Stihl MS 191 T Instruction Manual page 15

English / USA
Reactive forces including kickback
!
Warning!
Reactive forces may occur any time the
chain is rotating. Reactive forces can be
dangerous! In any chainsaw, the
powerful force used to cut wood can be
reversed (and work against the
operator). If the rotating chain is
suddenly stopped by contact with any
solid object like a log or branch or is
pinched, the reactive forces may occur
instantly.
These reactive forces may result in loss
of control which may, in turn, cause
serious or fatal injury. An understanding
of the causes of these reactive forces
may help you avoid loss of control.
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The most common reactive forces are
– kickback,
– pushback,
– pull-in.
Kickback
.Kickback may occur
when the moving saw
chain near the upper
quadrant of the bar nose
contacts a solid object or
is pinched.
The reaction of the cutting force of the
chain causes a rotational force on the
chainsaw in the direction opposite to the
chain movement. This may fling the bar
up and back in an uncontrolled arc
mainly in the plane of the bar. Under
some cutting circumstances the bar
moves towards the operator, who may
suffer severe or fatal injury.
Kickback may occur, for example, when
the chain near the upper quadrant of the
bar nose contacts the wood or is pinched
during limbing 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 saw. Many
factors influence the occurrence and
force of the kickback reaction. These
include chain speed, the speed at which
the bar and chain contact the object, the
angle of contact, the condition of the
chain and other factors.
The type of bar and saw 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.
ANSI B 175.1-2000 chainsaw
kickback standard
Section 5.11 of ANSI standard
B 175.1-2000 sets certain performance
and design criteria related to chainsaw
kickback.
To comply with section 5.11 of ANSI
B 175.1-2000:
a) saws with a displacement of less
than 3.8 cubic inches
– must, in their original condition,
meet a 45° computer derived
kickback angle when equipped with
certain cutting attachments.
– and must be equipped with at least
two devices to reduce the risk of
kickback injury, such as a
chainbrake, low kickback chain,
reduced kickback bar, etc.
MS 191 T