A sensor system designed to detect a chemical or poison gas attack will be installed at Pennsylvania Station now that transit officials have concluded they are satisfied with similar equipment at Grand Central Terminal.

The Metropolitan Transportation Authority plans to install the "sniffers" in the section of the train station under its control within six to eight months, said Lewis Schiliro, the agency's director of interagency preparedness. The MTA plans to spend $1.6 million on the project.

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Amtrak will install the sniffers in its section of Penn Station, and at stations in Chicago, Philadelphia and Washington, D.C., said spokeswoman Karina Romero.

The MTA's board has also agreed to spend about $2.3 million to upgrade the equipment at Grand Central and maintain both systems.

The system, which continually sucks in air and analyzes it for toxins, was developed after the sarin gas attack in the Tokyo subway in 1995.

Both Penn Station and Grand Central already have radiation monitors and sensors that can detect biological threats.