Manhole Monitoring: Underground, Under Pressure, and Underserved?

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By Jamie Moss | 4Q 2019 | IN-5619

New York energy supplier Con Edison is deploying Sentir, an Internet of Things (IoT) system developed by CNIguard and Plextec, to connect and monitor its network of manholes. Underground power cables generate heat, the corrosion of cable insulation is a fire risk, and gas pipes and sewers leak combustible gas. For the sake of ensuring public services and public safety, manholes cannot afford to not be constantly monitored.

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Covering the Covers


In September 2019, utility asset management specialist CNIguard launched a new Internet of Things (IoT) manhole and manhole cover monitoring system called Sentir, which was developed in conjunction with the U.K. design firm Plextec and is being deployed by the New York energy supplier Con Edison, with trials with other as of yet unnamed utility companies said to be ongoing. The system uses embedded sensors to monitor gas levels, salinity, temperature, and humidity, and can detect unusual voltages as well as the presence of electrical arcing. Sentir is placed in the voids beneath manholes to collect data that is then passed to CNIguard’s SensorCore cloud-based analytics platform to identify conditions that could cause dangerous situations. It also allows for notification and protection against unauthorized access, which can result in the theft or vandalism of public infrastructure.

Once processed, the system’s sensor data is routed to a maintenance dashboard on a mobile device for field force workers so that they can attend to any problems. Sentir is being white-labeled by Con Edison as its Structure Observation System (SOS). According to CNIguard, Con Edison manages 267,000 manholes and has deployed 3,600 Sentir monitors so far. The Sentir system is an example of the intelligent combination of stock sensor types to test for specific environmental triggers. The cleverness lies in how the data is interpreted and acted upon, and therein lies the value for the enterprise or municipality deploying the system: a guarantee of quality of service to their own customers, the protection of their physical assets, and the optimization of their maintenance and repair resources.

Unseen Terror


The need to connect manholes stems from what they conceal public access to; namely, electrical cables and equipment and sewer systems carrying potentially dangerous gases. Faulty equipment can cause electrical fires that can in turn ignite any combustible gases that have built up, causing an underground explosion. Such so-called “manhole events” have resulted in lengthy power outages for large numbers of people in dense urban environments. People have also been injured, both directly by flying manhole covers and indirectly by the damage caused to nearby property. Depending on the thickness and diameter, manhole covers weigh between 50-100 kg. Their weight is effective at suppressing signs of underground pressure build-up from air and other gases, but when that resistance is exceeded the result is sudden, violent, and dangerous.

Cities, especially the most densely populated ones, with the oldest and most heavily utilized public infrastructure are among the most vulnerable locations to manhole events. These are also the locations with the most manhole covers and, ergo, the greatest difficulty in regularly monitoring and ensuring their safety. Manhole events can happen anywhere in the world and at any time of the year. In the summer, the en masse use of air conditioning can demand an excessive power supply from underground cables, making them hot enough to ignite any combustible gas present. In the winter, underground power cable insulation can become badly corroded by the salt that is used to melt ice on the road, which then washes down the drains and into the underground system. Once the insulation is compromised on low voltage cables, they can catch fire and cause columns of flame and noxious smoke.

Like lightning strikes, manhole events appear to be rare but in fact happen every day. Similarly, despite how dangerous they are, it is still unusual for people to be hurt. Sometimes, though, manhole events result in lawsuits that cost tens of millions of dollars in compensation. In the United Kingdom, the home market of Plextec, more than 50 flaming/explosive manhole events are reported each year, while in the United States, the home market of Con Edison, as many occur annually in New York alone, in addition to many other minor events. As a preventable incident, which utility companies and public municipalities are responsible for, and with a very rapidly urbanizing global population, there is increasing pressure to connect and monitor manholes. As simple as the task sounds, securing such a large number of assets is not a trivial exercise.

The Cost of Inaction


Systems like Sentir don’t only stop dangerous manhole events from occurring, but also provide advance warning of the need to repair underground power cables or fix gas leaks. Catching these problems early allows the repair and replacement of infrastructure to be prioritized rather than carried out systematically, perhaps not directing efforts where they are most needed at any one time due to a lack of insight. The use of such systems also makes repairs cheaper, as the additional damage caused by a manhole explosion greatly increases the cost of putting things right. A reactive maintenance situation is turned into an active one. While these outcomes may be standard fare for any valid IoT system, connected manholes as a market is buoyed by the facts that there are so many of them worldwide and that ensuring the public is safe from known and preventable dangers is something that can never be defensibly ignored.

Established cities with aging infrastructure and newly developed smart cities are all guaranteed to have tens of thousands of manholes. Even if only some conceal critical and potentially dangerous equipment, they all stand to benefit from being monitored for unauthorized access and tampering. Missing manhole covers, removed by flooding or metal theft, cause fall-in accidents and vehicle crashes. Manhole locks can make legitimate access more difficult, and are not always failsafe or appropriate, so remote monitoring is preferable. Many of the burgeoning IoT connections in China are suspected to be for the sake of connected manhole covers. Cellular module manufacturers in China are now explicitly listing manholes as a typical target application for their Narrowband IoT (NB-IoT) modules in particular.

With the high attention of radio signals underground, Low-Power Wide Area (LPWA) radio technologies seem ideal for the job. The low-cost nature of NB-IoT allows it to affordably scale to secure a large number of stationary assets. Sensor systems that connect and monitor manholes and/or manhole covers may not need to report much data and may only need to activate with the triggering of a specific pre-programmed alarm, which may mean that they never actually need to be used. Yet, for the sake of knowing that everything is operating correctly, and considering the consequences of the alternative, it is increasingly the case that manholes cannot afford to not be constantly monitored. Considering the fact that they are so numerous and so visible, it is ironic that manholes are often one of the least well-protected, and therefore most vulnerable, assets in the utilities sector.


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