# Falling Tree Top and Limb Failure Simulation

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```					       Falling Tree Top and Limb Failure Simulation
Olympic National Park Fuels Crew
Robert Palmer, Crew Supervisor
September 7, 2008

Abstract

Given the different methods of communicating with a sawyer, which notification method(s)
provides the greatest safety margin for the cutter and the spotter, and which notification
method(s) demonstrate the worst safety margin for the cutter and the spotter?

We evaluated seven notification methods: Yell, Whistle, String, Stick, Rock, Spotter with
Hand on Shoulder, and Self. Utilizing a remote spotter method (Yell, Whistle, String, Stick,
Rock), the limb struck the cutter every time. Only the Spotter on Shoulder method, escape rate
of 54%, and the Self method, escape rate of 100% (but see Conclusion), resulted in the cutter
“escaping” the falling limb.

This exercise was very pointed and indicated some significant safety issues with traditional
falling operations. The remote notification methods were blatantly ineffective and provided a
false sense of security. Unless the Spotter is on your Shoulder, then the traditional ideology
that a remote spotter can alert you to an immediate overhead hazard is a fallacy and the act
needs to stop. Because it is realistically impossible for a cutter to constantly keep eyes up and
with less than second to escape, the Spotter on Shoulder method provides the best safety
margin. However, given the almost 50/50 chance that a cutter could escape a falling hazard, a
cutter should not engage any tree with an indentified loose overhead hazard.

This exercise also illustrates that only a cutter and spotter are essential to a falling operation.

   Scratchline #17: Chainsaw Safety and Snag Falling Lesso ns Learned
   Paul Chamberlin’s Sim Limb/ Top Drop issue paper
   USFS video describing Sim Limb/Top Drop
   USFS Sim Limb Job Hazard Analysis
Falling Tree Top and Limb Failure Simulation

Olympic National Park Fuels Crew
Robert Palmer, Crew Supervisor
September 7, 2008

Purpose
Mathematically, a cutter has less than 1 second to escape from a falling hazard that was 16 feet
up; less than 2 seconds to escape from a falling hazard that was 64 feet up; or less than 3
seconds to escape from a falling hazard that was 144 feet up. Considering the extremely
limited time to escape, cutters need to know what notification methods provide the best safety
margin.

Given the different methods of communicating with a sawyer, which notification method(s)
provides the greatest safety margin for the cutter and the spotter, and which notification
method(s) demonstrate the worst safety margin for the cutter and the spotter?

Method
In light of the Andy Palmer fatality incident, a fellow engine crewmember, the crew discussed
ways to improve the safety of cutting and falling operations. We heard about the “Sim
Limb/Top Drop Exercise,” and we wanted to try it. Following information found in
Scratchline #17, Paul Chamberlin’s issue paper, the USFS video, and the USFS Sim Limb Job
Hazard Analysis, we conducted the exercise at the Deer Park Ranger Station flag pole.

   We used a 25’ tall flag pole adjacent to a wide dirt road and driveway.
   For the limb/top, we used a foam sleeping pad double rolled around a cardboard map
tube. The limb was attached to the flagpole halyard via a slipknot and raised to various
heights.
   Four crewmembers participated in each exercise: one cutter, one spotter, one “limb
operator” who determined when the limb would fall, and one stopwatch operator. We
tried to eliminate the cutter and spotter from having any insight as to the timing of the
failure (due to shadows, movement, etc) by strategically positioning the limb and
operator. In general, the limb was dropped between 10-30 seconds after the cutter had
engaged.

To test the raw abilities of the cutter/spotter pair, we deviated from our normal procedure by
asking the cutters to focus their attention solely on the cutting and completely use the spotter
to observe overhead hazards and notify the cutter. The one exception involved the “Self”
notification method where the cutter constantly kept “eyes up.”

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Yell (remote spotter)
Due to the limitations of shadows and limb location                   Whistle, (remote spotter)
on the flagpole, we classified a “hit” as any of the                  String (attached to cutter, pulled by
following: (1) if the failed limb reached the level of                remot e spotter)
the cutters helmet before the cutter escaped the area,                Stick (poke, remote spotter)
(2) if the limb contacted the saw, or (3) if the limb                 Rock (tossed, spotter remote)
contacted the cutter.                                                 Spotter hand on Shoulder
Self
We conducted the exercise for 3.5 hours and spent an hour performing an After Action
Review.

Deer Park Location. Note: The wood shed was later moved to provide more room for the exercise.

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Results
Raw Dat a                              Ordered Data
Fall Time                             Fall Time
Method      Escaped   (seconds)        Method     Escaped   (seconds)
1   shoulder    y                      1   yell       n
2   whistle     n                      2   yell       n               0.6
3   shoulder    y                      3   yell       n              0.62
4   rock        n                      1   whistle    n
5   yell        n                      2   whistle    n
6   whistle     n                      3   whistle    n               0.6
7   whistle     n               0.6    4   whistle    n              0.94
8   stick       n              0.53    1   string     n              0.87
9   shoulder    y              0.81    2   string     n               0.9
10   self        y              0.33    1   stick      n              0.53
11   self        y              0.63    2   stick      n
12   shoulder    y               0.5    3   stick      n              0.56
13   stick       n                      4   stick      n              0.74
14   string      n              0.87    1   shoulder   y
15   rock        n              0.76    2   shoulder   y
16   shoulder    n                      3   shoulder   y              0.81
17   shoulder    ?              0.82    4   shoulder   y               0.5
18   rock        n              0.59    5   shoulder   n
19   shoulder    n              0.71    6   shoulder   ?              0.82
20   shoulder    ?              0.59    7   shoulder   n              0.71
21   stick       n              0.56    8   shoulder   ?              0.59
22   whistle     n              0.94    9   shoulder   y              0.77
23   string      n               0.9   10   shoulder   n              0.69
24   shoulder    y              0.77   11   shoulder   y              0.89
25   self        y              0.89   12   shoulder   y              0.55
26   self        y              0.65   13   shoulder   n              0.57
27   self        y              0.87   14   shoulder   n              0.43
28   yell        n               0.6   15   shoulder   n              0.34
29   yell        n              0.62    1   self       y              0.33
30   self        y              0.73    2   self       y              0.63
31   stick       n              0.74    3   self       y              0.89
32   self        y              0.61    4   self       y              0.65
33   self        y               0.5    5   self       y              0.87
34   shoulder    n              0.69    6   self       y              0.73
35   shoulder    y              0.89    7   self       y              0.61
36   shoulder    y              0.55    8   self       y               0.5
37   shoulder    n              0.57    1   rock       n
38   shoulder    n              0.43    2   rock       n              0.76
39   shoulder    n              0.34    3   rock       n              0.59

4
Method                    Attempts   Escaped    Escape Rate        Note s
Yell, spotter remote          3         0            0%
Whistle, spotter remote       4         0            0%
String (pulled)               2         0            0%
Stick (poke)                  4         0            0%
Rock (tossed)                 3         0            0%
Spotter on Shoulder          13         7           54%         2 discarded
Self                          8         8          100%

Conclusions

The results of this exercise demonstrate the limited effectiveness of traditional spotter
notifications. In every trial, the cutter had less than one second to escape the falling limb. From
approximately 25 feet high, there was insufficient time (1) for the spotter to alert the cutter, (2)
for the cutter to react, and (3) for the cutter to escape the area. Utilizing a remote spotter
method (Yell, Whistle, String, Stick, Rock), the limb struck the cutter every time (n=16). Only
the Spotter on Shoulder method, escape rate of 54% (n=13), and the Self method, escape rate
of 100% (n=8), resulted in the cutter “escaping” the falling limb.

The Yell and Whistle methods were completely ineffective; often, the limb struck the cutter
prior to the cutter hearing the spotter. Even if the cutter heard the spotter, distractions like
checking kerf alignment(s) or chainsaw noise caused a slower response time. The String and
Stick methods were similarly ineffective. In each trial, the limb had fallen by the time the
cutter reacted to the pull or poke. The Rock method was arguably the worst notification
method. Generally, the rock and limb struck the cutter at the same time.

The results of this exercise could
lead one to believe that the Self
method, using the cutter as the
only eyes, is the most reliable
method. The Self method
eliminated the time required for a
spotter to identify and
communicate the hazard to the
cutter, which allowed more time
(¼ to ½ second) for the cutter to
escape.

"S tick" method: Hit.

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However, there are practical limitations to the Self method when applied to a realistic cutting
environment. When using the Self method, the cutter did not necessarily focus on the cutting
but constantly kept “eyes up” during the exercise. If a cutter can make all of the cuts without
looking down (to line up cuts, to check kerf depth, or to check holding wood), then the Self
method is the most reliable. However, in actual cutting operations, cutters need to check their
cuts and thus temporarily lose overhead situational awareness. Because the cutter has less tha n
one second to react and escape, even a quick glance down to check a cut could prove fatal.
For these reasons, the Self method is not a reliable technique for most cutters, agency or
contract.

The Spotter on Shoulder was the only other effective method. We found this method to be
most efficient when the spotter physically pulled and guided the cutter into an escape route as
the spotter continued to look up. The cutter should not rely on the spotter’s eyes (as in this
exercise), but should operate as if cutting independently, constantly keeping “eyes up”. The
spotter must constantly keep “eyes up” and provide a means to alert the cutter to any hazards.
By practicing this method, the cutter and spotter will generally both have “eyes up” throughout
the cutting operation; when the cutter looks down, the spotter maintains “eyes up” as insurance
for the cutter. The method has associated drawbacks and constraints: (1) exposure increases
with two people in the immediate cutting area; (2) confined space requires good rapport
between the spotter and cutter; (3) the individuals must trust each other’s judgment; and (4) the
cutting area must have adequate space for the pair to work including appropriate escape routes.
Even with the constraints, we feel that the Spotter on Shoulder provides the greatest overall
safety margin for falling operations.

Recommendations

After going through this exercise, I question if a cutter should engage any tree or cutting
location that has an identified loose overhead hazard such as burning branches, broken-top,
loose bark, or an unsecure “widow- maker.” I would also question engagement given a
situation that a cutter states “The tree is too risky or there are too many overhead hazards,
therefore I will cut it alone; you spot from just over here.” Our results indicate that from about
25 feet and with less than a second to identify a hazard, notify the cutter, and successfully use
an escape route; a cutter should not engage a tree with a known unsecure hazard.
If a cutter states or thinks that the falling situation or overhead hazards indicate that the cutter
“should” cut without a Spotter on Shoulder, then the operation needs to be suspended—
terminate the hero complex—attitudes, egos, and cultures need to change.

We shall not engage a cutter under an identified loose overhead hazard that cannot be
mitigated:
o If a tree has loose bark, then you must either cut from the opposite side
or leave the tree.
o If a “widow- maker” exists, then cut from the opposite side or leave the
tree.
o If it is burning, then let it burn, and leave the tree.

This exercise was very pointed and indicated some significant safety issues with traditional falling
operations. Only two notification methods offered some success at avoiding the falling limb: a

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Spotter with a hand on the cutter’s Shoulder, and the cutter working independently (Self). The
other methods were blatantly ineffective and provided a false sense of security. Unless the Spotter
is on your Shoulder, then the traditional ideology that a remote spotter can alert you to an
immediate overhead hazard is a fallacy and the act needs to stop. This exercise also illustrates that
only a cutter and spotter are essential to a falling operation. Other individuals, except a qualified
evaluator, are not essential to the cutting operation and thus need to be beyond two tree lengths.

Finally and most importantly, this exercise indicates that given the presence of an imminent
overhead hazard failure, recognized as a substantial risk of causing injury, we must not engage the
falling operation.

Rob Palmer
Rob_Palmer@nps.gov
Fuels Crew Supervisor
Olympic National Park

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