NEW DELHI — In tens of millions of homes in rural India, the kitchen is a cramped space with walls blackened by soot from open fire hearths.

Women spend hours every day in unventilated spaces cooking meals over smoky fires fueled by wood, dung and other biomass, often with small children in tow. The daily routine of inhaling toxic fumes is exacerbated by the long blow pipes that women use to keep cook fires burning.

This everyday scene has deadly consequences. Each year more than 1.5 million people worldwide die prematurely from lung cancer, emphysema, childhood pneumonia and other ailments caused by indoor air pollution — fumes from open cooking fires — according to the World Health Organization. In addition, millions of tons of carbon dioxide and other greenhouse gases are generated every year because about three billion people worldwide rely on open cooking fires.

The easy solution would be to switch to cleaner fuel, like liquefied petroleum gas or kerosene. But these fuels are too expensive for many people in developing countries. Groups like Envirofit, a nonprofit organization based in Colorado, are offering another solution: clean cookstoves.