industry and the heavy economic losses that accrue when providers go off air. Another incentive is the
"good neighbor" image that is gained when commercial broadcasters can stay on the air and switch to
emergency community-service broadcasting during a storm.
Cellular telephone technology is rapidly becoming the communication tool of choice and it
has greatly improved emergency communications capability. Cellular communications can some-
times be the most reliable communications system during an emergency because they do not
require overhead wires that are vulnerable to falling trees. Working in the 800 to 900 MHz range,
signal propagation and reception are virtually unaffected by ice accumulation. Of further benefit
during periods of emergency operations is an industry practice of reserving certain bandwidths
for use during periods of high-volume calling. Cellular systems are composed of line-of-sight
networks of towers to carry the signal. The loss of signal from any tower will result in lost com-
munications capability in all service areas farther down the network. All sites generally have bat-
tery backup that will keep the site operating for 8 to 20 hours in the event of external power loss.
Sites that are major hubs in the cellular network are usually backed up with auxiliary generators
that are generally configured to start up automatically when power is interrupted. If external
power is restored before batteries or fuel run out, no interruption in service occurs.
Falling ice is a more common problem for cellular and microwave systems. Both require
meticulous antenna alignment to maintain tower-to-tower transmission integrity. Ice impact on
tower components could easily disrupt this alignment enough to sever communications. How-
ever, ice guards can usually prevent all but the heaviest ice impact from disrupting service.
Cellular providers often lease space for their equipment on existing towers, in which case new
structural loads are determined to ensure that tower modifications meet current design standards.
Self-supporting towers are favored by cellular and PCS providers, because they require less area
and lower maintenance. They are less sensitive to extreme icing conditions than guyed structures
and hence have a lower risk of collapse. However, when designed for the ice conditions occur-
ring at a site, both types of towers will perform satisfactorily.
The damage index in Table 1 is by no means absolute. Even moderate winds increase the
damage to ice-covered trees and structures by combining a significant lateral load with the
already high vertical load. The overall health and age of trees and any past damage may increase
their susceptibility to ice loads. For man-made structures the age, design loads, and load combi-
nations considered in design, factor of safety, maintenance history, and failure containment
provisions all influence the risk of failure, as well as the extent of the failure, of a particular over-
head line system or network of communication towers.
6. THE JANUARY 1998 ICE STORM
The ice storm caused extensive damage to trees, long outages in the electrical distribution
system, communication problems, transmission line damage and outages, and the failure of com-
munication towers. In this section we discuss the level of damage, the ice loads that caused that
damage, and the history of severe ice storms in the northeastern United States.
6.1 Damage
6.1.1 Trees
This ice storm damaged trees, many of them severely, over all three states covered by the
Region 1 disaster declaration as well as in New York and the neighboring provinces of Quebec,
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