answer:I don’t know the answer to your question, but I will be watching the newspapers for news of the explosion. I wouldn’t want to use electrical equipment (such as the ultrasonic humidifier you mention) around atomized gasoline. You’re talking about the same kind of explosive vapor that fuel injectors place into the compression chamber of an internal combustion engine, combine with air and ignite with a spark. In any kind of “room-size” experiment, that could level a house. So be careful, whatever you do. Welcome to Fluther, for now, anyway…