Lage Burström

Absorption of vibration energy in the human hand and arm.

A possible basis for the risk assessment for hand-transmitted vibration may be to determine the amount of energy absorbed in the human hand and arm. In the present study, the mechanical energy absorption in the hand-arm system was measured within the frequency range of 4 to 1000 Hz. The study was carried out on ten healthy subjects during exposure to sinusoidal vibration. The influence of various experimental conditions, such as vibration direction (Xh, Yh, Zh), grip force (25-75 N), vibration level (8-45 mm/srms), and hand-arm posture were studied. The outcome shows that the energy absorption in the human hand and arm depended mainly on the frequency and direction of the vibration stimulus. Higher vibration levels, as well as firmer handgrips, resulted in higher absorption of energy. Varying hand-arm postures had only a small influence on the amount of absorbed energy, while the constitution of the hand and arm affected the energy absorption to a larger extent.

Risk assessment of vibration exposure and white fingers among platers

SummaryThe dose-response relationship between vibration exposure and vascular disorders in the hands was examined in platers. The study was based on a cross section of 89 platers and 61 office workers divided according to exposure to vibration into four groups. Vibration exposure was assessed by measuring the acceleration intensity on a sample of tools, together with both subjective rating and objective measurements of the exposure time. The frequency-weighted energy equivalent acceleration for 4 h was 4.6–4.7 m/s2. The point prevalence of white fingers was 42% for the plater category currently exposed with an odds ratio of 85. The time laps before contraction of white fingers (latency time) was four years for the 10th percentile, and was shorter than predicted according to the ISO-5349 standard. The prevalence of white finger symptoms staged according to the Taylor-Pelmear scale was comparable to the prevalences according to the Stockholm Workshop Scale. Vibration exposure was the dominant source of white fingers and each year of vibration exposure increased the odds ratio for white fingers by 11%. Distal circulation in the hands was assessed by a timed Allen test. The odds ratio for a positive Allen test was higher for the workers exposed to vibration compared to the non-exposed workers. The use of the timed Allen test is suggested in the clinical examination for vibration white fingers. The observed high risk for contracting white fingers could be prevented by exposure level reduction and/or restriction of exposure duration.

Comparison of different measures for hand-arm vibration exposure

Abstract Vibration measurements have been done on hand-held tools in a group of 48 platers by evaluating the individual vibration acceleration and absorption of vibration energy. The measurement of the acceleration has been done frequency-weighted and frequency-unweighted in accordance with ISO 5349 and NIOSH (USA) recommendations for hand–arm vibration standards, respectively. The acceleration and the energy absorption have been measured simultaneously in the three orthogonal directions, the latter by using a specially designed adapter. The exposure time has been determined by both subjective assessments and objective measurements. Individual energy-equivalent accelerations and vibration dosages have been calculated from these data. The results show that the type of tool was critical to vibration load intensity when the different measures for determining vibration levels were used. Of the methods used, the evaluation specified by ISO 5349 makes most consideration of low frequencies of vibration ( 200 Hz). The results show a poor correlation between the three methods used. The same was found between mean subjective assessment and objective measurement of the average exposure time. Further studies of the relation between results presented here and generated disturbance will be conducted, which may clarify any exposure–response relationship.

Mechanical impedance of the human hand-arm system

Abstract The mechanical impedance of the human hand-arm system was measured within the frequency range of 20–1500 Hz. A handle, specially designed for such measurements, was used. The studies were carried out on eight healthy male subjects during different experimental conditions defined by three different hard-arm postures, hand grip forces (25–75 N) adopted by the subjects, the amplitude (27–53 mm/ srms; 1.4–2.8 g at 80 Hz) and direction of the vibration stimuli. The outcome shows that the mechanical impedance of the hand-arm system depends on the frequency of the vibration stimuli. Above 200 Hz, the impedance, in general, increases quite rapidly, from about 150 Ns/m up to about 500 Ns/m at 1500 Hz, with the frequency. At lower frequencies, however, various shapes of the impedance curves were found which were most pronounced between different hand-arm postures. For the transverse direction, the impedance increased from about 50 Ns/m at 20 Hz to maximum about 100 Hz followed by a slight decrease. For the proximal-distal direction the impedance decreased from about 150 Ns/m at 20 Hz to minimum at about 100 Hz. More firm hand grips, as well, as higher vibration levels, resulted in higher impedance magnitudes for frequencies above about 100 Hz. Remarkably enough, for lower frequencies an almost opposite relationship was found. Furthermore, the results indicate a non-linear relationship between mechanical impedence and the studied experimental variables. Therefore, prior to setting up future standards, the mechanical properties of the hand-arm system should be taken into careful consideration.

Mechanical energy absorption in human hand-arm exposed to sinusoidal vibration

SummaryA possible basis for risk assessment of human exposure to vibration when using hand-held tools may be to determine the amount of mechanical energy that is absorbed by the hand-arm system. The aim of this investigation was to study the absorption of mechanical energy in the human hand-arm system during exposure to sinusoidal vibration within the frequency range of 20 to 1500 Hz. A handle, specially designed for this type of experiments, was used during the measurements. The influence of various experimental conditions, such as three different hand-arm postures, grip force (25–75 N) and vibration levels (27–53 mm/srms), were studied on eight subjects. The outcome clearly shows that the energy absorption properties of the human hand-arm system are more or less dependent on all of the experimental conditions studied, but mainly to the frequency of the vibration stimuli. Furthermore, the results indicate a non-linear relationship between the energy absorbed and all other variables studies.

Portable equipment for field measurement of the hand's absorption of vibration energy

Abstract Risk assessments for hand-transmitted vibration, according to international Standard ISO 5349, are based solely on the acceleration level measured directly on the vibrating surface. An alternative method could be to measure the quantity of vibration transmitted to and absorbed by the operator. These types of measurements have until now only been possible to conduct in laboratory environments using specially-designed handles. The aim of the present project has therefore been to develop portable equipment for field measurements of the hands absorption of vibration energy. The developed equipment consists of a hand-held adapter placed in the contact area between the hand and the vibrating surface. The adapter is equipped with transducers for measurement of vibration and dynamic forces. For the force measurements, four different technical solutions were tested. An adapter, equipped with a triaxial piezo-electric force transducer as well as piezo-electric accelerometers, was found to be the most suitable solution for field measurements. The adapter is small, has a low weight and can be used for measurement on tools with different handle designs. The adapter has been tested by laboratory measurements and reliable and accurate measurement results were obtained within the frequency range of 3 to 1900 Hz, for all the three orthogonal directions in accordance with ISO 5349.

Measurement of the Mechanical Energy Absorption in the Hand and Arm Whilst Using Vibrating Tools

The mechanical energy absorption in the human hand and arm during exposure to simulated vibration from five common types of hand-held tools within the frequency range of 5 to 1500 Hz, has been directly measured and indirectly determined. The study was carried out on ten healthy subjects, five males and five females. A special handle was used during the measurements. The influence of various experimental conditions, such as vibration level, vibration direction and grip force were also studied. The results show that the energy absorption depends upon the frequency spectra of the tools. The differences between the amount of absorbed energy for the hand-held tools correspond to a factor 3.1 although the frequency weighted acceleration is equal. Furthermore, the results show that experiments conducted with different exposure directions have a significant influence on the amount of absorbed energy. On the other hand, the grip force has only a minor influence. The results also show that it is possible to theoretically calculate the amount of absorbed energy by using the vibration characteristics for the hand-held tool and the mechanical characteristics of the hand and arm.