Civil Engineering Reference
In-Depth Information
defined by the large middle knuckle of the hand (Figure 46.1). Typically, the worker's feet are not
aligned with the midsagittal plane, as shown in Figure 46.1, but may be rotated inward or outward.
If this is the case, then the midsagittal plane is defined by the worker's neutral body posture as
defined above. If significant control is required at the destination (i.e., precision placement), then H
should be measured at both the origin and destination of the lift. Also, if the worker leans over on
one foot during lifting, concentrating nearly all of their support on one foot, while using the other
leg and foot as a counterbalance so that they can reach out further to pick up the load, the H
variable is measured from a point directly below the weight bearing foot, rather than the midpoint
between the ankles. In cases where it is not clear that the weight is concentrated primarily on one
foot, the point between the ankles should still be used as the reference point for measurement of
the horizontal location (H). It also important to note that it has also come to our attention that
users sometimes overestimate the magnitude of the horizontal location (H) and the asymmetric
angle (A) for some types of lifts because they mistakenly measure the task variables at the incorrect
location for the origin of the lift. This may occur when the lifters stand with the side of their body
next to a table or shelf and reach over to slide the object horizontally toward the front of the body
as they begin the lift. When the lift is performed this way, the load actually moves horizontally
toward the front of the body before it actually begins to move vertically. When this type of lift is
analyzed, the task variables should be measured at the actual location where the object first begins
to move upward (liftoff point), rather than at the point where the object first begins to move hori-
zontally. This change will generally result in smaller H values than would have been determined if
the measurements had been taken at the point where the object first began to move horizontally
rather than vertically.
Horizontal distance (H) should be measured. In those situations where the H value cannot be
measured, then H may be approximated from the following equations:
Metric
(all distances in cm)
U.S. Customary
(all distances in in.)
H
20
þ
W
2
H
8
þ
W
2
¼
/
¼
/
for V
25 cm
for V
10 in.
H
25
þ
W
2
H
10
þ
W
2
¼
/
¼
/
for V
25 cm
for V
10 in.
,
,
where W is the width of the container in the sagittal plane and V is the vertical location of the hands from
the floor.
46.4.1.2 Horizontal Restrictions
If the horizontal distance is less than 10 in. (25 cm), then H is set to 10 in. (25 cm). Although objects can
be carried or held closer than 10 in. from the ankles, most objects that are closer than this cannot be lifted
without encountering interference from the abdomen or hyperextending the shoulders. While 25 in.
(63 cm) was chosen as the maximum value for H, it is probably too large for shorter workers, particularly
when lifting asymmetrically. Furthermore, objects at a distance of more than 25 in. from the ankles nor-
mally cannot be lifted vertically without some loss of balance.
46.4.1.3 Horizontal Multiplier
The horizontal multiplier (HM) is 10
H for H measured in
centimeters. If H is less than or equal to 10 in. (25 cm), the multiplier is 1.0. HM decreases with an
increase in H value. The multiplier for H is reduced to 0.4 when H is 25 in. (63 cm). If H is greater
than 25 in., then HM
H for H measured in inches, and HM is 25
/
/
0. The HM value can be computed directly or determined from Table 46.1.
¼
Search WWH ::
Custom Search