> does a bad equipment or a too high signal could break an optical fiber silica
Not likely. To actually damage the fiber, you'd need very high transmit power (several Watt) not common with off-the-shelf transceivers. If you had that kind of equipment you wouldn't be asking that question.
It's more likely that either the fiber installation has some problems (nicked/overbent fiber, bad splices, bad termination) or that there is a problem with the transceivers (wrong type, blinded receiver).
If you add more details to your question we might be able to provide a more detailed answer.
* type and length of fiber (SMF/MMF? OM2/3/4/5?)
* type of termination (SPC/APC?)
* type of patch cables (mode conditioning?)
* types of transceivers (short/long wave? compatible with switches/routers?)
* a bit of history what happened before the failures - firmware updates, new installations, any other changes