Just broke the upper filter glass on my 26-1K today. I think what happened was that there was a small contact printing frame resting on the top of the box, and it partially covered the fan. The exposure was particularly long, 300 joules with a very dense negative a student had made. The glass shattered while a group of 9th graders was in the same room processing their film. It scared the crap out of them. So...the lesson is, don't block the fan, even just a little. You might have 'shattering' results. Now, to order a new one. Ugh.