U. S. Department of Labor

Occupational Safety and Health Administration

Directorate of Science, Technology & Medicine

Office of Science and Technology Assessment

SHIB 04-16-2008

Hazards of Wood Chippers

Safety and Health Information Bulletin

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 OSHAapproved 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:

• 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,

• Inform employers and employees about safe

work practices,

• Stress the importance of following the

manufacturer’s instructions for operating,

inspecting and maintaining chippers, and

• 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.

2
Bottom Feed Stop Bar

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.

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.

Panic Bar

Feed Control Bar

Emergency Pull Ropes

3

Panic Bar

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.
4

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.

Curtain Flaps

Flexible Rubber Curtain/Flaps
• 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)).

5

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 Z89.1-

1986 (.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.

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.

The investigation revealed that the location of the

winch boom directly above and in front ofthe feed

rollers, coupled with the simultaneous operation of

the feed rollers, created this fatal “struck-by” hazard.

6

Chain choker installed on limb and winch

line attached to choker.

Chain that fatally struck employee.
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.

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.

7

Enlarged Loop

Winch line Safety Interlock and

Storage Hook

Detachable Choker
8

• 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 www.osha.gov/SLTC/

treecare/standards.html.

References

1. IMIS. OSHA Integrated Management

Information System, 1996-2005.

2. ANSI. American National Standard for

Arboricultural Operations-Safety

Requirements. Z133.1-2006. International

Society of Arboriculture, P.O. Box 3129,

Champaign, IL 61826-312929.

3. 29 CFR 1910.212, General Requirements for

all Machines.

4. 29 CFR 1910.266, Logging Operations

standard.

5. Subpart I-Personal Protective Equipment.

 29 CFR 1910.132, General Requirements.

6. 29 CFR 1910.138, Hand Protection.

7. 29 CFR 1910.133, Eye and Face Protection.

8. 29 CFR 1910.135, Head Protection.

9. 29 CFR 1910.147, The Control of Hazardous

 Energy.

Edwin G. Foulke, Jr.

Assistant Secretary

Occupational Safety and Health Administration