More than three billion people are at risk from indoor air pollution because of the heating or cooking fuels they use. Most live in Africa, India and China. They use biomass fuels like wood, crop waste, animal waste or coal. These solid fuels may be the least costly fuels available. But they are also a major cause of health problems and death.

For more than thirty years, the Aprovecho Research Center has been designing cleaner, low-cost cooking stoves for the developing world. Dean Still is the director of the group which is based in the United States. He notes a World Health Organization estimate that more than one and a half million people a year die from breathing smoke from solid fuels.