|
Fire
detection in transit stations is an important
consideration for the protection of life and
property. The general environment of a rapid transit
system lends itself to many peculiar and difficult
fire safety problems. Typical underground stations
are multilevel structures with a labyrinth of
passages, shafts and tunnels. Large numbers of
people who move through these subterranean
enclosures and elevated structures compound the life
safety dangers. On an average commuting day, a large
metro station may handle nearly 220,000 passengers,
and during peak daily periods, 2000 passengers a
minute may pass through the station.
Click to enlarge.
Fires within subways and rapid
transit stations consequently have caused great
concern and worldwide attention over the years due
to passengers who must evacuate these areas through
smoke and fire filled track ways and other emergency
exit ways. Almost all of the documented causes of
fires in subways and rapid transit stations were
attributed to mechanical failure of under car
components, electrical short circuits, accumulations
of combustible debris along track way, vent shafts
and escalator running gear, accumulation of oil and
road film under vehicles, combustible materials in
car components, train ways, crossways, and various
hazards associated with the human factor, such as
carelessness, arson, and pranks. The need to detect
overheat and fire at the early stages of development
in this aggressive environment is the key to
reducing large property loss while enhancing life
safety of passengers. The application of linear heat
detection technology within this environment has
many advantages over conventional detection methods
since it may be installed in the truss works,
framing, and machinery areas of escalators where
other types of detection are unsuitable. The
following installation techniques represent typical
applications of linear heat detection cable in areas
of a rapid transit facility.
Escalators
Click to enlarge.
The general construction of
escalators present a unique environment for rapid
fire spread. Totally enclosed framework in areas of
drive gear, chain haulage motors, and a combination
of heavy grease deposits on running and chain rails
covered with dust and cellulose deposits create the
potential for serious fire hazards. The
configuration of the escalator lends itself to a
very rapid fire spread from within the framework due
to the trench effect of the enclosed structure. The
importance of providing a linear heat detection
system on escalators becomes quite evident when one
considers the risk and hazard involved.
Early detection of overheat and fire in escalators
may be accomplished by installing a continuous loop
of linear heat detection (LHD) cable beginning at
the lower machine room of the escalator and along
the steel truss section of the lower platform and
tension carriage gear box. Continue the loop toward
the upper machine room along the inside frame edge
below the skirt board which runs next to the chain
chute. Maintain an adequate clearance from the chain
to prevent contact with the chain mechanism. At the
top end of the escalator, continue loop down to the
machine room area around drum pulley boxes and
controllers then return to the opposite side of the
escalator to the chain chute area framework and down
to the lower machine room where the loop is
terminated. Refer to Dwgs #596922EP and #596012.
Attach LHD cable to frame work with unistrut clips
and rubber grommet to prevent chaffing of cable.
If horizontal fire stops are used inside of
balustrades, install a loop of LHD within the upper
inside portion of the balustrade beneath the
handrail and the handrail drive boxes. If the LHD
system is to compliment a water spray or sprinkler
system, it may be required to configure the
escalator into multiple zones of detection. Refer to
Drawing #5972E for multiple zoning. For escalator
installations, use Protectowire type PHSC-190-EPR
industrial grade LHD cable. |
Passenger Platforms
Click to enlarge.
Passenger platforms may include
trackside waiting areas, ticket booths, concession
areas, and electrical rooms. The primary areas of
concern for overheat and fire detection should focus
along the trackside waiting areas, particularly when
trains are in the station. Install LHD cable beneath
platforms in a continuous loop with a longitudinal
pattern for the full length of the platform and
spaced up to 25 foot intervals between runs. LHD
loop should be installed in close proximity to cable
trays, culverts, or areas with electrical cables
subject to overheat and/or insulation breakdown.
Many areas beneath passenger platforms may not
provide adequate mounting surfaces for the LHD loop.
LHD cable shall be installed using messenger wire
supporting the detector with stainless steel
turnbuckles located between every 250 feet of
messenger wire. A standoff with rubber grommet shall
be placed at 50 foot intervals to additionally
support the LHD cable and messenger wire. Terminate
each zone with an end-of-line resistor within an
IP-65 water-tight enclosure. Attach wire turnbuckles
and eyebolts at no further than 250 feet apart along
the platform area to fixed points. Unwrap the
Protectowire from messenger far enough to form a
loop in the messenger wire. Clamp the loop with a
U-bolt and slip the loop over the turnbuckle until
the messenger wire has only a small amount of sag.
Provide additional support at 50 foot intervals
using Protectowire beam clamp #BC-2.
Tunnels
Click to enlarge.
Railway tunnels contain system power
cables, communication and auxiliary operating
cables, running the full length of the tunnel.
Overheat and fire caused by catenary arcing,
trackside sparks, under car mechanical failures and
electrical short circuits are but a few of the
potentially dangerous sources of fire within this
aggressive environment. The application of linear
heat detection cable in tunnels is the most suitable
method of fire detection in view of its high
reliability, low maintenance, and long monitoring
lengths available.
Click to enlarge.
A continuous loop of Protectowire
type PHSC-190-EPR LHD cable is installed in all
tunnels, cross passages, and ventilation rooms. A
maximum of 3,500 feet (1066 meters) of LHD cable is
installed for each detection zone. Where possible,
detection zones should coincide with tunnel
ventilation zones to provide fan control and
shutdown in the event of fire. The LHD cable is
installed at the apex of the tunnel supported by
messenger wire and must maintain adequate clearance
from overhead conductors, catenary equipment and the
vehicle envelope. Cable and culverts containing
power, telecommunication, and auxiliary cables
should have a loop of LHD cable along the length of
the tray in a sinusoidal pattern in close proximity
to the face of cables in order to maximize the area
of detection. Each level of tray should be
monitored.
Ventilation
Early warning of heat detection plays an important
part in the operation of metro tunnels. During
tunnel emergencies involving fire or the generation
of smoke, the products of combustion produce gasses
which are potentially toxic or incapacitating.
During the fire the intended purposes of emergency
ventilation equipment is to provide control of smoke
mitigation and a means to purge smoke and supply
fresh air to the tunnel.
|
It therefore becomes critical to
control smoke back layering and heat release rates
after the onset of a fire and ventilation fan
control becomes important. Air velocities of at
least 2.5 m/s to 2.95 ms must be maintained to
prevent back layering of smoke.
The time interval between the start of a fire and
fan activation must be minimized because hot smoke
layers typically can spread from 490m to 580m during
the initial 2 minutes of a fire. The early detection
of heat or fire therefore becomes a primary
consideration in tunnel design. Various heat sources
may exist in the tunnel environment that would
require different detection and alarm modes
depending on the severity of the heat rise.
Typically in stations heat increases may be expected
from trains entering the station and the subsequent
expulsion of heat from motors, wheel tracks, or air
conditioning equipment associated with the operation
of the vehicle. These temperatures, while not to a
critical fire stage are treated as a lower-than-fire
mode and should be detected as they represent an
increase above a normal ambient temperature. It
becomes quite obvious that early detection of
overheat or fire and consequently, the early control
of ventilating systems be seriously considered when
designing ventilation for tunnels. Tunnel fire
detection is limited to linear heat detection
technology since the high reliability and long term
use has proven to be acceptable in these aggressive
environments where other types of detection are
unsuitable and have slow response times.
Control Panels
The LHD Control Panel shall be multiple zoned and
configured to accept a maximum of 5,000 feet (1,524
meters) per detection zone. A digital point location
meter, model #PDM-1000 shall bean integral part of
the panel with an automatic scanner to allow
instantaneous notification of the point of alarm. A
Protectowire FS2000 or 2600HD series panel shall be
used and configured to comply with the environment
in NEMA -1, NEMA-12, or NEMA-4 (IP-65) type
enclosures. Detection zones as well as water valve
releasing circuits, supervisory circuits and multi-
output audible circuits are typically configured for
the LHD system to include monitoring escalators,
platforms and tunnels. Where detection zones are
required to operate in hazardous areas,
intrinsically safe barriers are placed in the
control panel for each required zone. Control panels
contain required number of zone alarm relays for
remote annunciation, as well as, a computerized RS
232C output to annunciate alarming zones, distance
to overheat or fire, and systems status. Typical
interface of control panels with RS- 232 C is
connected to central monitoring controls or PLC's
for operator control.
Conclusion
The foregoing is a necessarily brief summation of
linear heat detection technology and its application
in rapid transit and metro facilities. The most
important single criteria in the selection of a
detection system is the ability of the system design
to reliably perform the necessary early warning
functions in an adequate amount of time and
accurately determine the location of the fire.
Adequate amounts of time is addressed not only in
day-to-day needs, but for future needs also.
Obviously, a fire detection system must be properly
designed, installed, inspected, and maintained on a
regular basis. The installation of a fire detection
system does not mean the facility is safe. Fire
safety is maintained only by constant vigilance and
careful pre-planning for the possibilities of
overheat and fire.
A representative users list of Protectowire systems
installed in Metro and Transit facilities:
Bay Area Transit Systems - San Francisco, USA
Amtrak Systems - Philadelphia, Florida, USA
Newark International Airport People Mover –
New Jersey, USA
Shanghai Metro - #1 Line - Shanghai, China
Taipei Metro - Taiwan
PATCO line - Philadelphia-Delaware
Istanbul Metro - Istanbul, Turkey
Mosmetrostroy - Moscow, Russia
Seoul Subway System - Seoul, Korea
LRT-2 Metro - Kuala Lumpur, Malaysia
Guangzhou Metro - Guangzhou, China
Bilbao Metro - Bilbao, Spain
SRT, Singapore Metro - Singapore
LRT Manila - Philippines
|
