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It
happened early on a January morning as a rapidly
moving thunderstorm passed over Texas City, Texas, A
huge 750,000-barrel crude oil storage tank in
Amoco's tank farm was struck by lightning. Luckily,
the tank was equipped with a state-of-the-art heat
detection system, and what could have been a major
disaster was averted.
"Nine of our largest tanks are protected with these
advanced detection systems," says Amoco Fire Chief
John P. McLemor. "and the tank in question, 345 feet
in diameter, is one of our largest."
Click to enlarge
The heat and fire detection systems
at Amoco are manufactured by The Protectowire Co.,
Inc. in Pembroke, Massachusetts, and are designed
specifically for overheat and fire detection in
floating roof fuel storage tanks. At the time the
tank was struck by lightning, the system had been in
service only a little more than a month. Fire
detection and alarm were the two functions initially
in operation, and fire department personnel
responding to the alarm manually operated a foam
suppression system that quickly controlled the fire.
Today, all systems at Amoco are designed to
automatically release foam should fire strike.
"If we have a tank seal fire, which this one was, we
want to catch it at that level and extinguish it
immediately to keep things from becoming fully
involved," say McLemore. |
The
system itself consists of a temperature sensing
Linear Heat Detector made up of two current-carrying
wires separated by heat-sensitive insulation. The
linear Heat Detector, installed along the perimeter
of the floating roof in the area between the
secondary weather seal and the the primary tube
seal, is connected to a remote fire alarm control
panel via a buried cable.
If temperatures in or around the seal area reach a
predetermined level, the heat-sensitive insulating
material that separates the current-conducting wires
melts bringing the wires together at the point of
overheat. This condition pinpoints the exact
location of the fire on the fire control panel, and
instantaneously sounding the alarm and releasing the
foam suppressant.
To allow for changes in floating roof elevation, the
cable connecting the Linear Heat Detector with the
control panel is coiled inside a tube on the
floating roof. As the roof drops lower, the cable
uncoils. As the roof rises, the cable folds back
into the tube.
all systems protecting Amoco's tanks are complete
24VDC closed circuit, electrically supervised,
zone-annunciated fire alarm systems that include
power supplies, alarm initiating and
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indicating devices,
foam release controls, and all accessories required
to meet requirements of National Fire Protection
Association Series 72 Standards. A control panel
Annunciator is equipped with zone lights that
indicate where a fire is located.
Standby batteries supply system power in the event
of power failure and are designed to operate the
entire system, including supervision, for a minimum
of 24 hours. All functions automatically switch back
to regular power when power is restored.
The heat detection systems at Amoco adapt easily to
either retrofit or new installations in both
internal and external floating roof tanks.
In Addition to early warning of lightning caused
fires in tank seal areas, the systems can also be
used to warn of overheating in the motor and shaft
of mixing blades.
Click to enlarge
McLemore reports that the system
worked flawlessly when lightning struck the tank
farm.
"The automatic detection systems we have on our
tanks provide protection by detecting fire in its
earliest stages and automatically activating
suppression systems. On that January morning when
lighting struck, only a minimal of foam was required
to extinguish the blaze, and only minor repairs were
necessary to the damaged seal. The system not only
saved us from what could have been serious financial
loss but also avoided possibly disastrous
environmental damage." |
