Geothermal energy in the United States Geothermal Data System (NGDS). Through the NGDS, many older paper archives and drill logs that are stored at state geological surveys are now being digitized and made available for free to the public. The underground hot water and steam used to generate geothermal power may contain chemicals that could pollute the air and water if released at the surface. Hydrogen sulfide, which is toxic in high concentrations, is sometimes found in geothermal systems. Newer methods of generating geothermal power separate the hot steam collected underground from the steam used to power turbines, and substantially reduce the risk of releasing air-polluting
London Underground cooling hot air. Conventional brakes on trains rely on friction to slow the train down, transforming kinetic energy into heat. More modern trains feature regenerative braking systems that can feed the energy from braking back into the power supply, minimising heat generation. This has the additional advantage of reducing the amount of brake dust produced by the trains. London Underground cooling In summer, temperatures on parts of the London Underground can become very uncomfortable due to its deep and poorly ventilated tube tunnels: temperatures as high as 47°C (116 °F) were reported in the 2006 European heat wave. Posters may be