The explosion happened at around 7:30 p.m. Wednesday at the power plant, which is located on 20th Avenue in Astoria.
Witnesses say there was a plume of smoke, but no fire.
No injuries were reported, but one man was taken to the hospital for observation.
Some of the windows of the 11-story building were blown out.
The power plant is operated by US Power Generating Company.
US Power Gen released a statement Wednesday night: "US Power Generating Company, owner and operator of the Astoria Generating Station (Queens) confirmed that at approximately 7:28 p.m., today, July 27, 2011, the Astoria Generating Station Unit 4 tripped off line due to a tube rupture in the reheat boiler, resulting in window breakage and noticeable shaking of the building. According to John Reese, Senior Vice President for Government Affairs, FDNY was at the scene and there was no fire. The incident caused no injuries, however one employee was taken for medical evaluation.
Astoria Generating Station Unit 4 underwent asbestos abatement in the 1990s when under ConEd ownership. Regardless, precautionary air sampling is being undertaken to confirm no airborne asbestos is present.
The unit will remain out of service for an undetermined amount of time, however, Astoria Generating Company staff and contractors have already begun to assess conditions at Unit 4 in order to develop the scope of work necessary to restore service.
Unit 4 is one of the four Astoria Generating Station units and this incident had no effect on the remaining three units 2, 3 and 5. Units 3 and 5 were also operating at the time of the incident and have continued to operate without interruption. The incident poses no threat to continued electric supply from the remaining units at the Station."
Dozens of calls were made to 911 from people who heard and felt the explosion.
The explosion had no impact on the Con Ed system, which does buy some power from the plant.