RESEARCH AND DEVELOPMENT
Test #03-003, Advanced Fire and Smoke Sensor System (AFSSS) in DCETF/DCT Phase 2
DAMAGE CONTROL ENGINEERING TEST FACILITY
ADVANCED FIRE AND SMOKE SENSOR SYSTEM (AFSSS)
INTRODUCTION: An Advanced Fire and Smoke Sensor System (AFSSS), which is a (Simplex Corporation) Commercial Off The Shelf (COTS) individually-addressable fire detection system, was installed at the Damage Control Trainer (DCT) and the Damage Control Engineering Test Facility (DCETF) at the Naval Reserve Center in Baltimore, Maryland in April, 2001. The system consists of 10 photoelectric smoke sensors, 1 heat sensor, 4 flood detectors, and 2 door switches (located throughout the DCT and DCETF), all powered and monitored by an alarm panel (located in Damage Control Central (DCC)). The alarm panel also sends all pertinent monitoring and alarm information to a user-friendly color graphic display (called Graphical Command Center (GCC)) which can be located in either DCC, Repair 2, or the Ops Control Room).
Photoelectric smoke sensor – Photoelectric smoke sensors (see photo below) provide a fire alarm indication upon detection of smoke. In general, photoelectric smoke sensors are very proficient in detecting smoldering fires, but tend to be slightly more sluggish in detecting flaming fires (Ionization smoke sensors, which were not used in this installation, are very proficient in detecting flaming fires, but tend to be more sluggish in detecting smoldering fires). In addition, photoelectric smoke sensors respond well to fires producing white or gray smoke, but can be sluggish in certain fires producing black smoke.
All of the photoelectric smoke sensors currently installed are set to alarm when the amount of smoke exceeds 2.0 % obscuration per foot (similar to the amount of smoke required to alarm a household smoke detector). This alarm threshold can be raised (made less sensitive) or lowered (made more sensitive) at the alarm panel or color graphic display. If false alarms due to nuisance sources of smoke or airborne particles become a problem for specific smoke sensors, an alarm verification feature can be enabled for those specific sensors which helps to minimize their false alarms without significantly delaying their ability to detect fires.
In addition to providing a fire alarm indication at a set smoke threshold, these photoelectric smoke sensors can be interrogated from the alarm panel or the color graphic display and can provide a measurement of the amount of smoke at the sensor, whether it is in an alarm state or not.
Heat sensor – Heat sensors (see photo below) provide a fire alarm indication when the temperature at the sensor exceeds the sensor’s alarm threshold temperature or when the rate of temperature rise at the sensor exceeds the sensor’s rate of temperature rise alarm threshold. The heat sensor is currently set to alarm at 135 degrees Fahrenheit. A rate of temperature rise threshold can also be set to alarm when the rate of temperature rise reaches or exceeds either 15 or 20 degrees Fahrenheit per minute. For the heat sensor installed, no rate of rise alarm threshold was set, since the normal initialization of heat for the facility on a cold day might exceed the rate of rise threshold, thus providing unwanted nuisance alarms. In addition to providing a fire alarm indication at a set temperature (or, if chosen, a rate of temperature rise) threshold, these heat sensors can be interrogated from the alarm panel or the color graphic display and can provide a measurement of the actual temperature at the sensor, whether it is in an alarm state or not. (Note: this measurement of actual temperature is limited by software to a maximum of 180 degrees Fahrenheit. Thus, a temperature reading of 162 degrees Fahrenheit means that that is the actual temperature at the sensor, whereas a temperature reading of 180 degrees Fahrenheit means that the actual temperature at the sensor is either 180 degrees Fahrenheit or (probably) a higher temperature.)
Sensor base – All smokes and heat sensors mount on a universal sensor base. This base contains dipswitches that are set so that each sensor on the cabling loop has a unique address. These sensor bases with their unique addresses communicate with the alarm panel so that fire alarms or troubles from each sensor can be individually identified at the alarm panel or the color graphic display. In addition, the base contains a red LED that blinks when the sensor is powered and operating, but glows steady when the sensor is in an alarm state. Once alarmed, the red LED on the sensor base will latch (stay steadily energized) until a "System Reset" is accomplished at the alarm panel or the color graphic display. After that reset, if the temperature or smoke level at the sensor has subsided below the sensor's alarm threshold, then the system will clear the fire alarm and the red LED on the sensor will return to its blinking/normal status. If the temperature or smoke level at the sensor has not subsided below the sensor's alarm threshold, then the system will not clear the fire alarm and the red LED on the sensor will continue to glow steadily. Finally, these sensor bases also have an area marked with the raised phrase: "Test." A large magnet can be held against this "Test" area on the bases of either the heat or smoke sensors to cause an alarm at the panel and the color graphic display. This allows for a simple test of the sensor base, without the need to generate actual smoke or heat at the sensor.
CAUTION: Smoke and heat sensors and their bases are NEITHER waterproof nor splash-proof. While isolators (explained later) will protect other (upstream or downstream) sensors from short circuits caused by water damage, water sprayed against a sensor can damage the smoke or heat sensor head and/or the base. Red plastic covers have been temporarily placed on the smoke sensor heads to help shield (but not fully protect) the sensors from water spray during flooding exercises. In order to detect smoke, these red plastic covers must obviously be removed. If water spray is later expected, these red plastic covers should again be temporarily installed to help protect the sensors. In addition, plastic shields have been installed around smoke sensors #5, 12, 14, and 17 to help shield the sensors from water spray. These plastic shields might delay the smoke from entering the sensor, which would delay the sensor's alarm.
Individually Addressable Module (IAM) – While the smoke and heat sensors mentioned above are all mounted on universal sensor bases that are wired to and communicate (directly) with the alarm panel, the flood detectors and door switches need an Individually Addressable Module (IAM) to communicate with the alarm panel. This IAM contains a dipswitch that is set so that each flood detector or door switch has a unique address. These unique addresses allow the IAM to communicate with the alarm panel so that alarms or troubles for each IAM (i.e., flood detector or door switch) can be individually identified at the alarm panel or the color graphic display.
Flood switches - These are standard flood switches (see photo below) that are used on Navy ships. They are third party devices that are integrated into AFSSS via IAMs. Flood switches are simply floats that rise with rising water to close a switch, thereby providing a "Priority 2" alarm indication on the alarm panel and color graphic display. Note: Since the flood switches do not indicate a fire, they do not provide a "fire alarm" indication at the alarm panel and color graphic display. Instead, they provide a "Priority 2" alarm indication. Flood switches are mounted 2 to 4 inches above the deck and, thus, when in alarm, indicate that there is at least 2 to 4 inches of water in the space. Flooding Priority 2 alarm indications will latch at the alarm panel and color graphic display; that is, even if the water subsequently subsides below the flood switch, the Priority 2 alarm indication will not automatically reset until an operator flips down the small hinged "Operational Interface Panel" flap on the alarm panel and pushes (on the left side) the top button on the "Control" keys to reset all of the flood switches (assuming the water has subsided to below the flood switches). Alternately, the operator can click on the "Alarm Reset" box of the color graphic display and then click on the "Priority 2" alarm reset box to reset flood switches.
Door switches - These are standard COTS door switches, similar to ones used in residential homes, to supervise the status (i.e., open or closed, but not the degree of dogging) of a door. They are third party devices that are integrated into AFSSS via IAMs. The magnetic part of the door switch is mounted on the door; the other part, containing the normally-closed relay, is mounted on the bulkhead. When the door is closed, the magnet is located approximately one-half inch away from the relay and will hold the normally-closed relay open, which is the "normal" state of the door. When the door is opened, the magnet will swing away with the door and the relay will close, providing a "Supervisory" alarm indication on the alarm panel and the color graphic display. Note: Since the door switches do not indicate fire or flood, they do not provide a "fire alarm" or Priority 2" alarm indication at the alarm panel and color graphic display. Instead, they supervise the real-time status of the door and thus provide a "Supervisory" alarm indication for an open door. Supervisory alarm indications will NOT latch at the alarm panel and color graphic display; that is, the real-time indication of the status of the door will be given as the door is opened or closed, and no operator resets are required.
Isolators – These devices are located after every few sensors on the sensor (power and monitoring) cable “loop,” which begins and ends at the alarm panel. If a short occurs between the two conductors on the sensor loop cable, these isolators will isolate that short to only those sensors between the isolators. Thus, only those sensors between the two isolators containing the short will be rendered inoperative (until the short location is found and repaired). All sensors located beyond the two isolators containing the short will remain operative. Of course, the alarm panel and color graphic display will provide a trouble signal, alerting the operator that several sensors are missing from (i.e., not reporting to) the system.
Alarm panel – Powers and monitors all sensors and detectors on the sensor loop. Displays all sensor alarm and trouble conditions via energized LEDs, audible horns, and in an alphanumeric text display containing specific information about the sensor(s) in alarm or trouble. Also contains a back up battery for full operation in the event all primary power is lost. Contains key pads for operation of the system, including keys to acknowledge alarms and troubles (silencing the audible alarms), reset the system (after alarms are cleared), access chronological logs of all alarms and troubles, and obtain detailed information about specific sensors (e.g., current temperature or smoke level at the sensor, highest temperature or smoke level attained at the sensor, alarm threshold for the sensor, etc.).
Color graphic display (Graphical Command Center (GCC)) – Monitors all sensors and detectors on the sensor loop, similar to the alarm panel, but in a much more user friendly color graphic display. Displays (see photo below) all sensor alarm and trouble conditions via red and yellow “boxes” that appear, respectively, in addition to audible alarms. Displays specific information about the sensors, including current temperature or smoke levels at the sensor, highest temperature or smoke level attained at the sensor, and alarm threshold for the sensor. Allows operator to acknowledge and reset all alarms and troubles. Provides chronological logs of all alarms and troubles.