BMP - Utility Tree Risk Assessment - 1
1. Introduction
Trees that grow into and fall onto energized overhead utility lines and equipment can damage utility facilities and interrupt energy delivery. They may
also present risks to safety, reliability, and regulatory compliance. Vegetation
interference with utility system operations is one of the most common
causes of electrical outages on distribution systems and has initiated transmission grid failures that have subjected millions of people to lengthy blackouts, and, in some cases, provided a source of ignition for wildfire.
While trees provide numerous benefits, which typically increase as the age
and size of the trees increase, they are also more likely to shed branches or
develop decay or other conditions with age that can predispose them to failure. Environmental conditions such as weather, animal (and human) impacts,
wildfire, drought, flood, insects, and disease vectors can affect tree health,
structure, and mechanics. In assessing and managing the risks that trees pose
to overhead utility lines, utilities should strike a balance between the risk and
the benefits that individuals and communities derive from trees.
Many trees in proximity to overhead power lines pose a low risk because the
likelihood of failure within a typical time frame (e.g., 12 to 36 months) is
improbable, and/or the consequences of failure are often minor or negligible.
In other cases, the consequences of tree failure resulting in a line strike may
be significant or severe. Decisions on whether tree inspections are required-
and what level of assessment is appropriate-should be made with consideration for what is reasonable and proportionate to the specific conditions
and situations.
The large population of trees managed by utilities presents challenges. Utility
infrastructure is often exposed to hundreds of thousands of trees within and
along each mile of right-of-way (ROW). Given the constraints that resource
limitations can impose, it is unreasonable to expect utilities to identify every
tree with the potential to strike a line for potential defects and to proactively
remedy the risks they present. Moreover, utilities may be hindered from mitigating or abating tree risks due to property owner opposition and limited
access to private properties. Most trees that pose risks to overhead electric
lines are privately owned, and utilities do not have rights to enter these
properties to conduct assessments or mitigation tasks. For this reason, it is
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BMP - Utility Tree Risk Assessment
Table of Contents for the Digital Edition of BMP - Utility Tree Risk Assessment
Table of Contents
BMP - Utility Tree Risk Assessment - Cover1
BMP - Utility Tree Risk Assessment - Cover2
BMP - Utility Tree Risk Assessment - i
BMP - Utility Tree Risk Assessment - ii
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