Field of Science

Easter fires: Rainbow demonstration rises again

It the the custom in many Christian denominations to light a Pascal fire at their Easter rites. For Catholics, this is done after sunset on Saturday night. The fire is kindled outside the church and in many traditions a large candle and/or many candles are lit from the flames. Lighting the fire is often problematic, it should be visible to the people assembled, but confined to prevent hazards. It can be smoky.  This weekend I became aware of an alternative to the traditional wood fire, replacing it with a rock salt and alcohol mixture.  This sounds like a great idea.  It is smoke free — you could do it inside — and that as these sets of directions suggest, you can add other salts to make beautiful colors in the flames.  It is, in fact, a TERRIBLE idea.

This is just a version of a chemistry demonstration, often called the rainbow demonstration, that is so dangerous it should not be done. Period. The rainbow demonstration has led to many serious burn injuries in onlookers and teachers, the Washington Post has an overview here.  Under certain circumstances it can produce a flame jet. See this notice from the American Chemical Society, and this longer article about the hazards at the Journal of Chemical Education.

The dangers is that vapors from the alcohol can travel out of the container or the salt/alcohol mixture and along the ground, then ignite in a ribbon of flame. I note that the National Altar Guild
link with instructions recognizes the vapors might escape, but doesn't seem to realize the hazard this presents.

Some years back the American Chemical Society urged chemists to contact their local high school chemistry teachers about the rainbow demonstration to be sure the warnings reached them. It might be time to encourage chemists to reach out to their local churches to be sure they are aware as well.