Fire Detection and Alarm Systems Study Notes

FIRE DETECTION AND ALARM SYSTEMS

FIRE AND INTRUSION ALARMS

The WMATA (Washington Metropolitan Area Transit Authority) fire and intrusion alarm systems are specifically designed to detect any abnormal conditions that may arise within the Metrorail system. These abnormal conditions can range from fire, smoke, and hazardous vapors to derailments and unauthorized entries into sensitive, unoccupied, or remote areas of the transit system. It is crucial for Fire/Rescue personnel to be well-acquainted with the location and functionality of these alarm systems, as they have the ability to be triggered to request Fire/Rescue assistance and provide relevant information during emergency operations.

FIRE AND INTRUSION SYSTEM

The fire and intrusion (F&I) system consists of several vital components: the F&I cabinets, the F&I panel, and the fire and intrusion sensors. This system is interfaced with the automatic fare collection equipment and the data transmission system (DTS). Each station is equipped to accommodate up to 24 fire zones and 24 intrusion zones; however, it's common for not all zones to be utilized, and any unused zones are designated as spares.

F&I CABINET

The fire and intrusion cabinet is strategically installed in the communication equipment room of each Metrorail station. These cabinets serve as the central collection points for all fire and intrusion signals received from the various sensors scattered throughout the station. They also provide an interface connecting the F&I panel, DTS, and the automatic fare collection equipment. Each Metrorail station will have at least one F&I cabinet.

F&I PANEL

Located within every station kiosk, the F&I panel is crucial for monitoring alarm conditions and potential sensor malfunctions. Under normal conditions, with no alarms or sensor malfunctions present, the zone indicator is illuminated in white signaling a "normal" state. Conversely, if an activation occurs—whether from a fire or an intrusion sensor—the zone alarm indication will begin to flash red, accompanied by an audio alarm signal. To acknowledge a fire alarm, personnel should depress the "alarm ack" (acknowledge) button, resulting in a steady red illumination of the alarm indication. Pressing the "trouble ack" (acknowledge) indicator will halt the audio alarm. Once the alarm condition is resolved, the system can be returned to normal state by pressing the "reset" push button. An activated malfunction within a detector circuit will lead to the extinguishing of the "normal" indication.

Panel Button Functions

  1. LAMP TEST: This button illuminates all buttons on the panel to ensure proper operation.

  2. MANUAL FIRE ALARM: This button allows a station attendant to manually initiate a fire alarm upon discovering or being informed of a fire.

  3. MANUAL INTRUSION ALARM: A station attendant can utilize this button to send an intrusion alarm if unauthorized entry is noticed or reported.

FIRE ALARM SENSORS

The fire alarm system is equipped with five different types of sensors: two types of ionization detectors, a combination fixed temperature and temperature rate-of-rise detector, a fixed-temperature detector, and water flow switches.

IONIZATION DETECTORS

There are two distinct types of ionization detectors integrated into the fire alarm system. One is designated for sensitive or critical areas, which includes locations such as train control rooms and communication rooms. The second type is installed within the air duct plenums of mechanical equipment rooms.

COMBINATION FIXED-TEMPERATURE AND TEMPERATURE RATE-OF-RISE DETECTORS

These detectors will trigger an alarm if the ambient temperature exceeds 135 degrees Fahrenheit or if there is a rapid temperature increase of more than 15 degrees Fahrenheit within a one-minute timeframe. They are predominantly found in escalator pits, sensitive and critical rooms, as well as in service rooms, hallways, lavatories, and elevators.

FIXED-TEMPERATURE DETECTORS

Designed strictly for fan and vent shafts, these detectors activate when the ambient temperature reaches or exceeds 135 degrees Fahrenheit.

WATER FLOW SWITCHES

Attached to fire sprinkler systems, deluge sprinkler systems, and standpipe systems, these sensors transmit alarms in response to water flow within the system. They come in two forms: one type utilizes a paddle within the piping that moves as water flows through, while the other is a pressure switch that activates due to a drop in pressure upon system activation.

INTRUSION ALARM SENSORS

The intrusion alarm system is composed of magnetic switches, mechanical switches, and wire and foil loops. Fire/Rescue personnel should be mindful that entering the Metrorail system may inadvertently trigger one of these alarm systems. Communicating with the Operations Control Center (OCC) prior to entering the system—or immediately after entry—will enable OCC to respond appropriately to any alarms.

MAGNETIC SENSORS

Two different types of magnetic sensors are utilized within the system. The first type possesses a key override capability, which is meant for use inside doors requiring opening by Metro employees. A push button that operates with a key overrides the regular alarm signal, permitting the door to be opened from within the Metro system. The second type is non-overridable and is typically found on street access hatches, gratings, and doors.

MECHANICAL SENSORS

These are spring-operated limited switches that cannot be overridden, primarily placed on overhead doors to detect the opening of said doors.

WIRE AND FOIL LOOPS

Used in ventilation openings and windows, these sensors employ a strand of wire or a foil circuit that encompasses the opening or window. Should an unauthorized entry be attempted and the wire or foil is cut, this action breaks the circuit and triggers an alarm signal to the OCC.

ALARM RESPONSE

Upon the receipt of any alarm, it is displayed on the F&I panel located within the station kiosk, as well as on a computer screen at OCC. The responsibility of OCC includes contacting Fire/Rescue services for incidents involving fire, smoke, or hazardous atmosphere, and notifying Transit Police regarding intrusion alarms. However, OCC operators do not have the capability to pinpoint the exact location of a fire or intrusion alarm. Emergency Response Maps, which are carried by the Fire/Rescue units and stored in the Kiosk, can be utilized to identify the zones of fire or intrusion alarms. The zone identifiers on these response maps will correspond to those displayed on the Kiosk F&I panel.

FLAMMABLE VAPOR AND GAS DETECTION (FV&G)

FV&G systems are installed in areas where it is likely for flammable gas or vapor to infiltrate the system. The flammable gases and vapors typically encountered near the Metrorail right-of-way include gasoline, liquid propane gas (LPG), and natural gas. Gasoline and LPG are the most probable substances found in this context as their vapors tend to stay near the ground, accumulating in lower-lying areas.

Ventilation shafts lacking a protective raised curb will feature a detection system at the base of the shaft; these detectors are calibrated for the specific type of product anticipated in that area. Right-of-way detection systems are positioned every 800 feet in conjunction with ETS boxes located at right-of-way gates.

For tunnel applications, sensors are situated in the lowest points of tunnels where gas or vapor is likely to accumulate.

Detection System Priority

The priority for detector location is determined by one of the following criteria:

  1. Areas prone to vehicle traffic or accidental spills are likely to pose risks.

  2. Locations where flammable liquefied gas is stored or utilized, or where potential leaks may arise.

Alarm Response for FV&G Systems

An alarm is activated by sensors once ambient vapor concentrations surpass allowable levels. The systems are calibrated such that a warning is triggered when vapor reaches 20% of the lower flammable limit for the specific product. An alarm will sound at 40% of the lower flammable limit, amplifying and being transmitted to the system monitor situated in the communications room serving that particular area. Subsequent to this, the alarm will be relayed to OCC.

RIGHT-OF-WAY INTRUSION DETECTION SYSTEM

In areas where Metro shares its right-of-way with railroads and/or highways, intrusion detection systems are in place to alert OCC if any object breaches the right-of-way. The Intrusion Detection and Warning (IDW) system runs parallel to the Metro right-of-way, with a tilt switch installed on every fourth fence post; if a fence post tilts by more than 30 degrees, it activates an alarm. Additionally, a low-voltage wire runs the full length of the fence, sending an alarm if interrupted. OCC receives alerts for the specific zones designated for monitoring, with these zones typically spanning approximately 2000 feet. Upon receiving an alarm, OCC will establish radio communications with all approaching trains and inform them of the intrusion, advising them to reduce speed to a safe limit that would allow for a complete stop if necessary.