BMP - Utility Tree Risk Assessment - 31

The utility industry and regulators often use IEEE 1366 (2017) as a standard
reference defining a major outage event as one that " exceeds reasonable
design and/or operational limits of the electric power system. " There is no
expectation of eliminating all risk to an overhead electric utility system due
to tree failure during adverse weather. Some level of tree and tree part failure must be expected and accepted.

Tree Failures

Trees and parts of trees fail when the load on them exceeds their strength.
Many tree failures can be predicted because certain structural defects or conditions lead to structural weaknesses. However, in many cases, post-incident
inspections have shown that most tree failures-those that cause interruption and outages to utility customers-did not exhibit symptoms that would
have been apparent, and suggest that they were at elevated likelihood of failure. This is because trees that were obviously compromised were identified
and addressed by previous vegetation maintenance.
Utility tree risk assessors need to be able to recognize and evaluate the common conditions that predispose trees and parts of trees to failure in order
to categorize the likelihood of failure (see Appendix 3). It is important to
recognize that through response growth (see Appendix 4), trees can
strengthen weak areas and support normal loads, thereby reducing the likelihood of failure.
Typically, more than one defect or condition is present in a tree, and the possible effects of that combination must be considered. However, not all conditions and defects have a significant impact on tree structure. For example,
a trunk lean of 10 degrees may not be of great concern on many trees, but
if there is a large, decayed root on the side opposite the lean, then the likelihood of failure increases if significant loads are likely to occur and the tree
has not compensated for the defect with response growth.
Tree failures usually occur when there is a critical combination of tree defects,
conditions, and contributing environmental factors such as wind, rain, freezing rain, or snow. With the exception of sudden branch drop, calm-day tree
failures are rare and typically associated with severe defects.

31



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
BMP - Utility Tree Risk Assessment - Table of Contents
BMP - Utility Tree Risk Assessment - iv
BMP - Utility Tree Risk Assessment - v
BMP - Utility Tree Risk Assessment - vi
BMP - Utility Tree Risk Assessment - vii
BMP - Utility Tree Risk Assessment - viii
BMP - Utility Tree Risk Assessment - ix
BMP - Utility Tree Risk Assessment - x
BMP - Utility Tree Risk Assessment - xi
BMP - Utility Tree Risk Assessment - xii
BMP - Utility Tree Risk Assessment - 1
BMP - Utility Tree Risk Assessment - 2
BMP - Utility Tree Risk Assessment - 3
BMP - Utility Tree Risk Assessment - 4
BMP - Utility Tree Risk Assessment - 5
BMP - Utility Tree Risk Assessment - 6
BMP - Utility Tree Risk Assessment - 7
BMP - Utility Tree Risk Assessment - 8
BMP - Utility Tree Risk Assessment - 9
BMP - Utility Tree Risk Assessment - 10
BMP - Utility Tree Risk Assessment - 11
BMP - Utility Tree Risk Assessment - 12
BMP - Utility Tree Risk Assessment - 13
BMP - Utility Tree Risk Assessment - 14
BMP - Utility Tree Risk Assessment - 15
BMP - Utility Tree Risk Assessment - 16
BMP - Utility Tree Risk Assessment - 17
BMP - Utility Tree Risk Assessment - 18
BMP - Utility Tree Risk Assessment - 19
BMP - Utility Tree Risk Assessment - 20
BMP - Utility Tree Risk Assessment - 21
BMP - Utility Tree Risk Assessment - 22
BMP - Utility Tree Risk Assessment - 23
BMP - Utility Tree Risk Assessment - 24
BMP - Utility Tree Risk Assessment - 25
BMP - Utility Tree Risk Assessment - 26
BMP - Utility Tree Risk Assessment - 27
BMP - Utility Tree Risk Assessment - 28
BMP - Utility Tree Risk Assessment - 29
BMP - Utility Tree Risk Assessment - 30
BMP - Utility Tree Risk Assessment - 31
BMP - Utility Tree Risk Assessment - 32
BMP - Utility Tree Risk Assessment - 33
BMP - Utility Tree Risk Assessment - 34
BMP - Utility Tree Risk Assessment - 35
BMP - Utility Tree Risk Assessment - 36
BMP - Utility Tree Risk Assessment - 37
BMP - Utility Tree Risk Assessment - 38
BMP - Utility Tree Risk Assessment - 39
BMP - Utility Tree Risk Assessment - 40
BMP - Utility Tree Risk Assessment - 41
BMP - Utility Tree Risk Assessment - 42
BMP - Utility Tree Risk Assessment - 43
BMP - Utility Tree Risk Assessment - 44
BMP - Utility Tree Risk Assessment - 45
BMP - Utility Tree Risk Assessment - 46
BMP - Utility Tree Risk Assessment - 47
BMP - Utility Tree Risk Assessment - 48
BMP - Utility Tree Risk Assessment - 49
BMP - Utility Tree Risk Assessment - 50
BMP - Utility Tree Risk Assessment - 51
BMP - Utility Tree Risk Assessment - 52
BMP - Utility Tree Risk Assessment - 53
BMP - Utility Tree Risk Assessment - 54
BMP - Utility Tree Risk Assessment - 55
BMP - Utility Tree Risk Assessment - 56
BMP - Utility Tree Risk Assessment - 57
BMP - Utility Tree Risk Assessment - 58
BMP - Utility Tree Risk Assessment - 59
BMP - Utility Tree Risk Assessment - 60
BMP - Utility Tree Risk Assessment - 61
BMP - Utility Tree Risk Assessment - 62
BMP - Utility Tree Risk Assessment - 63
BMP - Utility Tree Risk Assessment - 64
BMP - Utility Tree Risk Assessment - 65
BMP - Utility Tree Risk Assessment - 66
BMP - Utility Tree Risk Assessment - 67
BMP - Utility Tree Risk Assessment - 68
BMP - Utility Tree Risk Assessment - 69
BMP - Utility Tree Risk Assessment - 70
BMP - Utility Tree Risk Assessment - 71
BMP - Utility Tree Risk Assessment - 72
BMP - Utility Tree Risk Assessment - 73
BMP - Utility Tree Risk Assessment - 74
BMP - Utility Tree Risk Assessment - 75
BMP - Utility Tree Risk Assessment - 76
BMP - Utility Tree Risk Assessment - 77
BMP - Utility Tree Risk Assessment - 78
BMP - Utility Tree Risk Assessment - 79
BMP - Utility Tree Risk Assessment - 80
BMP - Utility Tree Risk Assessment - 81
BMP - Utility Tree Risk Assessment - 82
BMP - Utility Tree Risk Assessment - 83
BMP - Utility Tree Risk Assessment - 84
BMP - Utility Tree Risk Assessment - 85
BMP - Utility Tree Risk Assessment - 86
BMP - Utility Tree Risk Assessment - 87
BMP - Utility Tree Risk Assessment - 88
BMP - Utility Tree Risk Assessment - 89
BMP - Utility Tree Risk Assessment - 90
BMP - Utility Tree Risk Assessment - 91
BMP - Utility Tree Risk Assessment - 92
BMP - Utility Tree Risk Assessment - 93
BMP - Utility Tree Risk Assessment - 94
BMP - Utility Tree Risk Assessment - 95
BMP - Utility Tree Risk Assessment - Cover4
https://www.nxtbookmedia.com