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U. S. Department of Labor
Occupational Safety and Health Administration
Directorate of Science, Technology & Medicine
Office of Science and Technology Assessment |
Hazards of Wood Chippers
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Safety and Health Information Bulletin |
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SHIB 04-16-2008 |
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This Safety and Health Information Bulletin (SHIB) is not
a standard or regulation, and it creates no new legal obligations. The SHIB is
advisory in nature, informational in content, and is intended to assist
employers in providing a safe and healthful workplace. The Occupational Safety
and Health Act requires employers to comply with safety and health standards
promulgated by OSHA or by a state with an OSHA-approved state plan. In addition,
pursuant to Section 5(a)(1), the General Duty Clause of the Act, employers must
provide their employees with a workplace free from recognized hazards likely to
cause death or serious physical harm. Employers can be cited for violating the
General Duty Clause if there is a recognized hazard and they do not take
reasonable steps to prevent or abate the hazard. However, failure to implement
any recommendations in this SHIB is not, in itself, a violation of the General
Duty Clause. Citations can only be based on standards, regulations, and the
General Duty Clause. |
Preface
Operating wood chippers can be dangerous for operators and others working
nearby. When employees feed tree limbs and branches into chippers they are at
risk of getting caught in the machine and being pulled into the fast-turning
chipper knives.
This Safety and Health Information Bulletin (SHIB) discusses ways to reduce or
eliminate "caught-in" and "struck-by" chipper-related accidents. It discusses
training and proper work practices and identifies controls that manufacturers
have installed to reduce the risk of serious injury. Although the hazards
associated with chipper use are generally known, awareness of these hazards and
the associated safeguards needs to be highlighted and reinforced.
Additionally, a recent fatality involving a chipper equipped with a winch line
assembly revealed that these chippers can pose unique "struck-by" hazards.
Special considerations for the safe operation of these chippers are also
highlighted and discussed below.
Purpose
The purpose of this SHIB is to:
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Alert employers, employees and manufacturers to the
hazards involved during the use of chippers, and the unique hazards associated
with operating a chipper equipped with a winch line assembly,
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Inform employers and employees about safe work practices,
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Stress the importance of following the manufacturer's instructions for
operating, inspecting and maintaining chippers, and
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Inform employers and employees about chipper safety devices, including recently
developed devices.
Background
According to the OSHA Integrated Management Information System (IMIS), 39
employees were killed in chipper accidents from 1996-2005.1 Of those fatalities,
the vast majority (78 percent) resulted from being caught in the chipper, and
most of the remainder resulted from "struck-by" accidents.
Equipment
Chippers are used to dispose of tree trimmings and other wood debris. Chippers
generally consist of a powered feed mechanism, knives mounted on a rotating disc
or drum, and an internal combustion engine. Typically, employees feed branches
into the infeed chute by hand. Feed rollers at the end of the infeed chute grab
the branches and force them into the chipper knives. The chipper knives
generally rotate from 1,000 to 2,000 revolutions per minute. The drum and its
knives chip the branches and force the chips through a discharge chute. The
housing that contains the point-of-operation chipper disc is sectioned and
includes a removable hood to allow access to the components for maintenance and
repair.
Many chippers are equipped with a mechanical feed control bar that activates the
feed rollers when it is pulled. The bar is mounted across the top and along the
sides of the infeed chute for quick and easy access. The American National
Standards Institute (ANSI) ANSI Z133.1-2006 standard, "Safety Requirements for
Arboricultural Operations," requires that chippers equipped with a mechanical
feed control bar must have quick-stop and reverse feed devices for emergencies.2
The chipper involved in the accident described below met this ANSI requirement.
Accident Discussion
The Denver, Colorado OSHA Area Office investigated a fatal accident in which a
chipper operator was killed when he was pulled into the chipper.
At the time of the accident, the operator was feeding branches into the chipper.
The operator usually stood to the side of the chipper feed table in order to
have easy access to the feed control bar. However, the investigation indicated
that, in this incident, the operator was standing directly in front of the
infeed chute. Further, the leather gloves that the operator was wearing to
protect his hands from cuts and scrapes had cuffs. While the operator stood in
front of the infeed chute, it is possible that a tree branch snagged the cuff of
his glove and pulled him into the chipper. He was killed instantly upon contact
with the rotating chipper knives.
Engineering Controls
Employees must be protected from contacting operating chipper components such as
knives, feed rollers and chip discharge spouts. OSHA's general industry machine
guarding standard requires that all machines be equipped with one or more
methods of guarding to protect the operator and other employees in the work area
from hazards such as those created by rotating parts and flying chips (29 CFR
1910.212(a)(1)).3 In addition, the point of operation of such machines must be
guarded appropriately (29 CFR 1910.212(a)(3)). Moreover, OSHA's Logging
Operations standard, to the extent that it applies to a particular chipping
operation, requires that infeed and outfeed chutes be guarded to prevent contact
with the disc, knives, or blades (29 CFR 1910.266(h)(4)).4
Chipper safety devices are available to reduce the risk of "caught-in" or "struck-by" accidents. Some manufacturers have equipped chippers with one or
more of these devices, including:
Feed Control Bar – Many chippers in use today have mechanical feed control bars
that meet the ANSI Z133.1 requirement to include emergency stop devices. Pushing
the feed control bar to the center (neutral position) stops the feed rollers,
and pushing it toward the discharge spout reverses the feed rollers.
Feed control bar (in red) on top and sides with handles.
Bottom Feed Stop Bar – To address the hazard of being pulled into the chipper,
one manufacturer has developed and installed a "bottom feed stop bar" (patent
pending) on all its new models. It is a pressure sensitive device that cuts off
all power completely when 34 pounds of force are applied to the lower edge of
the feed table.
According to the manufacturer, the device cannot be retrofitted onto older
models due to its electronic and
mechanical requirements.
Panic Bar - Another manufacturer has equipped its chippers with a "panic bar"
(patent pending) to stop the feed system in an emergency. When the operator
grabs the "panic bar" it instantly stops the hydraulic system that operates the
feed rollers. The "panic bar" is not attached to the feed control bar and
operates independently. It has two grab bars, one in front and one behind the
feed control bar, for quick access from almost any location around the feed
area.
Emergency Pull Ropes – Emergency pull ropes or cables are another emergency
shut-off device installed by some manufacturers. Pulling the ropes immediately
reverses the action of the feed rollers. The two ropes are located on both sides
of the throat of the infeed chute for quick access. However, if the ropes become
entangled in branches, they may be difficult to locate and pull in an emergency.
These ropes can be retrofitted onto existing machines.
Emergency Pull Ropes
Feed Tray Extensions – Many chippers have longer feed trays (i.e., tray
extensions or fold down trays) to reduce the potential for employees getting
pulled into the chipper. These trays can increase the length of the infeed area
by as much as four feet, thus making it more difficult for employees to reach
into the feed rollers. Many chippers have these trays and retrofit kits are also
available. Using extended trays is effective in creating a physical barrier
between the operator and the point of operation.
Wooden Push Tools – Push tools are used to push branches, particularly shorter
ones, and other debris into the infeed chute. Using push tools prevents
employees from using their hands and feet to push material into the feed
rollers.
Flexible Rubber Curtain/Flaps – Rubber curtains installed at the front of the
infeed chute may reduce both "caught-in" and "struck-by" accidents. The curtains
serve as physical warnings to operators to keep their hands away from the infeed
chute. They also prevent objects from kicking back and striking employees
standing nearby.
Flexible Rubber Curtain/Flaps
Discharge Spout Deflector/Guard – This device reduces the risk of being struck
by flying debris. It redirects the discharge of wood chips into a chipper truck
or in a safe direction away from employees.
Chipper Hood Safety Latch – This device serves as an interlock by preventing the
operator from starting the chipper before the chipper hood is locked and by
preventing the operator from opening the hood before the disc/drum has stopped
running. This device reduces "struck-by" and "caught-in" injuries.
Training and Work Practices
The following recommended training and work practices will help to ensure safe
operation of chippers:
Training - Employers and employees should be trained to understand the hazards
associated with chippers. Training should cover the following:
- Correct operation of the chipper and its safety controls,
- Manufacturer's instructions on operation, inspection and maintenance of the
chipper,
- Proper procedures for machine start-up and shutdown, and
- Correct use and maintenance of personal protective equipment.
Training should be provided in an effective manner and should make provision for
those employees who speak or read little or no English.
Employers should closely supervise newly-hired employees to ensure that they are
safely operating the chipper and should reinforce training through regular
safety talks and unannounced site visits. When an employee engages in unsafe
work practices, or disables existing safety devices, immediate corrective
action, including refresher instruction and/or disciplinary measures, should be
taken.
When chipping is being done as part of a logging operation, training is required
by the Logging Operations standard (29 CFR 1910.266(i)). The logging standard
establishes specific training requirements for all employees, including
provisions on training content, frequency and portability.
Work practices - Proper work practices are essential for safe operation of
chippers. Employers should reinforce proper work practices on a regular basis,
such as during "toolbox talks".
The following are recommended safe chipper work practices to reduce "caught-in"
and "struck-by" hazards:
- Designate one or more employees as a safety watch to be stationed near emergency
shut-off devices while other employees feed material into the chipper.
- Stand to the side of the infeed chute when feeding material into the chipper.
This reduces the "caught-in" hazard and allows quick access to emergency stop
devices.
- Keep hands and feet out of the immediate infeed chute area while the
chipper is running.
- Push material into feed rollers with a wooden tool or a long branch.
- Feed branches into the chipper butt-end first.
- Place shorter branches on top of longer branches being fed into the chipper.
- Place small debris into trash cans instead of feeding it into the chipper.
- Never stand, sit or climb onto any part of the chipper while it is running.
- Shut down the chipper and remove the ignition key when it is unattended.
- Before starting a chipper, ensure that the chipper's disc hood is completely
closed and latched, and that there are no foreign objects in the infeed area.
- Ensure that the discharge chute is positioned to prevent chips from hitting
employees.
- Do not stand in front of the feed table when the chipper is running.
- Check material to be fed to ensure that it is free of metal and other foreign
objects.
- Use proper locking pins to immobilize the disc cutting wheel when attempting to
clear a clogged chipper chute or changing chipper blades.
When chipping is being done as part of a logging operation, the Logging
Operations standard requires:
- Employers hold safety and health meetings as necessary and at least monthly (29 CFR 1910.266(i)(11)),
- Chipper access covers or doors must not be opened until the drum or disc comes
to a complete stop (29 CFR 1910.266(h)(4)),
- Employees be trained in the recognition of safety and health hazards associated
with specific work tasks, including work practices to prevent or control those
hazards (29 CFR 1910.266(i)(3)(iii)).
Personal protective equipment and clothing –
Employers must "assess the workplace to determine if hazards are present, or
likely to be present, which necessitate the use of personal protective
equipment" (29 CFR 1910.132(d)(1)).5
Employees must take the following precautions:
- Use appropriate hand protection ... relative to the task(s) to be performed,
conditions present ... and the hazards and potential hazards identified (29 CFR
1910.138(a) and
(b)).6
- Use appropriate eye and face protection (29 CFR 1910.133).7 Devices purchased
after July 5, 1994 must comply with ANSI Z87.1-1989 (.133(b)).
- Wear a protective helmet (29 CFR 1910.135). Helmets purchased after July 5, 1994
must comply with ANSI Z89.11986 (.135(b)).8
The following are industry and ANSI recommended clothing and apparel to prevent
entanglement hazards:
- Wear gloves with no cuffs (non-gauntlet) (ANSI Z133.1-2006-3.4 4, 8.6.3).
- Wear close-fitting and tucked-in clothing with no stray straps or strings.
Jewelry should not be worn while operating chippers (ANSI Z133.1-2006-8.6.3).
Inspection and maintenance – Employers need to inspect and maintain chippers in
accordance with the manufacturer's specifications. Employers should inspect and
test the chipper at the start of each workshift to ensure that all parts and
safety devices are functioning properly. This should include looking for broken
parts, cracks, worn hinges, and missing parts and pins.
Before beginning any servicing operation, lockout/ tagout procedures must be
utilized to control hazardous energy related to start-up of the chipper (29 CFR
1910.147).9
When chipping is being done as part of a logging operation, the Logging
Operations standard requires that employers ensure that machines, including
chippers, are maintained in serviceable condition (29 CFR 1910.266(f)). To that
end, the logging standard requires that each machine be inspected before every workshift and that damage or defects be repaired before the machine is used.
Chippers Equipped with a Winch Line
Equipment and Procedures
Generally, a chipper with a winch assembly mounted on top has the same standard
and safety features as one without a winch line. The winch assembly is used to
secure and pull large diameter, heavy branches or trunks to the chipper. The
winch is located directly above and in front of the chipper infeed chute. The
winch in the fatal accident described below, had the capacity for handling
logs/trees up to 2,000 pounds and 19-inches in diameter. Although winch lines
can be wire rope or braided synthetic rope depending on the application, the
winch line in this incident was a double-braided nylon rope approximately 150
feet long and 7/16-inch in diameter. Additionally, a 5-foot, 1/4-inch diameter
metal chain with hook was attached to the end of the winch rope. This "chain and
hook" assembly at the working end of the winch line is referred to as a "choker." The choker is used to attach the butt end of the tree limb to the
winch line. When activated, the winch pulls the heavy limb toward the chipper
and into the feed chute.
Chain chocker installed on limb and winch line
attached to chocker.
Accident Discussion
OSHA's Boise, Idaho Area Office investigated a fatality involving a chipper
equipped with a winch line.
The chipper operator stood to the side of the chipper to operate the controls
while the winch line handler pulled the line out from the winch. As the handler
pulled the line out, a section of the line that was slackened became entangled
in the tree limb that was being fed into the chipper. The tree limb pulled the
slackened line into the chippers's cutter drum causing the winch line and choker
to snap and recoil with such force and speed that the chipper operator suffered
fatal head injuries despite wearing ANSI-approved head protection.
Chain that fatally struck employee.
The investigation revealed that the location of the winch boom directly above
and in front of the feed rollers, coupled with the simultaneous operation of the
feed rollers, created this fatal "struck-by" hazard.
Engineering Controls and Work Practice Strategies for
Chippers with a Winch Assembly
In response to this accident, the manufacturer of the chipper involved in this
incident is now providing the following additional safety measures for its
chipper models equipped with a winch option:
For existing chipper:
- Supplying a detachable choker. A detachable choker that can be removed from the
end of the winch line during line handling operations reduces the weight of the
line.
- Increasing the size of the loop on the winch line from 5 to 10 inches. The
enlarged loop reduces the chance of the loop snagging or pinching the operator's
hand and pulling the operator with great force towards the chipper.
- Providing a lighter weight winch line. In addition to the removable choker
chain, this will help to reduce the recoil hazard if the winch line is
accidentally pulled into the feed rollers and chipper knives.
- Providing a winch line transport/storage hook so that the line can be stored
away from the branches being fed into the chipper.
- Providing a new chipper and winch operation safety video to address the
potential hazards.
- Providing safety signs on the chipper to warn employees of the potential hazard
of a winch line getting caught in the feed rollers and chipper knives.
- Revising the instructions in the chipper operating manual to reflect the new
parts, safety signs and the proper operating sequence.
For new models
Safety Interlock
New chipper models from this manufacturer will include a safety interlock
system. This system will require that the winch line be safely stored before the
feed rollers can be operated. The interlock system will also prevent the winch
line from accidentally being pulled into the chipper.
Winch line Safety Interlock and Storage Hook
Recommendations for Use of Chippers with a Winch
Assembly
- Employers should ensure that employees follow all safe work practices for the
operation of the winch.
- Employers who own chippers with winch lines should contact their equipment
supplier to investigate the application of strategies to minimize the
"struck-by" hazard posed by the winch line assembly.
- Employers should otherwise ensure that all employees are trained on the safe
operation of chippers equipped with a winch line and should also train their
employees to recognize and avoid possible "pinch point" hazards where the winch
line enters the winch boom and where the choker connects to the log.
Conclusion
Chipper operations can be dangerous and result in severe injury or death when
proper precautions and work practices are not followed. Implementing the actions
described in this SHIB will help protect employees from serious or fatal
injuries during chipper operations.
For additional information on the tree care industry as well as other
information on applicable OSHA standards, compliance directives, letters of
interpretation, alliances, and compliance assistance materials, please refer to
the
Tree Care Industry - Standards Safety and Health Topics Page.
References
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IMIS. OSHA Integrated Management Information System, 1996-2005.
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ANSI. American National Standard for Arboricultural Operations-Safety
Requirements. Z133.1-2006. International Society of Arboriculture, P.O. Box
3129, Champaign, IL 61826-312929.
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29 CFR 1910.212, General Requirements for all Machines.
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29 CFR 1910.266, Logging Operations standard.
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Subpart I - Personal Protective Equipment.
29 CFR 1910.132, General Requirements.
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29 CFR 1910.138, Hand Protection.
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29 CFR 1910.133, Eye and Face Protection.
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29 CFR 1910.135, Head Protection.
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29 CFR 1910.147, The Control of Hazardous Energy.
Edwin G. Foulke, Jr.
Assistant Secretary
Occupational Safety and Health
Administration
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