Guidelines for Emergency Ventilation Smoke Control in Roadway Tunnels (2017)

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64 Tunnel Fire Detection and Warning Systems The most common tunnel fire detection principles are based on the parameters determined by the fire and could be applied individually or in combination: • Smoke and gases, • Heat, and • Flames (radiation). There are a range of methods available to detect fire and smoke within road tunnels including: linear (line-type) heat detection (LHD); CCTV video image smoke detection; flame detection; smoke and heat detectors; spot-type heat detec- tors; and smoke and gases detection. The selection of the type of fire detection system(s) should be made depending on the fire safety goals/objectives and the overall fire safety strategy, which includes notifying occupants to allow for safe evacu- ation, modifying tunnel operations, initiating fire life safety systems operations, and notifying emergency responders. Linear (Line-Type) Heat Detection There are several types of line-type heat detectors used today. The three main types are: Analog (Integrating) Linear Heat Detectors; Digital Linear Heat Detectors; and Fiber Optic Linear Heat Detectors. • Analog (Integrating Heat Detectors) systems incorporate a multilayer cable. It consists of a core conductor covered by a temperature sensitive semiconductor with an outer conductor. The inner and outer wires are connected to a control panel that monitors the resistance of the semicon- ductor. A temperature rise in the cable causes a reduction in the conductor’s resistance, and detection occurs when the monitored resistance reaches a pre-determined setting. • Digital Linear Heat Detectors consist of two polymer insu- lated conductors. The insulation melts at a set tempera- ture. Detection in this system occurs when the insulation melts which allows the conductors to make contact with each other. In some systems, the control panel connected to the sensing element is able to determine the distance where the conductors made contact and determine the location of the fire. • Fiber Optic Linear Heat Detectors consist of a control panel and quartz optical fibers. The control unit houses a laser that sends a beam through the fiber optic cable. These systems provide detection using the Raman-Effect which senses temperature changes by evaluating the amount of light scattered. The rate of raise of temperature is adjust- able and defines sensitivity. One of the main advantages of this type of detection is that the cable is suitable for harsh environments. In addition, because these products are essentially a two conductor cable, there is flexibility in the installation: patterns can be used to meet spacing requirements and the cable can be routed around obstructions. Many of these products can determine the approximate location of the fire based on either a reduction in the conductor’s resistance or light scattered for fiber optic systems. Some manufacturers of these systems also claim a useful system life of about 30 years. Recent tests demonstrated that linear heat detectors can detect shielded and unshielded tunnel fires with desired accuracy within 90 seconds or faster. Their sensitivity can be adjusted for no nuisance alarms and fast detection. Due to such advantages and relative simplicity, they are currently the most commonly used devices for fire detection in road tunnels. It is important to acknowledge that most of these modern devices have a proven reliable history in road tunnel applications. There are disadvantages to using linear heat detectors. Their performance can be impacted by tunnel airflow which cools down air temperature, moves heat along the tunnel, and reduces the rate of rise of the air temperature. Some models require replacement of the heat detection cable after a fire event. With tunnels typically being extremely large, long A p p e n d i x A

65 open spaces, providing detection using linear heat detection can require a large amount of cabling. If the objective is to detect a fire from a moving vehicle, such as a tractor-trailer, the design will need to assess whether the cable will be heated sufficiently as the vehicle moves to activate the alarm. It should be noted that some old types of linear heat detection systems failed to detect large size tunnel fires, or detected them too late, or generated numerous nuisance alarms which required their deactivation in the past. There are known past bus tun- nel fire events in tunnels furnished with a linear heat detection system which were unable to detect the fire. In addition to airflow, considerations should be given to shielded fires initi- ated inside or under vehicles or under vehicle’s hood, which makes rapid heat detection at the tunnel ceiling level difficult. Flame Detectors Flame detectors are fixed devices that are capable of sensing fire by the amount of radiant energy that is emitted. Detec- tors in this category include UV, IR, combination UVIR, or multiple wavelength IR. Flame detection systems have a number of advantages. These systems typically work well in and are suited for harsh environments such as those found in tunnels. Some of the more challenging fires in road tunnels involve combustible and flammable liquid. Flame detectors are well suited for detecting these types of fires. These devices are also capable of detecting fire signatures that include a range of varying wave- lengths, which provides design flexibility when developing the system. The latest IR detectors are equipped with a video camera which allows for verification of the fire location. In recent fire tests, the latest IR devices detected road tunnel fires (both shielded and unshielded) within 60 seconds—faster than any other competing devices and with no nuisance alarms over a testing period of a year [49]. Disadvantages for some old systems are that historically, they have been prone to nuisance alarms caused by interference from arc welding, electrical arcs, lightning, metal grinding, artificial lighting and, in some cases, even sunlight. However, some models have a proven successful operation history of over 20 years in Japan where “fire[s] should be detected in 30 seconds or less for a .5 m/sq. gasoline pool fire with wind speeds of 0–12 m/s” [53]. Newer designs account for these interferences. Like many other systems, detection could be delayed when dealing with shielded fires or smoldering fires with invisible flame. They have a long range for fire detection and as a result, several IR cameras installed in a line could detect the same fire, which could cause confusion in identi- fication of the fire zone. The control system should utilize an algorithm which allows for verification and identification of the proper fire zone. Tunnel airflows may also deflect flames which might also impact the accuracy of detecting the correct fire zone. CCTV Video Image Smoke Detection (VISD) Video detection is a relatively new smoke detection tech- nology that uses real time video images. Through proprietary software, this technology is able to detect fires by analyzing changes such as brightness, contrast, edge content, loss of detail, and motion. Video smoke and heat detection has a number of advan- tages. First, the system cameras can be used for other systems such as traffic control monitors, security, as well as smoke and fire detection. Second, detection is based on real time video images, so each camera can cover a large area. Third, this technology is capable of detecting fires from moving vehicles. Fourth, emergency responders can be provided with real time video information about the fire. The visuals can provide use- ful information such as fire size, fire source, and the location of the fire, which can help operators and responders efficiently react to the incident. Interest in the use of the automatic video image detec- tion (VID) system for road tunnel protection has increased because of its quick response to the fire or security incident, real time video images for use in monitoring events, and in guiding evacuation, rescue and firefighting. Many tunnels are already equipped with VID systems for traffic manage- ments and for security protection. Recent studies conducted by the Fire Protection Research Foundation (FPRF) at NFPA also showed that the VID fire detection system was one of the promising detection technologies for use in road tunnel protection. A new generation of video detection technology is being developed. It includes volume sensors, which look for fire and smoke within the entire observation space of the IP address of the camera. This fundamental advantage results in faster fire and smoke detection and, most importantly, provides a visual picture of the situation to the on-duty operator. Some cam- eras are both UL Listed and Factory Mutual (FM) approved and have flame and smoke detection devices that are also FM approved. The cameras have passed tunnel tests in Canada, New York and China. Use of camera based detection systems may fulfill multiple purposes if the camera image can be used for security, traffic and/or road conditions. The main disadvantage of the CCTV Video Image Smoke Detection is the nuisance alarms at the required sensitivity setting for rapid fire detection. To prevent nuisance alarms, multiple detections/confirmations are required before noti- fication or system activation can occur. This also provides redundancy in case one detector fails. When the alarm condi- tions are met, the event file is created and sent to the remote

66 monitoring station operating the system. The on-duty opera- tor receives the notification of the alarm with live video from the location. It is recommended to test this system and to review listings and approvals with the authorities to determine the suitabil- ity of these devices for specific projects. Because these systems rely on video imaging, some of them may have a difficult time in detecting shielded fires. This is a disadvantage for other systems as well. Note that the Traffic Surveillance and Control System with pan-tilt-zoom (PTZ) CCTV cameras are often used in tun- nels for incident detection. Such systems use image process- ing algorithms to extract pertinent information from CCTV cameras while providing automatic traffic data collection, travel time, and digital video recording capabilities during an incident, which could be used for fire detection purposes. Tunnel operators could use the video images to verify inci- dent information, and to search and validate the conditions of other tunnel subsystems. Such systems cannot be considered as an automatic fire detection system. However, they could be very effective for verification of fire incidents detected by fire detection devices. Spot Detection A number of traditional smoke and heat detection sys- tems were used to detect fires in road tunnels. These systems include the use of projected beam type smoke detectors, duct smoke detectors, and heat detectors. • Duct Smoke Detectors are provided in the tunnel venti- lation ducts. Typically the actual detector is mounted on the outside wall of the duct. The detector is connected to a metallic tube that extends across the duct. The tube has calibrated holes which draw air into the tube that is then directed to the detector. • There are many different types of Heat Detectors. Typi- cally detection is either by an abnormally high temperature or a pre-determined temperature rise. Some heat detec- tors are capable of detecting both temperature and rate of temperature rise. One of the main advantages for these systems is that they are readily available and there is a wide pool of contractors capable of installing these systems, so there is no need to hire a specialized contractor. Compared to the other systems, these systems are relatively inexpensive. Projected Beam Smoke Detectors typically consist of a detector unit with a receiver. A beam of light is sent from the detector to the reflector and if the beam is obstructed, it will cause an alarm. Disadvantages for projected beam and duct mounted detectors are that they are prone to nuisance alarms from diesel exhaust, which is almost always present in road tunnels. They are also rather slow to detect road tunnel fires when the sensitivity is adjusted to eliminate nuisance alarms. Application of two different types of fire detection systems in a tunnel significantly enhances the fire detection capabilities and tunnel fire safety. For example, installation of a linear heat detection system along with IR cameras equipped with CCTV ensures that air cooled fires or shielded fires will be detected in a timely manner and easily verified by the operator. Besides the automatic fire detection systems, fire can also be detected by the tunnel operator using CCTV pan-tilt- zoom cameras installed in tunnels, by tunnel users notifying the operator using manual fire alarm boxes installed at inter- vals of not more than 90 m (300 ft) and at all cross passages and other means of egress, or from tunnel users calling 911 and notifying emergency services about the tunnel fire. Caution is placed when automatic notification is used for the motorists. Tunnel fires may change quickly and can be difficult to predict. Using fire detection systems to decide which direction to exit the motorists and to initiate suppres- sion and ventilation is not foolproof. Directing the escaping motorists in the wrong direction could dramatically increase their risks. However, using automatic detection to close the entrance portal and to warn motorists who are approaching an incident in the tunnel is an accepted practice. Conversely, using traffic controls to encourage motor- ists to continue to drive out of the tunnel may be important for tunnels that utilize longitudinal ventilation. In this case, traffic controls downstream of the portal may be essential to clear the tunnel past the incident and to provide room for motorists so that they can drive out to safety before being overwhelmed by smoke and heat that has been pushed along the tunnel by longitudinal ventilation. These notifications are a key ingredient for the incident command by providing the location, type of incident, condi- tions and size of the incident. In turn, the motorists can be instructed on what to do while emergency responders are en route and tunnel staff initiates emergency procedures. Intelligent evacuation notification technologies are now available. They use electroluminescent lighting technology— an uninterrupted illuminated path to the exits with a continu- ous light source located near the walkway floor, to be visible in a smoky environment, and a multi-directional low-level LED guidance system. The advantage of those technologies is that they can be preprogrammed to direct tunnel users in the direction depending on the ventilation system response. This is especially important to eliminate the wrong direction for evac- uation when complicated tunnel ventilation schemes are used.