Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

Jack F. Wasserman

Committee Members

Judy L. Cezeaux, John H. Forrester

Abstract

Hand Arm Vibration Syndrome (HAVS) is a pathological condition, associated with the use of a hand-held vibrating tool, that affects over one million United States workers. This condition was first discovered in the early twentieth century Stages of the disease, with its associated neurological and peripheral vascular components, have been clearly defined Currently, there are three hand-arm vibration safety standards in use: ISO 5349, ACGIH-TLV, and ANSI S3.34. Since the 1960's, numerous studies have been conducted for various commercial grade hand-held tools known to be associated with the disease. The majority of all reported tool testing has involved tools used by workers who have developed HAVS symptoms The standards have been used as guidelines for maximum recommended vibration exposure times for these tools.

Standard inexpensive hobby grade hand-held vibratory tools, usually used on a short term non-continuous basis, are not associated with HAVS. Until now, there has been no data to estimate the risk factors associated with these tools. Therefore, there is a question as to whether this is due to low vibration levels, limited daily exposure, or possibly a combination of factors Vibration acceleration amplitude testing for this thesis was conducted using 3/8 hand-held electric drills, a standard hobby grade tool commonly used both by commercial contractors and laymen.

This study was conducted to: 1) compare measured vibration amplitudes to the current safety standards, 2) compare measured vibration amplitudes for four different common bit/material combinations, 3) determine any effects that tool age and usage might have on measured vibration amplitudes, 4) verify repeatability of experiments, 5) determine any statistical correlations that might be present from examination of the experimental data, 6) examine the most appropriate method for testing such tools as those used in the study, and 7) make any necessary recommendations regarding usage and exposure to vibration from these tools

Ten 3/8" electric drills, representing a wide variety of tool ages and manufacturers were obtained from various local sources. Using conditions designed to simulate the workplace where they might commonly be used, vibration testing was conducted for these tools using four different material/drill bit combinations Triaxial accelerometer assemblies mounted to the tools in accordance with the current ANSI safety standard were used to obtain accelerations which were recorded on digital audio tape (DAT), The raw unweighted data was then digitized and computer analyzed to obtain Fourier vibration spectra, which were then converted to the third-octave frequency bands and root mean square (rms) acceleration values required by the ANSI S3.34 and ACGIH current safety standards. The results, weighted in accordance with the standards, were then compared to the standards to determine recommended maximum acceptable vibration exposure times.

It was hypothesized that: 1) the vibration amplitudes measured for this class of hobby grade tools would be well within current safety standards, 2) concrete would show the largest vibration amplitudes, followed by steel, wood, and finally plastic, in order of decreasing amplitude, 3) older drills obtained from local rental agencies would show much higher vibration levels than newer/refurbished ones, 4) repeatability would be verified by performing several vertical trials for each material^it combination and taking an average, 5) certain statistical patterns would be clearly evident from the experimental data obtained, 6) the reason for lack of HAVS prevalence would be determined, and 7) recommendations regarding usage, exposure, limitations, and testing procedures could be made, based on the results obtained from this study

All plotted third-octave vibration spectra and rms acceleration values were examined from the perspectives of basicentric axis comparisons and material comparisons. Unfortunately, the experimental testing results did not show clearly definable patterns. Therefore, generalizations could not be made. According to the data obtained, none of the tools drilling in any of the materials tested here could be thoroughly evaluated, based on the limited amount of experimentation conducted for this thesis. Although, in most cases, the results did not exactly support the proposed hypotheses, they did provide some valuable information about this class of hobby grade tools

In most cases acceleration amplitudes measured for the tool barrel were much higher than those at the tool handle. Student t-tests were performed for four randomly chosen accelerometer mounting location comparisons trials. These results did show statistically significant differences in acceleration magnitudes measured at the handle and barrel mounting locations during two-handed drilling. This seems to suggest that the standard contains some ambiguities concerning accelerometer placement and grip position during two handed drilling. when one hand is used for stabilization. The drills themselves appear to matter more than the specific materials with the appropriate bits, which are optimized for them. The condition of each tool also appears to be critical to measured acceleration levels.

Based on the results obtained herein it is recommended that vibration testing for hobby grade tools, such as those used for this study, should be conducted at the specific workplace under the exact conditions that they will be used These tests should also be conducted with the specific worker(s) using the tool upon the specific materials for which it will be used Both handle and barrel mounted acceleration amplitude measurements should be taken simultaneously The focus of future research should be narrowed to help reduce the number of outstanding variables. Multi-factorial statistical analysis, which takes into account several variables that might affect measured vibration acceleration values should also be performed.

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