Helium Balloon Popping Sounds

My mother had the following experience and I can't quite figure out what was happening. I think static electricity may be involved but that is as far as I get. Her message to me was: "I got a helium filled balloon. I put it in the center of my dining room table and thought it would come down in a week but it kept on staying up there. Two days ago I noticed it had come down a bit so decided to cut it loose from its anchor and , lo and behold, it wouldn't come down. It just stayed there about 3 feet from the ceiling. But now because it was free it started moving around. I just let it go as it seemed to stay in the dining room. Today as I was dicing green onions in my kitchen, there was this terrible loud shot like something big had crashed in the kitchen. Because my refrigerator sometimes makes little banging noises, I thought for sure it was the fridge that had blown up. Then there was another very loud bang and then another but they came from different areas of my kitchen. When I finally looked up, there was my balloon going crazy and every time it touched something, ceiling, fridge, cabinets, it would let out this terrible loud bang, like a shot gun blast. I managed to grab hold of the string and pull it down. I immediately took a scissors and cut it's tip to let the air out and put it into the waste basket. Can anyone explain why it did that?"
- Kevin Gross (age 52)
Goshen, IN, USA

This story is amazing and fun to think about. Don't take our ideas on it too seriously, because we never heard of anything like it. Basically, we suspect you're right.

How could the balloon float stably? That's not too weird, since the air near the ceiling can be a little warmer and less dense than the air near the floor. So the balloon can float at the mid-density height. I suppose that would be particularly likely if there are air-conditioning vents in or near the floor, as in my house.

A colleague (Mike Stone) tells me that it's common for electrically isolated objects to pick up rather large voltages from static charge. (Maybe some sort of ion generation in an air-conditioner filter could play a role here.). So the balloon could pick up static charge.

Then we get to the part where the discharge makes a series of very loud noises. Sparks always make some noise. Maybe having the spark shake the balloon gives it much better coupling to sound waves than you'd get for just a bare spark between rather rigid objects. So these sparks are unusually loud.

If I were you I'd try to reproduce the whole thing, and even try making a video.  If that's possible, then we can consider what might be done to test the idea. (E.g. does a thin conducting polymer coat on the balloon have a big effect, ...) I believe that there's no danger to anyone, so long as the balloon doesn't get sucked into a fan or some such normal problem.

Mike W.

(published on 09/12/2013)