Bulkheads & Broken Glass

[Whys]

To my knowledge, I have not broken a sheet of glass due to torq or leverage placed upon a bulkhead, but I am curious. By what manner does it break, when it does?

Can compression force, such as over tightening the bulkhead, crack the glass or does it usually only happen with angled leverage?

Does the use of reefsafe silicone grease help prevent this from happening by eliminating stick-slip when tightening, or does it make disaster more likely by making over tightening easier?

Most important, what does it sound and look like? Will it typically shatter thru to the edge of the glass, or can it create a small hair-line fracture behind the o-ring in a manner that doesn't leak and is not obvious, but can eventually spread out from under the o-ring and start leaking?

I have a particularly delicate bulkhead and heard a strange sound while tightening down an adjoining union. It did not sound obviously like glass, but am not entirely certain. What I know for certain is that nothing is leaking, at the moment.

[Jay180reef]

I generally silicone the water side of the bulkhead (not the rubber gasket side) and hand tighten the nut. No leaks or problems.