By Kim Smiley
A fire in a DC Metro tunnel early on March 14, 2016 caused delays on three subway lines and significant disruption to both the morning and evening commutes. There were no injuries, but the similarities between this incident and the deadly smoke incident on January 12, 2015 (see our previous blog on this incident) led officials to order a 24-hour shutdown of the entire Metro system for inspections and repairs.
The investigation into the Metro fire is still ongoing, but the information that is known can be used to build an initial Cause Map. A Cause Map is built by asking “why” questions and visually laying out all the causes that contributed to an incident. Cause Mapping an issue can identify areas where it may be useful to dig into more detail to fully understand a problem and can help develop effective solutions.
So why was there a fire in the Metro tunnel? Investigators have not released details about the exact cause, but have stated that the fire was caused by issues with a jumper cable. Jumper cables are used in the Metro system to bridge gaps in the third rail, essentially functioning as extension cords. The Metro system uses gaps in the third rail to create safer entry and exit spaces for both workers and passengers because of the potential danger of contact with the electrified third rail. The third rail carries 750 volts of electricity used to power Metro trains and could cause serious injury or even death if accidently touched.
The jumper cables also carry high voltage and fires and/or smoke can occur if one malfunctions. Investigators have not confirmed the exact issue that lead to this fire, but insulation failures have been identified in other locations and is a possible cause of the fire. (Possible causes can be added to the Cause Map with a “?” to indicate that more evidence is needed.)
One of the things that is always important to consider when investigating an incident is the frequency of occurrence of similar issues. The scope of the investigation and possible solutions considered will likely be different if it was the 20th time an incident has occurred rather than the first. In this case, the fire was similar to another incident in January 2015 that caused a passenger death. Having a second incident occur so soon after the first naturally raised questions about whether there were more unidentified issues with jumper cables. The Metro system uses approximately 600 jumper cables and all were inspected during the day-long shutdown. Twenty-six issues were identified and repaired. Three locations had damage severe enough that Metro would have immediately stopped running trains through them if the extent of the damage had been known.
The General Manger of the DC Metro system, Paul J. Wiedefeld, is relatively new to his position and has been both praised and criticized for the shutdown. Trying to implement solutions and reduce risk is always a balancing act between costs and benefits. Was the cost of a full-day shutdown and inspections of all jumper cables worth the benefit of knowing that the cable jumpers have all been inspected and repaired? At the end of the day, it’s a judgement call, but I personally would be more comfortable riding the Metro with my children now.