It's the law of unintended consequences: things happening that you don't expect from a seemingly unrelated area. This article talks about a data center having leaks from carpet cleaning above. The concrete floor had aged and the carpet cleaners dumped water on the carpet to soak it through and it leaked. I'm not sure how people have data centers below office floors, but I know I've had a number of them at different companies where I've worked.
It goes to show you just how wide and varied the issues that your disaster recovery plans might need to deal with. All types of strange things can happen to your servers and it helps to have an idea of what to do when there is some type of issue. Can you imagine if there weren't sheets of plastic nearby? (see the article)
Not every disaster results in your setting up shop at another location and while many are serious, they can be resolved relatively quickly with good administrators that can think outside the box.
The situation is a good example of why you need to have good communication and information available to people working in the production areas. They should be able to contact someone that can give them access or at least accompany them to closed off areas, like offices, electrical closets, etc. They should also be able to contact someone with the authority to authorize expenditures and changes in policy because of some disaster event.
These types of things will always happen, but they shouldn't compromise your security or the integrity of your systems. Make sure that your disaster plans have accounted for different types of problems. Not specifics like fire, flood, but categories, like an event in that's limited in scope, that affects a whole floor or building, that occurs off hours, that could affect your block or even city, etc.
The one thing that probably applies here that I learned a long time ago is the Boy Scout Motto: Be Prepared.
PS - For those of you in the US, a moment of silence for those lost on 9/11.