NEW YORK—Drilling angled holes rather than vertical holes was one error that led to underground blasting for the Second Avenue subway thrusting debris to street level, according to an internal investigation by the Metropolitan Transportation Authority (MTA).
The blast happened around midday Aug. 21, causing no injuries as rock, smoke, and dust was hurled through the air at the 72nd Street and Second Avenue intersection.
Five windows were damaged at 260 E. 72 St., including at the street-level Kolb Art Gallery and apartments on higher floors.
All work on the new subway line was stopped for five days and blasting is scheduled to begin Sept. 14, and the following week in the shaft where the errant blast occurred.
Usually, when holes are drilled vertically, the “blast energy” focuses horizontally. The angled holes were not approved by the city and had not been properly tested, the report concluded.
These holes were drilled at an angle, sending most of the “blast energy” upward, and causing the shifting of two sections of the steel deck plates, which are there to prevent flying rock from exiting the shaft, according to the MTA’s report.
The steel plates were also not fully anchored, and the steel decking system was not adequate to withhold the upward pressure. The damage was accentuated by an improper blast timing sequence, causing excessive blast force.Corrective actions stemming from the investigation include replacing the “blaster-in-charge,” who has now lost his license, having a superintendent sign off on a pre-blast checklist, and a second licensed blaster checking that each blast is prepared correctly. Blasters get licenses from the city’s Fire Department.
The MTA has also hired an independent company to monitor the contractor’s compliance with blasting standards. An MTA representative said Thursday the added costs for the changes are “negligible.”
The Epoch Times publishes in 35 countries and in 19 languages. Subscribe to our e-newsletter.