|Oregon Case Report: 03OR006
On April 18, 2003, a 42-year-old logger, working as a chaser,
was killed while standing on the landing site during a cable
yarding operation. A Madill 071 yarder was in
the process of completing a turn when the tower collapsed.
The tower fell on the boom of a delimber that
was also operating on the landing site. The force
of the impact caused a sheave (cable pulley guide) to sheer off from the
side of the delimber’s boom. The falling sheave struck the chaser
on the head, and punched through his hard hat. Life Flight was summoned.
The victim was pronounced dead at the scene shortly after emergency help
When guyline support failed, the yarder
tower fell onto a nearby delimber (right).
- Plan the landing site for yarding requirements beforehand. Make sure
nearby anchor stumps are left at an appropriate height to secure guylines,
and the guylines will not interfere with decking
the logs at the landing.
- Set up yarder guylines according to manufacturer’s recommendations,
making sure lines are at no more than a 50-degree angle, equally sharing
the load, and secured by additional support for the anchors.
- Check integrity of the guyline anchors daily, before and during operation.
- Maintain proper deflection in the skyline to
reduce stress on the yarder tower.
Shortly after 7 a.m., on April 18, 2003, a 42-year-old logger, working
as a chaser, was killed when a yarder tower collapsed during a cable yarding
operation. OR-FACE was notified of the incident by OR-OSHA, through the
Department of Consumer & Business Services, on April 21. An OR-FACE
investigator visited the site and interviewed the employer on July 8.
The equipment was in the same position as the day of the incident. This
report is based on the OR-FACE investigation, reports from OR-OSHA, the
county sheriff,medical examiner, and expert consultation. Recommendations
were drafted with the assistance of an experienced logger and logging
The yarding operation was being conducted on a private tract of second-growth
timber, which had been clearcut. The logging company had six employees
at the site, and two others working as cutters. The employer was also
onsite. The chaser had been on the job 6 weeks. The company had a written
safety program, but no safety committee.
The timber on the unit being logged consisted of 20-22 inch dbh (diameter
at breast height) Douglas fir. A Madill 071 yarder was used to yard the
felled timber to the landing site. A delimber was located on the landing
The chaser’s regular duties included unhooking the turns of logs
that were yarded onto the landing, and also bucking
and limbing logs that the delimber could not handle. At the time of the
incident, the chaser was standing to the front left of the delimber, near
the cab. The position was considered a safe spot on the landing, according
to a coworker and the employer.
The crew was sending in a turn of four tree-length
logs when the incident occurred, according the OR-OSHA report. The report
states that the logs hung up on a stump in the road line, which put stress
on the yarder tower. The back-right guyline came
off of its stump, which increased pressure on the next stump to its left,
and that guyline came off of its stump as well. With two guylines down,
the other two guylines could not hold the tower in its upright position.
Tower hinge and box beam
(arrows) broke, allowing tower to come down.
The tower fell forward in the direction of the turn, striking the boom
of the delimber, operating in front of and below the yarder. A sheave
located midway along the boom, attached by a solid steel pin (about 1
3/8-inch diameter), sheared off and was forced downward, though still
attached to the cable running through it. The sheave struck the chaser
on the head and punched through his hard hat.
#1. The cable pulled over the top of the stump. Note proximity of
log deck to stump (see Recommendation
#2. Fresh dirt indicates the stump pulled out of the ground and
released its guyline.
Tower stability in a skyline yarding operation involves several primary
factors: skyline deflection, skyline braking,
and the size of turns and anchorages. It is unclear if the tower failure
in this incident was the immediate result of the tower setup, or in the
guyline setup. An engineering failure analysis would be necessary to isolate
the initial cause of the incident.
Illustration of proper deflection in
(Source: Garland, 1997).
The employer believed the skyline deflection on the setup was appropriate
for the size of trees in the turns and for the loads exerted on the skyline,
while OR-OSHA called the deflection “minimal.”
The two anchor stumps that failed were both 20-22 inch dbh
Douglas fir, 35-40 years old. The third and fourth anchors were guyed
off to notched stumps and double-tied back to green
trees. The employer reported checking the anchors daily, during the course
of several turns, for signs of failure. One logging expert consulted in
this investigation believed the notch cut into the first stump was in
the root swell and not in the holding wood, and this may have contributed
to the tower failure.
Cause of Death
Acute trauma to the head.
Recommendation #1: Plan the landing site for yarding requirements beforehand.
Make sure nearby anchor stumps are left at an appropriate height to secure
guylines, and the guylines will not interfere with decking the logs at
Sufficient stump height for guyline anchors must be available around
a landing site. In this incident, one guyline was evidently attached to
the bowl of the stump, with not much room above the notch, which may have
contributed to the guyline pinching off the top of the stump and coming
When planning units, it is also important to give the logger sufficient
space around the landing to deck the logs waiting to be shipped. Make
sure the decking areas do not interfere with the guylines in any way.
A guyline can possibly shake loose when bumped.
Recommendation #2. Set up yarder guylines according to manufacturer’s
recommendations, making sure lines are at no more than a 50-degree angle,
equally sharing the load, and secured by additional support for the anchors.
When setting up the tower, it is important to make sure the guylines
are not steeper than 50 degrees, measured horizontally. An angle steeper
than 50 degrees puts more downward pressure on the tower, rather than
pressure to hold the tower from tipping forward under the weight of the
skyline. The downward pressure can cause the tower to buckle if a turn
is too heavy. If guylines must be rigged steeper than 50 degrees, the
operator needs to back off on turn size.
It is also important that the guylines are placed into the proper guying
zones. Zones are spelled out in the manual that came with the yarder,
or can be found in OR-OSHA (2005) regulations. If guylines can not be
placed into these zones, because of obstructions or lack of good anchors,
the operator needs to place additional guylines to share the load of the
guyline that cannot be placed within its zone.
All guylines must share the load being placed on the tower. Guylines
attached to anchors at different distances from the tower need to be tensioned,
so all guylines share the load equally. Guyline anchors that are closer,
for example, need to be set slightly looser than those that are farther
away, so the guylines will all have the same tension on them when the
tower is under load.
Use only healthy trees or stumps as anchors. Cut notches for guyline
cable placement 1½ times the circumference of the cable, and no
more, to ensure the cable stays in the groove, without reducing the integrity
of the anchor. A deeper notch effectively decreases the diameter and holding
power of the stump, and increases the risk of parts slabbing
If notching will be too deep (or too high or too low) on anchor stumps,
consider alternative guyline anchorage systems. Trees harvested today
are smaller than their predecessors, and the use of tie-back
anchors and other alternatives for additional support for the guyline
anchor is not uncommon. Alternatives for securing guylines and stabilizing
the tower include (but are not limited to): use of heavy logging equipment,
logs placed in open trenches (“deadman”), tie-back stumps,
or specialized equipment such as tipping plates.
Recommendation #3. Check security of the guyline anchors daily, before
and during operation.
Stumps used as anchors should be observed daily for signs of failure:
pulling out of the ground, slabbing off, becoming loosely attached, wire
rope eating too deeply into the notch, and so on. Check anchors (stumps)
while the operation is in progress. Do not attempt to continue logging
operations if an anchor stump/tree shows signs of failure.
Recommendation #4. Maintain proper deflection in the skyline to reduce
stress on the yarder tower. Consider using slightly less pressure on the
Insufficient deflection (sag) in the skyline may have been a contributing
factor in this tower failure. Deflection helps to absorb and dissipate
forces exerted upon the skyline during the yarding cycle. With insufficient
deflection, the forces on the tower will be transferred directly onto
the yarder guylines and anchors. If the operator is unable to achieve
proper line deflection, payloads on the skyline
should be backed off.
Also in this incident, a hangup may have increased pressure on the yarder
tower. By using slightly less pressure on the skyline brake, the skyline
will reel out in the event of an overload situation. A brake will hold
tension in the skyline, but under extreme tension will slip and reel out
more skyline to increase deflection and load capacity. The operator needs
to be careful when using this method when minimal lift is involved, as
the carriage can hit the ground if the skyline reels out too fast, or
- Garland, J. (1997). Logging woodland properties [Reprint]. In Oregon
State University Extension Service, The woodland workbook.
Available online: http://extension.oregonstate.edu/catalog/pdf/ec/ec956.pdf
(Link no longer available 01/07/2010)
- Occupational Safety & Health Administration. (n.d.). Glossary
of logging terms. Available online: https://www.osha.gov/SLTC/etools/logging/glossary.html
- Oregon Occupational Safety and Health Division. (2005). OR-OSHA
rules/laws: Division 7, forest activities. Available online: http://www.cbs.state.or.us/external/osha/standards/div_7.html
- Timber Buyers Network. (2000). Glossary of terms used in timber
harvesting and forest engineering. Available online: http://www.timberbuyer.net/glossary.shtml
- Workers’ Compensation Board of British Columbia. (2004). Cable
yarding systems handbook. Available online: http://www2.worksafebc.com/Portals/Forestry/YardingAndSkidding.asp?_from=
forestry.healthandsafetycentre.org (Link updated
Bucking: To saw felled trees into shorter lengths.
Cable yarding: The movement of felled
trees or logs from the area where they are felled to the landing on a
system composed of a cable suspended from spars and/or towers. The trees
or logs may be either dragged across the ground on the cable or carried
while suspended from the cable.
Chaser: Member of a logging crew
who unhooks the logs at the landing and does other odd jobs.
Dbh: Diameter at breast height.
Deck: A pile of logs on a landing.
Deflection: Vertical distance
between the skyline, measured at midspan, and the straight-line “chord”
between the two endpoints; frequently expressed as a percentage of the
horizontal span length
Delimber: A multifunction machine
used to delimb trees and arrange logs in piles on the ground.
Guyline: An anchored
line used to support a tower or spar in yarding operations.
Landing: Flat ground where logs
are yarded and loaded on transport; a collection point for logs.
Payload: Gross weight of a loaded
vehicle minus the weight of the vehicle itself.
Sheave: A wheel or disk with a
grooved rim, especially one used as a pulley.
Skyline: Cableway stretched taut
between two spar trees and used as a track for a skyline carriage.
Slabbing: When a stump or tree
crushes under pressure and a lateral split in the grain sheers off.
Tie-back anchor: Additional anchor
tied to the main anchor stump to reduce pressure on the root system of
the main stump (double-tied indicates two tie-back
Turn: Any log or group of logs attached
by some means to power and moved from a point of rest to a landing.
Yarder: System of power-operated
winches used to haul logs from a stump to a landing.
Oregon FACE Program
The Center for Research on Occupational and Environmental Toxicology
at Oregon Health & Science University performs Fatality Assessment
and Control Evaluation (FACE) investigations through a cooperative agreement
with the National Institute for Occupational Safety and Health (NIOSH),
Division of Safety Research (DSR). The goal of these evaluations is to
prevent fatal work injuries in the future by studying the working environment,
the worker, the task the worker was performing, the tools the worker was
using, the energy exchange resulting in fatal injury, and the role of
management in controlling how these factors interact.
To contact Oregon
State FACE program personnel regarding State-based FACE reports, please
use information listed on the Contact Sheet on the NIOSH FACE web site.
Please contact In-house
FACE program personnel regarding In-house FACE reports and to gain
assistance when State-FACE program personnel cannot be reached.
Oregon FACE reports are for information, research, or occupational injury
control only. Safety and health practices may have changed since the investigation
was conducted and the report was completed. Persons needing regulatory
compliance information should consult the appropriate regulatory agency.