IEC Surge Test / Fast Transient Test

Hope some CR4 friends can help. Ref to IEC / EN 61000-4-5 Test :

1.Can anyone explains the difference between these 2 tests, the cause/origin of these?

2. Is the pulse for this surge test (1.2/50µs into open circuit and 8/20µs into short circuit) a voltage or current pulse ? The last time I read the standard, was a little unclear to me. Some say the surge pulse is in kV, some say is in kA .

3. Most installers of electronic equipment for buildings complain that lightning cause the most trouble to equipment. Some says that , by installing lightning arrestor ( spike) on roof top give more problem, it attract lightning strike ! How true is this ?

4. What is the mechanism for damage caused by lightning strike ? Is it by induction,i.e lightning strike/discharge a hugh current to earth, inducing a surge current in near by Mains supply transmission line , OR by conduction, i.e, lighting strike at or near transmission line, causing the hugh voltage surge in the transmission line and conducted to the rest of system ?

Thank you.