Soon, the flame temperature begins to drop because the combustion is less vigorous. The lower temperature slows down the melting and vaporization of the candle wax. Candles onboard the first United States Microgravity Laboratory, launched in June 1992, burned from 45 seconds to about 1 minute before being extinguished because of the dropping temperature and reduction of wax vapor. Combustion studies in microgravity are important to spacecraft safety. Unlike house fires on Earth, you can not run outside of a space station and wait for the fire department to arrive.
Fires have to be extinguished quickly and safely.
To do this it is essential to understand how fires are ignited in microgravity and how they spread. The goal is to make sure that a fire never gets started. In the absence of buoyancy-driven convection, as in microgravity, the supply of oxygen and fuel vapor to the flame is controlled by the much slower process of molecular diffusion. Heat lost to the top of the candle causes the base of the flame to be quenched, and only a portion of the sphere is seen. The diminished supply of oxygen and fuel causes the flame temperature to be lowered to the point that little or no soot forms.