Handsomedan:Every now and again you'd hear an explosion in the staff room and upon investigation, you'd find shattered brown glass everywhere, from where a cup had spontaneously exploded - for no apparent reason.
Rubbish US-made "Pyrex" cookware will do that too. In Europe it's still borosilicate glass which was what Pyrex originally was, in the US it's been replaced by cheap tempered glass which will shatter/explode spectacularly when it feels like it.
So if you want quality, avoid the line that has "Made in USA" on it. Or more generally look for an explicit mention of borosilicate glass.