You don't, adding liquid fuel to stove with a live flame is never recommended.
Related meta post Do we want a post notice for questions where people are using equipment in ways that are clearly incorrect or dangerous?
Believing the stove to be out of fuel, she tried to pour more denatured alcohol into it from a large container that exploded, shooting burning fluid and flames onto her daughter.
“We recreated the accident conditions in a ‘fire lab’ and the results were scary to say the least,” Barrett said. “The most dangerous aspect of denatured alcohol is that you can’t see it burning if you are in daylight conditions. In fact, my client and the rest of her group did not know why she was getting burned for a few seconds because they could not see any flames on her. It was not until the flames from her shirt burning became visible, that they realized that she was ‘on fire.’”
Source; Concord attorney warns of danger of denatured alcohhol
