important consideration of the Mass Rapid Transit system of Singapore. MRT fire prevention standards are adapted from the guidelines of the American National Fire Prevention Authorities (NFPA), which were established for enhancing fire safety within metro systems. Underground stations and tunnels have smoke extraction and tunnel ventilation fans to expel smoke and supply fresh air in case of a fire. All MRT trains are built to strict safety standards, with materials that are fire-retardant and toxicity-minimising. Trains are also installed with fire and smoke detection systems, as well as two fire extinguishers in each train. Emergency readiness drills are conducted by the LTA to test the operators' responsiveness to fire incidents. Platform screen doors and gates The Singapore Mass Rapid Transit (MRT) was the first rapid transit system in Asia to incorporate glass platform screen doors, in its underground stations in 1987. These platform doors cost S$1 million per platform. Full height PSDs mainly manufactured by Westinghouse are installed at all existing underground MRT and sub-surface stations in Singapore. Future underground MRT stations will also have full-height doors installed upon opening. Half-height platform screen doors mostly manufactured by ST Electronics have been retrofitted into all elevated stations by March 2012 (starting with three elevated MRT stations in 2009), as well as all future elevated MRT stations. There are two series of the full-height platform screen doors in use. The first series, made by Westinghouse, was installed at all underground stations along the North South Line and the East West Line from 1987 to the completion of the initial system in 1990. The second series of PSDs sport a sleeker design, producing less sound when the doors were opened and closed while incorporating more glass. The first station with these doors was Changi Airport MRT station which opened in 2002. All stations in the fully underground North East Line and Circle Line, which opened in 2003 and 2009 respectively, sport these new doors, also made by Westinghouse, although there are slight differences in their designs. The same doors used in the Circle Line also equip the rebuilt North South Line platforms at Bishan MRT station in 2009 following renovations in conjunction with the Circle Line interchange at the station. The Downtown Line features Westinghouse doors of a still-newer design, which is also found in Marina South Pier MRT station which opened in 2014. The Thomson-East Coast Line uses full-height doors by