Sprinkler Line above a data rack?

[zbang]

What's a fire sprinkler doing in data room.

Probably nothing, might be satisfying a regulation (like that second ground rod).

Electrical fires should not be doused with water . . . .not even with wet chemicals.
Most common is CO2 to displace oxygen.

Yes, and....
I don't think the OP, or the rest of us, have been talking about an engineered "data room"; more like a closet where someone stuffed a comm cabinet.

but the first few seconds to half a minute are something rare and special

That's being polite about it (same goes for the contents of an old hot-water heating system).