Civil Engineering Reference
In-Depth Information
to elbow height. For the 95th percentile female operator, this situation is not so critical
because the sitting elbow height is much greater. In this case
H
=5.2 cm.
TABLE 9.3
Measures (cm) of preferred Hand
Height Over the floor
Type of
Task
Hand
Height
Elbow
Height
(Range)
Preferred Hand Height Over Floor* (cm)
Standing (5th to 95th)
Sitting (5th to 95th)
Male
Female
Male
Female
Heavy
lifting
−15 −20 to −10
91 to 110
85 to 110
Not
recommended
Not
recommended
Light
assembly
−5 −10 to 0
101 to 120
95 to 110
59 to 79
55 to 73
Typing
+3
0 to +6
109 to 128
103 to 118
67 to 87
63 to 81
Precisiom
work
+8
+5 to +10
Not
recommended
Not
recommended
72 to 92
68 to 91
The ranges are for females and males from 5th to 9th percentile (see Table 3.2) and were obtained
by deducting or adding the value for hand height. shoe height of 3 cm is included. 1 in=2.54 cm.
9.5
WORK AT CONVEYORS
Conveyors are increasingly being used in manufacturing, not only for transportation, but
also at assembly lines and for temporary storage. Often these systems are physically
connected. At a workstation this arrangement has the advantage that an operator can push
items from a moving conveyor to a storage or an assembly line conveyor and is not paced
by the line. The operator can thus work faster or slower, as long as the buffer capacity of
the storage conveyor is not exceeded (Konz, 1992a).
There is a common belief in industry that the height of the conveyor line must be fixed
and consistent throughout a plant. The commonly preferred height is 92 cm (36 in),
which is the same as for industrial standing workstations. This may not always be ideal.
Obviously one must avoid downhill and uphill slopes, but there are biomechanical
reasons why heights could be different at different locations.
For people working at the conveyors, one should adopt the same rules for determining
work height as for regular sitting and standing workstations (see Table 9.3).
The purpose is to make the conveyor height convenient for manual work (not for the
engineers who design the plant). Thus, the conveyor height should depend on the size of
the object that is being handled. For example, if there are large steel drums transported on
the conveyor, and if they are handled by workers, then the conveyor height must be very
close to the floor to make such handling convenient. Nagamachi and Yamada (1992)
demonstrated that the concept of variable conveyor height worked well in a Japanese
plant that manufactured air conditioners. The conveyor line was used for assembly and
depending on the height of the work items, the height of the conveyor shifted. They
referred to this as a “Panama Canal” conveyor. Productivity and quality improved with
this design.
