This is a strange question, but I'm gonna attempt to answer it anyway.
All electrical fires must be extinguished carefully. Especially if they're still live. Fire departments will all recommend the use of a CO2 extinguisher.
In a datacentre environment, however, I'd (But I don't recommend you) do one of two things.
- Hit the EPO (Emergency Power Off) and the fire alarm button.
- Find a CO2 or Halon* extinguisher and attempt to extinguish the fire
- If that doesn't work. Goto 1.
- Unconditional Jump: Run out of Fire Exit.
I'd be more concerned about the protection of the rest of the suite than the expense or damage caused by following their procedure for fires in the building. You're operating as a business, so you've got insurance, both for your hardware, and Public Liability. It'll all be covered by that if you've got a decent insurer.
It'd be better all around to hit the fire alarm and let the professionals deal with it. Electrical fires produce evil acrid choking smoke, often containing horrible toxins, and I sure as hell wouldn't wanna be trying to extinguish it without breathing apparatus.
*Halon is a bit of an odd one. It's a fantastically efficient extinguishing agent, but has a nasty side-effect of destroying the Ozone layer. I've only seen Halon extinguishers in datacentres, and even then, there's a lot of paperwork if you discharge one.
It works by depleting the oxygen in the applied area, and as a result, it'll suffocate the fire, and you at the same time if you linger too long. Again, this kind of lends itself to calling the fire service. Or activating the building's fire supression system.
Don't worry about the expense, that's what insurance is for.
Also.. has this just happened? I can't resist this.
(Disclaimer: I'm an ex fire-cadet, so I've got a pretty good knowledge of fire and it's extinguishing. )