A wire mesh made of steel is placed directly on top of an unlit Bunsen burner. The Bunsen burner is then lit and produces flames as expected. When the wire mesh is lifted up, the flame continues burning but only above the mesh, not underneath.
How does it work?
As steel is a good conductor of heat, the mesh quickly dissipates the heat of the gas burning above it. This heat is therefore spread out over a large surface area. Because of this, the temperature beneath the mesh is not high enough to ignite the gas from the Bunsen burner.
Mining lamps also work using the same principle. A mesh prevents the ignition and possible explosions that could be caused by a leak of gas.
