Why do pcb's (nic's and power supply's) blow?

[cmpelser]

Has anyone got some sort of letter or formal discription of why a certain pcb will blow or pop etc. (esd, power dips,spikes or lightning)
We need to give it to customers for insurance claims etc.
Thanks guys!

[emujo]

No need for a letter, just wait for the key op to say " we had a lightning strike this weekend and now machine wont print" and hand them the bill. Maintenance does not cover abuse, neglect, acts of god etc... That why the buliding is insured. If their adjuster balks at this it may be a good idea to have the bad power suppy/NIC on hand to offer it to him/her for his own testing. Odds are they wont bother due to the cost. EMujo