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New environmental technologies in heating, lighting, ventilation and sanitation were also critical to creating taller buildings that were attractive to work in. Central heating could not be easily extended to serve larger buildings; in the 1850s, a system using low-pressure steam and steam-operated fans became adopted in the construction of the later skyscrapers. Many U.S. buildings were lit by gas, but this carried safety risks and was difficult to install in taller buildings. As an alternative, electric lights were installed from 1878 onwards, powered by basement generators. Ventilation was also a challenge, as smoke drifting into offices from the streets and the fumes from the gas lighting made air quality a major health issue. A steam-driven, forced-draft ventilation system was invented in 1860 and became widely used in taller buildings by the 1870s, overcoming much of the problem. Improvements in iron piping permitted running hot and cold water and sanitation facilities to be installed throughout taller buildings for the first time.