Lack of awareness of new chemists
A new chemist tried to diazotise aminotetrazole and was entertained by by sparking and deflagration, and despite the observations, continued adding to the stoichiometric value.
The lack of experience is a major problem, but also the lack of awareness and the lack of where to go to find if a hazard exists. The increased safety need in universities often means that the student may never see any real hazardous chemistry.
Webmaster's comment: I had two (small) fires and one well sprayed fume cupboard in just a few years when studying my degree. Those experiments would not be carried out thesedays....