A review of terminology used by electric utilities to characterize the threat from trees

Geoff KempterAsplundh Technical Services

Danger Tree?https://www.sciencealert.com/do-not-stand-under-world-s-most-dangerous-tree-manchineel-tree

Manchineel Tree“Manzanilla de la muerte”

-- or --“Little Apple of Death”“When it's raining the raindrops carrying the diluted sap can still severely burn your skin.”

Arctic Whirlw

ind

Electric utilities operate within both the disciplines of forestry and arboriculture

Forestry: the science of developing, caring for, or cultivating forests i.e. MACRO, large scale management

Arboriculture: the cultivation of trees and shrubs especially for ornamental purposes i.e. MICRO, individual trees and properties

Entire Systems Individual Properties

Millions of trees

Tree by tree

Practitioners in UVM often have credentials from both disciplines Forestry degree from an accredited

institution Professional Arborist Certification

Various regulatory agencies have jurisdiction: OSHA Canadian Centre for Occupational

Health and Safety State and Provincial health and safety

agencies FERC/NERC/NEB State/Provincial PUCs/PSCs

Consequences of tree-line contact vary enormously:2003 US/Canada Blackout Localized outage

Regarding trees, utilities have

adopted terminology from both forestry and

arboriculture

Forestry

In the U.S. and Canada, “Danger Tree” is often used when describing a tree that poses a threat to workers

Forestry

Danger Tree Indicators

“Dangers can vary by location of trees, condition of trees and changing conditions around trees.”

“Not all dead trees are dangerous, not all live trees are safe”

https://ww

w.fs.fed.us/t-d/pubs/pdfpubs/pdf11672M13/pdf11672M

13dpi300.pdf

ForestryUSDA Forest Service, 2011https://www.fs.fed.us/t-d/pubs/pdfpubs/pdf11512815/pdf11512815dpi72.pdf

Danger Tree:“A standing tree that presents a hazard to employees due to conditions such as, but not limited to, deterioration or physical damage to the root system, trunk, stem or limbs, and the direction and lean of the tree.”—Occupational Safety and Health Standards, Title 29, CFR Part 1910.266(c)

ForestryUSDA Forest Service, 2016, Danger Tree IDhttps://www.fs.fed.us/t-d/pubs/pdfpubs/pdf11512815/pdf11512815dpi72.pdf

“Identifying risk of tree failure and making decisions in areas where dangerous trees pose a threat to individuals along forest roads or work sites.” (i.e. employees, workers, etc.)

“This guide is not intended for developed sites in forested areas; instead, refer to Field guide for hazard-treeidentification and mitigation on developed sites in Oregon and Washington forests, 2014”

ForestryUSDA Forest Service Hazard Tree Guide (2014)https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3799993.pdf

“We recommend that this guidebook be used for identifying and mitigating hazard trees in and around developed sites such as campgrounds, picnic areas, ski areas, boat launches, parking lots, trailhead parking areas, buildings, and administrative complexes.” (i.e. fixed targets and high-use areas)

Forestry

Wildlife/Danger TreeBritish Columbiahttps://www.unbc.ca/continuing-studies/courses/wildlife-danger-tree-assessor-certificate-parks-and-recreation-module

“Danger trees” are also recognized as beneficial to wildlife.

University of Northern British Columbia offers a Certificate

Forestry

Danger Tree Blastinghttps://www.fs.fed.us/t-d/pubs/htmlpubs/htm11512815/page04.htm

-USDA Forest Service

“Explosives provide a safe and reliable way to mitigate danger trees in both fire and nonfireenvironments.”

“Blasting typically is used to remove trees that cannot safely be removed using chain saws or mechanical equipment.”

Forestry

Danger Tree Blastinghttps://www.fs.fed.us/t-d/pubs/htmlpubs/htm11512815/page04.htm

Felling trees with explosives results in a natural look called "fuzzy stumping.“

-USDA Forest Service

Hazard Tree Guidelines for Forest Service Facilities and Roads in the Pacific Southwest Region (2012)https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5332560.pdf

“These hazard tree guidelines provide a means to identify and abate hazard from trees that are likely to fail and cause injury to either people or property on Forest Service system roads or at Forest Service facilities (i.e. campgrounds, boat ramps, trailhead parking, summer home tracts, administrative sites, kiosks, information centers, etc.) in California.”

Hazard Tree Guidelines for Forest Service Facilities and Roads in the Pacific Southwest Region (2012)https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5332560.pdf

This publication cites arboriculture sourcesIt is about managing trees on individual sites to protect users and incidental passers by.

Arboriculture1988 NAA Pruning Standards (Pre-ANSI A300)

“Hazard pruning is recommended where safety considerations are paramount. Hazard pruning shall consist of the removal of dead, diseased, decayed, and obviously weak branches….”

ArboricultureA Photographic Guide for the Evaluation of Hazard Trees in Urban Areas. Matheny and Clark, 1991, 1994

Included an evaluation form and rating procedure

Arboriculture

Shigo Brochure, 1990sDiscusses: Target Tree architecture History of failures Edge trees Dead branches Cracks Poor attachments Topping And more

Publication was directed at homeowners, but is still relevant as a training tool for professional arborists.

Arboriculture/Utility

Matheny and Clark, 1993

Distilled information in a pocket guide for working utility arborists

Arboriculture/Utility

ANSI A300 Part 1, Pruning 1995

Reasons for Pruning“The reasons for tree pruning may include, but are not limited to, reducing hazards, maintaining or improving tree health and structure, improving aesthetics, or satisfying a specific need.”

Utility pruning “The purpose of utility pruning is to remove branches in order to prevent the loss of service, prevent damage to equipment, avoid impairment and uphold the intended usage of the facility/utility space.”(No mention of “hazard”)

Arboriculture/Utility

ANSI A300 Part 1, Pruning, 2001/2008

Reasons for Pruning“The reasons for tree pruning may include, but are not limited to, reducing risk, maintaining or improving tree health and structure, improving aesthetics, or satisfying a specific need.”

Utility pruningThe purpose of utility pruning is to prevent the loss of service, comply with mandated clearance laws, prevent damage to equipment, avoid access impairment, and uphold the intended usage of the facility/utility space.

Arboriculture

PNW T.R.A.C.E. Program, 2005 “Tree Risk Assessment

Course and Exam” Emphasized “risk” over

“hazard”

Arboriculture

ANSI A300 Part 9, Tree Risk Assessment, 2011Described process for three levels of tree risk assessment

Arboriculture

ISA Tree Risk Assessment BMP; ISA TRAQ Course, 2011-2013

ISA TRAQ Tree Risk MatricesLikelihood of Failure

Likelihood of Impacting TargetVery low Low Medium High

Imminent Unlikely Somewhat likely Likely Very Likely

Probable Unlikely Unlikely Somewhat likely Likely

Possible Unlikely Unlikely Unlikely Somewhat likely

Improbable Unlikely Unlikely Unlikely Unlikely

Likelihood of Failure and Impact

Consequences

Negligible Minor Significant Severe

Very Likely Low Moderate High Extreme

Likely Low Moderate High High

Somewhat likely Low Low Moderate Moderate

Unlikely Low Low Low Low

TRAQ Tree Risk Assessment MethodLikelihoodof Failure and Impact

Consequences

Negligible

Minor Significant

Severe

Very Likely Low Moderate High Extreme

Likely Low Moderate High High

Somewhat likely

Low Low Moderate Moderate

Unlikely Low Low Low Low

Risk is characterized as LOW, MODERATE, HIGH, or EXTREMEBased on a combination of objective and subjective criteria.

This method of risk characterization is used broadly by other industries including the insurance and legal fields.

Arboriculture/Utility

ANSI A300 Part 1, Pruning, 2017

Reasons for PruningReasons for pruning include reducing risk, improving or maintaining health, developing desired structure and appearance, preventing interference with the built environment, and other specific objectives.

Utility pruning section was eliminated

Objectives should include…: Manage risk (see ANSI

A300 Part 9, Tree Risk Assessment, and ANSI A300 Part 3, Supplemental Support Systems).

Utility Forestry

George Blair, 1951:Tree Clearance for Overhead LinesBlair did not use the terms “hazard tree” or “danger tree” in his book. The term hazard and danger appear in descriptions, e.g.: “Dead wood overhanging or otherwise

adjacent to conductors is an imminent hazard….

“Such limbs are a constant source of danger to persons and property, also to trees of which they are a part….”

Utility Forestry

Ragland v Alabama Power Co., 1978https://www.leagle.com/decision/19781463366so2d109711412

Danger trees…. “…Trees of such size and contiguity to the

transmission line right-of-way that, if they fell, they would strike and likely damage or endanger the lines on that right-of-way.”

In this case, the trees cut and topped were “healthy and disease free.”

Alabama Supreme Court found in favor of the utility, setting a precedent for characterizing “healthy and disease free trees” within striking distance of lines as “danger trees.”

Utility Forestry

Simpson and Van Bossyut, 1996Journal of Arboriculture 22(3): May 1996

The Danger Tree Mitigation Project on Eastern Utilities: “The removal of structurally unsound trees

and performing storm-proof pruning reduced Customer Outage Hours from tree failure by 20% to 30% on the primary electrical circuits where it has been implemented.”

Note that the term “danger tree” was not explicitly defined.

Utility Forestry

California Forest Practice Rules 1999

Danger Tree means any tree located on or adjacent to a utility right-of-way or facility that could damage utility facilities should it fall where: the tree leans toward the right-of-way, or the tree is defective because of any cause,

such as: heart or root rot, shallow roots, excavation, bad crotch, dead or with dead top, deformity, cracks or splits, or

any other reason that could result in the tree or a main lateral of the tree falling.

Utility ForestryEffects of Tree Mortality on Power Line Security(Guggenmoos, July, 2003)

“Trees may be power line hazards because of lean; a poor anchoring medium; poorly formed, narrow angle crotches; codominant leaders; and other structural defects. Such trees are removed in a hazard tree program.”

Note that the term “hazard tree” is not explicitly defined. The term “danger tree” does not appear in this article.

August 2003Third major blackout in seven years…

Utility ForestryANSI A300 Part 7 Integrated Vegetation Management, 2006

Danger tree: A tree on or off the right-of-way that could contact electric supply lines.

Hazard tree: A structurally unsound tree that could strike a target when it falls. In this case the target of concern is electric supply lines.

Danger Trees(possible hazard

trees –“structural soundness” TBD)

Hazard Tree(structurally unsound)

For utilities, all hazard trees are danger trees, but not all danger trees are hazard trees.

Confused?

Hazard Tree

Danger Trees

Utility Forestry“Outside Right-of-Way Tree Risk Along Electrical Transmission Lines”(Guggenmoos, and Sullivan, 2010)

Danger tree: any tree which, on failure, is capable of interfering with the safe, reliable transmission of electricity.

Hazard tree: a danger tree that has both a target and a noticeable defect that increases the likelihood of failure.

Utility ForestryMcLoughlin, 2012 “Various terms are used to describe a danger tree

throughout the country…mostly referring to trees off the ROW” “Large trees along the edge…” “Often diseased or otherwise damaged…” “Dead, dying, diseased, or severely leaning…” “A danger tree can be alive or dead…”

…A danger tree is “located off the ROW and has the distinct possibility that it will fall towards the facility and contact it, be prone to bending into the ROW or has horizontal boughs growing out from the main stem close to the wire security zone.”

In general: The timber industry and OSHA have used the term

“danger tree” to describe trees that pose a threat to forestry workers.

Increasingly USDA Forest Service is using “hazard tree” when describing incidental threat to users and facilities in high-use areas such as campgrounds.

Electric utilities have used both terms, often overlapping, with ambiguous and confusing results

Arboriculture has adopted the term “risk” and uses descriptors to categorize the relative level of risk posed.

Other considerations

Signal Wordshttp://npic.orst.edu/factsheets/signalwords.pdf

“DANGER,” “WARNING” and “CAUTION” are “signal words” recognized by the US EPA. Products with the “danger” signal word are the most toxic.

We are conditioned to be ready for disaster when we see these words

What do people associate with “Danger?”

Danger!

Image courtesy of Stefson

Lonelyplanet.com

What do people associate with “Hazard?”

Image courtesy of Stefson

Lonelyplanet.com

Hazard!

Conclusion: Danger > Hazard > Risk

In UVM, the terms “danger tree” and “hazard tree” are largely ambiguous jargon - often used synonymously, but just as often to mean quite different things altogether.

Conclusion: Danger > Hazard > Risk

Canadian Centre for Occupational Safety and Health defines “hazard” as “any source of potential damage, harm or adverse health effects on something or someone.”

“Hazard” and “hazardous” have been and still are used widely in many industries, including forestry and arboriculture.

Conclusion: Danger > Hazard > Risk

The term “danger tree” is used by OSHA and in the timber industry to describe risk to workers

This aligns well with “DANGER” as a signal word.

For the UVM industry, the use of the term “danger tree” to characterize risk to workers would align with existing forestry industry and OSHA definitions.

Conclusion: Danger > Hazard > Risk

We all want to reduce risk – to workers, assets and the public

Systematic risk assessment uses empirical analysis to determine relative risk posed in various situations.

Decision makers can then make informed decisions about possible courses of action.

This is done recognizing hazards such as danger trees and individual tree defects, by stratifying targets, and systematically addressing and managing these situations.

Conclusion: Danger > Hazard > Risk

Industry standards, best practices and training for tree care professionals have moved toward categorizing the threat from trees to in terms of risk posed (e.g. low, moderate, high, extreme).

The UVM industry could reduce confusion and ambiguity by aligning their terminology accordingly.

A review of terminology used by electric utilities to characterize the threat from trees

Geoff KempterAsplundh Technical Services