Correct. When I was in college (Boston) we'd fill small weather balloons with a mixture of air and natural gas. We'd take a balloon to the roof of the apartment building (at night of course), tie a fuse on it, and let it go. Had one explode enroute to the Prudential Building. Another one blew up about 300 ft over a neighborhood in Roxbury.
Guess we could get into big trouble if we did that today.
That must have bee fun sending those balloons up and watching them go “poof” like mini Hindenburgs.
When I was a kid, I saw plans for making illuminated hot air balloons from laundry bags with small birthday candles held by plastic straws. I was always afraid to try it because I figured I would start a forest fire.