5. ICE STORM DAMAGE
The level of damage is a good qualitative indicator of the severity of freezing-rain storms.
Both trees and man-made structures differ in their ability to withstand ice loads. In Table 1 is
shown our ice-load index that associates different kinds of damage with increasing ice load.
Very slight amounts of freezing rain can cause slippery roads, significantly increasing the
driving hazard and causing numerous fender benders and injury accidents. This hazard can be
reduced by encouraging people to stay home and by salting and sanding roads. With somewhat
Table 1. Ice load index.
Damage to trees and structures, in order of increasing ice load.
High winds concurrent with the ice load increases the level of damage.
Slippery roads
Ice on trees shining in the sun
Outages in the communications and power distribution and transmission systems caused
by trees
Bending birch trees
Broken branches on susceptible trees
Characteristics: fine branching
included bark
brittle wood
broad or unbalanced crowns
old or injured trees
Examples:
poplars
maples
beeches
willows
trees at edges of a clearing or pruned on one side
Outages to transmission lines caused by galloping
Broken branches on resistant deciduous trees
Characteristics: coarse branching
excurrent branching pattern
narrow crowns
young, sound trees
Examples:
oaks
black walnut
trees in dense woods
Outages, not caused by trees, in the distribution system
Broken branches on evergreen trees
Outages, not caused by trees, in the transmission system
Communication tower failures
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