uming no external shocks, can a fluorescent bulb crack/break, liberating mercury, prior to end of usage?

I have seen small cracks towards the cap end of a tube with no impacts for the cause, more than likley just a defect in the gl tube as it does not happen often or it might have been smacked prior to installation. I have not once seen one just shatter while in the fixture. Also the amount of murcury in a tube is very minimal and does not pose as a health hazard. Most cities let you just throw those away in the regular dumpsters due to that fact.