The utility initially reported that instrument readings did not indicate any pressure buildup prior to the explosion. There was a broken water main at the bottom of the crater, near the broken steam pipe, but it is not known if this was a cause, or an effect. Runoff from the heavy rain that day, or possibly a water main break, have been suggested as possible triggers. It is a phenomenon that can occur when cold water comes in contact with a hot steam pipe, causing the steam inside to condense into liquid water, resulting in multi-phase flow which can damage piping. Steam hammer was suggested as a possible cause. As a precaution, the utility replaced more than 1600 similar valves throughout the system, but did not find any other clogs. Then, when heavy rains on the day of the event cooled the pipe causing excess condensate to collect in the steam pipe, the valves could not remove it. The report said that excess sealant, previously used to repair a leaking joint, migrated to two steam trap valves used to drain excess condensed water, clogging them. The official report released by the utility company on December 27, 2007, cited a combination of factors, accepting responsibility for deficient repair work done by a contractor that ultimately led to the rupture. Engineers were unable to access the crater to assess the damage until the tow truck was removed on July 22, and the on-site investigation was complicated by the asbestos contamination in the crater. The investigation report was issued on December 18, 2007. A witness reported that the tow truck was lifted 12 feet (4 m) by the escaping steam, higher than a nearby city bus.
The most seriously injured victims were a 23-year-old tow truck driver from Brooklyn, who was scalded over 80 percent of his body by the 400 ☏ (204 ☌) steam and had to be put in a medically induced coma, and his passenger, a 30-year-old woman, who was being driven back to Brooklyn after her car broke down. 45 people were injured, with two injured critically. A 51-year-old New Jersey woman, who worked a block from the site, died of a heart attack suffered while fleeing the disaster area. The escaping steam shook nearby office buildings, causing many occupants to immediately evacuate.
The towering cloud of billowing steam, higher than the nearby 1,047-foot (319 m)-tall Chrysler Building, persisted for at least two hours, leaving a crater about 35 feet (10 m) wide and 15 feet (4 m) deep. The pipe was located at 41st Street and Lexington Avenue, near Grand Central Terminal. local time, near the peak of the evening rush hour, was caused by the failure of a Consolidated Edison 24-inch (0.61 m) underground steam pipe installed in 1924.
The explosion, which occurred just before 6:00 p.m. The utility reported that in 2007, the average age of the steam pipes was 54 years, but some were near 100 years old. It provides steam service to nearly 2,000 customers serving more than 100,000 commercial and residential establishments in Manhattan south of 96th Street. Con Edison is now the largest operator of the New York City steam system, which is the largest commercial steam system in the world with more than 100 miles (160 km) of steam pipe. The New York Steam Company began providing service in lower Manhattan in 1882. A steam pipe explosion at Washington Square in 2000 near the New York University Bobst Library left a 15-foot (4.5 m) crater in the pavement on Washington Square South, scattering debris and leaving traces of asbestos in the air.
The utility eventually pleaded guilty to lying about asbestos contamination from that accident, and paid a $2 million fine. One of the most significant events occurred near Gramercy Park in 1989, killing two Con Edison workers and one bystander, and causing damage of several million U.S. More than 12 similar Con Edison steam pipe explosions have occurred in New York City since 1987.