Civil Engineering Reference
In-Depth Information
Since the total work time (75 min) exceeds 1 h, the job is classified as moderate duration. On the
other hand, if the recovery period between lifting sessions was increased to 30 min, then the short-
duration category would apply, which would result in a larger FM value.
A special procedure has been developed for determining the appropriate lifting frequency (F) for
certain repetitive lifting tasks in which workers do not lift continuously during the 15-min
sampling period. This occurs when the work pattern is such that the worker lifts repetitively
for a short time and then performs light work for a short time before starting another cycle.
For work patterns such as this, the lifting frequency (F) may be determined as follows, as long
as the actual lifting frequency does not exceed 15 lifts per minute:
(i) Compute the total number of lifts performed for the 15-min period (i.e., lift rate times work
time)
(ii) Divide the total number of lifts by 15
(iii) Use the resulting value as the frequency (F) to determine the FM from Table 46.5
For example, if the work pattern for a job consists of a series of cyclic sessions requiring 8 min of
lifting followed by 7 min of light work, and the lifting rate during the work sessions is ten lifts
per minute, then the frequency rate (F) that is used to determine the FM for this job is equal
to (10
min. If the worker lifted continuously for more than 15 min,
however, then the actual lifting frequency (10 lifts
8)
/
15 or 5.33 lifts
/
min) would be used.
When using this special procedure, the duration category is based on the magnitude of the recovery
periods between work sessions, not within work sessions. In other words, if the work pattern
is intermittent and the special procedure applies, then the intermittent recovery periods that
occur during the 15-min sampling period are not considered as recovery periods for purposes
of determining the duration category. For example, if the work pattern for a manual lifting job
was composed of repetitive cycles consisting of 1 min of continuous lifting at a rate of 10 lifts
/
/
min, followed by 2 min of recovery, the correct procedure would be to adjust the frequency accord-
ing to the special procedure (i.e., F
[10 lifts
min
5 min]
15 min
50
15
3.4 lifts
min).
¼
/
/
¼
/
¼
/
TABLE 46.5
Frequency Multiplier Table
Work Duration
Frequency
a
Lifts
1h
1 but
2h
2 but
8h
.
.
V
b
min (F)
30
V
30
V
30
V
30
V
30
V
30
/
,
,
,
0.2
1.00
1.00
0.95
0.95
0.85
0.85
0.5
0.97
0.97
0.92
0.92
0.81
0.81
1
0.94
0.94
0.88
0.88
0.75
0.75
2
0.91
0.91
0.84
0.84
0.65
0.65
3
0.88
0.88
0.79
0.79
0.55
0.55
4
0.84
0.84
0.72
0.72
0.45
0.45
5
0.80
0.80
0.60
0.60
0.35
0.35
6
0.75
0.75
0.50
0.50
0.27
0.27
7
0.70
0.70
0.42
0.42
0.22
0.22
8
0.60
0.60
0.35
0.35
0.18
0.18
9
0.52
0.52
0.30
0.30
0.00
0.15
10
0.45
0.45
0.26
0.26
0.00
0.13
11
0.41
0.41
0.00
0.23
0.00
0.00
12
0.37
0.37
0.00
0.21
0.00
0.00
13
0.00
0.34
0.00
0.00
0.00
0.00
14
0.00
0.31
0.00
0.00
0.00
0.00
15
0.00
0.28
0.00
0.00
0.00
0.00
.
15
0.00
0.00
0.00
0.00
0.00
0.00
a
For lifting less frequently than once per 5 min, set F
0.2 lifts
min.
¼
/
b
Values of V are in inches.
Search WWH ::
Custom Search