If there's one thing I do not compromise on, it's safety glasses. As soon as my students enter lab, they are required to don their safety glasses. After a few terse reminders early in the semester, they usually catch on and rarely need any reminders.
Through the course of my chemistry career, there have been a number of times I was thankful I was wearing safety glasses. Today was another.
In Organic Chemistry lab today, we were doing the oxidation of cyclohexanol to cyclohexanone using sodium hypochlorite (bleach) and then the oxidation of the ketone to adipic acid using nitric acid.
The nitric acid oxidation of cyclohexanone to adipic acid is done on a small scale. About 1 mL of concentrated nitric acid is used in the reaction. The ketone is added to the reaction, and it is heated in a sand bath for about a minute. One of my students was heating the reaction. She called me over to say it didn't seem to be reacting. The boiling chip was either floating on the surface or stuck to the wall of the tube. I tapped the reaction tube and the boiling chip sank. Suddenly, the reaction fired out of the tube like a 1 mL volcano. Some of the hot nitric acid flying through the air hit me in the face and on the arm. My student was hit on the hand. We both paused for a second and then went to the sink to wash off and neutralize any acid left with sodium bicarbonate.
Hindsight being 20/20, I realize now the sand was very hot and the reaction was probably superheated. The boiling chip sent the boiling into overdrive.
Having hot nitric acid land on bare skin feels like having an exacto knife stuck through to the subcutaneous tissue. It is unpleasant. My burgundy colored shirt was turning white in spots.
As for the safety glasses, if I wasn't wearing them, I am sure to have been in a real world of hurt. Who knows, from serious pain to blindness. I'm pretty sure hot concentrated nitric acid on the cornea is not going to do any good.
The good news is no one was seriously hurt.
The moral of the story safety glasses are NOT optional under any circumstance in a laboratory... even if you are a biochemist. Biochemists are, in my experience, the worst offenders of this policy.
UPDATE: No serious harm done. My face is in good shape. Surprisingly, only one yellowish spot formed and that was gone by today. No scars. I didn't shave today, because I didn't want to irritate the skin. My shirt survived an initial washing, but I'm not expecting it to survive too long. If experience serves me correctly, it's structural integrity has been compromised by the acid catalyzed hydrolysis of the beta-1,4-glycosidic linkages holding the glucose molecules together. Not to mention all of the other possible things boiling concentrated nitric acid can do.
Allow me to repeat the moral of the story. Safety glasses are not optional. I've had students complain about having to wear them when we weren't using anything dangerous. I tell them (and will continue to do so with renewed vigor) at that point it is not about the safety, it is about the habit. I am training my students to be habitual safety glasses wearers. You never know.