Civil Engineering Reference
In-Depth Information
The use of the ILO values is complex. Remembering that fatigue allowances are given only for work
time (not machine time), the applicable fatigue allowance points are to be totaled. Then, using
Table 38.1, the points are converted to percentage of time. A large fatigue allowance is an indication
that there is a large potential for improved ergonomics.
Fatigue allowances will be divided into physical, mental, and environmental.
38.6.1 Physical Fatigue Allowances
There are four subcategories of physical fatigue allowances: physical fatigue, body posture, short cycle,
and restrictive clothing:
1. Physical fatigue. Table 38.2 has three fatigue categories: push (including foot pedal as well as car-
rying a load on the back), carry (hand
lowering. All three categories are
straight lines when force is plotted versus percentage of allowances.
Carrying items on the back is rare in present industrial practice. For pedal force, the rec-
ommended maximum pedal force is 90 N (9 kg) (Konz and Johnson, 2004). However, a 9-kg
pedal force seems excessive in present industrial practice — especially for a repetitive operation.
Carrying items in the hand
/
arm carry), and lifting
/
arms probably would be intermittent rather than continuous so the
stress would be on local muscle systems rather than a cardiovascular load. Mital et al. (1993) give
recommended weights for intermittent carrying for one- and two-handed carrying. They do not
give any recommendations for fatigue of carrying but do recommend reducing the weight carried
by 30% if the carrying is done frequently. The ILO lifting allowances probably are best compared
versus the National Institute of Occupational Safety and Health (NIOSH) lifting guidelines (see
Chapter 46). The ILO uses only the single variable of weight lifted while NIOSH considers vari-
ables of lift origin, lift destination, frequency of move, angle, and container design to determine
the permissible weight to be lifted. However, NIOSH does not give fatigue allowances for lifting.
2. Body posture. Table 38.3 gives posture allowances. Sitting easily is 0 points with 10 points the
maximum in present industrial practice. Activities given an allowance include standing, carrying
/
TABLE 38.1 Conversion from Points Allowance to Percentage Allowance for ILO
Points
0
1
2
3
4
5
6
7
8
9
0
10
10
10
10
10
10
10
11
11
11
10
11
11
11
11
11
12
12
12
12
12
20
13
13
13
13
14
14
14
14
15
15
30
15
16
16
16
17
17
17
18
18
18
40
19
19
20
20
21
21
22
22
23
23
50
24
24
25
26
26
27
27
28
28
29
60
30
30
31
32
32
33
34
34
35
36
70
37
37
38
39
40
40
41
42
43
44
80
45
46
47
48
48
49
50
51
52
53
90
54
55
56
57
58
59
60
61
62
63
100
64
65
66
68
69
70
71
72
73
74
110
75
77
78
79
80
82
83
84
85
87
120
88
89
91
92
93
95
96
97
99
100
130
101
103
105
106
107
109
110
112
113
115
140
116
118
119
121
122
123
125
126
128
130
Note: The second column (0) gives the 10 s, and the remaining columns give the units. Thus, 30 points (0 column)
¼
15%;
31 points (1 column)
17%.
The percentage allowance is for manual work time (not machine time) and includes 5% personal time for coffee breaks.
Note that 0 points gives 10% allowance. In addition, at “low” points (say 0 to 20), it takes about six points to get an additional
1% allowance while at “high” points (say 100), one point gives about an additional 1% allowance.
Source: International Labor Office. 1992. Introduction to Work Study, 4th ed. Geneva, Switzerland: ILO. With permission.
¼
16%; 34 points
¼
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