Phenyl Azide Solution Erupts During Vacuum Distillation

A Post-Doc was purifying a fluorinated phenyl azide compound via vacuum distillation over a heating/stirring mantle. The resulting explosion caused the ceramic mantle fragments to cut and embed themselves in the experimenter's face. Fortunately, she was not seriously hurt and she was wearing her safety glasses.  

What Can be Done to Prevent this from Occurring Again?

There is no substitute for pre-planning your experiment and to discuss various techniques with your supervisor. Heating mantles are not good choices for vacuum distillation if the materials used are heat sensitive or unstable (such as most azides). This is because it is difficult to regulate precise temperature control with a heating mantle. A better choice would have been to use a hot oil bath or use chromatographic techniques to isolate the substances.

While the Post-Doc was wearing eye protection, the fume hood sash was in the wide-open position. This allowed the fragments to strike her face. If the sash must be open during the experiment, a portable blast shield should be used. If you know that the materials are unstable, safety glasses with a full face shield would be appropriate choices for PPE.