ISO 2631-1:1985
(Main)Evaluation of human exposure to whole-body vibration — Part 1: General requirements
Evaluation of human exposure to whole-body vibration — Part 1: General requirements
Estimation de l'exposition des individus à des vibrations globales du corps — Partie 1: Spécifications générales
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International Standard @ 263111
INTF RNATIONAL ORGANIZATION FOR STANDARDIZATIONDMEmOYHAPOnHAR OPrAHH3AUHA no CTAHAAPTH3AUHH~ORGANlSATlON INTERNATIONALE DE NORMALISATION
Evaluation of human exposur whole-body vibration -
Part I : General requirements
Estimation de l'exposition des individus à des vibrations globales du corps - Partie 7 : Spécifications générales
First edition - 1985-05-15
UDC 534.1 : 614.872.5 Ref. No. IS0 2631/1-1985 (E)
Descriptors : humans, human body, exposure, vibration, measurement, ergonomics.
Price based on 17 pages
---------------------- Page: 1 ----------------------
~ Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work-of preparing International
Standards is normally carried out through IS0 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, govern-
mental and non-governmental, in liaison with ISO, also take part in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
at
the IS0 Council. They are approved in accordance with IS0 procedures requiring
least 75 % approval by the member bodies voting.
International Standard IS0 2631 /I was prepared by Technical Committee
ISO/TC 108, Mechanical vibration and shock, and results from the combination of
IS0 2631-1978 with its Amendment 1-1982, changes in content being editorial. The ad-
denda to IS0 2631-1978 which had been published or were in preparation will become
subsequent numbered parts of IS0 2631.
O International Organization for Standardization, 19M O
Printed in Switzerland
---------------------- Page: 2 ----------------------
INTERNATIONAL STANDARD IS0 2631/1-1985 (E)
Evaluation of human exposure to whole-body vibration -
Part 1 : General 'requirements
O Introduction
example, when high intensity sound in air or water excites
vibrations of the body.
Vehicles (air, land and water), as well as machinery (for
example, in industry and agriculture), expose man to
b) Vibrations transmitted to the body as a whole through
mechanical vibration which can interfere with comfort, working
the supporting surface, namely, the feet of a standing man,
efficiency and, in some circumstances, health and safety.
the buttocks of a seated man or the supporting area of a
Various methods of rating the severity of exposure and defining
reclining man. This kind of vibration is usual in vehicles, in
limits of exposure based on laboratory or field data have been
vibrating buildings and in the vicinity of working machinery.
developed in the past for specific applications. None of these
methods can be considered applicable in all situations and con-
c) Vibrations applied to particular parts of the body such
sequently none has been universally accepted.
as the head or limbs; for example, by vibrating handles,
pedals or head-rests, or by the wide variety of powered
In view of the complex factors determining the human
tools and appliances held in the hand.
response to vibrations, and in view of the shortage of consis-
tent quantitative data concerning man's perception of vibration
It is also possible to recognize the condition in which an indirect
and his reactions to it, this International Standard has been
vibration nuisance is caused by the vibration of external objects
prepared first, to facilitate the evaluation and comparison of
in the visual field (for example, an instrument panel).
data gained from continuing research in this field; and, second,
to give provisional guidance as to acceptable human exposure
This International Standard, however, applies chiefly to the
to whole body vibration. The limits proposed in this Interna-
common condition (b) above; and, in particular, where the
tional Standard seem to be a fair compromise between the
vibration is applied through the principal supporting surface to
available data and should satisfy the need for recommendations
the body of a standing or seated man. In the case of vibrations
which are simple and suitable for general application. These
applied directly to a reclining or recumbent man, insufficient
limits are defined explicitly in numerical terms to avoid ambi-
data are available to make a firm recommendation; this is par-
guity and to encourage precise measurement in practice.
ticularly true of vibration transmitted directly to the head, when
However, when using these criteria and limits it is important to
tolerability is generally reduced. Tolerance may also be reduced
bear in mind the restrictions placed upon their application.
when conditions (b) and (c) exist together. Provisionally,
however, the limits for the standing or seated man may also be
Because of the wide variety of possible conditions and effects
It shall be appreciated
used for the reclining or recumbent man.
of human exposure to vibrations, and because of the existing
that some circumstances will arise in which the rigorous ap-
shortage of firm data, more detailed guidance is hardly war-
plication of these limits would be inappropriate.
ranted at the present time. Nevertheless, it is hoped that this In-
ternational Standard not only proves useful in the assessment
This International Standard comprises the following parts :
of existing or predicted vibration environments but also
stimulates the reporting and critical evaluation of new findings
Part 1 : General requirements.
about the effects of vibration on man.
Part 2 : Evaluation of human exposure to vibration and
There are basically three kinds of human exposure to vibration,
shock in buildings (1 to 80 HzI.1)
namely :
Part 3 : Evaluation of exposure to whole-body z-axis vertical
vibration in the frequency range 0,l to 0,63 Hz.
a) Vibrations transmitted simultaneously to the whole
body surface or substantial parts of it. This occurs when the
Part 4 : Evaluation of crew exposure to vibration on board
body is immersed in a vibrating medium. There are cir-
cumstances in which this is of practical concern; for sea-going ships (1 to 80 Hz1.1)
1) At present at the stage of draft.
1
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IS0 2631/1-1985 (E)
1 Scope and field of application complicated individual factors not simply related to the intensity, fre-
quency or duration of the provocative motion. Mechanical vibrations
applied to the feet or buttocks above the frequency range considered in
This part of IS0 2631 defines and gives numerical values for
this part of IS0 2631 increasingly produce sensations and effects
limits of exposure for vibrations transmitted from solid surfaces
which are highly dependent upon local factors such as the precise
to the human body in the frequency range 1 to 80 Hz. It may be
direction, site and area of application of the vibration to the body and
applied, within the specified frequency range, to periodic vibra-
the presence of damping materials (for example, clothing or footwear)
tions and to random or non-periodic vibrations with a
which may control the vibratory response of the skin and superficial
distributed frequency spectrum. Provisionally, it may also be
layers of the body. For these reasons, therefore, it is not possible on
so far as the
applied to continuous shock-type excitation in
the basis of present data to formulate generally valid recommendations
energy in question is contained within the 1 to 80 Hz band. for frequencies outside the 1 to 80 Hz band.
In some applications, constant sensitivity to accelerations has been
These limits (defined in detail in clause 4) are given for use ac-
tentatively assumed for the frequency range 0,63 to 1 Hz.
cording to the three generally recognizable criteria of preserv-
ing comfort, working efficiency, and safety or health. The limits
set according to these criteria are named respectively in this
part of IS0 2631 the "reduced comfort boundary", "fatigue-
2 References
decreased proficiency boundary" and the "exposure limit". For
example, where the primary concern is to maintain the working
IS0 266, Acoustics - Preferred frequencies for measure-
efficiency of a vehicle driver or a machine operator working in
ments.
vibration, the "fatigue-decreased proficiency boundary" would
be used as the guiding limit in laying down vibration specifica-
IEC Publication 184, Methods for specifying the characteristics
tions or in carrying out vibration control measures, while, in the
of electro-mechanical transducers for shock and vibration
design of passenger accommodations, the "reduced comfort
measurements.
boundary" should be considered.
IEC Publication 222, Methods for specifying the characteristics
According to the criteria mentioned, these limits are specified
of auxiliary equipment for shock and vibration measurement.
in terms of vibration frequency, acceleration magnitude, ex-
posure time and the direction of vibration relative to the torso.
IEC Publication 225, Octave, half-octave and third-octave band
This direction is defined according to the recognized
filters intended for the analysis of sounds and vibrations.
anatomical axes of the human body (see clause 3).
This part of IS0 2631 is applicable only to situations involving
people in normal health : that is, persons who are considered fit
to carry out normal living routines, including travel, and to
3 Characterization of vibration exposure
undergo the stress of a typical working day or shift.
3.1 Direction of vibration
No information given in this part of IS0 2631 shall be ex-
trapolated to frequencies outside the range 1 to 80 Hz (see
notes below).
3.1.1 Rectilinear vibrations transmitted to man should be
measured in the appropriate directions of an orthogonal co-
It has been well established that differences in response to
ordinate system having its origin at the location of the heart
vibration occur both between and within individuals. These dif-
(see figure 1).
ferences affect the level and shape of the curves and the
relative effects of simple and complex motions. The guidance
NOTE - The terminology commonly used in biodynamics relates the
given in this part of IS0 2631 is based on the average response
coordinate system to the human skeleton in a normal anatomical pos-
of subjects in a variety of situations. Thus two motions, which ition, Accelerations (motion) in the foot-(or buttocks-)to-head (or
longitudinal) axis are designated f a,; accelerations in the fore-and-aft
are assessed as equally severe by the recommended evaluation
or chest-to-back) axis, rt and in the lateral (right-
(anteroposterior
procedure may have different effects. Individuals, and groups
to-left side) axis, f au These axes are illustrated in figure 1.
of individuals, will sometimes disagree on which of two mo-
tions is worse and variables such as posture and subject ac-
tivities can have large effects.
3.1.2 Angular (or rotational) vibrations about a centre of ro-
tation are frequently an important part of a vibration environ-
NOTES
ment. For example, in tractors going over rough terrain, or in
aircraft flying through turbulence, the pitching or rolling mo-
1 The limits specified in this part of IS0 2631 are based upon data
tions of the seat may be more disturbing than the rectilinear
available from both practical experience and laboratory experimenta-
vibration up and down. However, little information on the ef-
tion in the field of human response to mechanical vibration. To date,
useful observations have been made mainly in the frequency range be- fects of angular (or rotational) vibration is yet available. In prac-
tween about l and 100 Hz. The frequency range, its subdivisions and
tice, the centre of vibratory rotation can often be assumed to lie
the corner frequencies defined in this part of IS0 2631 have been
far enough from the point of application of vibration to the
selected in accordance with IS0 266 and with national standards in
body for the resulting motion to be represented by translatory
several countries.
vibrations alone. Nevertheless, whenever practicable, rota-
tional vibrations in roll, pitch and yaw (as related to the
2 Vibrations in the frequency range below about 1 Hz are a special
anatomical axes) should be measured and reported, in order to
problem, associated with symptoms such as kinetosis (motion
increase our knowledge of the human response to such excita-
sickness) which are of a character different from the effects of higher
tion.
frequency vibrations. The appearance of such symptoms depends on
2
a,;
---------------------- Page: 4 ----------------------
/I-I985 (E)
tor (ratio of maximum peak to r.m.s. value) of the time function
3.1.3 In this part of IS0 2631 separate limits are specified ac-
shall be determined or estimated : the limits given in this part of
cording to whether the vibration is in the (anatomically)
IS0 2631 should be regarded as very tentative in the case of
longitudinal If oz) direction or transverse 1 f a, or f oui
vibrations having high crest factors (that is, greater than 3; see
plane.
below).
Recent research has indicated that motions with crest factors
3.2 Location of measurement
greater than 3 can often be compared satisfactorily with the
limits given in this part of IS0 2631. However, ,it is clear that the
Because the limits given in this part of IS0 2631 apply to vibra-
importance of some motions which contain occasional ex-
tion at the point of entry into the human body itself (that is, at
tremely high peak values may be underestimated by the recom-
the body surface, but not, for example, at the substructure of a
mended evaluation method. Work is in progress to determine
resilient seat, which may transform the vibration en route to the
how such motions may be meaningfully compared with the
man), vibration measurements shall be made as close as poss-
limits. Until this information is available the following procedure
ible to the point or area through which the vibration is trans-
is tentatively recommended.
mitted to the body. For example, if the man is standing on a
floor or sitting on a platform without any resilient material be-
The acceleration signal should be weighted by the appropriate
tween the body and the supporting structure, then the measur-
filter network defined in table 3 and described in 4.2.4. The
ing transducer or pick-up should be fastened to that rigid struc-
maximum peak value of this weighted signal is its maximum
ture. Where some resilient element, such as a seat cushion,
deviation from the mean value. The crest factor is then the ratio
does exist between the body and the vibrating structure, it is
of this maximum peak value to the weighted r.m.s. value of the
permissible to interpose some form of rigid transducer support
signal. Accelerations with crest factor as great as 6 can be
(for example, a thin, suitably formed metal sheet) between the
evaluated by this part of IS0 2631. When the crest factor is
subject and the cushion; but care shall be taken to ensure that
greater than about 6, the recommended vibration evaluation
such a device does not significantly influence the transfer of
method may underestimate the effect of the motion.
vibration through the cushion to the man or introduce rota-
it is not practicable to
tional motions otherwise not present. If
In practice, the crest factor will depend on the period over
measure the vibration at the point of input to the man in such a
which the peak value and the r.m.s. value are determined. The
way, then the transmission characteristics of the seat cushion
is 1 min. In ad-
minimum period for evaluating the crest factor
or other resilient element shall be determined and taken into ac-
dition to occasional peak values, the large variations in level
count when calculating the actual vibration transmitted to the
which can occur over periods longer than 1 min can raise the
body. In such cases, the characteristics of the cushioning
crest factor. However, these motions may often be evaluated
system shall be reported.
using the equivalent exposure time calculations described in
4.4.
NOTE - For research purposes which require the precise definition of
the vibratory input to human subjects, it has become customary in
It is sometimes inconvenient to determine the peak value of the
laboratory studies of biodynamic and physiological responses to
replace seat cushions by rigid packs or platforms, because variation of weighted signal as described above. Peaks determined on an
the measuring conditions by different arbitrary seating arrangements
unweighted signal (with band-pass filtering between 1 Hz and
can significantly affect the experimental results. Some of the variability
80 Hz only) will normally be greater than those from a weighted
of published research results in this field arises from differences be-
signal. An upper estimate of the crest factor may therefore be
tween the experimental conditions adopted in different laboratories.
determined from unweighted signals first. If the value exceeds
6 it will be necessary to weight the signal to determine whether
the criterion is really exceeded. The r.m.s. value should always
3.3 Intensity of vibration
be determined from the weighted signal.
The primary quantity used to describe the intensity of a vibra-
NOTE - Measurements of rotational vibrations, whenever made,
tion environment, irrespective of the type of transducer or pick-
should be reported in units of r.m.s. angular acceleration, radians per
up used in actual measurements, shall be the acceleration. Ac-
second squared (rad/&.
celeration should normally be expressed in metres per second
squared (m/s2).
3.4 Measuring equipment
NOTE - In physiological work, it is frequently the custom to express
accelerations non-dimensionally in g units where lg is the value of the
Vibration measuring equipment generally consists of the
standard acceleration due to gravity acting at the earth's surface. This
following parts : a transducer or pick-up, an amplifying device
usage is permissible within the context of experimental work in hand
(electrical, mechanical or optical), and an amplitude or level in-
provided that, when reference is made to the limits given in this part of
dicator or recorder. Where practicable (as in electronic in-
IS0 2631, the international standard value of g, is used for conversion
strumentation) and appropriate, networks may be included to
to values of acceleration expressed in metres per second squared.
limit the frequency range of the equipment and to apply the
The magnitude of a vibration, that is, the acceleration (or, if recommended frequency-weighting to the input signal. For
many applications, where it is not essential to rely solely upon
quoted, the velocity or displacement), should be expressed as a
on-the-spot determinations, the use of a suitable tape recor-
root-mean-square (r.m.s.1 value. When peak values are
ding system to obtain representative records for subsequent
measured, these shall be converted as appropriate to r.m.s.
values before reference to the limits given in this part of analysis will be the method of choice. An r.m.s.-rectifying
device may also be included for convenience, so that r.m.s.
IS0 2631. For the adequate description of vibration which is
values may be read off or recorded directly.
markedly non-sinusoidal, random or broad-band, the crest fac-
3
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E)
All vibration measuring equipment should be properly which a physical description can be given in terms of those fac-
calibrated. This should be done in accordance with existing tors, three main human criteria can be distinguished. These
are :
standards or recommendations governing the calibration of
such equipment. The basis of operation and the characteristics
a) the preservation of working efficiency ("fatigue-
of any measuring equipment used should be reported together
with the results obtained with it. It is important to report such decreased proficiency boundary");
characteristics as the frequency sensitivity, the dynamic
properties (for example, the time constant), the dynamic range b) the preservation of health or safety ("exposure limit");
and resolution of the equipment; and when appropriate, the and
precision of r. m.s.-rectifying, frequency-weighting, tape recor-
ding, frequency analysis or such other operations as may be c) the preservation of comfort ("reduced comfort boun-
dary").
performed upon the signal.
NOTES The recommended limits of exposure set according to these
three criteria are defined in 4.1.1 to 4.1.3. Each of these limits is
1 It is recommended that IEC Publication 184 be used for specifying
defined graphically for the longitudinal (a,) direction (figures 2a
the vibration-transducers and IEC Publication 222 for specifying the
and 2b) and the transverse (a,, a,,) directions (figures 3a and
auxiliary equipment, including amplifiers, frequency-selective equip-
3b). Numerical definition of the graphs in figures 2 and 3 is
ment and carrier systems.
presented in tables 1 and 2. Typically, as in most transport
2 With respect to the subjective judgement of the vibration intensity,
situations, a, (longitudinal) vibration will be applied to a sitting
it appears that the integration time for the human vibration perception
or standing person (a situation popularly referred to as "vertical
decreases from 2 to 0.8 s over the frequency range from 2 to 90 Hz.
vibration").
3.5 Random or broad-band vibration analysis
NOTE - It will be seen that, other factors being equal, somewhat
higher levels of vibration are acceptable when health or safety is the
In the measurement of random or distributed vibration, of
criterion, in comparison with the limits appropriate to working ef-
ficiency; and, conversely, lower limits are set when the criterion is the
which narrow-band analysis not exceeding one-third octave is
preservation of comfort. This is in general accord with experimental
the appropriate method of description, the one-third octave
observation and experience, but it should not be taken as implying that
band filters used in any recording or analytical network shall be
there exists in all circumstances a simple hierarchical relationship be-
in accordance with IEC Publication 225. The frequency range
tween the intensities of vibration likely to impair health, working effi-
given in IEC Publication 225 shall be extrapolated accordingly
ciency or comfort.
to corresponding lower frequencies.
For some applications, it will be appropriate to equip electronic
4.1.1 Fatigue-decreased proficiency boundary
vibration measuring apparatus with a frequency-weighting net-
work defined as corresponding to the limits for vertical (a,) and
The fatigue-decreased proficiency boundary as a function of
horizontal (a, and a,,) vibration respectively given in clause 4,
frequency and exposure time is shown in figures2a and 2b
tables 1 and 2 and figures 2a and 3a (see note 2 of 4.2.4). A net-
(longitudinal vibration) and 3a and 3b (transverse vibration) for
work so defined shall not deviate from the recommended
daily exposure times from 1 min to 24 h. The numerical values
values by more than I 1 dB at two fixed frequencies; 6,3 Hz
defining the boundary are presented in tables 1 and 2 respec-
and 31,5 Hz for az measurements and 1,25 Hz and 313 Hz for
tively. The boundary specifies a limit beyond which exposure to
a, and U,, measurements.
vibration can be regarded as carrying a significant risk of im-
paired working efficiency in many kinds of tasks, particularly
3.6 Exposure time those in which time-dependent effects ("fatigue") are known
to worsen performance as, for example, in vehicle driving.
This part of IS0 2631 includes a computational procedure (see
4.4) for assessing the effective daily exposure to vibration. This The actual degree of task interference in any situation depends
is intended to take account, as far as is possible, of variations in on many factors, including individual characteristics as well as
the intensity of vibration and any intermittency or interruption the nature and difficulty of 4he task. Nevertheless, the limits
recommended here show the general level of onset of such in-
of exposure to vibration which may occur during the period in
question. Whenever measurements are made of human ex- terference, the frequency dependence and the time
dependence commonly observed. The data upon which these
posure to vibration which is varying in intensity, or which is
discontinuous, the time-history of such exposure should be limits are based come mainly from studies on aircraft pilots and
drivers.
reported in detail.
It should be noted that for man the most sensitive frequency
ranges (in which the limit is accordingly set lowest) are 4 to
4 Vibration evaluation guide
8 Hz for longitudinal (a,) vibration and below 2 Hz for
transverse (U,, a ) vibration; and that human tolerance of vibra-
tion decreases (demanding increasingly stringent limits) in a
4.1 General considerations
characteristic way with increasing exposure time (figures 2b
and 3b). It is seen from a comparison of figures 2a and 3a that,
There are four physical factors of primary importance in deter-
whereas the tolerance for transverse vibration is lower than that
mining the human response to vibration, namely, the intensity,
for longitudinal vibration at very low frequencies, the converse
the frequency, the direction, and the duration (exposure time)
is so for higher frequencies (above approximately 2,8 Hz).
of the vibration. In the practical evaluation of any vibration of
4
---------------------- Page: 6 ----------------------
IS0 2631/1-1985 (E)
NOTE - It is anticipated that with experience in the practical applica- vibration in transport and near industrial machinery. These limits may
tions of this part of IS0 2631, correction tables will be worked out to
not be very powerful in the evaluation of disturbance due to building
vary the level of the fatigue-decreased proficiency boundary according vibration (for example, caused by traffic or footfall) in private homes,
to different environmental conditions of task requirements. For exam- offices or similar situations in which the socio-psychological and
ple, a more stringent limit may have to be applied when the task is of a
economic factors related to human disturbance are more subtle or
particularly demanding perceptual nature or calls for an exercise of fine complex. Acceptable vibration levels in residential buildings, for
manual skill. By contrast, some relaxation of the limit might be possible
example, may not lie much above the threshold of perception,
in circumstances in which the performance of the task (for especially during the night, but shall, in any case, be expected to vary
example, heavy manual work) is relatively insensitive to vibration. Ten-
greatly with individual circumstances. The threshold of perception
tative data, as yet too few to provide a basis for a firm recommenda- varies from one subject to another and depends upan the conditions of
tion, suggest that a range of correction of + 3 dB to - 12 dB (that is, measurement. The upper range of the threshold of perception has ap-
a modifying factor of 1,4 to 0,25 times the r.m.s. acceleration specified proximately the same frequency dependence as the curves of figures
by the boundary) may be envisaged. 2a and 3a. In the frequency bands of maximum sensitivity, namely 4 to
8 Hz for longitudinal and 1 to 2 Hz for transverse vibrations, the
threshold lies at approximately 0.01 m/s2 (about 10W3g). The in-
dividual threshold for many people may lie at still lower levels.
4.1.2 Exposure limit (health or safety)
2 It is anticipated that additional tables will be developed through the
The exposure limit as a function of frequency and exposure
practical use of this part of IS0 2631, providing for a finer differen-
time is of the same general form as the fatigue-decreased pro-
tiation of comfort in various situations, such as in offices, in various
ficiency boundary, but the corresponding levels are raised by a types of private residence, on ships, etc. The range of such correction
factors might extend from + 3 dB to - 30 dB (approximate threshold
factor of 2 (6 dB higher). In other words, maximum safe ex-
of perception), but their formulation awaits more substantial data than
posure is determined, for any condition of frequency, duration
are available at present.
and direction, by doubling the values allowed according to the
criterion of fatigue-decreased proficiency (see figures 2a, 2b
and 3a, 3b and tables 1 and 2).
4.2 Evaluation of frequency spectrum
Exceeding the exposure limit is not recommended without
special justification and precautions, even if no task is to be
4.2.1 Evaluation of discrete (single) frequencies
performed by the exposed individual.
The limits shown in figures 2 and 3 and given in tables 1 and 2
NOTES
are valid for discrete frequency vibrations acting in the foot-to-
1 The exposure limit recommended is set at approximately half the
head (a,) or the transverse directions (ax, a,,) respectively.
level considered to be the threshold of pain (or limit of voluntary
tolerance) for healthy human subjects restrained to a vibrating seat.
(Such limit levels have been explored for male human subjects in
4.2.2 Evaluation of discrete (multiple) frequencies
laboratory research.)
When vibration o
...
International Standard @ 263111
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION*MEWiYHAPOnHAR OPrAHMJAUMR no CTAHllAPTM3AUMM*ORGANlSATlON INTERNATIONALE DE NORMALISATION
Evaluation of human exposur whole-body vibration -
Part I : General requirements
Estimation de l'exposition des individus à des vibrations globales du corps - Partie 1 : Spécifications générales
First edition - 1985-05-15
UDC 534.1 : 614.872.5 Ref. No. ISO2631/1-1985 (E)
Descriptors : humans, human body, exposure, vibration, measurement, ergonomics.
Price based on 17 pages
---------------------- Page: 1 ----------------------
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of
national standards bodies (IS0 member bodies). The work of preparing International
Standards is normally carried out through IS0 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, govern-
mental and non-governmental, in liaison with ISO, also take part in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the IS0 Council. They are approved in accordance with IS0 procedures requiring at
75 % approval by the member bodies voting.
least
International Standard IS0 2631 /I was prepared by Technical Committee
ISO/TC 108, Mechanical vibration and shock, and results from the combination of
IS0 2631-1978 with its Amendment 1-1982, changes in content being editorial. The ad-
denda to IS0 2631-1978 which had been published or were in preparation will become
subsequent numbered parts of IS0 2631.
O international Organization for Standardization, 1985
Printed in Switzerland
---------------------- Page: 2 ----------------------
INTERNATIONAL STANDARD IS0 2631/1-1985 (E)
Evaluation of human exposure to whole-body vibration -
Part 1 : General 'requirements
O Introduction or water excites
example, when high intensity sound in air
vibrations of the body.
Vehicles (air, land and water), as well as machinery (for
example, in industry and agriculture), expose man to
b) Vibrations transmitted to the body as a whole through
mechanical vibration which can interfere with comfort, working
a standing man,
the supporting surface, namely, the feet of
efficiency and, in some circumstances, health and safety.
the buttocks of a seated man or the supporting area of a
Various methods of rating the severity of exposure and defining
reclining man. This kind of vibration is usual in vehicles, in
limits of exposure based on laboratory or field data have been
vibrating buildings and in the vicinity of working machinery.
developed in the past for specific applications. None of these
methods can be considered applicable in all situations and con-
c) Vibrations applied to particular parts of the body such
sequently none has been universally accepted.
as the head or limbs; for example, by vibrating handles,
pedals or head-rests, or by the wide variety of powered
In view of the complex factors determining the human
tools and appliances held in the hand.
response to vibrations, and in view of the shortage of consis-
tent quantitative data concerning man's perception of vibration
It is also possible to recognize the condition in which an indirect
and his reactions to it, this International Standard has been
vibration nuisance is caused by the vibration of external objects
prepared first, to facilitate the evaluation and comparison of
in the visual field (for example, an instrument panel).
data gained from continuing research in this field; and, second,
to give provisional guidance as to acceptable human exposure
This International Standard, however, applies chiefly to the
to whole body vibration. The limits proposed in this Interna-
common condition (b) above; and, in particular, where the
tional Standard seem to be a fair compromise between the
vibration is applied through the principal supporting surface to
available data and should satisfy the need for recommendations
the body of a standing or seated man. In the case of vibrations
which are simple and suitable for general application. These
applied directly to a reclining or recumbent man, insufficient
limits are defined explicitly in numerical terms to avoid ambi-
data are available to make a firm recommendation; this is par-
guity and to encourage precise measurement in practice.
ticularly true of vibration transmitted directly to the head, when
However, when using these criteria and limits it is important to
tolerability is generally reduced. Tolerance may also be reduced
bear in mind the restrictions placed upon their application.
when conditions (b) and (cl exist together. Provisionally,
however, the limits for the standing or seated man may also be
Because of the wide variety of possible conditions and effects
used for the reclining or recumbent man. It shall be appreciated
of human exposure to vibrations, and because of the existing
that some circumstances will arise in which the rigorous ap-
shortage of firm data, more detailed guidance is hardly war-
plication of these limits would be inappropriate.
ranted at the present time. Nevertheless, it is hoped that this In-
ternational Standard not only proves useful in the assessment
This International Standard comprises the following parts :
of existing or predicted vibration environments but also
stimulates the reporting and critical evaluation of new findings
Part 1 : General requirements.
about the effects of vibration on man.
Part 2 : Evaluation of human exposure to vibration and
There are basically three kinds of human exposure to vibration,
(1 to 80 HzI.1)
shock in buildings
namely :
Part 3 : Evaluation of exposure to whole-body z-axis vertical
vibration in the frequency range 0,l to O,@ Hz.
a) Vibrations transmitted simultaneously to the whole
it. This occurs when the
body surface or substantial parts of
Part 4 : Evaluation of crew exposure to vibration on board
body is immersed in a vibrating medium. There are cir-
sea-going ships (1 to 80 Hzi.1)
cumstances in which this is of practical concern; for
II At present at the stage of draft.
1
---------------------- Page: 3 ----------------------
/1-1985 (E)
1 Scope and field of application
complicated individual factors not simply related to the intensity, fre-
quency or duration of the provocative motion. Mechanical vibrations
applied to the feet or buttocks above the frequency range considered in
This part of IS0 2631 defines and gives numerical values for
this part of IS0 2631 increasingly produce sensations and effects
limits of exposure for vibrations transmitted from solid surfaces
which are highly dependent upon local factors such as the precise
to the human body in the frequency range 1 to 80 Hz. It may be
direction, site and area of application of the vibration to the body and
applied, within the specified frequency range, to periodic vibra-
the presence of damping materials (for example, clothing or footwear)
tions and to random or non-periodic vibrations with a
which may control the vibratory response of the skin and superficial
distributed frequency spectrum. Provisionally, it may also be
layers of the body. For these reasons, therefore, it is not possible on
so far as the
applied to continuous shock-type excitation in
the basis of present data to formulate generally valid recommendations
energy in question is contained within the 1 to 80 Hz band.
for frequencies outside the 1 to 80 Hz band.
In some applications, constant sensitivity to accelerations has been
These limits (defined in detail in clause 4) are given for use ac-
tentatively assumed for the frequency range 0,63 to 1 Hz.
cording to the three generally recognizable criteria of preserv-
ing comfort, working efficiency, and safety or health. The limits
set according to these criteria are named respectively in this
IS0 2631 the "reduced comfort boundary", "fatigue-
part of
2 References
decreased proficiency boundary" and the "exposure limit". For
example, where the primary concern is to maintain the working
IS0 266, Acoustics - Preferred frequencies for measure-
efficiency of a vehicle driver or a machine operator working in
ments.
vibration, the "fatigue-decreased proficiency boundary" would
be used as the guiding limit in laying down vibration specifica-
IEC Publication 184, Methods for specifying the characteristics
tions or in carrying out vibration control measures, while, in the
of electro-mechanical transducers for shock and vibration
design of passenger accommodations, the "reduced comfort
measurements.
boundary" should be considered.
IEC Publication 222, Methods for specifying the characteristics
According to the criteria mentioned, these limits are specified
in terms of vibration frequency, acceleration magnitude, ex- of auxiliary equipment for shock and vibration measurement.
posure time and the direction of vibration relative to the torso.
IEC Publication 225, Octave, half-octave and third-octave band
This direction is defined according to the recognized
filters intended for the analysis of sounds and vibrations.
anatomical axes of the human body (see clause 3).
This part of IS0 2631 is applicable only to situations involving
people in normal health : that is, persons who are considered fit
to carry out normal living routines, including travel, and to
3 Characterization of vibration exposure
undergo the stress of a typical working day or shift.
3.1 Direction of vibration
No information given in this part of IS0 2631 shall be ex-
trapolated to frequencies outside the range 1 to 80 Hz (see
notes below).
3.1.1 Rectilinear vibrations transmitted to man should be
measured in the appropriate directions of an orthogonal co-
It has been well established that differences in response to
ordinate system having its origin at the location of the heart
vibration occur both between and within individuals. These dif-
(see figure 1).
ferences affect the level and shape of the curves and the
relative effects of simple and complex motions. The guidance
NOTE - The terminology commonly used in biodynamics relates the
given in this part of IS0 2631 is based on the average response
coordinate system to the human skeleton in a normal anatomical pos-
of subjects in a variety of situations. Thus two motions, which
ition. Accelerations (motion) in the foot4or buttocks-)to-head (or
are assessed as equally severe by the recommended evaluation longitudinal) axis are designated k a,; accelerations in the fore-and-aft
(anteroposterior or chest-to-back) axis, I and in the lateral (right-
procedure may have different effects. Individuals, and groups
to-left side) axis, I a,,. These axes are illustrated in figure 1.
of individuals, will sometimes disagree on which of two mo-
tions is worse and variables such as posture and subject ac-
tivities can have large effects.
3.1.2 Angular (or rotational) vibrations about a centre of ro-
tation are frequently an important part of a vibration environ-
NOTES
ment. For example, in tractors going over rough terrain, or in
aircraft flying through turbulence, the pitching or rolling mo-
1 The limits specified in this part of IS0 2631 are based upon data
tions of the seat may be more disturbing than the rectilinear
available from both practical experience and laboratory experimenta-
vibration up and down. However, little information on the ef-
tion in the field of human response to mechanical vibration. To date,
useful observations have been made mainly in the frequency range be- fects of angular (or rotational) vibration is yet available. In prac-
tween about l and 100 Hz. The frequency range, its subdivisions and
tice, the centre of vibratory rotation can often be assumed to lie
the corner frequencies defined in this part of IS02631 have been
of application of vibration to the
far enough from the point
IS0 266 and with national standards in
selected in accordance with
body for the resulting motion to be represented by translatory
several countries.
vibrations alone. Nevertheless, whenever practicable, rota-
tional vibrations in roll, pitch and yaw (as related to the
2 Vibrations in the frequency range below about 1 Hz are a special
anatomical axes) should be measured and reported, in order to
problem, associated with symptoms such as kinetosis (motion
increase our knowledge of the human response to such excita-
character different from the effects of higher
sickness) which are of a
tion.
frequency vibrations. The appearance of such symptoms depends on
2
a,;
---------------------- Page: 4 ----------------------
tor (ratio of maximum peak to r.m.s. value) of the time function
3.1.3 In this part of IS0 2631 separate limits are specified ac-
shall be determined or estimated : the limits given in this part of
cording to whether the vibration is in the (anatomically)
IS0 2631 should be regarded as very tentative in the case of
longitudinal (f U,) direction or transverse (f a, or f au)
vibrations having high crest factors (that is, greater than 3; see
plane.
below).
Recent research has indicated that motions with crest factors
3.2 Location of measurement
greater than 3 can often be compared satisfactorily with the
limits given in this part of IS0 2631. However, .it is clear that the
Because the limits given in this part of IS0 2631 apply to vibra-
importance of some motions which contain occasional ex-
tion at the point of entry into the human body itself (that is, at
tremely high peak values may be underestimated by the recom-
the body surface, but not, for example, at the substructure of a
mended evaluation method. Work is in progress to determine
resilient seat, which may transform the vibration en route to the
how such motions may be meaningfully compared with the
man), vibration measurements shall be made as close as poss-
limits. Until this information is available the following procedure
ible to the point or area through which the vibration is trans-
is tentatively recommended.
mitted to the body. For example, if the man is standing on a
floor or sitting on a platform without any resilient material be-
The acceleration signal should be weighted by the appropriate
tween the body and the supporting structure, then the measur-
filter network defined in table 3 and described in 4.2.4. The
ing transducer or pick-up should be fastened to that rigid struc-
maximum peak value of this weighted signal is its maximum
ture. Where some resilient element, such as a seat cushion,
deviation from the mean value. The crest factor is then the ratio
does exist between the body and the vibrating structure, it is
of this maximum peak value to the weighted r.m.s. value of the
permissible to interpose some form of rigid transducer support
signal. Accelerations with crest factor as great as 6 can be
(for example, a thin, suitably formed metal sheet) between the
evaluated by this part of IS0 2631. When the crest factor is
subject and the cushion; but care shall be taken to ensure that
6, the recommended vibration evaluation
greater than about
such a device does not significantly influence the transfer of
method may underestimate the effect of the motion.
vibration through the cushion to the man or introduce rota-
tional motions otherwise not present. If it is not practicable to
In practice, the crest factor will depend on the period over
measure the vibration at the point of input to the man in such a
which the peak value and the r.m.s. value are determined. The
way, then the transmission characteristics of the seat cushion
is 1 min. In ad-
minimum period for evaluating the crest factor
or other resilient element shall be determined and taken into ac-
dition to occasional peak values, the large variations in level
count when calculating the actual vibration transmitted to the
which can occur over periods longer than 1 min can raise the
body. In such cases, the characteristics of the cushioning
crest factor. However, these motions may often be evaluated
system shall be reported.
using the equivalent exposure time calculations described in
4.4.
NOTE - For research purposes which require the precise definition of
the vibratory input to human subjects, it has become customary in
laboratory studies of biodynamic and physiological responses to It is sometimes inconvenient to determine the peak value of the
replace seat cushions by rigid packs or platforms, because variation of
weighted signal as described above. Peaks determined on an
the measuring conditions by different arbitrary seating arrangements
unweighted signal (with band-pass filtering between 1 Hz and
can significantly affect the experimental results. Some of the variability
80 Hz only) will normally be greater than those from a weighted
of published research results in this field arises from differences be-
signal. An upper estimate of the crest factor may therefore be
tween the experimental conditions adopted in different laboratories.
If the value exceeds
determined from unweighted signals first.
6 it will be necessary to weight the signal to determine whether
the criterion is really exceeded. The r.m.s. value should always
3.3 Intensity of vibration
be determined from the weighted signal.
The primary quantity used to describe the intensity of a vibra-
NOTE - Measurements of rotational vibrations, whenever made,
tion environment, irrespective of the type of transducer or pick-
should be reported in units of r.m.s. angular acceleration, radians per
up used in actual measurements, shall be the acceleration. Ac-
second squared (rad/&.
celeration should normally be expressed in metres per second
squared (m/s2).
3.4 Measuring equipment
NOTE - In physiological work, it is frequently the custom to express
accelerations non-dimensionally in g units where Ig is the value of the
Vibration measuring equipment generally consists of the
standard acceleration due to gravity acting at the earth’s surface. This
: a transducer or pick-up, an amplifying device
following parts
usage is permissible within the context of experimental work in hand
(electrical, mechanical or optical), and an amplitude or level in-
provided that, when reference is made to the limits given in this part of
dicator or recorder. Where practicable (as in electronic in-
IS0 2631, the international standard value of g, is used for conversion
strumentation) and appropriate, networks may be included to
to values of acceleration expressed in metres per second squared.
limit the frequency range of the equipment and to apply the
The magnitude of a vibration, that is, the acceleration (or, if recommended frequency-weighting to the input signal. For
quoted, the velocity or displacement), should be expressed as a many applications, where it is not essential to rely solely upon
on-the-spot determinations, the use of a suitable tape recor-
root-mean-square (r.m.s.1 value. When peak values are
measured, these shall be converted as appropriate to r.m.s. ding system to obtain representative records for subsequent
values before reference to the limits given in this part of analysis will be the method of choice. An r.m.s.-rectifying
device may also be included for convenience, so that r.m.s.
IS0 2631. For the adequate description of vibration which is
values may be read off or recorded directly.
markedly non-sinusoidal, random or broad-band, the crest fac-
3
---------------------- Page: 5 ----------------------
/1-198!5
E)
All vibration measuring equipment should be properly which a physical description can be given in terms of those fac-
calibrated. This should be done in accordance with existing tors, three main human criteria can be distinguished. These
standards or recommendations governing the calibration of are :
such equipment. The basis of operation and the characteristics
of any measuring equipment used should be reported together a) the preservation of working efficiency ("fatigue-
with the results obtained with it. It is important to report such decreased proficiency boundary");
characteristics as the frequency sensitivity, the dynamic
properties (for example, the time constant), the dynamic range b) the preservation of health or safety ("exposure limit");
and
and resolution of the equipment; and when appropriate, the
precision of r. m.s.-rectifying, frequency-weighting, tape recor-
ding, frequency analysis or such other operations as may be c) the preservation of comfort ("reduced comfort boun-
performed upon the signal. dary").
NOTES
The recommended limits of exposure set according to these
three criteria are defined in 4.1.1 to 4.1 -3. Each of these limits is
1 It is recommended that IEC Publication 184 be used for specifying
defined graphically for the longitudinal (a,) direction (figures 2a
the vibration-transducers and IEC Publication 222 for specifying the
and 2b) and the transverse (U,, a,) directions (figures 3a and
auxiliary equipment, including amplifiers, frequency-selective equip-
3b). Numerical definition of the graphs in figures 2 and 3 is
ment and carrier systems.
presented in tables 1 and 2. Typically, as in most transport
2 With respect to the subjective judgement of the vibration intensity,
situations, U, (longitudinal) vibration will be applied to a sitting
it appears that the integration time for the human vibration perception
or standing person (a situation popularly referred to as "vertical
decreases from 2 to 0,8 s over the frequency range from 2 to 90 Hz.
vibration").
3.5 Random or broad-band vibration analysis
NOTE - It will be seen that, other factors being equal, somewhat
higher levels of vibration are acceptable when health or safety is the
In the measurement of random or distributed vibration, of
criterion, in comparison with the limits appropriate to working ef-
which narrow-band analysis not exceeding one-third octave is ficiency; and, conversely, lower limits are set when the criterion is the
preservation of comfort. This is in general accord with experimental
the appropriate method of description, the one-third octave
observation and experience, but it should not be taken as implying that
band filters used in any recording or analytical network shall be
there exists in all circumstances a simple hierarchical relationship be-
in accordance with IEC Publication 225. The frequency range
tween the intensities of vibration likely to impair health, working effi-
given in IEC Publication 225 shall be extrapolated accordingly
ciency or comfort.
to corresponding lower frequencies.
For some applications, it will be appropriate to equip electronic
4.1 .I Fatigue-decreased proficiency boundary
vibration measuring apparatus with a frequency-weighting net-
(a,) and
work defined as corresponding to the limits for vertical
The fatigue-decreased proficiency boundary as a function of
horizontal (a, and a,,) vibration respectively given in clause 4,
frequency and exposure time is shown in figures2a and 2b
tables 1 and 2 and figures2a and 3a (see note 2 of 4.2.4). A net-
(longitudinal vibration) and 3a and 3b (transverse vibration) for
work so defined shall not deviate from the recommended
h. The numerical values
daily exposure times from 1 min to 24
values by more than f 1 dB at two fixed frequencies; 6,3 Hz
defining the boundary are presented in tables 1 and 2 respec-
and 31,5 Hz for az measurements and 1,25 Hz and 31,5 Hz for
tively. The boundary specifies a limit beyond which exposure to
a, and a,, measurements.
vibration can be regarded as carrying a significant risk of im-
paired working efficiency in many kinds of tasks, particularly
3.6 Exposure time those in which time-dependent effects ("fatigue") are known
to worsen performance as, for example, in vehicle driving.
This part of IS0 2631 includes a computational procedure (see
4.4) for assessing the effective daily exposure to vibration. This The actual degree of task interference in any situation depends
is intended to take account, as far as is possible, of variations in on many factors, including individual characteristics as well as
the intensity of vibration and any intermittency or interruption the nature and difficulty of ,the task. Nevertheless, the limits
of exposure to vibration which may occur during the period in recommended here show the general level of onset of such in-
question. Whenever measurements are made of human ex- terference, the frequency dependence and the time
posure to vibration which is varying in intensity, or which is dependence commonly observed. The data upon which these
discontinuous, the time-history of such exposure should be limits are based come mainly from studies on aircraft pilots and
reported in detail. drivers.
It should be noted that for man the most sensitive frequency
ranges (in which the limit is accordingly set lowest) are 4 to
4 Vibration evaluation guide
8 Hz for longitudinal (a,) vibration and below 2 Hz for
transverse (ax, a 1 vibration; and that human tolerance of vibra-
tion decreases (demanding increasingly stringent limits) in a
4.1 General considerations
characteristic way with increasing exposure time (figures 2b
and 3b). It is seen from a comparison of figures 2a and 3a that,
There are four physical factors of primary importance in deter-
whereas the tolerance for transverse vibration is lower than that
mining the human response to vibration, namely, the intensity,
for longitudinal vibration at very low frequencies, the converse
the frequency, the direction, and the duration (exposure time)
is so for higher frequencies (above approximately 2,8 Hz).
of the vibration. In the practical evaluation of any vibration of
4
---------------------- Page: 6 ----------------------
IS0 2631/1-1985 (E)
NOTE - It is anticipated that with experience in the practical applica- vibration in transport and near industrial machinery. These limits may
tions of this part of IS0 2631, correction tables will be worked out to not be very powerful in the evaluation of disturbance due to building
vary the level of the fatigue-decreased proficiency boundary according
vibration (for example, caused by traffic or footfall) in private homes,
to different environmental conditions of task requirements. For exam- offices or similar situations in which the socio-psychological and
ple, a more stringent limit may have to be applied when the task is of a
economic factors related to human disturbance are more subtle or
particularly demanding perceptual nature or calls for an exercise of fine complex, Acceptable vibration levels in residential buildings, for
manual skill. By contrast, some relaxation of the limit might be possible
example, may not lie much above the threshold of perception,
in circumstances in which the performance of the task (for especially during the night, but shall, in any case, be expected to vary
example, heavy manual work) is relatively insensitive to vibration. Ten- greatly with individual circumstances. The threshold of perception
tative data, as yet too few to provide a basis for a firm recommenda- varies from one subject to another and depends upan the conditions of
tion, suggest that a range of correction of + 3 dB to - 12 dB (that is,
measurement. The upper range of the threshold of perception has ap-
a modifying factor of 1,4 to 0.25 times the r.m.s. acceleration specified proximately the same frequency dependence as the curves of figures
by the boundary) may be envisaged. 2a and 3a. In the frequency bands of maximum sensitivity, namely 4 to
8 Hz for longitudinal and 1 to 2 Hz for transverse vibrations, the
threshold lies at approximately 0,Ol m/s* (about lO-3g). The in-
dividual threshold for many people may lie at still lower levels.
4.1.2 Exposure limit (health or safety)
2 It is anticipated that additional tables will be developed through the
The exposure limit as a function of frequency and exposure
practical use of this part of IS0 2631, providing for a finer differen-
time is of the same general form as the fatigue-decreased pro-
tiation of comfort in various situations, such as in offices, in various
ficiency boundary, but the corresponding levels are raised by a types of private residence, on ships, etc. The range of such correction
factors might extend from + 3 dB to - 30 dB (approximate threshold
factor of 2 (6 dB higher). In other words, maximum safe ex-
of perception), but their formulation awaits more substantial data than
posure is determined, for any condition of frequency, duration
are available at present.
and direction, by doubling the values allowed according to the
criterion of fatigue-decreased proficiency (see figures 2a, 2b
and 3a. 3b and tables 1 and 2).
4.2 Evaluation of frequency spectrum
Exceeding the exposure limit is not recommended without
special justification and precautions, even if no task is to be
4.2.1 Evaluation of discrete (single) frequencies
performed by the exposed individual.
The limits shown in figures 2 and 3 and given in tables 1 and 2
NOTES
are valid for discrete frequency vibrations acting in the foot-to-
1 The exposure limit recommended is set at approximately half the
head (a,) or the transverse directions (a, ay) respectively.
level considered to be the threshold of pain (or limit of voluntary
tolerance) for healthy human subjects restrained to a vibrating seat.
(Such limit levels have been explored for male human subjects in
4.2.2 Evaluation of discrete (multiple) frequencies
laboratory research.)
When vibration occurs simultan
...
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