The NTSB said a preliminary review of Con Edison records indicated that an abnormal concentration of gas had been detected shortly after an explosion leveled two East Harlem buildings. Credit: Getty Images
Soon after two East Harlem buildings were destroyed in a fatal explosion Wednesday, Con Edison found an abnormal concentration of natural gas below ground near the scene, a preliminary investigation by the National Transportation Safety Board found.
Board member Robert Sumwalt said Friday that a review of Con Edison records indicated a "bar test" taken after the blast found concentrations of natural gas up to 20 percent in some areas.
During the test, Con Edison drilled at least 50 holes 18 to 24 inches deep and probed for natural gas. At least five of those tests had a gas concentration from about 5 to 20 percent.
"Normally, the soil in New York City 18 to 24 inches down into the ground would have zero concentration of natural gas, so the fact that in at least five of the holes, the concentration of gas ranged between 5 and 20 percent, that tells us that's a pretty good concentration of natural gas in that area," Sumwalt said. "That further leads to the hypothesis that this may be a natural gas leak."
Sumwalt said that pressure tests are still needed to check if a leak from a gas pipeline sparked the explosion. The tests will help determine the location of a possible leak and will be conducted by Con Edison with NTSB supervision in the next 24 to 48 hours, once the fire department deems the area safe.
The explosion and building collapse killed eight people and injured more than 60 others.
Several residents described a lingering smell of gas in the area before the blast. But Con Edison said Thursday that they received no recent complaints apart from a local resident at 9:13 a.m., about 18 minutes before the explosion.
The caller described smelling gas the night before during the report, but did not alert authorities until the next morning. Partially because only one call had been received, Con Edison did not alert the fire department of the reported leak and company crews arrived about 20 minutes after the call, at 9:40 a.m.
The NTSB investigation will continue with document review and collection. Interviews with first responders, Con Edison employees and witnesses will be conducted in the next few days.
Witnesses can contact the NTSB about what they have seen or smelled at email@example.com.