Civil Engineering Reference
In-Depth Information
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Hand Activity Level
FIGURE 41.2 The ACGIH TLV for monotask hand work. The solid line depicts combinations of hand activity level
and peak finger force that should not be exceeded to prevent excessive risk of hand and wrist MSDs. The dashed line is
an action limit at which some people may be elevated risk. The action limit should trigger additional job analysis and
worker training. (From ACGIH (2005a). Documentation of the TLVs and BEI with Other Worldwide Occupational
Exposure Values 2005. Cincinnati, OH: ACGIH Worldwide; ACGIH (2005b). Hand Activity Level. 2005 Threshold
Limit Values for Chemical Substances and Physical Agents and Biological Exposure Limits. Cincinnati, OH: ACGIH,
pp. 112-117. With permission.)
There is strong biomechanical support for the contribution of non-neutral wrist postures to hand-
wrist-forearm MSDs (Armstrong and Chaffin, 1979; Moore et al., 1991; Armstrong et al., 1993; Moore,
2002; NRC, 1999; NRC and IOM 2001; Clark et al., 2004). In contrast, Marras and Schoenmarklin
(1993) showed that angular wrist velocity and acceleration may be more important than posture.
Angular velocity and acceleration are captured with the speed consideration in HAL (see
Figure 41.1a). Presently, posture is deferred to professional judgment.
There is a growing body of literature concerned with organizational issues (NRC, 1999; NRC and IOM,
2001). The mechanism by which organizational factors contribute to MSDs is not clear or at least not
clear enough to specify a TLV for these factors at this time.
Several studies of the TLV have been reported since it was proposed. Franzblau et al. (2005) examined
the prevalence of symptoms and specific disorders among 908 workers from seven different job sites in
relation to the TLV. Worker exposures were categorized as below the action limit, between TLV and the
action limit, or below the action limit. Elbow
forearm tendonitis was found to be significantly related to
TLV category as were all measures of carpal tunnel syndrome. Still, there was a substantial prevalence of
symptoms and specific disorders below the TLV action limit. These results suggest that adherence to the
TLV and action limit will reduce, but not eliminate symptoms and
/
or upper extremity MSDs and that a
/
control program may still be necessary.
Gell et al. (2005) conducted a prospective study of 432 industrial and clerical workers over a period of
5.4 yr. Incident cases were defined as diagnosed with CTS in workers who had no history of CTS at the
beginning of the study. There was elevated incidence of new CTS cases among workers whose jobs exceed
the TLV (relative risk 1.6); however, the relationship was not statistically significant at p
0.05.
Werner et al. (2005) studied upper extremity pain in a cohort of 501 active workers from four indus-
trial and three clerical work sites for an average of 5.4 yr. Cases were defined as workers who were asymp-
tomatic or had a discomfort score of two or less at baseline testing, but reported a discomfort score of
,
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