I am a consultant and work for a number of data centers. Disasters are my best marketing tool (i.e. Data Center Managers, CIOs etc call me after they have a problem and realize that they need some professional help).
The most common elements: Lack of understaning, Poor Maintenance and stupid stuff.
The data center infrastructure must be thought of a system. Too many managers think that I have my electrician and my hvac service company, and the ups vendor comes twice a year, etc....
This is a recepe for disaster.
It's very common to see power systems loaded such that a single failure will cause a cascading failure.
This is truly a case where what you don't know will bite you.
The other thing is poor design/construction: water lines above data center, lack of separation between data center and non-data center functions, etc.
Ken Baudry
www.kjbaudry.com