MS 441 C-M
English
13
The reaction of the cutting force of the
chain causes a rotational force on the
chain saw in the direction opposite to the
chain movement. This may fling the bar
up and back in a lightning 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 chain saw kickback
standard
§ 5.11 of ANSI standard B 175.1-2000,
sets certain performance and design
criteria related to chain saw kickback.
To comply with § 5.11 of ANSI
B 175.1-2000:
a) Saws with a displacement of less
than 3.8 cubic inches (62 cm³)
– 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 chain
brake, low kickback chain, reduced
kickback bar, etc.
b) Saws with a displacement of
3.8 cubic inches (62 cm³) and
above
– must be equipped with at least one
device designed to reduce the risk
of kickback injury, such as a chain
brake, low kickback chain, reduced
kickback bar, etc.
The computer derived angles for saws
below 3.8 cubic inches (62 cm³)
displacement are measured by applying
a computer program to test results from
a kickback test machine.
WARNING
The computer derived angles of § 5.11
of ANSI B 175.1-2000 may bear no
relationship to actual kickback bar
rotation angles that may occur in real life
cutting situations.
In addition, features designed to reduce
kickback injuries may lose some of their
effectiveness when they are no longer in
their original condition, especially if they
have been improperly maintained.
Compliance with § 5.11 of ANSI
B 175.1-2000 does not automatically
mean that in a real life kickback the bar
and chain will rotate at most 45°.
WARNING
In order for powerheads below 3.8 cubic
inches (62 cm³) displacement to comply
with the computed kickback angle
requirements of § 5.11 of ANSI
B 175.1-2000 use only the following
cutting attachments:
– bar and chain combinations listed
as complying in the "Specifications"
section of the instruction manual or
– other replacement bar and chain
combinations marked in
accordance with the standard for
use on the powerhead or
– replacement chain designated "low
kickback saw chain."
See the section on "Low kickback saw
chain and reduced kickback bars."
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