What causes the pop in the squeaky pop test?

The pop in the squeaky pop test is caused by the rapid expansion of gases when a sample, often containing a small amount of hydrogen, is ignited. When the gas is exposed to a flame, it reacts and combusts, creating a small explosion that produces the characteristic "pop" sound. This test is commonly used to identify the presence of hydrogen gas, as it burns with a distinct noise. The sound is a result of the rapid release of energy during the combustion process.