Ergonomics - Atlas Copco

88
Weight
The weight of a hand-held tool is a typi-
cal external load to which the operator
is subjected. Depending on the working
posture, the weight of the tool applies
different torques to the joints of the
hand-arm-shoulder system. The risk of
a tool causing work-related musculo-
skeletal disorders varies according to the
amplitude of the torques as well as the
duration of the task performed.
In modern industrial situations, many hand-
held tools are electrically or pneumatically
powered in order to reduce the effort
required from the operator.
However, this approach sometimes
results in a heavy tool, especially when stiff,
heavy hoses are used. It is not uncommon to
find hand-held tools weighing more than
5 kg. Even if a tool of this weight is held in
an ergonomically optimal position, it will
still exert a torque on the shoulder joint
equivalent to about 20% of the person’s maxi-
mal force generating capacity (20% MVC) for
a male operator and 30% for a female opera-
tor. The weight-related exposure on opera-
tors is therefore a major ergonomic concern.
Tool weight limit
There are no simple recommendations spec-
ifying tool weight limits for all situations.
As an external load, the weight should be
limited according to the working conditions,
and the frequency, speed and duration of
the operation to be performed. Weight as
a load factor should be added to the other
vertical forces applied to the operator.
As a general rule, if the weight of the
tool has to be borne by the operator during
operation, tools heavier than 2.5 kg should
be suspended, counter-balanced, or have
two handles. For precision operations, tools
weighing more than 0.4 kg are not recom-
mended. For tougher jobs, such as drilling
concrete, heavier tools may be necessary to
help absorb vibrations and supply feed force.