Despite wettest year on record, DC Metro insulator fire incidents drop following tunnel waterproofing and new preventive maintenance efforts

Washington Metropolitan Area Transit Authority will end 2018 with the lowest number of insulator-related smoke/fire incidents in years – 66 percent fewer compared to 2016 – despite record rainfall this year. 

Water infiltration in Metro’s tunnels has historically been the leading cause of such incidents, especially along the stretch of the Red Line between Friendship Heights and Medical Center stations. In past years, that 3-mile segment—representing less than 3 percent of the system—accounted for almost half of such incidents. That's because the Red Line’s deep tunnels from Dupont Circle to Medical Center were constructed in the late 1970s and early 1980s, prior to the widespread use of a modern tunnel-waterproofing technique called NATM, the New Austrian Tunneling Method. Many of Metro’s younger tunnels feature NATM.

Tunnels built before NATM were designed to be porous, with the water channeled to a system of drains and pumping stations. Over the years, water caused premature deterioration of metal rail components, brought muck and sediment into the tunnels that degraded the reliability of switches and signals, and created a damp environment where electrical current could easily take a wayward path. The most common electrical problem, known as an “arcing insulator,” would occur when moisture allowed the high-voltage electricity in the third rail to infiltrate an insulator, the structure that holds the third rail in place. When electricity takes an undesired path, the insulator can begin to smoke or burn ("arcing"). The situation is typically resolved as soon as power is turned off; however, crews have to inspect the area and replace the insulator before train service can resume.  

In 2017, following a series of Red Line disruptions, Metro General Manager/CEO Paul J. Wiedefeld directed staff to find a long-term solution for the Red Line water problem, and a pilot using an innovative “curtain grouting” solution was approved. Over several months, working on weekends, crews drilled hundreds of holes in the tunnel ceiling, and then injected a proprietary polymer-based emulsion (PBE) into the holes at high pressure. The grout spreads over the exterior of the tunnel and hardens, giving the structure some protection from unchecked water infiltration. 

Metro attributes Red Line waterproofing to a sharp decline in insulator-related smoke/fire incidents. In 2016, there were 29 insulator fires between Friendship Heights and Medical Center. The number dropped to 17 in 2017. And in 2018, despite being the wettest year on record, there have been three such incidents.

Metro also credits the expanded maintenance hours, approved in mid-2017 by the Metro Board of Directors, with the broader reduction in insulator incidents systemwide. Metro crews now have more time overnight to address tunnel leaks and clean debris from the trackbed. 

In 2016, Metro had 65 insulator fire incidents across the system, dropping to 54 in 2017. In 2018, despite Washington’s wettest year on record, there have been 22.

Metro plans to continue waterproofing other parts of the system in the years ahead. In 2019, Metro plans to address a section of the Red Line near Forest Glen.