Manholes are located at strategic locations throughout most municipal water, wastewater, and other underground utility systems. Manholes are designed to provide access to the underground utilities, and therefore they are potential entry points to a system. For example, manholes in water or wastewater systems may provide access to sewer lines or vaults containing on/off or pressure reducing water valves. Because many utilities run underneath other infrastructure (roads, buildings), manholes also provide potential access points to other critical infrastructure as well as water and wastewater assets. In addition, because the portion of the system to which manholes provide entry is primarily located underground, access to a system through a manhole increases the chance that an intruder will not be seen. Therefore, protecting manholes can be a critical component of guarding an entire community.

There are multiple methods for protecting manholes, including preventing unauthorized personnel from physically accessing the manhole, and detecting attempts at unauthorized access to the manhole. Various products for locking manholes have been discussed in the Manhole Locks Product Guide. This Guide will focus on manhole intrusion sensors, which can be used to detect unauthorized entry into a manhole.

A manhole intrusion sensor is a physical security device designed to detect unauthorized access to the utility through a manhole. Monitoring a manhole that provides access to a water or wastewater system can mitigate two distinct types of threats. First, monitoring a manhole may detect access of unauthorized personnel to water or wastewater systems or assets through the manhole. Second, monitoring manholes may also allow the detection the introduction of hazardous substances into the water system.

Several different technologies have been used to develop manhole intrusion sensors, including mechanical systems, magnetic systems, and fiber optic and infrared sensors. Some of these intrusion sensors have been specifically designed for manholes, while others consist of standard, off-the-shelf intrusion sensors that have been implemented in a system specifically designed for application in a manhole.

Mechanical intrusion sensors use mechanical switches or other types of mechanical devices that depend on a physical connection between the manhole cover and the manhole frame, or between other parts of the manhole assembly. For example, STABILOC LLC is investigating connecting various types of intrusion sensor technology, including mechanical switches and fiber optic sensors, to their STABILOC® manhole lock (see the Manhole Locks Product Guide for more information about the STABILOC® manhole lock). Although there may be some minor differences in where the sensor is located within the system, any intrusion sensor tied in with a STABILOC® manhole lock will function in a similar manner. As described in the Manhole Locks Product Guide, the manhole lock is locked in place in the manhole cover, and a specialized plastic cap is placed into the STABILOC®. A radial tab on the cap depresses a plunger that sets the sensor. When the manhole or the STABILOC® is opened or tampered with, the cap is disturbed, tripping the sensor. This generates an alarm signal, which is sent to a central monitoring station through the utility's SCADA system. The STABILOC® also has a microchip embedded in the cap which allows authorized users to access the manhole without setting off the alarm. When maintenance crews arrive to service the manhole, they use a handheld reader to scan the chip and send the information back to the central monitoring location. This information is then used to deactivate the alarm on the sensor so that the manhole can be maintained.

StoneFly Technology, a communications system integrator, has implemented mechanical switches on various water utility assets, including vaults and reservoirs. While they have not yet used mechanical sensors for manhole intrusion detection, they may do so in the future.

Magnetic systems use magnets to detect when a manhole is opened. In these systems, a magnet is attached to the top of the sensor. The magnet creates a continuous magnetic field between the sensor and the manhole lid. When the manhole lid is removed, the magnetic field is disturbed. This sends an alarm signal to the control unit.

CGM Security Solutions' Sentry Sensor was originally designed to monitor shipping containers and other sealed structures; however, it has been used in other applications, including manhole monitoring. It consists of small sensors (approximate dimensions 1-inch by 3-inches) which are installed in the manhole, and a central monitoring unit, which can be located in a central location, such as in a control room or other secure area. The sensor has a magnet located in the top of the unit. This magnet creates a permanent magnetic field with the closed manhole lid. This continuous field is monitored by an internal chip within the sensor. The sensor also has a transponder that continually sends a signal to the central monitoring unit. When the manhole cover is removed, this magnetic field is broken. The chip reads this as a change in the magnetic field, and it sends an alarm signal from the transponder to the central monitoring unit using internal wireless cellular communications.

Fiber optic systems work by detecting changes in signal strength loss ("attenuation") in pulses of light that are sent through a fiber optic cable. The signal is sent from the transmitter/detector and is looped through integrated sensors in a predetermined pattern. The detector is programmed to expect pulses of a certain pattern, and if this signal is disturbed through some physical disturbance of the cable (i.e., disturbance when an intruder attempts to open the manhole), an alarm will be triggered.

The LightLoc™ system (Woven Electronics) is a non-contact system that consists of sensors, which are installed within the manhole approximately ? inch from the bottom of the cover, and a monitoring station located off-site. The sensor and the monitoring station are connected through fiber optic cable. The sensor, which is 1 ?-inches by 4-inches by 7/8-inches, contains an internal fiber optic loop. A magnet is located on one side of the loop, closest to the manhole lid. A spring is attached to the other side of the loop, away from the manhole lid. In the baseline condition when the manhole is closed, the magnet is attracted to the manhole lid. This magnetic force maintains the fiber optic cable in place. When the manhole lid is removed, the magnetic force is released, and the spring pulls the cable away from its resting position. This causes a change in the attenuation of the continuous fiber optic signal that is running through the fiber. This signal is continuously read at the central monitoring station, and so this change is recorded as an alarm at the central monitoring station.

The LightGard intrusion sensor (patent pending, Minatronics Corporation, distributed by World Security Corporation) consists of a LightGard control unit from which a loop of fiber optic cable extends. The detector is mounted on a non-metallic flat surface within 500 feet of the manhole lid (within 400 feet for the wireless application). The loop is extended out underneath the manhole frame, and then it is spliced and reconnected using two half moon-shaped connectors. One connector is mounted on the manhole cover, and the other is mounted adjacent to it on the manhole frame, so that the cable is continuous when the cover is closed. When the system is activated, the detector sends a randomly-pulsed signal which runs through the fiber optic loop. If the cover is opened, the connectors are pulled apart, and the connection between the fibers is broken. This sets off an alarm, which is communicated to a control panel, PLC, SCADA system, or other connected control system.

Pure Technologies is developing the Soundprint® manhole infrared intrusion sensor, which is able to communicate alarms using PureLink communications technology. This system consists of PureLink WMEM-1 (a wireless infrared/ambient light sensor), which is installed on the frame in the interior of the manhole. The sensor transmits an infrared beam across the manway below the manhole lid; this beam is reflected back to the sensor by a reflector installed on the other side of the frame. Physical disturbance of the infrared beam will cause the system to alarm. In addition, the sensor has an ambient light collector, and if the manhole cover is lifted, this sensor will detect a change in ambient light and will alarm.

Stonefly Technology has implemented an off-the-shelf passive infrared motion detector that it has connected to a SCADA system to monitor manhole intrusions. The sensor is positioned near the bottom of the manhole frame and is oriented up, such that its beam is projected onto the manhole lid. When the manhole is opened, or when there is other motion in the manhole cover, the alarm is triggered. The alarm sends a signal to a control unit (typically a standard SCADA system) using StoneFly's wireless technology.

Important features of a manhole intrusion sensor include:

The type of intrusion sensor chosen is important for several reasons. First, the sensor must be able to function in the ambient conditions in the manhole, where it is likely to be uninsulated and exposed to moisture. Second, the sensor must be aligned correctly to function properly. Most sensors merely need to be located near the manhole cover; however, some, such as the LightGard, must be aligned such that the contacts on the manhole cover and the manhole frame physically connect. This may influence the types of sensors that are chosen for these types of systems. For example, StoneFly Technology has opted to use an infrared intrusion sensor in a pressure-reducing valve vault because a magnetic contact switch would have to be re-aligned properly after every entry through the manhole in order for the system to function properly. In contrast, the infrared motion detector does not need to be aligned with the manhole; instead, it senses motion whenever the manhole cover is removed.

Once the manhole cover is removed or otherwise disturbed, the sensor must communicate an alarm. Different systems communicate using different technologies and different communications strategies. For example, some manhole intrusion sensor systems receive continuous signals from the sensors, and when these signals are not received, or when they are different from the norm, it indicates an alarm condition. Other systems operate on the opposite principle and only send signals when there is an alarm. In addition, some systems are linked together such that one signal runs through all of the sensors in a system (the system may encompass individual sensors placed in each of the manholes in a system), whereas other systems are configured such that each unit produces its own signal. Some systems are hardwired (i.e., fiber optics-based systems), while others are wireless. Wireless systems may have limitations in terms of power supplies, communications range, and interference from intervening terrain or other electronic signals. On the other hand, it may be impractical to hardwire some sites with fiber optic cable. Each municipality must evaluate these factors to determine the most appropriate technology for their system.

Power requirements may also factor into decisions on the appropriate manhole intrusion sensor for a given application. Many manholes lack power supplies, and so sensors and communications devices must operate on batteries. If the manhole is remote, changing batteries may be an issue. Fiber optic systems do not require external power sources; however, they may not be ideal for remote locations, because laying fiber optic cable in these locations may be impractical.

There are currently no mechanical sensor systems that have been specially designed for manhole intrusion detection. However, several vendors have incorporated mechanical sensors that report to SCADA systems into manhole protection systems. In these types of applications, the vendor chooses the appropriate type of sensor and then rigs it to communicate with an existing communications system when the sensor is tripped. Therefore, the specific features and attributes of the manhole intrusion detection system will be dependent on the type of sensor and the existing communications system at the manhole.

In keeping with its development for the shipping industry, the Sentry Sensor can be set up so that it records opening transactions in its internal memory. The sensor can store up to 250 transactions at any one time. These transactions can then be read at a later date. This can be done locally or remotely. Alternately, the system can be set up so that it communicates an opening event in real time, using internal wireless cellular communications. This second arrangement is most useful for monitoring for manhole intrusion, because utilities can respond to these intrusions in real time as well. The Sentry Sensor's signal can reach up to two miles, and it is typically connected into the utility's SCADA system. These systems operate at a very low frequency, and they are not prone to interference from other communications. Unlike RFID systems, which require aboveground antennas and can receive interference from other electronic signals, the Sentry Sensor system does not require an antenna, and its low frequency reduces interference. It has its own internal lithium battery with an expected life of approximately 2 ? - 3 years. In addition, the Sentry Sensor software is Windows-based, and so it will be familiar to many users.

Fiber optic systems require physical disturbance of the cable to trigger an alarm. This physical disturbance may be triggered through a physical break in contact within the sensor (LightGard), or by a change in orientation of the fiber (LightLoc). Once the signal is disturbed, the alarm signal must be sent. Alarm notification protocols can be very different in different systems. In the LightLoc system, the system is monitored as an entire whole at the central monitoring location; when an individual sensor is tripped, an abnormal condition is detected in the system and an alarm is triggered. The system's optical time domain reflectometer (OTDR) technology then determines where the alarm occurred based on the changes in the received signal. The LightGard system functions as a series of independent signals, because each individual sensor must be tied into a communications system. Thus, only individual alarms will be recorded in this system. Alarms for these systems are discussed in more detail below.

As described above, the LightLoc system is designed to monitor a system of manholes. Individual sensors are installed in each manhole, and then the entire system is connected through fiber optic cable to a monitoring station, which is usually located at a central location. A continuous pulse is then sent from the monitoring station, through the fiber optic cable looped through the manhole sensors, and then back to the monitoring station. When any individual manhole is breached, the pulse in the fiber optic cable is attenuated, and this is reported as an alarm to the central monitoring station. LightLoc uses OTDR technology, which analyzes the light loss in an optical fiber, to determine the exact location of the intrusion. An OTDR injects a short, intense laser pulse into the optical fiber and measures the backscatter and reflection of light as a function of time. A baseline is established for the system, but if the manhole is opened, this baseline will be disturbed. The reflected light characteristics are analyzed to determine the location of any fiber optic breaks or splice losses. Thus, OTDR technology enables the system to identify the specific location that was accessed, and this information can be communicated to security personnel. Alarm notification options include audible signals, pages, e-mails, etc. The system also records all accesses for authorized purposes in a system log file.

The LightLoc system is very sensitive, and can detect intrusion events as short as 0.7 seconds in length. It has a long range, and can reach 15,000 ft with repeaters. The system is battery powered and does not require an outside power source. LightLoc's Enterprise configuration can monitor up to 40 sensors, while up to 200 individual sensors can be accommodated by the Network configuration.

LightLoc is ISO 9001 certified, and Woven Electronics can provide installation, training, and monitoring for their product.

The LightGard system is a stand-alone application that can be installed separately in each manhole to be monitored. One control box can monitor multiple manholes if the manholes are within the maximum length of the fiber optic loop (500 feet for hardwired applications, 400 feet for wireless applications). In these applications, multiple splices would be made in the loop, and individual connections would be made at each manhole cover. It should be noted that the maximum length of the loop is reduced by 50 feet for each splice/monitoring connection. In this type of application, intrusion/disturbance of any manhole monitored by the system will result in an alarm, and the system will not be able to distinguish specifically where the intrusion occurred.

The LightGard system is also specially designed to withstand applications in a manhole. The fiber optic cable consists of plastic fibers, and thus it is stronger and more durable than standard glass fibers. These individual fibers are also thicker than glass fibers, increasing their durability. This protects the cable from corrosive environments, such as the interior of a manhole. The system can also function in extreme temperature conditions (from below zero to 175?F). The fiber optic pulse generated in the cable is designed for a random pulse rate to reduce the chances that the system could be tapped into and compromised. In addition, because the pulse is random and not continuous, it reduces battery use. The system also has three sensitivity settings that allow the user to define the light attenuation that will register as an alarm; the potential for false alarms is further reduced because the system does not evaluate the amplitude of the light pulse. Thus, the system is robust with respect to vibrations or other factors that may shift the cables. Finally, LightGard is not susceptible to electromagnetic interference. A service indicator light will indicate if the system is not functioning properly (potentially due to excessive lengths of cable, improperly-aligned fiber optic splices, sharp bends in the fiber cable, etc.).

LightGard is available in hardwired and wireless formats. The hardwired format requires a 10-16V DC electrical supply. Its outputs can be connected to any 12 volt exterior monitoring or alarm system. The new wireless format is powered by 2 AA lithium batteries, which have a 4 year lifetime. This system has a 1,000-1,500 foot range and can transmit signals to standard SCADA systems. Unlike the other products discussed in this document, the LightGard is a stand-alone application, and the user must set up individual inputs from each location with a LightGard system so that the specific location of an alarm can be identified.

The LightGard system is easy to install, and it does not require specialized technicians for installation. The vendor indicates that installers can become proficient in system setup requirements in about an hour. Installers can also make the required splices and required connections as required.

Pure Technology Soundprint® manhole intrusion sensor transmits alarms to a PureLink base station located at a central location using a 900 MHz spread-spectrum analog RF transmission. Depending on the distance from each manhole to this central unit, this communication chain may require an intermediate relay unit, which is also supplied by Pure Technologies. The units are powered by lithium batteries which can last 6 months between recharging.

As discussed above, StoneFly Technology, which specializes in communications links for SCADA systems, has integrated off-the-shelf intrusion sensors as inputs into SCADA systems to monitor manhole intrusions. StoneFly determines the appropriate type of intrusion sensor depending on the specific type of application, the power requirements of the sensor vs. power capabilities in the sensor location, and other factors. For example, StoneFly opted to use an infrared intrusion sensor in a pressure-reducing valve vault because a magnetic contact switch would have to be realigned properly after every entry through the manhole in order for the system to function properly. In contrast, an infrared motion detector does not need to be aligned with the manhole; instead, it senses motion whenever the manhole cover is removed. Mechanical switches may be more effective in applications where the cover is hinged and the covers always re-align in the same orientation when they are closed - for example, in vaults with hinged hatches. StoneFly also considers the power requirements for its sensor units and must ensure that systems set up at remote locations with no power can run on batteries.

StoneFly has installed intrusion sensors on several water assets in mountainous areas of rural Utah, using both off-the-shelf infrared sensors and mechanical switches. When the sensors are tripped, alarms are sent to a data logger that is set up within the manhole, vault, or whatever asset is being protected. This data logger can then be set up to call the operator or to store data until it is downloaded. StoneFly uses a 900 MHz RF transmission to communicate the alarm to a central monitoring station (typically a central SCADA system). Depending on the location of this central unit, the system may require repeaters.

An intrusion system can be added to the STABILOC® manhole lock at an additional cost. This cost will be dependent on the type of intrusion sensor chosen. Please contact the manufacturer to determine what intrusion sensors can be installed for a specific application.

CGM Security Solutions' basic Sentry Sensor system, which consists of the central monitoring unit and 1 transponder, sells for approximately $3,200. Additional transponders can be added to the system for approximately $150 apiece.

All LightLoc systems are custom-designed. However, a small system monitoring one location would cost in the neighborhood of $8,000-$15,000. Enterprise systems that can monitor 15-20 locations would be in the $60,000-$100,000 range.

World Security Corporation sells the LightGard alarm package for $350. This includes the LightGard detector, 50m of fiber optic cable, and the specialized attachments for installing the cable in a manhole.

Pure Technologies' infrared sensor system is currently under development. Pricing information will be available from the manufacturer when the product becomes available.