ICFR – Chainsaw Safety and Operating Handbook
13
8.
REACTIVE FORCES
Chainsaw operators must understand the major
reactive forces that exist when cutting with a chainsaw
as they can be the cause of accidents.
The three reactive forces are kickback, pull-in and
pushback
8.1
k
ickbAck
Kickback occurs when the moving saw chain in
the upper quadrant of the bar nose (kickback zone)
contacts a solid object or is pinched. A rotational force
on the chainsaw, in a direction opposite to the chain
movement, is caused. This may kick the guide bar up
and back or sideways in a sudden, uncontrolled arc.
It is most common during debranching.
Figure 2: Kickback zone
Kickback may occur when the guide bar nose:
•
Is pinched unexpectedly.
•
Contacts solid material in the wood unintentionally.
•
Is used incorrectly to start a bore cut. (Refer to
section 9.2.3).
•
Hits hidden branches or light material.
•
Contacts ends of logs or obscured material.
Figure 3: Kickback situations
The greater the force of the kickback reaction, the more
difficult it is for the operator to control the chainsaw.
Many factors influence the occurrence and force of the
kickback reaction. These include saw chain speed, the
speed at which the guide bar and saw chain contact the
object, the angle of contact, the condition of the saw
chain and other factors.
The type of guide bar and saw chain used is an
important factor in the occurrence and force of the
kickback reaction. Some guide bar and saw chain types
are designed to reduce kickback forces.
Kickback can be minimised and the severity reduced
if the following are adhered to:
•
Avoid cutting with the upper quadrant of the bar
nose.
•
Hold the chainsaw firmly with both hands and
maintain a secure grip. Ensure that the left thumb
is around and under the handle.
•
Be aware of the location of the guide bar nose at
all times.
•
Avoid the nose of the guide bar making contact
with any object. Do not cut branches with the
nose of the guide bar. Be especially careful when
cutting small, tough branches, small size brush
and saplings which may easily catch the chain.
•
Do not over-reach.
•
Do not cut above shoulder height.
•
Start the cut at high engine speed and maintain
the speed as the cut proceeds.
•
Cut only one log at a time.
•
Use extreme caution when re-entering a previous
cut.
•
Do not attempt to bore cut if not trained and
experienced with this cutting technique.
•
Be alert for shifting of the log or other forces
that may cause the cut to close and pinch the saw
chain.
•
Maintain saw chain properly. Cut with a correctly
sharpened, properly tensioned saw chain at all
times. Improper lowering or shaping of the depth
gauges or sharpening of the cutters may increase
the likelihood of kickback occurring.
•
Stand to the side of the cutting path of the
chainsaw.
•
Ensure that a chain brake is fitted and serviceable.
•
Never operate a chainsaw without a serviceable
chain break lever.
•
Use suitable guide bars and kickback reducing
chains.