Stihl MSA 220.0 T Instruction Manual page 12

English
■ The powerful forces used to cut wood can be
reversed and work against the operator. If the
rotating saw chain is suddenly and signifi‐
cantly slowed or stopped by contact with any
solid object such as a log or branch, or is
pinched, the reactive forces may occur
instantly.
■ These reactive forces may result in loss of
control, which, in turn, may cause serious or
fatal injury.
► An understanding of the causes of these
reactive forces may help you avoid the ele‐
ment of surprise and loss of control. Sur‐
prise contributes to accidents.
The most common reactive forces are:
– Kickback
– Pull-in
– Pushback
6.2 Kickback
6.2.1 Kickback
WARNING
Kickback may occur when the moving
chain near the upper quadrant of the
bar nose contacts a solid object or is
pinched.
■ When this occurs, the energy driving the chain
can create a force that moves the chain saw in
a direction opposite to the chain movement at
the point where the chain is slowed or stop‐
ped. This may fling the bar up and back in a
lightning fast reaction mainly in the plane of
the bar and can cause severe or fatal injury to
the operator.
■ Kickback may occur, for example, when the
chain near the upper quadrant of the bar nose
contacts the wood or is pinched during limb‐
ing, or when it is incorrectly used to begin a
plunge or boring cut.
■ The greater the force of the kickback reaction,
the more difficult it becomes for the operator to
control the chain saw. Many factors influence
the occurrence and force of the kickback reac‐
tion. These include chain speed, the speed at
which the bar and chain contact the object, the
12
6 Kickback and Other Reactive Forces
location and angle of contact, the condition of
the chain, and how quickly the chain is slowed
or stopped, among other factors.
► The type of bar and chain you use is an
important factor in the occurrence and force
of the kickback reaction. Some STIHL bar
and chain types are designed to reduce
kickback forces.
► STIHL recommends the use of reduced
kickback bars and low kickback chains.
6.2.2 Chain Saw Kickback Standards
The following standards apply with respect to
kickback:
– CSA Z62.1
– CSA Z62.3
These standards, referred to as "the chain saw
kickback standards" in this chapter, set certain
performance and design criteria related to chain
saw kickback.
To comply with the chain saw kickback stand‐
ards, electric chain saws:
– must, in their original condition, meet a 25°
computer-derived kickback angle when equip‐
ped with certain cutting attachments; and
– must be equipped with at least two devices to
reduce the risk of kickback injury, such as a
chain brake, low kickback chain, reduced kick‐
back bar, etc.
The computer-derived angles for electric chain
saws are measured by applying a computer pro‐
gram to test results from a kickback test
machine.
WARNING
■ Compliance with the chain saw kickback
standards does not mean that the bar and
chain will rotate at most 25° in a real life kick‐
back.
■ The computer-derived angles of the chain saw
standards may bear no relationship to actual
kickback bar rotation angles that may occur in
a real life cutting situation.
■ Devices designed to reduce the risk of kick‐
back injuries may lose some of their effective‐
ness when they are no longer in their original
condition, especially if they have been improp‐
erly maintained.
► Read and follow the safety precautions and
instructions in this manual.
► When working, always position the chain
saw such that your body is clear of the cut‐
ting attachment and outside of the cutting
plane.
0458-007-8201-B