A test tube explosion!

An accident at a school lab in the US indicates the dangers of chemicals. A news article mentions the following: "It was a simple science experiment designed to create a small combustion in a glass container and teach high schoolers about chemical reactions.A mixture of three chemicals -- potassium chlorate, manganese dioxide and glycerin -- and a dash of sugar heated over a Bunsen burner in a test tube were supposed to cause a pop and a puff of smoke, demonstrating an exothermic reaction to a class of Grade 11 students at F.J. Brennan Catholic high school.But something went wrong Tuesday morning. The test tube exploded, launching shards of glass across the science lab and injuring teacher Steve Pellarin and three students.No one was seriously hurt, but Pellarin sustained cuts to his face and hands. The students had minor lacerations, and no one sustained any chemical burns, said Windsor-Essex Catholic District School Board spokeswoman Jill Braido".
Read the article in this link.
Wikepedia mentions the following:
"Potassium chlorate is often used in high school and college laboratories to generate oxygen gas[citation needed]; it is a far cheaper source than a pressurized or cryogenic oxygen tank. Potassium chlorate will readily decompose if heated in contact with a catalyst, typically manganese (IV) dioxide (MnO2). Thus, it may be simply placed in a test tube and heated over a burner. If the test tube is equipped with a one-holed stopper and hose, warm oxygen can be drawn off. The reaction is as follows:
2KClO3(s) + heat → 3O2(g) + 2KCl(s)
The safe performance of this reaction requires very pure reagents and careful temperature control. Molten potassium chlorate is an extremely powerful oxidizer and will spontaneously react with many common materials. Explosions have resulted from liquid chlorates spattering into the latex or PVC tubes of oxygen generators, as well as from contact between chlorates and hydrocarbon sealing greases. Impurities in potassium chlorate itself can also cause problems. When working with a new batch of potassium chlorate, it is advisable to take a small sample (~ 1 gram) and heat it strongly on an open glass plate. Contamination may cause this small quantity to explode, indicating that the chlorate should be discarded".
For folks operating chemical reactors in the industry, know what you are dealing with!