Nelson, Christopher Mark
Vibration-induced white finger in dockyard employees.
University of Southampton, Institute of Sound and Vibration Research,
Vibration-induced white finger (VWF) is a vascular condition associated with
occupational exposure to hand-transmitted vibration. The fingers are prone to
intermittent blanching attacks which may be triggered by cold conditions and are
usually accompanied by numbness and tingling or pain. VWF has been associated
with the use of various tools and processes, among which are the percussive and
rotary metal-working tools used in ship repair work. This thesis describes a
study of dose-effect relationships for VWF in dockyard employees.
A review of the literature revealed more than 40 epidemiological studies of VWF
in workers using hand-held metal-working tools. Measurements of tool vibration
have also been reported, but few researchers have combined epidemiological studies
of VWF with measurements of the vibration exposures Involved. Some dose-effect
relationships have been suggested and current standards contain tentative doseeffect
guidance. Some recent authors have suggested that the frequency weighting
and time-dependencies assumed In current standards are inadequate.
Methods for the measurement of hand-transmitted vibration were assessed. The
vibration characteristics of sixteen pneumatic tools commonly used in dockyard
work were measured in the laboratory. Repeated measurements were made In three
axes at each hand position and analysis included the computation of narrow-band
spectra, acceleration magnitudes in octave bands and overall frequency-weighted
and unweighted acceleration magnitudes.
A survey of vibration-exposed employees in a dockyard was conducted by
questionnaire. Information related to symptoms of VWF, and the history of use of
vibrating tools was obtained from each individual. The severity of blanching in
each affected individual was recorded using a scoring system.
The severity and prevalence of symptoms were related to various measures of
vibration 'dose' (i.e. combinations of measured vibration magnitudes and reported
exposure times) by logistic regression and survival analysis. A highly significant
relationship between VWF severity and exposure time was demonstrated. However,
the use of frequency-weighted acceleration in dose calculations reduced the
goodness of fit, while unweighted acceleration gave a small improvement in some
cases. This suggests that higher frequencies in the range 6.3 Hz to 1250 Hz are
of greater Importance than current standards imply. The effect of vibration
magnitude was found to be small compared with that of exposure time and no clear
effect of vibration direction or vibration frequency was demonstrated.
No evidence was found for a time-dependency of the form assumed in current
standards. It is possible that the risk of VWF may not be directly related to the
vibration magnitude, but that a 'threshold' magnitude exists, below which the
hazard is small and above which it is proportional to a function of the exposure
time. Further Investigation of this hypothesis is recommended.
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