They are successively ignited with a burner. CH 4 is a flammable gas and requires a certain amount of O 2 to explode.
Explosion is loud.
Prepare students for a shock. Do not use the gas cylinders on your own. In the past they have been left in an unsafe condition by users of room C120. Use displacement of water to measure the volume of gas in the balloons. A 3 L beaker filled with 1 L of water is about the right size.