International Standard 2631 (1997) is concerned with the standardisation of the measurement, evaluation and assessment of whole-body vibration. With respect to health effects of whole-body vibration, the standard offers a combination of alternative methods so that different conclusions can be reached according to what is measured, how it is evaluated and how it is assessed. Various matters requiring consideration during a revision of the standard are suggested. The guidance for assessing the severity of whole-body vibration in ISO 2631 (1997) is compared with equivalent guidance for assessing hand-transmitted vibration in ISO 5349 (1986). It is suggested that when revising these standards some consideration should be given to the apparent contradictions suggesting that some exposures to whole-body vibration may be acceptable even though the same conditions would be considered unacceptable for hand-transmitted vibration.
The influence of whole-body vibration on gastric motility was investigated by using an electrogastrography (EGG) in seven healthy men. The EGG is usually referred to as a noninvasive technique of recording gastric myoelectrical activity by means of placing electrodes on the abdominal surface. Sinusoidal vertical vibration at each of 3 different frequencies (10Hz, 20Hz, 40Hz) were randomly given to the subject seated on a platform of vibrator for 5min. The vibration magnitude was kept at a constant of 2.0msec-2 (r.m.s.) during operation. The mean dominant frequency of EGG at control period was prior to operation 3.3 cycles per min (cpm). During vibration exposure at 10Hz, the peak of dominant frequency increased to 3.9cpm, and the relative power of slow wave showed the statistically significant decrease (45.8%, p<0.05). The mean relative power of slow wave which is composed of frequencies ranged from 2.0 to 5.0cpm was 56.6% at control period. On the contrary the mean relative power of frequencies ranging from 5.0 to 9.0cpm, tachygastria increased from 29.5% to 39.1%. These results suggest that the short-term exposure to whole-body vibration effects on the gastric myoelectrical activity.
When trains pass level crossings or turnouts, they are momentarily subject to relatively strong vibrations. In railway engineering, evaluation of the riding comfort under such occasional vibrations is called the momentary evaluation, which is distinguished from the long-term evaluation. In order to identify the effective vibrational characteristics on the momentary evaluation now controversial in Japan, an experiment was performed with a riding comfort simulator. Twenty adult subjects were exposed to lateral vibration with varying peak acceleration and crest factor. Referring to the vibrations of real trains, the peak acceleration in the range of 0.35-2.00m/s2 were varied in steps of 0.35m/s2 and the crest factors in the range of 1.5-5.0 were varied in steps of 0.5. The frequency was set constant at 2Hz. The task was to rate the degree of discomfort under each vibration which was given them successively. Results indicate that changes in the peak acceleration are most effective, and application of the crest factor in parallel improves the correlation with the perceived discomfort. Whether subjects can perceive changes in the peak or not affects the evaluation. Weights of vibrational characteristics that make a cue to the evaluation by subjects differ from person to person.
The effect on discomfort of the frequency and the backrest angle of x-axis (fore-and-aft) vibration of backrest have been studied. The method of adjustment was employed to obtain contours of equivalent comfort for three types of rigid backrests, whose surface were vertical, inclined 20 degrees and 40 degrees from vertical. Eighteen subjects were required to adjust test vibration over the frequency range 2-80Hz to produce discomfort equivalent to that caused by 10Hz 0.25m/s2 r.m.s. sinusoidal reference vibration for each backrest. The direction of vibration was perpendicular to backrest surface. Results shows that the sensitivity at 20 and 40Hz on inclined backrests is significantly about 1.4 to 1.5 times greater than that on a vertical backrest (p<O.O1) but there is no significant difference between the two contours for inclined backrests. The contour for a ‘vertical’ backrest obtained in this experiment agrees with the contour calculated from the frequency weighting factors for x-axis back vibration, Wc, in ISO2631-1, but the contours for inclined backrests do not agree with the contour well.
The road traffic-induced building vibration was recorded continuously for 24hr in three orthogonal axes outside and inside the building. Several alternative objective methods of quantifying the severity of exposures to whole-body road traffic-induced building vibration are used. The relationship between the results of all objective evaluation methods of vibration-induced by road traffic and the subjective responses to building vibration are compared. It was conducted that the ISO 2631-2 z-axis frequency weighting combined with a measure of vibration dose value (VDV=[∫a4(t) dt)]1/4 may use a practicable objective evaluation procedure in buildings than L10 percentile vibration levels. It was also cleared that the L10 percentile vibration levels at the ground boundary of the regulation law of Japan Environmental Agency must be low levels.
Level fluctuating vibration has been evaluated by the cumulative index L10, but some investigators suggest that the L10 cannot represent an adverse comment on vibration. In order to clarify the compliant, various factors involving vibration need to be analysed together by statistical methods, for instance factor analysis or quantum theory. The authors investigated the relationship between an evaluation index and human sensation of vibration in a subjective experiment in a wooden house. The subjects were exposed to vertical road traffic vibration reproduced with an electrodynamic vibrator placed near the house. The range of vibration levels at surfaces in contact with the subjects were from 50dB to 70dB in root mean square of frequency weighted acceleration level, i.e. the vibration level. Numbers assigned by the subjects and evaluation indices of the vibration level were analysed by applying the Stevens power law. The results showed that L10 or Leq (55) could become an effective index for the assessment of subjective perception of level fluctuating vibration in a wooden house.
Recently farm mechanization has been widespread and developing rapidly, in particular riding farm machines are increasingly used in paddy fields in Japan. We have no information available on the actual situation regarding whole-body vibration on the seats of these farm machines from the standpoint of labour protection. Measurement and evaluation of whole-body vibration was performed on the seats of popular riding agricultural machineries. Whole-body vibration on the seats of combine harvesters and wheel tractors exceeded exposure limits and the fatigue-decreased proficiency boundary limit of 8hr and also shortened the reduced comfort boundary limits of ISO 2631 (1985). Some combines, tractors and carieers had only less than one hour exposure duration as compared with the ISO 2631-1 standard (1997). On the other hand a questionnaire was also performed on the subject of agricultural machine operators. Any specific injury or other effects, i.e. low back injuries were not found among the group of operators as compared with those in non-operator farmers. It seems to be difficult to find out the health effects of whole-body vibration itself, because there may be a lot of causes, i.e. working posture, operating heavy materials, in farm working conditions.
Seats have been newly developed with an anti-vibration suspension system for agricultural machinery. These seats were examined in a series of laboratory tests to determine their static and dynamic physical characteristics. These seats are specifically designed for the Japanese physique. An artificial track was constructed to simulate a farm field based on BSI (British Standard) and to examine vibration the transmissibility of the seats when installed in machinery. The results indicated that the transmissibility from under the seat to on the seat in the vertical direction was approximately 0.25, although little reduction of vibration was observed in the fore-aft direction. This suggests that these seats are applicable to the agricultural field.
In the 1950s, the introduction of portable power tools into the production process of many industries began on a large scale around the world and resulted in many cases of occupational vibration syndrome after the 1960s. There was an urgent world wide need to undertake preventive steps, medical assessment and therapy. At the end of 1964, our investigation began in Japanese national forests, and then in mines and stone quarries. The Japanese Association of Industrial Hygiene established a “Committee for Local Vibration Hazards” (1965), and many researchers in the medical and technological fields joined this Committee. After 10 years, a comprehensive system for the prevention of vibration syndrome was established in the national forestry. It consists of 1) improvements in vibrating tools, 2) hygienic regulation of operation time with an alternative working system, 3) health care system involving early medical checks, early therapy and age limitations in operation of vibrating tools, 4) protection against cold in the workplace and while commuting, and 5) education and training for health and safety. The prevention strategy for vibration syndrome in our national forests is to establish a comprehensive prevention system in cooperation among researchers in the medical and technological fields, workers and administration. The Ministry of Labor presented that strategy as good model of prevention for other industries (1976). New designs for this model were developed and adapted according to the special conditions of each industry. Thus comprehensive system for prevention of vibration syndrome developed successfully from the late 1970s to 1980s in Japan.
Peripheral neuropathy in the hand has often been reported in workers using hand-held vibrating tools. But the affected location in the hand is not clearly demonstrated. To elucidate the impaired segment of the median nerve within the hand, fractionated median sensory nerve conduction velocity (SCV) was measured in the digital, finger-to-palm, palm-to-wrist and wrist-to-elbow segments. Subjects were 56 patients with hand-arm vibration syndrome and 43 healthy controls of similar age. SCV in the digital and the wrist-to-palm segments was significantly slower in the patients than the controls. Slowed SCV in the digital segment was encountered in 36% of the patients, while the slowing in SCV in the wrist-to-palm segment (across the carpal tunnel) was found in 20% of them. The slowing in the digital segment was more frequently encountered in the advanced stage of the Stockholm sensorineural (SN) stage for hand-arm vibration syndrome: 10% in 0SN (no neurological symptoms) while 56% in 3SN (severe stage). The present study has demonstrated that vibration-induced nerve impairments dominantly exist both in the digits and across the carpal tunnel. Careful neurophysiological assessment is important to confirm the impaired location within the hand.
To clarify the trends in the number and the severity of vibration syndrome in Wakayama for these 23 years, the records of the medical examinations for vibration syndrome were analyzed with 4, 652 (a total of 9, 920) private forestry workers exposed to hand-arm vibration. The number of the subjects who took the medical examinations reached a maximum of 1, 242 in 1978. After that, it decreased year by year, but remained at about 300 or less from 1988. There was a corresponding increase in age and the number of years of operating chain saws among the subjects examined. The compensated cases reached a maximum number of 393 cases in 1977, and then a drastic decrease was noted. Year by year there was an increase in the number of cases whose medical examinations revealed no abnormality. The regional occupational health care system including the surveillance card, which has been active since 1975, has probably contributed to the decrease or prevention of occurrence of vibration syndrome in Wakayama.
For diagnosing the hand-arm vibration syndrome, peripheral circulation and sensory tests immersing one hand in cold water at 10°C for 10min have been performed widely in Japan. The authors investigated the effects of room temperature, seasonal condition and food intake on the test results, especially finger skin temperature. Six healthy males were examined repeatedly under six different room temperatures at 10°C, 15°C, 20°C, 22.5°C, 25°C and 30°C. Eight healthy males were examined under room temperatures at 10°C, 20°C and 30°C, repeatedly in winter, spring, summer and autumn. Six healthy males were examined in summer under room temperature at 22.5°C repeatedly 1hr after, 3hr after meal and after fasting for 13hr. The finger skin temperature was strongly affected by room temperature. The finger skin temperature was also affected by seasonal condition. No remarkable effect of food intake was observed. For estimating circulatory function of the upper extremities using the finger skin temperature, the room temperature should be strictly controlled and the effect of seasonal condition must be taken into consideration.
Objectives; This study was aimed to assess the peripheral circulatory functions of forestry workers exposed to hand-arm vibration, using simultaneous measurements of finger skin temperature (FST) and finger blood flow (FBF). Methods; The subjects were five men with vibration-induced white finger (VWF), four subjects with numbness in their hands and five exposed controls without any signs or symptoms related to vibration syndrome. Simultaneous measurements of FST and laser-Doppler FBF were performed before, during and following a 10-min recovery period after the hand was immersed in cold water (10°C, 10min). Partitional measurements of finger blood flows could be made between the capillaries and deeply located vessels using two laser-Doppler flow probes having narrower and wider optic fiber separations. Results; The FST as well as the FBF of the capillary and deeply located vessels during and following the cold immersion test in those with VWF and in the subjects with numbness had a slight increase immediately following the cold immersion and no tendency to be augmented as the time span increased. After the cold immersion test, the control group had significantly greater FST and FBF compared to other groups. Particularly, from the 5th to the 10th min after the cold provocation, the values of FBF of the deeply located vessels in those with VWF were significantly lower than the controls. During the course of observation, the FST had significantly linear relationship with the recorded capillary and deep FBF values, and that was much closely correlated with the deep FBF (i.e., P<0.01 in each selected condition). The slope of the regression lines in the capillary were steeper and shallow in the deep FBF. Conclusions; In addition to the measurement of capillary FBF, more detailed and accurate information on the peripheral circulatory functions of vibration-exposed subjects can be obtained by including the assessment of the deep FBF.
The long cane can be used as a mobility aid for visually handicapped people. According to a questionnaire completed by Japanese cane users, it seems they are not always satisfied with using long canes for a variety of reasons. In this study, hand-transmitted vibration from the long cane due to tapping the ground was measured because an exposure to repeated shock-type tapping vibration may affect the hand-arm system. A sighted female wearing a blindfold participated. The measurement was carried out in different conditions with three different ground materials both indoor and outdoors. The vibration at three axes of the cane grip and one axis at the wrist were measured. The pinch forces between an index finger and the grip were also measured using a strain gauge in order to observe how the vibration characteristics depend on the changing forces. Measurement, evaluation and assessment were based on the International Standard (ISO 5349). The estimated daily exposure time and the transmissibility were obtained in order to investigate the severity of the hand-transmitted vibration caused by the long cane. It was found that the characteristics of tapping vibration depend on different measurement conditions and the vibration might be associated with a health risk over a long life span.
Temporary Threshold Shift (TTS) is often used as an indicator of the effect of hand-transmitted vibration on the human body. An experiment for the prediction of TTS in exposure to intermittent vibration was conducted in the present study to examine the exposure equivalent rule, as well as the equations for growth and recovery TTS. It was found that the prediction of TTS obtained here was in good agreement with measured TTS. This estimation procedure for predicting TTS was compared with the notification of the Labor Ministry in Japan, in which control of the operation time and the rest time for hand-vibrating tools was described. The results suggest that the rest time of five minutes for a continuous exposure time of 30 minutes with low-level of vibration tools should be extended to 10 minutes of rest time.
The magnitudes of the hand-transmitted vibration, 297 hand-held tools and workpieces were measured at workplaces. The tools were used mainly in construction and manufacturing industries. The current standard for the measurement of hand-transmitted vibration has been based on the frequency-weighted acceleration of dominant axis method1, 2). According to the proposal of ISO/CD5349-13), the results of measurements (462 points) were recalculated by the method of the frequency-weighted acceleration sum. There is 32% of difference in average value between the acceleration sum and the dominant axis method.