This has been bugging me for a few months now, and I'm hoping that someone can provide me with an answer. A while ago, my colleague was soldering with an oxy-acetylene torch and paused for a few moments in between jobs, leaving only the pilot light on top of the unit burning. Sitting about 4-5 metres away, I happened to use my air pistol to clean a mechanical component, when he noticed that the pilot light had suddenly increased in length. He shouted and called my attention to it, which led to us speculating as to what might be causing it. The flame wasn't affected laterally - increasing only in length, so we ruled out air disturbance or pressure from sound waves. I also tried banging the bottles, humming at various pitches, shouting and clapping - all to no avail, Eventually I walked across the hall and tried with another air gun about 20 metres away and the result was the same as the original. Noticing that the flame on the pilot light turned from blue to a sooty yellow colour during the moments when the air gun was activated (indicating incomplete combustion), I reasoned that the sound of the escaping air was at a frequency which resonated with the acetylene, causing a disturbance in the mixture of the two gasses. I could be completely (even laughably) wrong, but it'd be great if I could get an answer as to what was causing it and finally set my mind at rest.