A flame arrester is basically a heat exchanger in front of the tubulure. It conducts the heat of flame to some other place (to the liquid and/or the container especially if the container is built from a metal material), thereby extinguishes the flame before getting into the container.
I built a simple flame arrester with a tea strainer in front of the bottle and dumped some drops of denaturated alcohol into the fire. A controlled experiment demonstrated that the flame arrester works and if there is no flame arrester, an explosion is inevitable.
However, I don't think I should use this approach in a real-life situation because I can't know how much flame the arrester could arrest in a real case.
How can I test a proper flame arrester if it is produced correctly?