 |
Reprinted courtesy of
Ericsson Inc.
 |
On October
28, 1998, winds and tidal surges from Hurricane Georges brought destruction to
homes on Dauphin Island, just south of Mobile Bay.
|
|
|
Mobile County's
radio communications withstand nature's toughest blows
FOR MOST, the
threat of a hurricane is either nonexistent or pretty remote. But what about
those who live in hurricane prone coastal areas? Some decide it is safer to
flee, while others make the choice to ride out the storm. But there is one
group that cannot evacuate -- public safety officials. Whether it is the
police, fire, EMS, public works, or communications division, these agencies'
skills and services are needed most during these times. How do they cope? How
do they handle the huge evacuations that are necessary? How do they communicate
with one another in the midst of the hurricane? For Eric Linsley, Mobile County
(Alabama) electronics systems analyst, it is simple. You design an effective
communications system and you rely on that system to perform when you need it
most.
Mobile County
first implemented its 800 MHz, five site, 24 channel radio system in 1992. To
better understand how they have expanded to their current six site, 39 channel
system, we must first look to the beginning.
Train crash
During the early morning hours of Sept.
23, 1993, an Amtrak train derailed while crossing the bridge spanning Bayou
Canot, a deep river gorge, plunging passenger cars into the river below. More
than 47 people lost their lives in the wreck, and 160 were
rescued.
This catastrophe
was the first real test of Mobile County's new radio system. Linsley remembers
the situation well. It is his job to ensure that the radio communications work,
and he says that no one was disappointed with the system's performance that
night.
"There were
EMS personnel, the sheriff's department, Saraland and Chickasaw municipalities,
state troopers, Marine police, fire departments, and dozens of other agencies
on the scene and all operating on the Ericsson system, on two or three talk
groups," Linsley says. "Natural disasters you can usually prepare
for. But there was no preparation for something like this."
During those hours
of rescue and recovery, the system logged approximately 73,000 push-to-talks
(PTT's), nearly doubling the county's monthly average of 35,000 PTT's. The
heroic efforts of rescuers are credited with saving many lives. For Linsley,
this situation provided him with vital information about the radio system. For
instance, Linsley has some interesting figures on one four channel tower site
that had 150-200 radios utilizing one talk group.
"A lot of
consultants think that a four channel site would be bogged down with this many
calls, but that's just not the case," Linsley says. "We logged
approximately 143,000 PTT's during the first two days of the incident, without
any queuing at all."
Living with hurricanes
Located on the Gulf Coast, Mobile
County is in a prime location to receive the brunt of most hurricanes that pass
through that region. Preparedness is always the key to successful
communications, especially during these trying natural
occurrences.
Since the Amtrak
train crash, Mobile County expanded its system by adding another site to boost
its coverage and beefing up channels to 39 from the original 24. The county's
average monthly PTTs jumped to about 100,000, up from about 35,000 two years
previous.
Nearly two years
to the day after the Amtrak train crash, Hurricane Erin began heading toward
the Gulf Coast. As Linsley has already said, at least the county can prepare
for something like this. And they did.
Erin skirted the
Northeast region of the county, and caused extensive damage, leaving trees
toppled everywhere. In fact, the road leading to one of the county's sites in
the town of Stockton needed quite a lot of clean up. Officials had to call in
the state forestry service to clear a path to the site. Despite the destruction
to hundreds of huge pine trees that lined the road, the tower site was
undamaged.
"During
Hurricane Erin, our peak calls reached 135,000, nearly doubling our On October
28, 1998, winds and tidal surges from Hurricane Georges brought destruction to
homes on Dauphin Island, just south of Mobile Bay. peak calls during the train
crash," Linsley states.
Unfortunately, as
the county was still cleaning up from Erin, Hurricane Opal struck one month
later. This category three hurricane possessed maximum sustained winds of up to
150 mph. Although the brunt of the Hurricane bore down on Florida's panhandle,
Mobile County and neighboring jurisdictions sustained serious damage from the
immense rain and subsequent flooding.
"During Opal,
we had peak usage on October 1st of about 117,000 PTT's. We had very high
winds, but we didn't get as much damage as we did with Erin," Linsley
says.
Mobile County went
through a two-year respite without expe-riencing a severe hurricane, but when
the next one hit, it made up for those two years.
"Danny was
the next big hurricane to hit us," says Linsley. "We had upgraded
channels on a number of our sites by this time. Danny dumped about 45 inches of
rain on the Southern part of the county, and it just seemed to sit in Mobile
Bay."
This torrential
rain strained the resources of the public safety agencies and caused them
severe problems in trying to reach victims. Linsley says the hurri-cane peaked
on July 19th, and that the county had an astonishing 206,000 PTT's that day.
That is nearly 100,000 more than with Hurricane Opal and almost 70,000 more
than with Hurricane Erin.
"Even with
this tremendous increase, the system continued to perform well," says
Linsley.
Prefer microwave links
All of Mobile County's six sites are
tied together using microwave links, except one, site six, which is owned by
the state of Alabama. Linsley holds strong views on the use of microwave links
versus using T1 (land) lines, especially during emergencies such as the
hurricanes.
Site six covers
the eastern portion of Mobile County and uses a leased T1 line. Although, none
of the county's sites has ever gone down during operation, site six has been
isolated during power outages.
"Leased T1
lines don't cut it," says Linsley. "We are dependent on our phone
carrier to make repairs to the T1 lines, and they don't go out in the middle of
hurricanes, which really hampered us during Danny."
"If lightning
strikes a T1 line, it can go out and be out for days, and there is nothing we
can do about it," states Linsley. "We can fix a
microwave."
Linsley does have
strong praise, however, for the remaining sites that are connected by microwave
links.
"Ericsson
recommended to us to use microwave on the other sites, and it was a good
idea," he says. "Police want to push the button and be able to talk
to all groups, and when tower six loses its T1 line, they lose that ability and
can only talk to the users on that one tower site's group. Ericsson did an
excellent job of engineering the microwave links and connecting them to our
control site."
The county also
discovered, during the most recent hurricane -- Hurricane Georges -- that T1
lines can be unreliable in any disaster. Hurricane Georges reached Southern
Alabama on October 28th of last year. Mobile County logged 224,000 PTT's on
that day, and recorded another 224,000 PTT's the following day.
Linsley says that
the only problem during Georges was the T1 line at site six. He believes that
the cost of upgrading that site to microwave will be recouped in its increased
reliability.
"During all
of these hurricanes, we never lost the microwave link between the sites and the
controller," Linsley says. "Again, that says a lot for the
engineers."
Investment, investment, investment
Linsley estimates that Mobile County
has invested more than one million dollars in the original system, including
the addition of 1,900 radios. By making and analyzing reports daily, Linsley
has been able to assess areas where the system needed to grow, and where
channels needed to be added to current sites.
"We like to
think we are on the cutting edge of radio technology," says Linsley,
"and we feel it is important that we stay up-to-date, and that is not
going to happen without additional investment."
The system covers
the 1,600 square miles of Mobile County, and users can go about 20 miles into
Mississippi and still maintain radio coverage. Confidently, Linsley says,
"I think we can easily cover 2,600 square miles with our
system."
From his past
successes with the network, no one seems to doubt him. Linsley says that Mobile
County has preliminary plans to add a seventh site and 10 more channels by the
year 2000.
 |
| Mobile County
has endured frequent emergencies due primarily to hurricanes. Detailed analysis
is extremely important to public safety system managers and reveals key
information about system operation. For example, this comparison of peak and
average traffic loading demonstrates how the peak emergency traffic has
actually grown at a faster rate than the system itself -- a critical factor in
assessing system performance now, and in the future. |
|