ISO 2631:1978
(Main)Guide for the evaluation of human exposure to whole-body vibration
Guide for the evaluation of human exposure to whole-body vibration
Guide pour l'estimation de l'exposition des individus à des vibrations globales du corps
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Standards Content (Sample)
INTERNATIONAL STANDARD 2631
INTERN"-TION"'l ORG . NIZ"'TION FOR STANDARDIZ"-TION•MEJI(llYHAPOllHAJI OPrAKKlAUHll no CTAKllAPTHlAUHH•ORGANISATION INTERNATIONAL£ DE NORMALISATION
Guide for the evaluation of human exposure to whole-body
vibration
Guide pour /'estimation de /'exposition des individus a des vibrations globales du corps
Second edition- 1978-01-15
UDC 534.1 : 612.014.45 Ref. No. ISO 2631-1978 (E)
Descriptors: humans, human body, exposure, vibration, measurement, human factors engineering.
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FOREWORD
ISO (the International Organization for Standardization) is a worldwide federation
of national standards institutes (ISO member bodies). The work of developing
International Standards is carried out through ISO technical committees. Every
member body interested in a subject for which a technical committee has been set
up has the right to be represented on that committee. International organizations,
in liaison with ISO, also take part in the work.
governmental and non-governmental,
Draft International Standards adopted by the technical committees are circulated
to the member bodies for approval before their acceptance as International
Standards by the ISO Council.
International Standard ISO 2631 was developed by Technical Committee
ISO/TC 108, Mechanical vibration and shock.
This second edition was submitted directly to the ISO Council, in accordance
with clause 6.12.1 of the Directives for the technical work of ISO. It cancels and
replaces the first edition (i.e. ISO 2631-1974), which had been approved by the
member bodies of the following countries :
Australia Ireland South Africa, Rep. of
Austria Italy Spain
Belgium Japan Sweden
Thailand
Czechoslovakia Netherlands
Egypt, Arab Rep. of U.S.A.
New Zealand
France Portugal
Germany Romania
The member bodies of the following countries had expressed disapproval of the
document on technical grounds :
United Kingdom
U.S.S.R.
Compared with the first edition, only modifications of minor importance have been
made (correction of some misprints in the text, correction of the first two columns
for 24 h and 16 h in table 1, correction of figures 2a and 2b).
© International Organization for Standardization, 1978 •
Printed in Switzerland
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ISO 2631-1978 (E)
INTERNATIONAL STANDARD
Guide for the evaluation of human exposure to whole-body
vibration
0 INTRODUCTION b) Vibrations transmitted to the body as a whole
through the supporting surface, namely, the feet of a
Vehicles (air, land and water), as well as machinery (for
the buttocks of a seated man or the
standing man,
example, in industry and agriculture), expose man to
supporting area of a reclining man. This kind of
mechanical vibration which can interfere with comfort,
vibration is usual in vehicles, in vibrating buildings and in
working efficiency and, in some circumstances, health and
the vicinity of working machinery.
safety. Various methods of rating the severity of exposure
c) Vibrations applied to particular parts of the body
and defining limits of exposure based on laboratory or field
such as the head or limbs; for example, by vibrating
data have been developed in the past for specific
handles, pedals, or head-rests, or by the wide variety of
applications. None of these methods can be considered
powered tools and appliances held in the hand.
applicable in all situations and consequently none has been
universally accepted.
It is also possible to recognize the condition in which an
In view of the complex factors determining the human indirect vibration nuisance is caused by the vibration of
external objects in the visual field (for example, an
response to vibrations, and in view of the paucity of
consistent quantitative data concerning man's perception of instrument panel).
vibration and his reactions to it, this International Standard
This International Standard, however, applies chiefly to the
has been prepared first, to facilitate the evaluation and
common condition (b) above; and, in particular, where the
comparison of data gained from continuing research in this
vibration is applied through the principal supporting surface
field; and, second, to give provisional guidance as to
to the body of a standing or seated man. In the case of
acceptable human exposure to whole body vibration. The
vibrations applied directly to a reclining or recumbent man,
I imits proposed in this International Standard seem to be a
insufficient data are available to make a firm
fair compromise between the available data and should
recommendation; this is particularly true of vibration
satisfy the need for recommendations which are simple and
transmitted directly to the head, when tolerability is
suitable for general application. These limits are defined
generally reduced. Tolerance may also be reduced when
explicitly in numerical terms to avoid ambiguity and to
conditions (b) and (c) exist together. Provisionally,
encourage precise measurement in practice. However, when
however, the limits for the standing or seated man may also
using these criteria and limits it is important to bear in
be used for the reclining or recumbent man. It must be
mind the restrictions placed upon their application.
appreciated that some circumstances will arise in which the
Because of the wide variety of possible conditions and
rigorous application of these limits would be inappropriate.
effects of human exposure to vibrations, and because of the
existing shortage of firm data, more detailed guidance is
11
1 SCOPE AND FIELD OF APPLICATION
hardly warranted at the present time. Nevertheless, it is
hoped that this International Standard not only proves
This International Standard defines and gives numerical
useful in the assessment of existing or predicted vibration
values for limits of exposure for vibrations transmitted
environments but also stimulates the reporting and critical
from solid surfaces to the human body in the frequency
evaluation of new findings about the effects of vibration on
range 1 to 80 Hz. It may be applied, within the specified
man.
frequency range, to periodic vibrations and to random or
There are basically three kinds of human exposure to non-periodic vibrations with a distributed frequency
vibration, namely : spectrum. Provisionally, it may also be applied to
continuous shock-type excitation in so far as the energy in
a) Vibrations transmitted simultaneously to the whole
question is contained within the 1 to 80 Hz band.
body surface or substantial parts of it. This occurs when
the body is immersed in a vibrating medium. There are
These limits (defined in detail in clause 4) are given for use
circumstances in which this is of practical concern; for
according to the three generally recognizable criteria of
example, when high intensity sound in air or water
preserving comfort, working efficiency, and safety or
excites vibrations of the body.
health. The limits set according to these criteria are named
1) Addenda to this International Standard. providing modified guidelines for particular applications, may be issued from time to time.
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ISO 2631-1978 (E)
respectively in this International Standard the "reduced IEC Publication 225, Octave, half-octave and third-octave
comfort boundary", "fatigue - decreased proficiency band filters intended for the analysis of sound and
boundary" and the "exposure limit". For example, where
vibrations.
the primary concern is to maintain the working efficiency
of a vehicle driver or a machine operator working in
vibration, the "fatigue - decreased proficiency boundary"
3 CHARACTERIZATION OF VIBRATION EXPOSURE
would be used as the guiding limit in laying down vibration
specifications or in carrying out vibration control measures,
while, in the design of passenger accommodations, the 3.1 Direction of vibration
"reduced comfort boundary" should be considered.
3.1.1 Rectilinear vibrations transmitted to man should be
According to the criteria mentioned, these limits are
measured in the appropriate directions of an orthogonal
specified in terms of vibration frequency, acceleration
co-ordinate system having its origin at the location of the
magnitude, exposure time and the direction of vibration
heart (see figure 1).
relative to the torso. This direction is defined according to
NOTE - The terminology commonly used in biodynamics relates
the recognized anatomical axes of the human body (see
the co-ordinate system to the human skeleton in a normal
clause 3).
anatomical position. Accelerations (motion) in the foot (or
buttocks)-to-head (or longitudinal) axis are designated ± az; accelera
This International Standard is applicable only to situations
tions in the fore-and·aft (anteroposterior or chest-to-back) axis, ±ax;
involving people in normal health : that is, persons who are
and in the lateral (right-to-left side) axis, ± ay. These axes are
illustrated in figure 1.
considered fit to carry out normal living routines, including
travel, and to undergo the stress of a typical working day or
shift. 3.1.2 Angular (or rotational) vibrations about a centre of
rotation are frequently an important part of a vibration
No part of this International Standard shall be extrapolated
environment. For example, in tractors going over rough
to frequencies outside the range 1 to 80 Hz (see notes
terrain, or in aircraft flying through turbulence, the
below).
pitching or rolling motions of the seat may be more dis
turbing than the rectilinear vibration up and down. However,
NOTES
little information on the effects of angular (or rotational)
1 The limits specified herein are based upon data available from
vibration is yet available. In practice, the centre of
both practical experience and laboratory experimentation in the
vibratory rotation can often be assumed to lie far enough
field of human response to mechanical vibration. To date, useful
from the point of application of vibration to the body for
observations have been made mainly in the frequency range between
the resulting motion to be represented by translatory
about 1 and 100Hz. The frequency range, its subdivisions, and the
corner frequencies defined in. this International Standard have been
vibrations alone. Nevertheless, whenever practicable,
selected in accordance with ISO 266, and with national standards
rotational vibrations in roll, pitch and yaw (as related to the
in several countries.
anatomical axes) should be measured and reported, in order
2 Vibrations in the frequency range below about 1 Hz are a special
to increase our knowledge of the human response to such
problem, associated with symptoms such as kinetosis (motion
excitation.
sickness) which are of a character different from the effects of
higher frequency vibrations. The appearance of such symptoms
depends on complicated individual factors not simply related to the
3.1.3 In this International Standard separate I imits are
intensity, frequency or duration of the provocative motion.
specified according to whether the vibration is in the
Mechanical vibrations applied to the feet or buttocks above the
(anatomically) longitudinal (± azl direction or transverse
frequency range considered in this International Standard
(±ax or± ay) plane.
increasingly produce sensations and ·effects which are highly
dependent upon local factors such as the precise direction, site and
area of application of the vibration to the body and the presence of
3.2 Location of measurement
damping materials (for example, clothing or footwear) which may
control the vibratory response of the skin and superficial layers of
Because the limits given in this International Standard
the body. For these reasons, therefore, it is not possible on the basis
apply to vibration at the point of entry into the human
of present data to formulate generally valid recommendations for
body itself (that is, at the body surface, but not, for
frequencies outside the 1 to 80 Hz band.
example, at the substructure of a resilient seat, which may
transform the vibration en route to the man), vibration
2 REFERENCES measurements shall be made as close as possible to the
point or area through which the vibration is transmitted to
ISO 266, Acoustics
Preferred frequencies for
the body. For example, if the man is standing on a floor
measurements.
or sitting on a platform without any resilient material
between the body and the supporting structure, then the
IEC Publication 184, Methods for specifying the
measuring transducer or pick-up should be fastened to that
characteristics of electromechanical transducers for shock
rigid structure. Where some resilient element, such as a seat
and vibration measurements.
cushion, does exist between the body and the vibrating
IEC Publication 222, Methods for specifying the structure, it is permissible to interpose some form of rigid
characteristics of auxiliary equipment for shock and
transducer support (for example, a thin, suitably formed
vibration measurement.
metal sheet) between the subject and the cushion; but care
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ISO 2631-1978 (E)
must be taken to ensure that such a device does not suitable tape recording system to obtain representative
significantly influence the transfer of vibration through the records for subsequent analysis will be the method of
cushion to the man or introduce rotational motions choice. An rms-rectifying device may also be included for
otherwise not present. If it is not practicable to measure the convenience, so that rms values may be read off or recorded
vibration at the point of input to the man in such a way, directly.
then the transmission characteristics of the seat cushion or
All vibration measuring equipment should be properly
other resilient element must be determined and taken into
calibrated. This should be done in accordance with existing
account when calculating the actual vibration transmitted
standards or recommendations governing the calibration of
to the body. In such cases the characteristics of the
such equipment. The basis of operation and the
cushioning system are to be reported.
characteristics of any measuring equipment used should be
NOTE - For research purposes, requiring the precise definition of reported together with the results obtained with it. It is
the vibratory input to human subjects, it has become customary in
important to report such characteristics as the frequency
laboratory studies of biodynamic and physiological responses to
sensitivity, the dynamic properties (for example, the time
replace seat cushions by rigid packs or platforms, because variation
constant), the dynamic range and resolution of the
of the measuring conditions by different arbitrary seating
equipment; and when appropriate, the precision of
arrangements can significantly affect the experimental results. Some
of the variability of published research results in this field arises
rms-rectifying, frequency-weighting, tape recording,
from differences between the experimental conditions adopted in
frequency analysis or such other operations as may be
different laboratories.
performed upon the signal.
NOTES
3.3 Intensity of vibration
1 It is recommended that I EC Publication 184 be used for
specifying the vibration-transducers and I EC Publication 222 for
The primary quantity used to describe the intensity of a
specifying the auxiliary equipment, including amplifiers,
vibration environment, irrespective of the type of
frequency-selective equipment and carrier systems.
transducer or pick-up used in actual measurements, shall be
2 With respect to the subjective judgement of the vibration
the acceleration. Acceleration should normally be expressed
intensity, it appears that the integration time for the human
in metres per second squared (m/s2).
vibration perception decreases from 2 to 0,8 s over the frequency
range from 2 to 90 Hz.
NOTE- In physiological work it is frequently the custom to
express accelerations non-dimensionally in g units where 1 g is the
value of the standard acceleration due to gravity acting at the earth's 3.5 Random or broad-band vibration analysis
surface. This usage is permissible within the context of experimental
work in hand provided that, when reference is made to the limits In the measurement of random or distributed vibration, of
given in this International Standard, the international standard value
which narrow-band analysis not exceeding one third·octave
of gn is used for conversion to values of acceleration expressed in
is the appropriate method of description, the third-octave
metres per second squared.
band filters used in any recording or analytical network
shall be in accordance with IEC Publication 225. The
The magnitude of a vibration, that is, the acceleration (or, if
frequency range given in IEC Publication 225 must
quoted, the velocity or displacement), should be expressed
as a root-mean-square (rms) value. When peak values are accordingly be extrapolated to corresponding lower
measured, these must be converted as appropriate to rms frequencies.
values before reference to the limits given in this
For some applications H will be appropriate to equip
International Standard. For the adequate description of
electronic vibration measuring apparatus with a
vibration which is markedly non-sinusoidal, random or
frequency-weighting network defined as corresponding to
broad-band, the crest factor (ratio of maximum peak to rms
the limits for vertical (az) and horizontal (ax and ay)
value) of the time function must be determined or
vibration respectively given in clause 4, tables 1 and 2 and
estimated : the limits given in this International Standard
figures 2a and 3a (see note 2 of 4.2.4). A network so
should be regarded as very tentative in the case of
defined shall not deviate from the recommended values by
vibrations having high crest factors (that is, greater than 3;
more than ± 1 dB at two fixed frequencies; 6,3 Hz and
see below).
31,5 Hz for az measurements and 1,25 Hz and 31,5 Hz for
NOTE - Measurements of rotational vibrations, whenever made, ax and ay measurements.
should be reported in units of rms angular acceleration (radfs2).
3.6 Exposure time
3.4 Measuring equipment
This International Standard includes a computational
Vibration measuring equipment generally consists of the
procedure (see 4.4) for assessing the effective daily
following parts: a transducer or pick-up, an amplifying
exposure to vibration. This is intended to take account, so
device (electrical, mechanical or optical). and an amplitude
far as is possible, of variations in the intensity of vibration
or level indicator or recorder. Where practicable (as in
and any intermittency or interruption of exposure to
electronic instrumentation) and appropriate, networks may
vibration which may occur during the period in question.
be included to limit the frequency range of the equipment
Whenever measurements are made of human exposure to
and to apply the recommended frequency-weighting to the
vibration which is varying in intensity, or which is
input signal. For many applications, where it is not essential
discontinuous, the time-history of such exposure should be
to rely solely upon on-the-spot determinations, the use of a
reported in detail.
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ISO 2631-1978 (E)
4 VIBRATION EVALUATION GUIDE below 2Hz for transverse lax. ay) vibration; and that
human tolerance of vibration decreases (demanding
increasingly stringent limits) in a characteristic way with
4.1 General considerations
increasing exposure time (figures 2b and 3b). It is seen from
There are four physical factors of primary importance in
a comparison of figures 2a and 3a that, whereas the
determining the human response to vibration, namely, the
tolerance for transverse vibration is lower than that for
intensity, the frequency, the direction, and the duration
longitudinal vibration at very low frequencies, the converse
(exposure time) of the vibration. In the practical evaluation
is so for higher frequencies (above approximately 2,8 Hz).
of any vibration of which a physical description can be
NOTE- It is anticipated that with experience in the practical
given in terms of those factors, three main human criteria
applications of this International Standard, correction tables will be
can be distinguished. These are :
worked out to vary the level of the fatigue - decreased proficiency
boundary according to different environmental conditions of task
a) the preservation of working efficiency
requirements. For example, a more stringent limit may have to be
("fatigue -decreased proficiency boundary");
applied when the task is of a particularly demanding perceptual
nature or calls for an exercise of fine manual skill. By contrast, some
b) the preservation of health or safety ("exposure
relaxation of the limit might be possible in circumstances in which
limit"); and
the performance of the task (for example, heavy manual work) is
relatively insensitive to vibration. Tentative data, as yet too few to
c) the preservation of comfort ("reduced comfort
provide a basis for a firm recommendation, suggest that a range of
boundary").
correction of + 3d B to- 12 dB (that is, a modifying factor of 1,4 to
0,25 times the rms acceleration specified by the boundary) may be
The recommended limits of exposure set according to these
envisaged.
three criteria are defined in 4.1.1 to 4.1.3. Each of these
limits is defined graphically for the longitudinal (az)
4.1.2 "Exposure limit" (health or safety)
direction (figures 2a and 2b) and the transverse lax, ay)
The exposure limit as a function of frequency and exposure
directions (figures 3a and 3b). Numerical definition of the
time is of the same general form as the fatigue - decreased
graphs in figures 2 and 3 is presented in tables 1 and 2.
proficiency boundary but the corresponding levels are
Typically, as in most transport situations, az (longitudinal)
raised by a factor of 2 (6 dB higher). In other words,
vibration will be applied to a sitting or standing person (a
maximum safe exposure is determined, for any condition of
situation popularly referred to as "vertical vibration").
frequency, duration and direction, by doubling the values
NOTE - It will be seen that, other factors being equal, somewhat
allowed according to the criterion of fatigue - decreased
higher levels of vibration are acceptable when health or safety is the
proficiency (see figures 2a, 2b and 3a, 3b and tables 1 and 2).
criterion, in comparison with the limits appropriate to working
efficiency; and, conversely, lower limits are set when the criterion is
Exceeding the exposure limit is not recommended without
the preservation of comfort. This is in general accord with
special justification and precautions, even if no task is to be
experimental observation and experience, but it should not be taken
performed by the exposed individual.
as implying that there exists in all circumstances a simple
hierarchical relationship between the intensities of vibration likely
NOTES
to impair health, working efficiency or comfort.
1 The exposure limit recommended is set at approximately half the
level considered to be the threshold of pain (or limit of voluntary
4.1.1 "Fatigue - decreased proficiency boundary"
tolerance) for healthy human subjects restrained to a vibrating seat.
(Such limit levels have been explored for male human subjects in
The fatigue - decreased proficiency boundary as a function
laboratory research.)
of frequency and exposure time is shown in figures 2a and
2b (longitudinal vibration) and 3a and 3b (transverse 2 At certain frequencies both above and below the band of
maximum sensitivity the acceleration levels permitted for short
vibration) for daily exposure times from 1 min to 24 h. The
exposure times according to the exposure limit and the
numerical values defining the boundary are presented in
fatigue - decreased proficiency boundary exceed 7 m/s2, which is
tables 1 and 2 respectively. The boundary specifies a limit
equivalent to a peak value of approximately 10 mfs2 or
beyond which exposure to vibration can be regarded as approximately 1 g for sinusoidal vibration. Such vibration in the
vertical direction can cause the subject to lift off his seat or
carrying a significant risk of impaired working efficiency in
platform, unless he is effectively restrained. Bouncing is unlikely to
many kinds of tasks, particularly those in which
be a real problem, however, at frequencies above 20 Hz where the
time-dependent effects ("fatigue") are known to worsen
relatively small displacement, even at high acceleration levels, can be
performance as, for example, in vehicle driving. taken up by the compliant tissues of the body.
The actual degree of task interference 'in any situation
4.1.3 "Reduced comfort boundary"
depends on many factors, including individual
characteristics as well as the nature and difficulty of the
The reduced comfort boundary, which is derived from
task. Nevertheless, the limits recommended here show the
various studies conducted for the transport industries, is
general level of onset of such interference, the
assumed in this International Standard to lie at
frequency dependence and the time dependence commonly
approximately one-third of the corresponding levels of the
observed. The data upon which these limits are based come
fatigue - decreased proficiency boundary, and is, moreover,
mainly from studies on aircraft pilots and drivers.
assumed to follow the same time and frequency
It should be noted that for man the most sensitive dependence. Values for the reduced comfort boundary are,
frequency ranges (in which the limit is accordingly set accordingly, obtained from the corresponding values for the
lowest) are 4 to 8Hz for longitudinal (az) vibration and fatigue - decreased proficiency boundary by a reduction of
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ISO 2631-1978 (E)
10 dB (see figures 2a, 2b and 3a, 3b and tables 1 and 2). In NOTES
the transport situation the reduced comfort boundary is
1 The above procedures assume that in respect of human tolerance
related to difficulties of carrying out such operations as
no significant interactions occur between vibration effects at
different frequencies. There exists at present no published evidence
eating, reading, and writing.
to decide between the accuracy of the presently recommended
rating procedure and the weighting procedure discussed as a
NOTES
permissible approximation in note 2 below.
In practice, there will be limits to the usefulness of this Inter
2 In order to allow the characterization of a vibration environment
national Standard. The fatigue - decreased proficiency boundary
with respect to its effects on man by a single quantity and to
and reduced comfort boundaries in particular are presumed to apply
simplify measurements for situations in which spectrum analysis is
most directly to vibration in transport and near industrial
difficult or inconvenient, the overall vibration signal for the
machinery. These limits may not be very powerful in the evaluation
frequency range 1 to 80 Hz may be weighted with an electronic
of disturbance due to building vibration (for example, caused by
network. This weighting network, to be inserted between the
traffic or footfall) in private homes, offices or similar situations in
vibration pick-up and the meter, shall have an insertion loss with a
which the socio-psychological and economic factors related to
frequency response according to the curves of figure 2a for az, and
human disturbance are more subtle or complex. Acceptable
vibration levels in residential buildings, for example, may not lie of figure 3a for ax or ay vibration measurements. The insertion loss
much above the threshold of perception, especially during the night, is to be zero for the band 4 to 8 Hz for az measurements, and for
but must, in any case, be expected to vary greatly with individual the band 1 to 2Hz for ax and ay measurements. The network
characteristics shall not deviate more than ± 1 dB between two fixed
circumstances. The threshold of perception varies from one subject
frequencies and more than ± 2 dB over the other frequency ranges.
to another and depends upon the conditions of measurement. The
upper range of the threshold of perception has approximately the The two fixed frequencies are 6,3 Hz and 31,5 Hz for az
measurements and 1,25 Hz and 31,5 Hz for ax and ay
same frequency dependence as the curves of figures 2a and 3a. In
measurements.
the frequency bands of maximum sensitivity, namely 4 to 8Hz for
longitudinal and 1 to 2Hz for transverse vibrations, the threshold
The overall weighted vibration values so measured shall be reported
lies at approximately 0,01 mfs2 (about 10-3 g). The individual
as azw and axw or ayw respectively, according to the direction of
threshold for many persons may lie at still lower levels.
measurement, and are to be compared to the permissible values in
2 It is anticipated that additional tables will be developed through the 4 to 8 Hz band for az and in the 1 to 2 Hz band for ax and ay
the practical use of this International Standard, providing for a finer vibration.
differentiation of comfort in various situations, such as in offices, in
It is appreciated that this proposed method for single number
various types of private residence, on ships, etc.
...
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