Howard
J. Doss
Michigan State University Extension
One
of the most hazardous areas on your tractor is the power takeoff
shaft. Without proper guards, shields, and constant operator
awareness of the risks involved with operating PTO-driven
equipment, this spinning shaft can quickly grab and entangle
an unsuspecting farmer or family member. Too often entanglement
results in a severe injury or death. Records show that eight
Michigan farmers were killed in PTO related accidents from
1985 to 1991.
There
are two common types of accidents resulting from PTO shafts,
entanglements and being struck by the shaft after it has separated
during operation.
Getting
caught by the shaft (entanglement) is the most common type
of PTO accident, and generally causes the most severe injuries
and deaths. Injuries resulting from shafts separating during
operation frequently result from the shaft striking someone
working or standing in the immediate area. Both of these types
of accidents can be avoided if the operator properly maintains
the equipment and limits access the PTO area when the equipment
is running.
Equipment manufacturers have made strides in reducing the risks
of PTO mishaps, but it is up to the operator to make sure that
all guards and shields are properly maintained. Removing a shield
or guard increases operator risk. Master
Shield
The first shield in the PTO driveline is the master shield on the rear of the tractor (Fig 1). This shield prevents the operator from accidentally coming into contact with the tractor stub shaft and the front universal joint of the equipment:s driveline. Operators should make it a practice to replace the tractor PTO shaft guard, which completely covers the tractor stub shaft, when the PTO is not in use.
Fully
Shielded Driveline
Most PTO-driven implements produced since the early 1970s were equipped with a fully shielded PTO driveline to protect the operator from accidental entanglement. This type of driveline shielding encases the shaft in a plastic or metal casing supported by bearings at each end of the shaft. The bearings allow the shield to stop spinning if someone or something comes into contact with the driveline, while the shaft inside continues to spin.
The
ends of the driveline shield are bell-shaped to cover the
universal joints of the shaft. Because universal joints are
irregularly shaped and prone to grab objects, operators should
never modify the bell-shaped shield to make maintenance, greasing
parts or connecting the shaft easier.
Guards
Manufacturer
installed guards must be replaced when removed for maintenance.
These guards are designed to protect the operator and equipment.
Guards not only reduce the risk of an injury, they also keep
dust and other foreign objects from damaging gears and other
moving parts.
Maintenance
Like any
moving part, the driveline shield must be maintained to ensure
proper operation. PTO equipment is frequently operated in inclement
weather and exposed to dust, chaff and other foreign materials
which can quickly damage the bearings that allow the shaft to
spin freely inside the shield. Rust, dirt and crop debris must
be cleaned frequently to allow the bearings to spin freely.
Replace any damaged or worn shields with the manufacturer:s
recommended parts. Storing equipment inside will also help extend
the lifetime of the equipment and reduce maintenance costs.
Positioning
the Drawbar to the PTO shaft
The length and height of a tractor:s drawbar may need to be
adjusted to match the implement manufacturer:s specifications.
It is important to make these adjustments to ensure that the
PTO driveline does not compress or separate during operation.
To make this adjustment, check the implement manufacturer:s
recommendations and adjust the height of the drawbar and the
distance from the PTO stub shaft to the center of the drawbar
hitch hole (see Figure 2).
Failure
to match the drawbar to the implement can result in the driveline
being compressed or separated when the tractor makes a sharp
turn or comes to the top or bottom of a hill. Separation or
compression frequently damages the protective shield to the
point where it no longer slides together or allows the shaft
to spin freely inside the shield.
Farmers
in a hurry to complete planting or harvesting operations may
be tempted to simply remove a damaged shield so they can continue
working. This places the operator or anyone near the equipment
at an unnecessary risk. Take time to make the necessary adjustments
to the tractor drawbar before using the equipment or be prepared
to stop and replace any damaged shields.
Shear
Pins and Bolts
Most PTO-driven equipment has some form of a shear pin to prevent
damage to the shaft or gearbox. Always follow the manufacturer:s
recommendations for size and hardness when replacing a damaged
shear pin or bolt. Using a pin or bolt that is longer than necessary
creates a potential catch point that may snag the operator:s
boot lace or clothing, resulting in a possible entanglement
(Figure 3).
- Always
disengage the PTO, shut off the engine and remove the key
before getting off the tractor. This protects you from
accidental entanglement while servicing the equipment and
ensures that no one else can start the tractor during maintenance
procedures.
- Keep
the master shield in place at all times. The master
shield should be removed only when required for hooking
up special equipment with equivalent shielding. Replace
the PTO tractor stub shaft guard whenever PTO driven equipment
is not being used.
- Check
that the PTO driveline shields are in good condition.
With the PTO stopped, the shield should rotate freely by
hand. Make any necessary repairs to damaged bearings or
shields (See Figure 4).
- Never
modify driveline shields to make servicing or connections
easier. Cutting or drilling a hole in the shield allows
dirt, chaff or other foreign materials access to shaft bearings.
This reduces the life of the shield and also increases the
risk of the operator getting clothing caught in the spinning
shaft.
- Never
step across a rotating PTO driveline. Always take the
time to walk around a rotating shaft. Although the shaft
may be enclosed in safety shields and guards, there is a
chance that clothing could be caught in the spinning shafts.
- Wear
snug fitting clothing. Bulky, loose fitting clothing
can quickly be caught in a spinning shaft, entangling an
unsuspecting operator. Boots or shoes without laces are
preferred because laces may become entangled in the shaft.
A study of reaction time shows that a shoe lace would have
to be 30-foot long for the farmer to have time to react
to a lace entangled in a PTO shaft spinning at 500 RPMs.
Nylon jackets can flap in the wind and catch on a PTO shaft;
likewise, hooded sweat shirts with drawstrings can catch
on moving equipment, entangling the operator.
Figure
5 is a checklist for safe PTO operation.
Figure
5. Checklist for safe PTO operation |
| Yes
| No
|
Is
the tractor master shield in place? |
___ |
___ |
Is
the drawbar height and length set to the implement manufacturer's
specifications? |
___ |
___ |
Does
the driveline shield float freely (with the engine off)
by hand? |
___ |
___ |
Is
the driveline shield free of dents and other damage? |
___ |
___ |
Are
all guards and shields in place? |
___ |
___ |
Are
shear bolts/pins of proper length and hardness? |
___ |
___ |
Are
you wearing snug fitting clothing with no hanging drawstrings
or frayed cuffs? |
___ |
___ |
Are
you wearing slip-on boots instead of shoes or boots with
dangling shoe laces? |
___ |
___ |
Will
you take the time to walk around the tractor instead of
stepping over the spinning PTO shaft? |
___ |
___ |
Did
you answer "Yes" to all of these questions? If not, take
time to repair the equipment or make changes in your operating
practices to protect yourself from a PTO shaft entanglement. |
___ |
___ |
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
Michigan
State University, Agricultural Engineering Department.
Howard
J. Doss, Agricultural Safety Specialist, Michigan State University
Extension, East Lansing, Michigan 48824. 5/93. Funded by the
National Institute of Occupational Safety and Health - #UO5/CC-4506052-02.
This
information is for educational purposes only. Reference to
commercial products or trade names does not imply endorsement
by the MSU Extension or bias against those not mentioned.
|