant parameters for thermal comfort
9.2.1 Activity and clothing
Because of individual differences, it is not possible to provide a thermal environment which will satisfy everyone
even if all persons wear the same clothing and perform the same activity. It is therefore important that the individual
should be able to achieve some control on her or his heat balance by adjusting some of the parameters of the
thermal environment or personal parameters.
© ISO ISO 9241-6:1999(E)
9.2.2 Temperatures
The acceptable operative temperature, i.e. the parameter used to describe the combined influence of air
temperature and velocity and of mean radiant temperature, depends mainly on the activity level and clothing of the
person. In addition, thermal comfort depends on the radiant temperature asymmetry, i.e. the difference of the
radiant temperatures of the surrounding surfaces.
At VDT workstations within office areas, the operative temperature may be assumed to be the simple mean of the
air temperature and the mean radiant temperature at a certain point. In buildings with well insulated windows and
walls, the air temperature and the mean radiant temperature may be assumed to be equal if there are no local heat
sources from equipment and lighting.
An unacceptable radiant temperature asymmetry can be caused by large cold or warm vertical surfaces (for
example, badly insulated windows in winter, direct sunshine through windows in summer) or warm or cold horizontal
surfaces (for example, heated or cooled ceilings). Humans are most sensitive to warm ceilings and cold vertical
surfaces. In buildings with small windows or well insulated windows and walls, the radiant temperature asymmetry is
normally not a problem.
In workrooms with VDTs, vertical temperature differences can become too high because of one or more of the
following factors:
 non-uniform vertical air temperature distribution caused by the heating or cooling or ventilating system;
 non-uniform vertical air temperature distribution caused by the heat dissipation of the equipment;
 cold air flow along cold surfaces towards the floor.
9.2.3 Air velocity
The air velocity affects the general thermal sensation. In most cases, it can also cause a draught sensation. The
sensation of draught is influenced by the mean air velocity as well as by the fluctuations of the air velocity
(turbulence) and air temperature. Air velocity can be caused by the air-conditioning or ventilation system and by
cold surfaces (air flow towards the floor).
The design of air conditioning or ventilating systems, if needed, should consider that humans working in normal
clothing are most sensitive to draughts around the ankle and neck region.
9.2.4 Floor surface temperature
Floor temperatures deviating from the air temperature (too high or too low) can cause thermal discomfort, especially
if direct contact is possible. The floor surface temperature is, however, of minor importance under the condition that
users of VDT wor
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