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flexibility. However, in the aftermath of a damaging
service. With this service, the line should be given
earthquake, high telephone system traffic may
priority in getting a dial tone. This will give the
severely impair the operation of the system. For
caller access to the local central office. If the call is
example, it may be difficult to call an office down
to another central office or if it is a long distance
the hall, as all calls must go through the telephone
call, it will have no special priority.
company's central office.
k. Miscellaneous systems. There are two sys-
(4) Other communication system issues are dis-
tems associated with dam facilities that can impact
cussed in paragraph B-4d.
system operation, suspended ceilings in control
rooms, and elevators, which although are not vital to
continued operations, can impact the postearthquake
j. External public switch network telephone
(1) Suspended ceilings in control rooms. Failure
(1) The seismic performance of public switch
of the control room ceiling can disrupt operations
networks, from a facilities point of view, has been
during critical moments after an earthquake. The
very good. There has been very little damage that
most vulnerable type of ceiling is the "T" bar sus-
has impacted telephone system operations. It should
pended ceiling. While new building codes have
be noted that with the introduction of optical fiber
reduced the problems, older systems have completely
lines and large computer-based switching, the degree
failed, and large numbers of panels and light fixtures
of system redundancy has been reduced and there
frequently fall. If the acoustical tile panel is light-
have recently been significant system disruptions
weight, it may not cause a problem, but falling light
from relatively minor damage. Thus, the perfor-
fixtures can cause severe injuries and damage the
mance during future seismic events is uncertain.
control panel. Even ceilings designed to the new
codes often drop a few panels, particularly around the
(2) Even when there has been little damage to
periphery of the room, and air diffusers can fall.
telephone facilities, the operation of the telephone
system has been severely impaired in recent earth-
quakes due to high system traffic. There are several
impacts on the system as a result of the increase in
(a) While elevators are not necessary for the
use of the telephone system after an earthquake.
continued operation of a dam, if there are problems
First, when a telephone is picked up, there may be no
and repair crews need to respond quickly, functioning
dial tone. If the only problem is high system traffic,
elevators are important.
that is, lines are not down and there has been no
central office damage, there may be a delay of sev-
(b) The seismic performance of elevators has
eral minutes before a dial tone is obtained. Once
been poor. The most severe problems are lack of
there is dial tone, a call can be made. If the number
anchorage of machine room equipment, including
dialed is serviced by the same central office, the call
control cabinets, motors, and the traction machine. A
will go through quickly if the called line is not busy.
common failure is the counterweight coming out of
If the party called is serviced by a different, nearby
its rails. If this happens and the elevator is used, the
central office, the call will probably not go through
counterweight, which can weigh 6,000 lb can strike
due to busy telephone trunks. If the call is to a dis-
the cab. Counterweight derailment has been assoc-
tant party so that long distance service is needed, the
iated primarily with the use of 8-lb guide rails. How-
call will probably not go through due to busy tele-
ever, in general, the problem is with flexible rail
phone trunks. Long distance calls coming from out-
supports or supports that are too far apart, rather than
side will have even a smaller chance of getting
with the rails themselves.
through. Busy telephone conditions can persist for
several days following an earthquake.
(c) Machine room equipment should be
anchored, and if the counterweight system appears
(3) A special grade of service is available to
vulnerable, stiff counterweight rail tie brackets can be
certain customers, and some lines to a dam should
added. Guidance for upgrading can be obtained from
qualify. This is usually referred to as an essential
ANSI A17.1, National Elevator Code.
service line. Some companies refer to this as class A