After two years of experimenting in secret, the Washington Metropolitan Area Transit Authority will activate sensors in two downtown stations next month and become the first subway in the world that can detect a toxic-chemical release, the Washington Post reported. Federal scientists told the Post that the sensor technology was ready for use in other subway systems and in airports, shopping malls and large, enclosed places. Anthony Policastro, an engineer at Sandai National Laboratory, which is overseeing the project at Washington's Metro System, was quoted by the paper as saying his team would continue to improve the sensors but the basic system worked. The Post reported that work on the $7.5 million sensors began in 1999 and was progressing quietly until Sept. 11, when terrorist attacks made it a priority among lawmakers and administration officials. The sensors, which are approximately the size of a shoebox, continuously suck in air and analyze it. When they detect one of several toxic chemicals, they sound an alarm in Metro's operations control center, the Post said. On Thursday, Congress approved $15 million to expand Metro's sensor program from two to 12 stations.