As a side to this I work at a facility that test sprinkler heads before approval.
I was lucky enough to watch them start a 15' x 15' x 1' deep 'pan' of ester (sp?) on fire to demonstrate the effectiveness of the sprinkler heads.
The building they do this in has a 65' inside height and the control room commentator reported that the flames where reaching 45' at 2 minutes in.
By 5 minutes into the test about 25 sprinkler heads where open creating quite a rainfall.
At 8 minutes the flames where close to out but the pan was also close to overflowing with water at that point so a air horn sounded signaling their in house firefighters to snuff the rest with foam.
But even still the effectiveness of the sprinkles could not be argued.
Fires cool when it is under control.