If you wish to detect temperature increases you could use Thermal camera's.
FLIR I believe is leader in that market. Their camera's can detect temperature differences and create alarm contacts based on that. We use them ourself to detect wether our large torches are burning or not.
Just wondering though, wouldn't you rather have your traditional flame detection systems for this ? Since they are build to be reliable. I'm not sure how an insurance company would react upon a camera.
Also, I have seen fire detection systems which use CCTV to detect flames. Can't recall the name anymore though. I have no clue how reliable these are.
I'm sure the fellahs on the site know a few good suggestions as well.
As Rogier had mentioned above FLIR may be an option.
If the detection system has to be UL listed for fire purposes, the Fike SigniFire system is the only listed flame detector camera I am aware of, and it has to be connected to their alarm panel for listing. IPVM did a review on it last year, which I just updated as their system's NVR is now ONVIF conformant and can connect to third party VMS's and analyze feeds from non-Fike cameras.
Both of these options are going to be rather pricey. You might want to consider installing rate-of-rise heat detectors in the area connected to a fire alarm panel and use a relay output from the panel to trigger an input on a camera to give the surveillance operator a warning signal or call up the camera.