A Safer Alternative to the Rainbow Demonstration

While serious accidents causing catastrophic injury in high school science activities are rare, when they occur their human toll can be devastating.  This post examines one potentially dangerous demo, its hazards and suggestions for safer alternatives.

The Rainbow Flame Demonstration:

Several of the most serious science accidents have resulted from the combustion of flammable liquids in teacher demonstrations like the rainbow flame demonstration.  In this demo, metals salts are heated in a ceramic dish containing burning methanol.  The flame colour observed is characteristic of the metal.  Click on this link for an example of how this demo is sometimes done. Please note that the procedure used in this video, in our opinion, is unsafe, inappropriate for students of any age and NOT recommended for teachers.

The Hazard:

Methanol vapours are extremely flammable. Furthermore, since the density of methanol is greater than that or air, methanol vapour can flow invisibly across surfaces like the demonstration desk and onto the floor towards unsuspecting observers. A flame, spark or even a hot surface can supply sufficient energy to ignite the vapour and create a sudden flash fire. The situation can be even more catastrophic if a nearby open container of methanol is present.

The Safer (and Better) Way: 

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