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Reactive forces including kickback
!
Warning!
Reactive forces may occur any time the
chain is rotating. Reactive forces can
cause serious personal injury.
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
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 element of
surprise and loss of control. Sudden
surprise contributes to accidents.
The most common reactive forces are:
–
kickback,
–
pushback,
–
pull-in.
16
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 a ligtening fast reaction 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:
MS 441 C
