Civil Engineering Reference
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four or above on a ten point visual analog scale at follow-up. Controls were defined as those who reported
pain of two or less at follow-up. The peak finger force was close to or exceeded the TLV for 65% of cases
versus only 39% of control (p
0.01). The peak finger force was higher among cases (3.4 versus 2.9, p
¼
0.04). Significant relationships were also reported between upper extremity discomfort and both peak
and average finger forces and both peak and average wrist postures.
These studies provide additional support for the TLV, but suggest that the action limit for a proactive
control program may be set too high. Users should consider lowering it to a peak finger force of 3 for an
HAL value of 1. The Werner et al. (2005) study also supports the concern about non-neutral wrist
postures.
¼
41.4 Applying the ACGIH TLV
Key points of the TLV on HAL.
.
Considers repetition and force and applies to monotask hand work performed for four or more
hours per day
.
The term “hand activity level” or “HAL” is used to refer to repeated and sustained exertions of the
hand
.
Peak finger force is the 90th percentile force value exerted with the fingers
.
Factors besides repetition and force, such as posture, contact stresses, vibration and psychosocial
stresses, are deferred to professional judgment of the analyst
.
The TLV specifies an exposure level that presents a significant risk of work-related MSDs and it
should not be exceeded
.
The action limit specifies exposure limits that may present a risk to some people — particularly if
combined with other work or personal factors. The action limit should trigger a proactive program
.
The TLV should be applied to the right and left hands separately
41.4.1 Monotask Hand Work
The ACGIH TLV is intended for monotask hand work for four or more hours per shift (ACGIH,
2005a,b). Many will think of a task as a way of organizing groups of work elements according to their
purpose. In this case, monotask work implies that there is a predictable pattern of work elements
throughout the work shift.
41.4.2 Hand Activity Level
HALwas adopted from Latko et al. (1997) and considers exertion frequency, recovery time, and the speed
of motion. The term hand was selected to emphasize that the TLV is concerned primarily with the actions
of the hand and wrist as opposed to other body parts. The term “activity” was selected over “repetition”
to emphasize both dynamic and static exertions that may contribute to MSDs in the hand, wrist, and
forearm. The term “level” was selected because the HAL is expressed on a relative zero to ten point
scale shown in Figure 41.1(a).
Latko et al. (1997) showed that the HAL was closely related to the frequency of exertion and the recov-
ery time in the work cycle. These data were used by the ACGIH Physical Agents committee to develop a
table of HALs versus frequency and duty cycle. Table 41.1 was adapted from ACGIH (2005a). Duty cycle
has been replaced with recovery time, the complement of duty cycle. Recovery time will be more familiar
to those concerned with setting up production standards. Work standards use allowances that are gener-
ally expressed as a percentage of work time. A second modification of Table 41.1 includes upper and lower
limits for each exertion frequency range. There are some gaps in the ACGIH table because of the range of
the available data. As many readers will inevitably encounter values outside of the range of the observed
data, values are suggested for extrapolation. Extrapolated values are indicated with an asterisk and are the
opinion of the author and do not reflect the views of ACGIH.
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