This part of ISO 2631 defines and gives numerical values for limits of exposure for vibrations transmitted from solid surfaces to the human body in the frequency range 1 to 80 Hz. It may be applied, within the specified frequency range, to periodic vibrations and to random or non-periodic vibrations with a distributed frequency spectrum. Provisionally, it may also be applied to continuous shock-type excitation in so far as the energy in question is contained within the 1 to 80 Hz band.These limits (defined in detail in clause 4) are given for use according to the three generally recognizable criteria of preserving comfort, working efficiency, and safety or health. The limits set according to these criteria are named respectively in this part of ISO 2631 the "reduced comfort boundary", "fatigue-decreased proficiency boundary" and the "exposure limit". For example, where 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" 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 "reduced comfort boundary" should be considered.According to the criteria mentioned, these limits are specified in terms of vibration frequency, acceleration magnitude, exposure time and the direction of vibration relative to the torso. This direction is defined according to the recognized anatomical axes of the human body (see clause 3).This part of ISO 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 undergo the stress of a typical working day or shift.No information given in this part of ISO 2631 shall be extrapolated to frequencies outside the range 1 to 80 Hz (see notes below).It has been well established that differences in response to vibration occur both between and within individuals. These differences affect the level and shape of the curves and the relative effects of simple and complex motions. The guidance given in this part of ISO 2631 is based on the average response of subjects in a variety of situations. Thus two motions, which are assessed as equally severe by the recommended evaluation procedure may have different effects. Individuals, and groups of individuals, will sometimes disagree on which of two motions is worse and variables such as posture and subject activities can have large effects.NOTES1 The limits specified in this part of ISO 2631 are based upon data available from both practical experience and laboratory experimentation in the field of human response to mechanical vibration. To date, useful observations have been made mainly in the frequency range between about 1 and 100 Hz. The frequency range, its subdivisions and the corner frequencies defined in this part of ISO 2631 have been selected in accordance with ISO 266 and with national standards in several countries.2 Vibrations in the frequency range below about 1 Hz are a special problem, associated with symptoms such askinetosis (motion 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 intensity, frequency or duration of the provocative motion. Mechanical vibrations applied to the feet or buttocks above the frequency range considered in this part of ISO 2631 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 damping materials (for example, clothing or footwear) which may control the vibratory response of the skin and superficial layers of the body. For these reasons, therefore, it is not possible on the basis of present data to formulate generally valid recommendations for frequencies outside the 1 to 80 Hz band.In some applications, constant sensitivity to accelerations has been tentatively assumed for the frequency range 0,63 to 1 Hz.
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