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Avoiding
Forklift Tipovers
What
are some of the actions of a forklift operator that
can cause a tipover?
- Driving too fast while turning with the forklift.
- Turning on a ramp.
- Braking sharply while loads are raised.
- Tilting a raised and loaded forklift forward past
vertical.
- Turning with a raised load.
These are just some of the mistakes that forklift operators
make everyday. There are many more. Understanding why
a forklift tips over can help to cut down on tipovers.
This can be done through training, which OSHA mandates
under 1910.178 of the OSHA regulations.
A forklift is stable at only three points, even if
it has four wheels. Two of those stable points are at
the front wheels; they are stable because the front
wheels are attached to the truck by axles, which connect
to the frame of the truck. The third stable point is
where the steer axle, in the rear of the truck, mounts
to the frame on a center pivot pin.
Stability Triangle
When you connect these three points it forms a triangle.
Inside this triangle is the forklift's center of
gravity, or COG. When the forklift is unloaded,
the COG is further back in the triangle, toward the
narrow part of the triangle. As the forklift is driven,
you can turn, raise and tilt loads, side shift your
loads, and brake and accelerate sharply with the forklift.
All these actions and more are called dynamic forces.
These forces will cause the COG of your truck to shift
inside of the triangle. Under safe operating conditions,
the COG will shift within the triangle in any direction
and the truck should remain stable. But if an operator
starts to get careless and tilts a raised load past
vertical, turns too fast with the forklift, turns on
a ramp or uneven ground, or is horse-playing, then these
actions can cause the COG to exit the triangle and the
forklift could tipover, either forward or sideways.
When you raise a load off the floor 4 to 6 inches for
traveling purposes, the center of gravity of the forklift
then travels to the front of the triangle or its base.
This is called the combined center of gravity,
or CCOG. It was formed by the center of gravity of the
load that was just put on the forks and the center of
gravity of the forklift. Where the center of gravity
of the load goes, the CCOG will follow.
Think of the stability triangle as a three-sided pyramid.
When the load is lifted in the air, the CCOG travels
up inside this pyramid. But the area of the pyramid
is much smaller at the top than it was at its base.
So now you are at a very dangerous time with your forklift
as the CCOG has very little room to travel inside of
this pyramid. The side-to-side movement and the front
to back movement of the CCOG has been cut down drastically.
It will not take much for this forklift to tipover in
any direction. That is why an operator of a forklift
should never turn with a raised load or tilt the loaded
forklift mast past vertical, or even travel with the
load raised.
A good rule of thumb is minimal travel speed with
your forks raised, loaded or unloaded! You will
not only be more stable with the mast collapsed, your
chances of hitting an overhead object are greatly reduced.
As an operator of a forklift, you should always keep
your loads low, turn and square up in front of the rack
or stack that you are in front of, raise the load (being
careful of any overhead objects), then set the load
or retrieve the load from the rack or stack. Next, you
should back away, always looking behind you before you
back-up. Then once your forks are clear of the rack,
stop, and lower them to a safe travel height of 4-6
inches off the floor.
System of Active Stability
Toyota Material Handling, U.S.A., Inc. has developed
a way to help make their forklifts safer than most conventional
lift trucks. It's called SAS or System of Active Stability.
One of the features of SAS that Toyota has added on
all their 7-Series 4-wheel forklifts is the Swing
Lock Cylinder. This cylinder is located between
the back steer axle and the frame of the truck. The
cylinder is also connected to a computer on board the
forklift. When the lift truck is turned sharply, a sensor
inside the computer will detect the force of this movement.
The computer then sends a signal to the cylinder to
lock out. Once this cylinder locks out, the forklift
will now have 4 stable points instead of the 3 that
most conventional forklifts have. When you connect these
4 stable points the result is a stability rectangle.
Now the COG of the truck has greater area of movement
inside the rectangle as opposed to the triangle. The
COG will have greater room to travel before the forklift
turns over. This makes the forklift much safer than
conventional forklifts. It does not eliminate all tipovers,
but many of the ones that could have occurred if operators
were using a conventional lift truck will be eliminated.
Another feature of the SAS system is the Active
Mast Function Controller, where basically a load
sensor is placed into the hydraulic system along with
a switch on the mast to indicate to the on-board computer
that the mast has a load on it and has been raised to
a certain height. The on-board computer can now override
some mistakes that are commonly made by forklift operators.
One of those mistakes an operator makes is tilting
a loaded forklift mast past vertical, This can cause
loss of the load or a tipover. The sensor in the hydraulic
system along with the on-board computer will override
the manual control of the operator and stop the mast
at 1-degree past vertical and it will not go any further.
This will make it more difficult to lose a load off
your forks or a potential forward tip of the forklift.
Another feature of this system is the rearward tilt
speed of the mast. It's reduced when a load is placed
on the forks. Some forklift operators are always in
a hurry, so they tend to increase the engines rpm's
to increase the speed of the hydraulics when tilting
the mast back. When picking a load out of a rack, the
on-board computer will sense the load and the rearward
mast tilt speed is slowed down drastically, no matter
how fast the operator races the engine rpm's. This will
help to prevent a rearward tip of the forklift and helps
to stabilize the load.
When trying to put high loads away, it is very difficult
for a forklift operator to tell when their mast is vertical.
To help assist operators, Toyota has added a button
to the top of the tilt lever. Once this button is depressed
and the operator holds the button down as they move
the tilt lever forward, the mast will automatically
stop at vertical or a 90-degree angle to the floor.
Many operators do not realize the great effect that
a raised load has on the forklift when the mast is 15
to 20 feet in the air. The distance moved by the tilt
is much greater at those heights, so slowing the mast
speed down and limiting how far forward you can tilt
the mast will go a long way in helping to prevent tipovers
and loss of product off the forks.
In conclusion, these safety functions on the Toyota
7-Series forklift are not the end all to forklift accidents.
Accidents will still continue to happen if an operator
is untrained, lacks enforcement of training rules, or
drives any forklift in an unsafe manner. However, through
ongoing training and the use of these safety functions
on the Toyota 7-Series forklift, a larger number of
accidents that would have occurred on conventional forklifts
can be drastically reduced. This will help to minimize
your business costs such as insurance or product loss
due to damage and make your work area a safer place
in which to work.
(Written By Dave Bennett, Safety Training Specialist)
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